DEPARTMENT OF THE INTERIOR

FRANKLIN K. LANE, Secretary

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, Director

Bulletin 678

CLAYS AND SHALES OF MINNESOTA

BY

FRANK F. GROUT

WITH CONTRIBUTIONS BY

E. K. SOPER

Work done in cooperation -with the Minnesota Geological Survey 

W. H. Emmons, Director

WASHINGTON

GOVERNMENT FEINTING OFFICE 

1919

CONTENTS.

Page.

Outline..................................'.................................. 11

Introduction................................................................ 13

Scope of paper......................................................... 13

Acknowledgments...................................................... 13

Bibliography......................................................... 14

Clays in adjoining States............................................... 15

Geology of clay............................................................ 15

Definition............................................................ 15

Origin................................... I............................ 15

Minerals from which clay is derived ............................... 15

"Weathering....................................................... 16

Erosion and sedimentation........................................... 17

Alteration........................................................ 18

Geologic types of deposits.......'................................'........ 19

. Residual clays........................................................ 19

Transported clays.................................................... 19

Marine deposits................................................ 19

Lake clays..................................................... 20

Alluvial clays.................................................. 20

Glacial clays...................................................... 20

Slates............................................................ 20

Relation of types................................................... 20

.Mineralogic and chemical properties of clay................................. 21

Constituents of the clays................................................ 21

Chemical composition............................................. 21

Essential constituents ............................................. 21

Silica ........................................................ 21

Alumina. ...................................................... 22

Combined water.............................................. 22

Nonessential constituents (impurities).............................. 22

Mechanical and hygroscopic moisture.. .................:..: ...... 22

Lime compounds..................... 1......................... 23

Iron oxides and sulphides...................................... 25

Magnesia... I................................................. 25

Sulphur....................................................... 26

Organic matter.................................................. 26

Titanium, copper, manganese, and phosphorus................... 27

Alkalies....................................................... 27

State of mineral combination........................................... "27

Value of chemical tests................................................. 28
4 CONTEXTS.

Page.

Physical properties of clays................................................. 29

Plasticity.............................................................. 30

Shrinkage............................................................. 32

Tensile strength........................................................ 33

Effects of heating...................................................... 34

Preheating........................................................ 34

Expulsion of volatile matter........................................ 34

Chemical reactions................................................. 35

Fusion............................................................ 35

Range of vitrification.............................................. 36

Quality of the product.............................................. 39

Minor physical properties............................................... 39

Classification and adaptability of clays.............................:......... 40

Classification.......................................................... 40

Basis..................................... 1......................... 40

Classification by uses.............................................. 40

Classification by geologic origin.................................... 41

Classification by physical properties................................. 41

Special classes.................................................... 42

Relation of physical properties to uses................................... 43

Tests of clays .....................................I.................... 45

Samples.......................................................... 45

Character of tests................................................... 45

Relation of tests to practice........................................ 48

Technology of clay, by E. K. Soper ....................................... 49

Prospecting. .............................^............................ 49

Usual method of prospecting....................................... 49

Stratigraphic prospecting.......................................... 50

Economic considerations.......................................... 50

Clay plants.......................................................... 51

Location.......................................................... 51

Mining the clay .................................................. 52

Transportation from pit to plant......................'.............. 53

Drainage...............................................'........... 53

Preparation of the clay................................................ 53

Preliminary treatment ........................................... 53

Grinding.......................................................... 54

Washing.......................................................... 54

Screening......................................................... 55

Overcoming the trouble from limestone pebbles..................... 55

Methods..................................................... 55

Hutcliinson process............................................ 55

Grinding and screening. ...................................... 56

Saturation of the burned bricks................'................. 56

Coloring. ".. ....................................................... 57

Mixing. .......................................................... 57

Preheating........................................................ 57

Tempering........................................................ 57

Soak pit ...................................................... 58

Ring pit...................................................... 58

Wet pan...................................................... 58

Pug mill...................................................... 58

Wedging...................................................... 59
CONTENTS. 5

Technology of clay Continued.

Preparation of the clay Continued. Page.

Molding.......................................................... 59

Brick molding................................................ 59

Soft-mud process.......................................... 59

Stiff-mud process......................................... 1 60

Re-pressing.............................................. 61

Dry-press process..................................... 1.... 61

Hollow ware and tile......................................... 62

Sewer pipe................................ v .................. 62

Pottery...................................................... 62

Glazing. ......................................................... 63

Drying. . . . .................................................;.... 63

', Methods..................................................... 63

Efflorescence................................................. 64

Burning the clay...................................................... 64

Kilns ........................................................... 64

Updraft kilns................................................ 64

Downdraft kilns............................................... 65

Continuous kilns.............................................. 65

Fuels............................................................. 65

Burning process................................................... 66

Technologic suggestions................................................ 67

Use of clay products....................................................... 67

Paving brick.......................................................... 67

Draintile.........................:................................... 68

Geology of Minnesota, by Frank F. Grout and E. K. Soper......... 1........ 70

Physiography........................................................ 70

Geologic history...................................................... 72

Archean period..................................................... 72

Algonkian period.................................................. 72

Cambrian period................................................. 73

Ordovician period................................................. 74

Devonian period................................................. 75

Pre-Cretaceous erosion interval..................................... 75

Cretaceous period................................................. 75

Quaternary period................................................. 76

Pleistocene epoch, by Frank Leverett.......................... 76

Recent epoch................................................ 78

Geologic formations and their clay deposits.............................. 78

Archean system.................................................. 78

Algonkian system................................................. 79

Huronian series ........................>...................... 79

Keweenawan series ........................................... 81

Algonkian (?) system. ............................................ 81

Red clastic series ............................................ 81

Cambrian system .................................................. 81

. Lower formations.............................................. 81

St. Lawrence formation........................................ 82

Jordan sandstone.............................................. 82

Ordovician system................................................. 82

Oneota dolomite............................................... 82

Shakopee dolomite............................................ 83

St. Peter sandstone............................................ 83
6 CONTENTS.

Geology of Minnesota Continued. 

Geologic formations Continued.

Ordovician system Continued. Page.

Platteville limestone............................................ 83

Decorah shale..............-............,............"......... 83

Galena limestone............................................. 85

Maquoketa shale............................................. 86

Devonian system.................................................. 86

Cretaceous system................................................. 87

General character............................................. 87

Basal Cretaceous clays......................................... 88

Later Cretaceous shales......................................... 89

Tertiary system................................................... 91

Quaternary system. .....................................:........ 91

Pleistocene deposits........................................... 91

General character......................................... 91

Aftonian (?) interglacial deposits.......................... 92

Gray drift clays........................................... 92

Gray laminated lake and river clays......................... 94

Red drift clays............................................. 96

Red laminated lake and river days........................ 96

Red clays ^of Lake Duluth.................................. 97

Outwash clays............................................ 98

Loess.................................................... 98

Clays of Red River valley.................................. 101

Recent deposits.............................................. 102

River clays............................................... 102

Lake and swamp clays..................................... 104

Geologic and economic summary of clay deposits................... 104

Statistics of clay products............................... 1.................. 106

Distribution of types of clay................................................ 106

Refractory clays....................................................... 106

Archean clays..................................................... 106

Cretaceous clays................................................... 107

Semirefractory clays................................................... 107

Vitrifying light-burning clays....................................... 107

Clays that melt suddenly. . . . ..................................... 108

Nonrefractory clays................................................... 108

Vitrifying clays.................................................. 108

Clays that melt suddenly. . . ...................................... 110

Clays of Minnesota, by counties............................................. Ill

Aitkin County....................................................... Ill

Anoka County........................................................ 113

Becker County...............................I...-...-......-.-.-.... 118

Beltrami County..................................'.................... 119

Benton County....................................................... 120

Big Stone County. ................................................... 121

Blue Earth County............................................... -^ ... 121

Brown County....................................................... 126

Carlton County...................'.................................... 134

Carver County....................................................... 140

Cass County. .........................................^................ 141

Chippewa County..................................................... 141

. Chisago County....................................................... 142
CONTENTS. 7

Clays of Minnesota, by counties Continued. Page.

Clay County.......................................................... 144

Clearwater County....................:................................ 145

Cook County. ........................................................ 145

Cottonwood County.................................................... 146

Crow .Wing County.................................................... 147

Dakota County...........................................;............ 149

Dodge County......................................................... 153

Douglas County...................................................... 154

Faribault County. .................................................... 156

Fillmore County...................................................... 158

Freeborn County.......................:................................ 162

Goodhue County......................................................... 165

Grant County......................................................... 173

Hennepin County. .................................................... 173

Houston County. ..................................................... 173

Hubbard County........................................................ 174

Isanti County........................................................... 174

Itasca County............................................................ 175

Jackson County.............................................................. 178

Kanabec County....................................................... 180

Kandiyohi County..................................................... 181

Kittson County............'...-.:...................................... 181

Koochiching County.................................................. 182

Lac qui Parle County................................................. 186

Lake County.......................................................... 186

Le Sueur County...................................................... 187

Lincoln County........................................................ 191

Lyon County.......................................................... 191°

McLeod County.......................................................... 191

Mahnomen County.................................................... 193

Marshall County....................................................... 193

Martin County........................................................ 194

Meeker County........................................................ 194

Mille Lacs County..................................................... 194

Morrison County...................................................... 197

Mower County. ...................................................... 200

Murray County............................:.......................... 203

Nicollet County....................................................... 203

Nobles County......................................................... 204

Norman County.......................................................... 205

Olmsted County...................................................... 205

Otter Tail County. ................................................... 208

Pennington County...................................................... 210

Pine County. ........................................................ 210

Pipestone County.................................................... 211

Polk County. ........................................................ 211

Pope County............................................................ 214

Ramsey County....................................................... 214

Red Lake County...................................................... 216

Redwood County........................................................ 216

Renville County. ..................................................... 220

Rice County......................................................... 222

Rock County.......................................................... 223
8 CONTENTS.

Clays of Minnesota, by counties Continued. Pago.

Roseau County. .................. '. .................................... 224

St. Louis County. ..................................... '. ............... 225

Scott County. ...................................................... 230

Sherburne County....... . ............................................. 232

Sibley County. . ............:......................................... 233

Stearns County. ..........................................:.....:.... 233

Steele County. ........................................................ 237

Stevens County ....................................................... 238

Swift County. .............:..............................:........... 238

Todd County. ......................................................... 238

Traverse County. ...................................... ... ............ 241

Wabasha County.. .. ................................................... 242

Wadena County. . ..................................................... 242

Waseca County . ...................................................... 242

Washington County. ................................................... 243

Watonwan County ...."........................,....................... 245

Wilkin County.. . ...........................................:......... 246

Winona County. ........................................................ 247

Wright County. ....................................................... 249

Yellow Medicine County .............................................. 251

Index ......................... .' ......................................... 253

ILLUSTRATIONS.

 PLATE I. Section in clay pit at Wrenshall.................................... . 20

II. A, Smooth and klinker brick from West St. Paul; B, Smooth and 

roughened brick from Coon Creek; C, Bricklets burned in laboratory 

tests; D, Limy concretions in gray laminated clay........'....... 36

III. A, Dry pan; B, Double 8-foot wet pan.............................. 54

IV. Soft-mud brick machine formerly used at Jackson............'.......: 55

V. A, Wire-cut brick made from pebbly clay; B, Auger structure in an

overburned brick; C, Brick drying in open sheds... '. ............. 60

A, Sewer-pipe press; B, Four-mold dry press brick machine......... 61

A, Brick drying on cars in tunnels; B, Hollow ware drying on a floor. 62 

A, Scove kiln, showing how brick are piled; B, Round downdraft kiln 

at Hopkins.................................................... 63

IX. General geologic section of Minnesota .............................. 72

X. Map of Minnesota showing large clay deposits and some of the active

plants.......................................................... 83

XI. A, Seger cones after heating to the temperature of the third cone of the

set; B, Concretionary or pebbly Cretaceous clay ................. 88

XII. A and B, Views showing examples of irregularity in the structure of

laminated clays in North Minneapolis............................ 114

XIII. A, Clay.bank at Coon Creek; B, Slate of Carlton County, showing

cleavage.................................................'...... 115

XIV. A and B, Disturbed Cretaceous clays at Clay Bank, near Red Wing. 168

XV. Molded stoneware at Red Wing ................................... 169

XVI. A, Sewer-pipe plant at Minneapolis; B, Clay pit at Belle Chester.... 170
CONTENTS. 9

Page. 

FIGURE 1. Sketch showing the origin of types of clay....................... 1G

2. Sketch showing the influence of thickness of drift overburden on

the depth of weathering of clay................................ 19

3. Temperature-porosity curves for refractory and semirefractory

clays....................................................... 37

4. Temperature-porosity curves for brick clays...................... 38

5. General arrangement of brick plant.............................< 52

6. Auger machine and wire cutter................................. 60

7. Diagram showing the gradual oxidation and disappearance of black

cores due to organic matter when bricks are kept at red heat.... 66

8. Diagram showing the decrease in porosity with increasing temperature exhibited by average clays of the several geologic formations 

in Minnesota................................................ 84

9. Map of southeastern Minnesota showing an area in which the drift is

largely covered with loess.................................... 99

10. Sketch map of the southwest corner of Minnesota showing an area of

old gray drift outside the young gray drift..................... 100

11. Geologic section of the laminated clay in North Minneapolis..... 113

12. Rattler test on paving brick from Coon Creek...................... 117

13. Section of Cretaceous clay at South Bend........................ 122

14. Section of Cretaceous clay near railroad bridge, Mankato......... 122

15. Section of Cretaceous shale at Farmers' Elevator, New Ulm....... 127

16. Section of Cretaceous shale on Cottonwood River, Brown County. 129

17. Geologic section on Cottonwood River, Brown County, showing

Cretaceous deposits and drift................................. 130

18. Geologic section at shale quarry, West St. Paul................... 150

19. Map of Fillmore County......................................... 158

20. Section of the loess at Preston.................................. 160

21. Section at quarry west of Rushford ........................._..... 161

22. Map cf Goodhue County. ......I................................ 166

23. Geologic section at Wanamingo................................. 167

24. Geologic section at Minneola................................... 168

25. Geologic section at Clay Bank................................... 169

' 26. Geologic section at Belle Chester............................:... 171

27. Geologic section at Coleraine.................................... 177

28. Geologic section at Brickton............................."...... 195

29. Geologic section along the west bank of Mississippi River near the

mouth of Two River.......................................... 198

30. Geologic section at Austin...................................... 201

31. Geologic section opposite New Ulm.............................. 204

32. Map of Olmsted County......................................... 206

33. Profile showing topographic features of Decorah shale outcrop in

Olmsted County.............................................. 207

34. Section across the gorge of Redwood River below Redwood Falls.. 217

35. Section on road from Morton to Redwood Falls................... 218

36. Geologic section of the Decorah shale south of Fairbault.......... 222

37. Geologic section south of Belle Plaine............................ 231

38. Geologic section west of Richmond.............................. 234

OUTLINE.

This bulletin comprises a discussion of the distribution, origin, 

properties, classification, and adaptability of the clays and shales 

of Minnesota. An attempt has been made to test all the more important deposits with sufficient exactness to determine for what purposes they may be used. Detailed'results of these tests are arranged 

by counties.

The technical terms used in the discussion are briefly explained iii 

the sections on " Physical properties " (pp. 20-40) and " Technology " 

(pp. 49-67). Washing and mixing clays are processes recommended 

for experiments in technology.

Certain areas are recommended for prospecting and development. 

Refractory residual cla}7 s and kaolins are found in the central and 

southwestern. parts of the State. Semirefractory clays are somewhat more widely distributed and should be sought by drilling. 

The area of Decorah shale in southeastern Minnesota is mapped in. 

detail. The upper Huronian slates near Duluth may be found worthy of development, as it is believed that excellent fancy brick can 

be made from them by a small addition of red-drift clay.

The general character of each geologic formation and the character of the clay products made from it by the several methods of 

manufacture are set forth.

The gray drift is widely distributed and is one of the most important sources of clay in the State. After its limestone pebbles have 

been removed, which can be done at an expense not so great as to be 

prohibitive, it can be made into excellent draintile, for which there 

Avill be an increasing market as the swamp lands of the State are 

drained. Some details of the process are given.

Deposits suitable for common brick are abundant and widely distributed in many accessible localities in the eastern part of the 

State. The red laminated clay of the eastern counties makes good 

red brick and may be used as a slip glaze for semirefractory ware.

The Minnesota products are not inferior to those now brought in 

large quantities from Wisconsin, Iowa, and Illinois at unnecessarily 

high prices.

11

CLAYS AND SHALES OF MINNESOTA.

By FRANK F. GROUT.

INTRODUCTION.

SCOPE OF PAPER.

This bulletin gives the results of an investigation of the clay 

resources of Minnesota made during 1912 and 1913. In general the 

object of the work has been to assist in the development of the clay 

resources of the State. The broader problems of ceramics are treated 

only incidentally, but some of the important scientific conclusions 

of the American Ceramic Society, of the Bureau of Standards, and 

of surveys of other States are briefly reviewed in order that they may 

be more readily available to those whose chief interests are technical 

and commercial. A more extended treatment of the scientific results 

of the investigation will be published later.

Specifically, the object has been to investigate the brick supply 

for every town of 1,000 or more inhabitants and for every county in 

the State, to ascertain the extent of several deposits now developed 

at only a few points, to find new deposits, and to determine the 

qualities of these deposits and of certain mixtures so as to ascertain 

whether it is possible to produce refractory wares, pottery, paving 

brick, and other high-grade products.

ACKNOWLEDGMENTS.

The work for this report was done by the United States Geological 

Survey, in cooperation with the Minnesota Geological Survey. Mr. 

E. K. Soper assumed the responsibility for the field work and county 

reports for those counties south of Minneapolis and St. Paul, including the mapping of the Decorah shale. Mr. Soper also wrote the 

section on the technology of clays and cooperated in the preparation 

of the section on the geology of Minnesota.

Acknowledgments are given to Messrs. Oliver Bowles, G. L. Harrington, and F. M. Handy, who assisted in the work; to Messrs.

13
14 CLAYS AND SHALES OF MINNESOTA.

Frank Leverett, F. W. Sardeson, and A. W. Johnston, who contributed certain geologic data; to Mr. Jefferson Middleton, of the 

United States Geological Survey, for lists of producers and statistics of production; to the Bureau of Standards, for tests; to the 

Minnesota School of Mines Experiment Station, for firing tests; to 

the experimental engineering department of the University of Minnesota, for tests of the products; to Mr. J. G. Houghton, Minneapolis 

inspector of buildings, for tests of brick and tile; and to Dr. C. P. 

Berkey, for unpublished data. Illustrations of some modern clayw.orking machinery have been copied by permission from catalogues 

of the American Clay Working Machinery Co. and Chisholm, Boyd 

& White Co. The work in the field has been greatly facilitated by 

the friendly cooperation of the commercial clubs and other organizations of the several towns throughout the State and by the aid of 

many individuals. Sincere thanks are due to Mr. M. C. Madsen, of 

Hutchinson; Messrs. E. S. Hoyt and J. H. Kich, of Red Wing; 

Dr. 0. C. Strickler, of New Ulm; and many others.

BIBLIOGRAPHY.

1880. Winchell, N. H., Preliminary report on the building stones, clays, limes, 

cements, etc., of Minnesota: Minnesota Geol. and Nat. Hist. Survey 

Misc. Paper 8.

Divides clays into three classes: (1) Ferruginous laminated clays 

of loess loam and river valleys deriving their iron coloring matter 

from the northeastern drift; (2) alkaline laminated clays of loess 

loam and river valleys charged with lime (enough to destroy the red 

color), which is derived from limestone of the northwestern drift; 

(3) Cretaceous alkaline clays, mentioned as occurring up the Minnesota Valley. Forty-two plants producing red brick and. 18 producing 

lighter cream-colored or gray brick are mentioned. Cretaceous clays, 

then used in a few potteries, were recommended as probably deserving 

more extended use.

1884, 1888, 1899, and 1900 Minnesota Geol. and Nat Hist Survey Final Repts., 

vols. 1, 2, 4, and 5; issued subsequently to annual reports of progress. 

Contain many references to clays.

1897. Sardeson, F. W., Glacial deposits of Driftless Area: Am. Geologist, vol. 

20, p. 392.

Mentions loess deposits of southeastern Minnesota.

1902. Berkey, C. P., Origin and distribution of Minnesota clays: Am. Geologist, 

vol. 29, p. 171. 

Groups the clays of the State as follows:

Residuary: (1) Kaolins from the Archean gneisses; (2) common 

residuary clays, grading into loess.

Transported: (1) Sediments Huronian slate, Ordovician shale, and 

Cretaceous shale; (2) glacial till, lake clays, and stream clays; (3) 

recent alluvium; (4) loess.

1906. Ries, Heinrich, Clays: their occurrence, properties, and uses, New York, 

John Wiley & Sons.

Reports that the residual clays are of little value and emphasizes 

the Cretaceous clay of Red Wing and the widespread Pleistocene 

clays.
GEOLOGY OF CLAY. 15 

CLAYS IN ADJOINING STATES.

In North Dakota along the Minnesota boundary throughout a belt 

many miles wide brick plants have used the silts of Red River 

valley, which cover the drift so deeply that the lower formations are 

not well known.

In South Dakota the area along the Minnesota boundary is mostly 

covered with drift. 

In Iowa, near the Minnesota boundary, the area, though mostly 

drift covered, is underlain by sediments ranging in age from Ordovician to Cretaceous. The most' important clay product made from 

these sediments, so far as Minnesota is concerned, is the Mason City 

tile, made of Devonian shale. The Devonian rocks extend only a 

very short distance into Minnesota. The Cretaceous on the west and 

the Ordovician on the east are little used in Iowa.

In Wisconsin occur red-burning glacial deposits that extend a few 

miles into Minnesota along the greater part of the border. Red brick, 

such as that made at Grantsburg, Wis., is the main product of the 

widespread laminated clays. Loess covers a large part of the Driftless Area in Wisconsin and in southeastern Minnesota and overlaps 

the older drift to a certain extent.

GEOLOGY OF CLAY.

DEFINITION.

Clay is defined in two ways as an earthy aggregate consisting 

essentially of kaolinite or some nearly related hydrous aluminum 

silicate and as any earthy mass that becomes plastic when wet. Usually a clay fulfills both these conditions. The mineral kaolinite has 

the composition H4Al2Si2 09 ; its specific gravity is 2.6. It is monoclinic in crystal form, white (unless impure), and insoluble in dilute 

acids, though decomposed by hot concentrated acids. Hall oysite, 

pyrophyllite, cimolite, bauxite, and opal are often found in association with kaolinite. Shale is a term frequently employed in the same 

sense as clay, but as a rule it is applied to hard laminated clays, gen: 

erally of marine origin.

ORIGIN.

MINERALS FROM WHICH CLAY IS DERIVED.

All or nearly all the clay minerals are secondary in origin, being 

formed by the hydrous alteration of other silicate minerals that 

make up the so-called crystalline rocks. The most common of these 

minerals are orthoclase (potassium-aluminum silicate), albite 

(sodium-aluminum silicate), anorthite (calcium-aluminum silicate), 

muscovite (hydrous potassium-aluminum silicate), biotite (iron-
16 CLAYS AND SHALES OF MINNESOTA.

magnesium-aluminum silicate), and hornblende and augite (complex 

silicates, containing as a rule iron, magnesia, lime, and aluminum).

WEATHERING.

By various natural reactions some or all of these minerals are 

altered to kaolinite or related clay minerals. Orthoclase, albite, anorthite, and muscovite are of greatest interest,- the others being of 

importance only because they introduce impurities into the resulting 

clays. The particular circumstances under which natural reactions 

produce kaolinite, especially in large bodies, from other minerals 

have been much discussed. Possibly the action of hydrofluoric acid 

may form kaolinite from orthoclase at great depths in the earth, but

^-r°v^°x:.?r^^K^^^H7-:H.7.>;^

B'IGUBE 1. Sketch showing the origin of types of clay. The primary rocks shown are 

granite, pegmatite, and limestone. Where these rocks have been long exposed to the 

weather the soluble constituents are more or less completely removed, leaving clays 

(a) and (d). The pegmatites are probably, in many places, partly altered before exposure and are deeply kaolinized. Clays of any sort exposed on a sloping surface are 

subject to wash by the rain, and such clays that have been transported short distances 

are known as colluvial (6). Clays carried by streams and deposited in a flood plain 

are alluvial (c).

it seems probable that little if any common clay has been so formed. 

The slower but more general action of weathering at the surface is of 

much greater importance, and kaolinite is the commonest product of 

such weathering, though under some conditions aluminum hydroxides 

may be the end products. (See fig. 1.)

Weathering is usually but not invariably accompanied by erosion 

and sedimentation. It includes both chemical effects, known as decomposition, and mechanical effects, known as disintegration, which 

are usually simultaneous and closely related. Many rock minerals 

are partly soluble in circulating water, and as a part of the mineral 

is removed, water may combine with the residue, producing hydrous 

minerals. These are usually softer and more loosely bound together 

than the original rock, and are hence more easily affected by mechanical processes, such as erosion by flowing streams carrying sediments, 

by wind-blown sand, or by ice, the pounding of the waves, and the 

unequal expansion resulting from alternations of heat and cold. All 

the mechanical processes break up rocks into finer particles and give
GEOLOGY OF CLAY. 17

the circulating waters easier access to the material and enable them 

better to bring about decomposition.

The solvent action of circulating water on minerals is greatly increased by the presence of dissolved gases and minerals. Carbonic 

acid and oxygen are especially effective, and the organic products of 

bacteria and other animal and vegetable life are in general noteworthy.

The results of rock weathering depend largely on the relative 

amounts of decomposition and disintegration. A powder formed 

chiefly by the breaking up of crystalline rocks must naturally .have 

properties different from those of powders left by the chemical solution of part of the rock. One is termed " rock flour " and 'the other 

" rock rot." Glacial erosion, for example, is mainly mechanical and 

yields rock flour. The finest particles that result from weathering 

of either sort usually constitute a clay, which, from the nature of its 

formation, is likely to contain remnants of the original minerals 

from which it was formed. . -,.

An elaborate discussion of weathering, with a bibliography, is 

given by Buckman.1

Comparison of fresh and weathered portions of two Minnesota 

rocks may be of interest, though each of the rocks is variable and it 

is not altogether certain that the altered rock is derived from one 

of exactly the composition of the fresh rock.

Analyses of fresh and weathered rocks of Minnesota.

Silica..........................................................

Soda ...........................................................

Potash .........................................................

Miscellaneous .............................................'.....

Granite gneiss of 

Morion.

Fresh.i

63.61 

16.71 

5.69 

2.78 

1.63 

4.03 

1.68 

2.49

.61

99.23

Weathered. >>

60.61 

18.12

| 7.51 

1.14 

.03 

.54 

3.56 

.28 

7.20 

1.30

100. 29

Diabase lava flow 

of Pine County.

Average 

fresh. 6

57.65 

14.97 

/ 6. 05 

\ 4.23 

4.00 

4.30 

2.01 

3.18 

.33 

1.91 

1.84 

.40

100.87

Weathered. 6

43. 39 

20.42 

13.57

5.17 

.27 

.35 

5.46 

4.24 

5.54 

.92

99.29

a Analysis by A. D. Meads. & Analysis by F. F. Grout. 

EROSION AND SEDIMENTATION.

The processes of erosion and sedimentation have a very intimate 

relation to the accumulation of workable clays. Particles of clay

1 Buckman, IT. 0., Am. Ceramic Soc. Trans., vol. 13, p. 336, 1911. 

64310° 19 2
18 CLAYS AND SHALES OF MINNESOTA.

formed by weathering are finer than those of sand and gravel and 

when washed by water are often separated from them. The carrying 

power of running water depends largely on its velocity, and a stream 

which under normal conditions would gather up and carry particles 

of clay might not flow fast enough to carry grains of sand except 

at times of great floods. This separation tends to cause the accumulation of large bodies of clay free from sand. Some streams flow 

fast enough at all seasons to carry both sand and clay, yet their burdens may be sorted where they reach a lake or the ocean; their currents are at first only partly checked and they deposit the coarser 

sand near shore and carry the clay farther out. Similarly, shore currents and waves separate sand from clay and may deposit the clay 

farther from the shore.

ALTERATION.

After the formation of a clay, geologic processes may modify it in 

many ways. Circulating waters may leach from it certain soluble 

elements or, on the other hand, may deposit mineral matter as cement 

or as concretionary masses. An analysis of a common type of concretion is given in the discussion of Anoka County (pp. 113-118). 

Again, an increase in temperature may dehydrate a clay and change 

the mineral combinations. Most clays accumulate in nearly horizontal tabular masses, but these masses may be folded or faulted by 

later earth movements.

In Minnesota the most notable alterations are probably the leaching and oxidation of the. upper layers of the clay and the deposition 

of concretions at lower levels. By this process a glacial deposit of 

" rock flour " may become altered to a more plastic kaolinite or even 

to minerals like bauxite, with an excess of aluminum. Leaching 

may improve some clays by removing the lime. In the Red River 

valley only the upper layers of the clay, from which the lime has 

been leached, are serviceable for brick material. The leaching has 

also improved them by somewhat reducing their plasticity and 

shrinkage, which are still too great in the lower joint clays. On the 

other hand, the leached surface clays (gumbo) at Wrenshall and 

Princeton show too much shrinkage and are more plastic than the 

lower clays, which are much better for brickmaking, though they are 

higher in lime content and in some layers are injured by concretions. 

The widespread gray drift of the central part of Minnesota is commonly somewhat leached to a depth of a few feet; in some places it 

has been much improved by removal of the lime, but in most places 

weathering has merely oxidized the iron minerals, changing the color 

to a yellowish gray but leaving the other properties essentially un-
GEOLOGY OF CLAY. 19'

changed. The gray unaltered clay has, if anything, greater plasticity, 

and shrinkage than the altered clay. (See fig. 2.)

GEOLOGIC TYPES OE DEPOSITS..

RESIDUAL GLAYS.

The weathering and superficial decay of granitic igneous rocks 

have in some places produced a sheetlike mantle of clay of great 

lateral extent and as much as 100 feet thick. As a rule such deposits 

follow the irregularities of the original rock surface, their base depending more or less closely on the water level and the topography at 

the time they were formed. Another less common form of residual 

clay results from the alteration of igneous dikes. Still other residual 

clays result from shaly sedimentary rocks. The impurities depend 

largely on the completeness of the alteration. The analyses of Minnesota material given in the discussion of weathering (pp. 16-17) 

furnish an example of partial alteration.

FIGURE 2. Sketch showing the influence of thickness of drift overburden on the depth 

of weathering of clay. Many blue-gray clays weather yellow when the organic matter 

and iron are oxidized and the lime leached out. This weathering affects even some 

clays that are buried under drift; but if the drift is thick, the oxygen and leaching 

solutions do not reach, the clay so freely.

Some kaolinite is present in the altered rocks, and all such residual 

clays that burn white are called kaolins. Bies 1 has summarized the 

theories of the origin of kaolins.

TRANSPORTED CLAYS.

MARINE DEPOSITS.

Sedimentation in the sea, usually at a distance from the shore, 

produces clay deposits which tend to have great lateral extent as 

compared with their thickness. Both horizontally and A^ertically 

the clay body may grade into limestone or sandstone, and vertically 

it may alternate with these rocks. In Minnesota the Decorah shale 

is a good illustration of such alternating beds. Subsequent concretionary action may add to the impurities; or leaching, under favor1 Ries, Heinrich, Am. Ceramic Soc. Trans., vol. 13, p. 73, 1911.
20 CLAYS AND SHALES OF MINNESOTA.

able conditions, may decrease them. If later marine formations 

cover the clay deeply, their pressure may consolidate the clay into a 

shale. If the shales are later exposed by erosion, they weather back 

into soft clays.

LAKE CLAYS.

Lake clays originate in much the same manner as marine clays, 

the chief difference being in their extent. The clays near Heron 

Lake, Minn., seem to have originated as lake, deposits.

ALLUVIAL CLAYS.

Rivers that carry large amounts of fine sediment .vary in the 

rapidity of their currents at different times and in different parts of 

their channels. Where flood waters spread over the bottom lands 

and where an eddy or other irregularity reduces the current very 

greatly sandy clays are likely to be deposited. These conditions are 

most common along the wide flood plains of the larger streams.

GLACIAL CLAYS.

The glacial drift as carried by the ice may have only a small proportion of clay, but this small proportion may be concentrated into 

valuable deposits by the .flow of: water from the melting ice.

The abrasive action of the ice has in some places ground up considerable amounts of rock to a fine powder that has not been extensively decomposed. This so-called rock flour has many of the properties of clay and has been' used as a brick material. It appears that 

in some places decomposition has later turned some of this flour 

into kaolinite.

Many lake and alluvial clays of glacial origin resemble lake and 

alluvial clays that are not connected with glacial action, but they are 

of sufficient importance and extent in Minnesota to warrant separate 

mention. (See PL I.)

SLATES.

Some great accumulations of clay in the older formations of Minnesota have been deeply buried and have been so greatly altered as 

to change their mineral composition and physical properties. These 

are classed as metamorphic slates.

RELATION OF TYPES.

The several geologic types of clay are not always easily distinguished in the hand specimen or even in the field. Even the fundamental genetic distinctions between residual and transported clays
TJ. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE I

SECTION IN CLAY PIT AT WRENSHALL.
MINEKALOGIC ASTD CHEMICAL PKOPERTIES OF CLAY. 21

are often most difficult to apply, and there are many gradations between the several types. The origin of the clays as here outlined 

bears little traceable relation to their applicability as ceramic material. One marine shale may be a good fire clay and another a fusible 

slip clay without any ascertainable distinction in the mode of their 

formation.

MINERALOGIC AND CHEMICAL PROPERTIES OF CLAY.

Few clays approximate very closely the composition of the mineral 

kaolinite. Alteration of original minerals is seldom complete, and 

the residues contaminate the product. Transportation and deposition rarely exert such selective action as will yield pure "kaolinite. 

Other minerals are deposited with the kaolinite, and after' deposition 

many solutions affect the deposits, rarely in a way to improve its 

quality. Each of the modes of formation, however, has produced 

some very high grade clays and many notably useful deposits." '

CONSTITUENTS OF THE CLAYS.

CHEMICAL COMPOSITION.

The chief chemical constituents of clay as estimated by common 

rock analysis are shown in the following table. Each constituent, 

whether abundant or rare, has a somewhat definite relation to the 

physical properties of the cla'ys and the wares burnt from them, but 

any conclusions based on such analyses must be very generalized.

Approximate range in percentage of certain constituents in clays of several, 

types, compiled from miscellanedits sources.

Silica................

Brick clay.

Maximum.

91

44 

32 

15 

7 

15

Minimum.

34 

10 

0 

0 

0 

0

Pottery clay.

Maximum.

87 

35 

7 

10 

5 

7

Minimum.

45 

14 

0 

0 

0 

0

Fire cjays.

Maximum.

97 

40 

3 

2 

1 

3

Minimum.

35 

2 

0 

0 

0 

0

Paving-brick clay.

Maximum.

70 

25 

9 

3 

3 

4

Minimum.

55 

11 

2 

0 

0 

0

ESSENTIAL CONSTITUENTS.

SILICA.

Silica .(SiO2 ) is present in the clays in a variety of forms. As 

quartz it is free from chemical combination. It is an essential constituent, forming 46 per cent of the kaolinite or the fundamental clay
22 CLAYS AND SHALES OF MINNESOTA.

substance, and is prominent in the many silicates from which 

kaolinite may be derived and which form secondarily with kaolinite. 

Silica, therefore,, usually constitutes more- than 50 per cent of the 

clay. The highest amount of silica in the ordinary clay silicates 

(p. 15) is about 65 per cent in pyrophyllite, and if the silica approaches that figure some of it probably occurs free as quartz. It 

is not considered an active flux, though when mixed with kaolin it 

lowers the melting point considerably. In the form of sand it may 

have a beneficial effect on the clay in reducing excessive shrinkage 

and plasticity. Its compounds are as a rule hard and rocklike when 

anhydrous, and to them is due the hardness of burned clay.

Alumina (AlgO3 ) is also an essential constituent of kaolinite,. of 

which it forms 40 per cent, a larger proportion than in any other 

common mineral. Some residual clays in Minnesota are exceptional 

in having more than 40 per cent of alumina. Lean sandy clays may 

have less than 10 per cent. Alumina is also present in most of the 

common clay silicates. As the basic element of kaolinite it is the 

most essential metallic element of clays and is in every way desirable. 

On it depend the properties of both raw and burned clay.

COMBINED WATER.

Combined water (H2 O) is the third important oxide in kaolinite, 

of which it forms 14 per cent, and it is found also in other minerals.- 

As numerous anhydrous minerals are mixed with common clay, few 

 analyses show as much as the theoretical 14 per cent of combined 

water. Burning expels it, leaving open spaces and thus increasing 

porosity. If it is very abundant sudden expulsion may cause " popping" or burst the ware into fragments.

NONESSENTIAL CONSTITUENTS (IMPURITIES ).

MECHANICAL AND HYGROSCOPIC MOISTURE.

Oven-dried clay greedily absorbs moisture from the air in considerable amounts, even as high as 10 per cent of the dry weight. 

This amount of water in a clay powder seems to have no appreciable 

effect in making the clay appear moist. As dug from the bank most 

clay contains water in even larger amounts, as much as 40 per cent, 

in the capillary pore spaces between grains, without being very 

soft. The relation of water to clay is further discussed in connection 

with plasticity (pp. 30-32). A clay that remains firm with a high percentage of water is likely to shrink greatly in drying. If the water
MIFEBALOGIC AND CHEMICAL PEOPEETIES OF CLAY. 23

is not removed before firing it must be removed in the kiln. This 

delays to some extent the firing and the later oxidation.

LIME COMPOUNDS.

The most abundant form of calcium in clay is the carbonate, calcite (CaC03 ). This may be residual from the original rock or it 

may have been transported and deposited with the clay mechanically 

or by the action of organisms or by circulating waters. It may be 

finely disseminated or may occur in laminae, strata, or pebbles. Its 

effects vary with its condition.

If finely divided and disseminated in the clay, calcite acts as a 

flux. At some temperatures above 600° C. carbon dioxide is evolved, 

and the lime (calcium oxide) remaining acts as a powerful base, 

combining with the acidic elements of the clay, mostly silica, to form 

fusible salts. If the temperature is not high enough to effect this 

fusion and combination, the fine-grained lime remains in the burned 

product and after exposure may be hydrated (slaked) by the moisture of the elements without much harm. If the temperature is high 

enough to cause fusion, the lime becomes a dangerous ingredient, reducing the range between incipient fusion and viscosity. A high percentage of lime makes it impossible to produce vitrified ware safely, 

but the exact percentage of lime that is allowable for a particular 

product is not determined with certainty. Good clay for common 

brick may contain as much as 15 per cent of lime. If the proportion 

of lime is about three times as great as that of iron and if the temperature is high enough, the red. color ordinarily resulting from iron 

is changed to buff.

Limestone pebbles in a clay cause more serious difficulties than 

finely divided lime. In burning, the pebbles give off large volumes 

of gas concentrated in certain, spots, and the lime formed has a 

tendency to expand and destroy the ware. The temperature may be 

raised to the point where the lirne reacts with the bases, but the 

pebbles are usually so large that reaction is only superficial. Before 

they are completely vitrified most bricks would be softened to a 

viscous condition. Worst of all is the effect of the lime formed 

from the pebbles after burning. As the brick is exposed to moist air 

or weathered, the lime hydrates .and swells. Very small grains do 

not disrupt the ware, but pebbles can break even a large well-burned 

brick; and many kilns of clay containing them have been burned 

without the production of a thousand satisfactory brick. To avoid 

these disastrous results, several processes, all of which involve added 

expense, have been devised. (See pp. 55-57.)

The variations in the mineralogic and physical condition of the 

elements in a clay make it impossible to predict with certainty from
24 CLAYS AND SHALES OF MINNESOTA.

an analysis how the clay will behave in the fire or what will be the 

value of the burned ware. The following table gives analysis of 

the gray drift as dug from the ground, unfit without washing for 

brick or tile, and of a good clay that can be sent directly to the brick 

machine. With the analysis of the original clay dug at Hutchinson 

(No. 1) may be compared that of the average clay used, after washing, as given in the section on McLeod County (p. 193)'.

Analyses of calcareous clays.

 '

Soda . ...............................................................................

Potash. . ............................................................................

Pebbly 

clay.o

58.85

7.25

4.97

3.45

9.42

1.37

1.76

11.20

2.10 .36'

100. 73

Finegrained 

clay'.b

53. 32'

8.87

4.71-

6.62,

9.21 ' -6.60'

2.26

6.07

1.94

.37

99.97

a Hutchinson gray drift; requires washing to remove pebbles before use.

b East Grand Forks, silt of Red River valley; used without treatment. ' -

Besides this uncertainty as to the effect of the lime reported in 

analyses, due to textural differences, there is a variation in the effect 

of lime, due to the presence of other impurities and the proportions, 

of the several oxides, even if the textures are uniform. If two substances like lime and clay combine to form a fusible mixture, the< 

particular mixture which fuses at a minimum temperature is called 

a eutectic. An excess of lime over the proportion required for a 

eutectic mixture will not flux so actively as the eutectic proportion. 

Therefore, the amount of lime that is most injurious in clays is uncertain and varies with the other constituents, but the' proportion 

of lime that commonly results in rapid vitrification is stated to be 

from 2 to 8 per cent. Very few clays containing more than 15 per 

cent of lime can be utilized for ceramic products of any sort, but. 

it has been demonstrated in practice that certain clays containinga much higher percentage make good common brick. No such clays 

are known in Minnesota, however, and a high proportion of lime is 

taken as a sign that the clay is unfit for brickmaking.

If the lime is present in the clay as a silicate, such as hornblende, 

instead of as the carbonate, calcite, the eutectic will contain otheringredients and vitrification may be more gradual. Iron and the 

alkalies, if present, also affect the fusion of lime and clays, making' 

it still more difficult to predict their behavior. Lime is never added 

to improve a clay, though small amounts of calcareous clay might, 

be added to some of the Minnesota fire clays to strengthen the brick.,
MINERALOGIC A.~NV CHEMICAL PKOPEKTIES OF CLAY. 25

Gypsum, the sulphate of calcium (CaSOJ, may be an original 

constituent of clays or it may form in clay by a reaction of sulphuric 

acid from iron sulphide minerals on crystals or veins of calcite. 

At high temperatures its effect on fusibility is much the same as 

that of calcite. It may produce an efflorescence in burning or after 

exposure to the weather. A careful study of the effect of gypsum 

on clays has been made by Kramm.1

IKON OXIDES AND SULPHIDES.

Iron is the main coloring element in clays, both raw and burned. 

Its compounds are easily fused and form easily fusible mixtures. 

Iron combines with oxygen in several proportions in hematite, limonite, magnetite, and the silicates. Hematite or ferric oxide (Fe2O3 ), 

more or less hydrated, is the most common. In vitrification its effect 

on clays is generally good, as it causes only a gradual softening of 

the heated mixture. Many analyses of clays show both ferrous and 

ferric oxide, but this is not of special importance, for in burning, 

after the early oxidation stage, all the iron is in the ferric form. It 

can be oxidized or reduced at will, by regulation of the fire, and 

color and fusibility of the product vary with the treatment it receives. If much organic matter is present, the oxidation of the iron 

may be delayed and the ware may be entirely ruined by the persistence of the ferrous compounds which differ greatly from the normal 

ferric compounds in fusibility and color. The total iron oxide in 

clays ranges froin a trace to over 30 per cent. The coloring and 

other effects it produces are complex and are discussed in the paragraph on heat effects.

The carbonate of iron, siderite (FeC03 ),and the several sulphides 

of iron, largely pyrite (FeS2 ), are somewhat more fusible than the 

oxides, but if the temperature is raised slowly they give off their 

acid vapors and become ferric oxide.

MAGNESIA.

Magnesia is a common constituent of the original silicates from 

which impure clays are derived, but most of the magnesia is removed 

in solution by weathering, and only traces of the silicates are usually 

found. Along with the calcium carbonate, some clays contain magnesium carbonate, apparently formed. by reaction of circulating 

water solutions on the. calcite. Dolomite, a mineral containing both 

calcium and magnesium, is common in Minnesota, and its effects 

may be assumed to be much like those of calcite. Magnesia does not

1 Kramm, H. E., Effects of gypsum on clay: Am. Ceramic Soc- Trans., vol. 13( 

p. 703, 1911.
26 CLAYS AND SHALES OF MINNESOTA.

increase the rate of vitrification so much as lime, nor does it destroy 

the red color of the oxidized-iron compounds so readily as lime. 

Sulphate of magnesium is a soluble salt which is sometimes reported 

in clays and which is capable of producing an unsightly efflorescence.

SULPHUR.

Sulphur occurs in iron, calcium, and magnesium compounds. In 

whatever form it is originally present in the clay, it soon becomes 

oxidized in the kiln, forming the gases S02 and S03 and, if metallic 

oxides are available, compounds known as sulphates. The gases 

formed must escape, even from the interior of a brick, and sometimes the sudden expansion, due to the escaping gases, does some damage. The sulphates formed are largely soluble, and if the temperature is not high enough to destroy them they may cause unsightly 

efflorescences. At a temperature of 800° C. more than half of the 

sulphur is given off and above 800° C. part of the remainder is 

very slowly removed. At the vitrification point the sulphates are 

mostly destroyed and gases given off. These gases may cause swelling and "bleb" structure. Pyrite (FeS2 ) and gypsum (CaSO4 .2H2O) 

occur in the Cretaceous and Decorah shales of Minnesota.

ORGANIC MATTER.

The organic matter scattered in the clay is usually of a peaty or 

bituminous nature and is lower in specific gravity than most minerals. It may give the clay a color ranging from green or blue 

to black or brown. It is thought by some that organic matter in 

colloidal form is the chief cause of the plasticity of clays and their 

dry tensile strength, but the relation is still uncertain. Much 

organic matter may accompany lean, weak clays.

In the burning process organic matter disappears, forming carbon dioxide and water vapor at temperatures depending largely on 

the supply of air. During its combustion it acts as a fuel and may 

cause a sudden rise in temperature. It has more affinity for oxygen 

than iron has, and it usually burns out completely before iron is 

thoroughly oxidized. It is this relation to the oxidation of iron that 

makes organic matter troublesome in certain clays. Furthermore, 

the removal of carbon leaves the clay mass porous and much lighter 

than it would otherwise be and causes a very high shrinkage when 

the mass is heated to the point of vitrification. If the ware is not to 

be vitrified, however, the porosity may be desirable, as it makes the 

product of lighter weight. For fireproof buildings, if an extra light 

brick is wanted, as much as 20 per cent of sawdust is often added to 

the clay to decrease the final weight.
MINERALOG-IC AND CHEMICAL PEOPEKTIES OF CLAY. 27

TITANIUM, COPPER, MANGANESE, AND PHOSPHORUS.

Titanium, copper, manganese, and .phosphorus are commonly 

present in clays in small amounts only, and their effects are not important. Experiments indicate that if exceptional quantities are 

present each of them has a decided effect on the quality of the burned 

clay. Titanium, the most abundant, commonly forms less than 1 

per cent of the clay and affects the fusion point of pure fire clays 

only a few degrees centigrade. , Manganese compounds are the only ones of the group that are 

ever purposely added to effect changes in the product. One-fourth 

of 1 per cent of manganese will noticeably change the color of many 

wares. The changes commonly desired are from red to brown or 

from buff to gray. The usual procedure is to mix one part of 

powdered manganese dioxide and nine parts of clay with water into 

a thin slip, and to use this as a stock reagent to be added to the clay 

in amounts to be determined by actual practice. Speckled brick are 

made by using granulated instead of powdered manganese.

ALKALIES.

Soda, potash, and small amounts of lithia are reported in clay 

analyses. These are present as remnants or residuals of the original 

alkaline silicates from which the clay minerals have formed, as 

partial decomposition products and less abundantly as other salts. 

Most of them, such as the feldspars, are no more plastic than sand 

and have about the same effect on the raw clay, but some, such as 

the micas, are soft and slightly plastic. In burning, these alkalies 

act as powerful fluxes and cause a slow and very desirable kind of 

vitrification. For the highest grades of chinaware, orthoclase, the 

potash feldspar, is usually added in definite proportions. As orthoclase melts it forms a highly viscous fluid, whose viscosity decreases 

very slowly as the temperature is increased. It can thus be melted 

without rapidly losing its form. Other alkaline minerals behave 

similarly, but the exact behavior of each is not clearly understood. 

Potash is much the most abundant and soda next, but few clays 

contain lithia in determinable amounts.

STATE OF MINERAL COMBINATION.

The constituents mentioned above behave differently, according 

to their state of combination that is, their behavior depends on tho 

minerals which are present.in the clay. The minerals observed in 

the clays of Minnesota are kaolinite and related aluminum silicates, 

pyrite (or marcasite), quartz, hematite, limonite, calcite, dolomite, 

siderite, hornblende, micas, gypsum, feldspars, chlorite, staurolite,
28 CLAYS AND SHALES OF MINNESOTA.

rutile, and glauconite. Other minerals likely to be present are the 

oxides of manganese, as well as alum, epsomite, and zeolites. No 

systematic classification has been devised to indicate the minerals 

or elements present, but such terms as calcareous clays, ferruginous 

clays, and micaceous clays may be used to indicate the presence of 

impurities.

Rational analyses of clays are attempts to estimate by chemical 

tests the proportions of the several minerals contained. If a clay 

is of high grade and contains only a few minerals (except in minute 

traces) such an estimate is easily made by determining the percentage of the clay soluble in certain reagents and making a few 

simple chemical determinations. For example, potters have long 

used- a combination of clay substance, feldspar, and flint, mixed 

according to some definite formula, By first treating the crude clay 

'with hot concentrated sulphuric acid and later with a solution containing 5 per cent of sodium carbonate, the clay substance or kaolinite can be dissolved and its amount determined. In the residue of 

feldspar and flint the determination of either the alkali or alumina 

is sufficient to determine both minerals. Then the potter can add 

flint and feldspar to meet the requirements of the formula. When 

the flint, 'feldspar, and clay have been derived from similar sources 

and treated in similar ways, such an analysis gives easy and satisfactory control; but with a new clay deposit or a change in the 

grinding or treatment it will be found that materials having the 

same rational analysis will vary a good deal in behavior. If the 

clay is impure, containing as it may a dozen or more minerals, it 

is absurd and misleading to report the material as consisting only 

of clay, flint, and feldspar.

The flint is often reported as "free" or " uncombined " silica. 

For cement mixtures uncombined silica is less desirable than combined silica, and the rational analysis thus serves as a test of the 

availability of a clay for the manufacture of cement.

VALUE OF CHEMICAL TESTS.

Chemical tests can determine very little as to the applicability of 

clay to any specific purpose. Certain general relations may, however, be stated:

1. High-grade clays, suitable for use in making refractory ware 

and as kaolins, should show nearly the percentages of alumina and 

water shown by kaolinite and should not be too high in silica. They 

should contain little else. Commonly accepted though arbitrary and 

not wholly reliable limits place the permissible total content of lime, 

magnesia, and alkalies at not over 4 per cent and of iron oxides at 

not over 3 per cent.
PHYSICAL PROPERTIES OF CLAY. 29

2. Fusibility is more or less closely related to the amount of impurities, and the relation is useful even if inaccurate, especially in 

considering refractory clays. In general, the greater the total sum 

of fluxing impurities the more fusible the clay. Detailed calculations are seldom of value.

3. The color of burned ware can be roughly foretold from the 

amounts of iron and lime. Clays with 3 per cent or more of iron 

oxide tend to burn red, unless an excess of lime is present. Other 

matters are involved, as for example the evenness of distribution 

and fineness of the grain of the iron and lime and the character of 

the gases in the kiln.

4. The shrinkage is related in some indefinite way to the water 

content. Usually a clay containing much hygroscopic water is. plastic and has a high air shrinkage. A clay with much combined water 

and organic matter will show high fire shrinkage on vitrification. 

A high proportion of silica usually accompanies a rather low water 

content, low shrinkage, and low plasticity.

5. The rate of vitrification is likely to be undesirably, rapidl if; as 

much as 5 to 10 per cent of lime is present, especially if the lime is 

accompanied by other fluxes.

6. Soluble salts likely to produce efflorescences are indicated by 

sulphur. Some analyses include estimates of " soluble salts."

7. The particular chemical constituents for making cement'can be 

estimated.

8. A comparison of two clays of similar type can sometimes be 

made by one or two chemical determinations.

All except the last two of these relations can usually be determined 

more accurately, in less time, and at less expense by physical tests 

than by chemical tests. The physical tests are more accurate because 

the behavior of a clay varies not only with the composition but also 

with the texture and the combination of elements. For this reason 

not many analyses have been made for this report. Widespread 

types have been analyzed, however, and the effects of washing, both in. 

practice and in laboratory tests, have been studied by analyses of 

all the materials involved.

PHYSICAL PROPERTIES OF CLAYS.

As clays are made up of many different materials, mixed in an 

infinite variety of proportions, it is to be expected that the range 

in their behavior and applicability will be great. Some of the qualities of the mixture called clay are extremely important and are the 

very foundation of most of its uses. These are plasticity when wet j 

shrinkage on drying; tensile strength when dry; behavior when 

heated, including temperature of fusion, rate of vitrification (tern- .
30 CLAYS AND SHALES OF MINNESOTA.

perature range), shrinkage, and loss of volatile parts, and color and 

toughness (strength and hardness) of products; and miscellaneous 

properties, such as slaking, bonding power, specific gravity, porosity, 

fineness, feel, odor, taste, and homogeneity.

PLASTICITY.

By plasticity is meant ability to be molded, involving change of 

form without rupture, and strength to retain the molded form, so 

that when complex forms are built up they are self-supporting. By 

virtue of plasticity, clay is molded into and retains the forms required for great building blocks or preserves the finest lines of the 

artist's tool.

Unfortunately there is no simple means of determining with accuracy the degree of plasticity shown by clays, but anyone who has 

handled a,great variety of clays can easily tell whether a clay is of 

high or low plasticity and can distinguish different kinds as well as 

different degrees of plasticity. For example, some clays run 

smoothly through a die and some will drag at the corners; some are 

" rubbery " and some " waxy." These minor variations, though hard 

to define clearly, are readily felt by the expert and may affect the 

uses of the clay. It is common to speak of clays as " very plastic " 

(" fat" and " rich ") or " nonplastic " (" lean " and " poor ").

In practice, if a clay is too plastic it is too difficult to mold, and its 

plasticity must be reduced by the addition of nonplastic material, 

usually sand or burnt clay (grog). The preheating experiments of 

Bleininger showed a similar reducing effect on plasticity. (See p. 34.) 

If it is too lean a highly plastic clay may be added, though not 

% always with satisfactory results; for instance, a plastic clay that is 

not refractory can not be added to a lean fire clay without injuring 

its refractory character. For these reasons other methods for improving plasticity have been sought. Fine grinding may be beneficial. A common method of increasing plasticity is to leave the clay 

exposed to weather and frost for a season. The exact nature of the 

effect thus produced is uncertain, but probably it extends both to the 

fineness and to the proportion of colloidal matter. A third method 

is the addition of alkalies, acids, salts, organic colloids like tannin, 

or other solutions.

In " tempering a clay " (preparing it for molding) water is usually 

added according to the judgment of the worker. Some clays are of 

proper consistency when dug from the pit. Different clays and 

different processes of molding require different proportions of water. 

The percentage of water present at the proper consistency for molding by hand is often called the "water required" or the "water of 

plasticity." It varies with the judgment of the operator but is usu-
PHYSICAL PROPERTIES OF CLAY. 31

ally reported because a. large amount of it indicates a tendency to 

crack on drying.

Plasticity is of such fundamental importance that its origin and 

causes have been the subject of much investigation. The minerals 

from which clays are derived are not notably plastic; neither are the 

majority of residual kaolins as first formed. No particular proportion of a certain chemical element, no particular physical property, 

and no particular geologic process has been determined to be necessary fpr the development of plasticity in wet clay. Yet no other 

mineral powder is so plastic, and no other has been made so plastic by 

the addition of reagents.

Study of the plasticity of clay must be directed, first, to finding 

an explanation of the ability of the clay to flow without fracture, 

and, second, to finding an explanation of its strength or resistance 

to flow, even when it can be molded by the use of force.

The flow age is ordinarily thought to be due to the water added. 

It is well known that the addition of water to any fine powder lubricates it, and if enough is added the whole mass becomes somewhat 

fluid and can be molded. This seems to be generally agreed upon and 

understood. Disagreement arises, however, in explaining the 

strength of the wet mass. Water has so little viscosity that it would 

seem at first glance that enough water to cause lubrication would 

result in very slight viscosity no strength at all.

For the strength shown by wet clay two explanations, and, thus far 

only two, have been offered, and both are explanations of the conditions under which water is rendered more viscous than in its ordinary state. One theory explains the increased viscosity of the water 

as being due to dissolved material and, as dilute solutions of ordinary matter are not very viscous, to colloidal solutions solutions of 

the particular form of matter known as colloids. This theory has 

met with widespread favor. The other theory attributes the viscosity of the water to a strong attraction between the clay grains and 

water, called molecular attraction, which is active through only a 

short distance.

The colloid theory is based largely on the known presence of colloids of some sort in a clay;1 on the analogy between some of the 

properties of clay, such as hygroscopicity, adsorption, and dry tensile 

strength, and those of some colloids (mostly organic); and on the 

fact that the addition of colloids improves the plasticity of lean clay. 

But, as opposed to a full acceptance of this theory at present, no one 

has yet shown that the colloids in a clay are quantitatively sufficient' 

to produce the results. Neither has anyone succeeded in making a

1 Schloessing, T., The constitution of clays: Compt. Rend., vol. 69, pp. 376, 473, 1874. 

Grout, F. P., and Poppe, F;, Plasticity of clay: Am. Ceramic Soc. Trans., vol. 14, p. 71, 

1912.
32 CLAYS AND SHALES OF MINNESOTA.

nonplastic mineral powder as plastic as common clay by the addition 

of colloids. The colloids in clay no doubt improve the plasticity and 

may be considered as a partial cause of it.

The molecular-attraction theory is based on the fact that when 

a liquid wets a solid a very thin film of liquid adheres to the solid so 

strongly as to be practically bound and is certainly rendered infinitely 

more viscous than the water outside the film.1 A calculation in some 

detail 2 shows that the amount of water required to produce such a 

film around each clay grain and fill the pores between such enlarged 

grains is about equal to the water usually added in tempering. The 

calculation, however, applies to any fine mineral powder, and it remain's to be shown why the viscosity should be greater with clay than 

with other minerals. The essential fact at the basis of the theory is 

that molecular attraction varies with the nature of the solid and 

liquid involved and seems to be greater between clay and water than 

between other minerals and water. Changes in plasticity on the addition of chemicals may be ascribed to changes in the nature of the 

solutions, and consequently in the molecular attraction. This also explains why some kaolin is plastic and some lean, for it is the chemical 

constitution (as distinct from composition or elements present) that 

determines the attraction. The molecular attraction, on which this 

theory is based, seems to be quantitatively sufficient to explain plasticity. As. factors that modify plasticity colloids are probably, of 

first importance. Fineness and shape of grain also have their influence on the amount of water bound in the viscous films.

SHRINKAGE.

The attraction between clay grains and water is so great that it 

is usually assumed that in plastic clay a film of water envelops each 

clay grain. The drying of such a clay would naturally affect the 

size of the mass. The outer part of the plastic mass, being exposed 

to air, gives up its water and the space between grains either decreases, resulting in a contraction of the mass, or remains open, 

being filled with air instead of water. However, under ordinary 

conditions, capillarity draws water from the center toward the drier 

outer part, and the lubricating action of the water allows a slight 

readjustment in the whole mass. As a total result the same amount 

of clay remains with a smaller amount of water, the film having 

become thinner throughout, without any great change in arrangement. The process may be continued until the clay grains are no 

longer well lubricated. When the clay grains are actually in contact, the removal of water can no longer bring them closer, but there

1 Daniell, Alfred, A textbook of the principles of physics, 3d ed., p. 306, Macmillan Co., 

1911.

2 Grout, F. F., and Poppe, F., op. cit, p. 75.
PHYSICAL PEOPEKTIES OF CLAY. 33

remains some water in the pores which will gradually be taken into 

the air and be replaced by air. Shrinkage may be measured as 

volume shrinkage or as linear shrinkage. It is usually assumed that 

one may be calculated from the other on the basis of volumes being 

proportional to the cubes of lines. But this is not always true, as a 

flat plate of wet clay will dry more rapidly from the large flat surface than from the edges, and the greater part of the shrinkage will 

be at right angles to the flat surface. Shrinkage ranges from 1 to 

15 per cent linear measure and from 3 to 48 per cent volume measure. 

In the arts the shrinkage of clay is important. If bricks or chinaware of a certain size are required, allowance for shrinkage must be 

made by molding them just enough larger than the required size. 

If large masses of clay must be dried or if shrinkage is great, there 

is often danger that the outside will dry and shrink faster than 

internal readjustment can take place.. The rate of capillary flow 

varies with the fineness of the grains, the distance to be covered, and 

other factors. If cracks form or the shape is badly distorted and 

warped, the mass is injured if not entirely ruined. The phenomenon 

is identical with the formation of cracks on the surface of a mud 

flat. In the arts the process is called checking. If the shrinkage is 

great it may be necessary to dry masses the size of common brick 

with great care for a long time to avoid cracking. Many clays 

otherwise of good quality are now neglected because they check so 

badly on drying. Such clays, which are often spoken of as "joint 

clays," are, as a rule, highly plastic, but require much water to develop their plasticity. There is, however, no constant relation! 

between shrinkage and plasticity. Sandy clays and flint fire clays 

and kaolins show little shrinkage. The accepted remedy for checking is the addition of sand, " grog" (burnt clay), or other nonplastic material just such material as corrects excessive plasticity.

TENSILE STRENGTH.

The term " tensile strength " usually means the tensile strength of 

dry clay. The strength of wet clay is not tested except in so far 

as it relates to plasticity. Probably the measure of crushing strength 

would be more useful, as clay ware is more often subjected to pressure than to tension. Usually, however, a clay of good tensile 

strength is strong enough, and the test is more easily made by following roughly the standard methods of testing cement. The tensile 

strength of clays ranges from 30 to 350 pounds to the square inch: 

100 pounds is enough for most purposes. From the plastic state 

to the dried state the tensile strength increases continuously. Clay 

grains, originally separated by films of water, have been left in inti64310° 19 3
34 CLAYS AND SHALES OF MINNESOTA.

mate contact by the evaporation of that water and at last adhere to 

one another strongly. The gluelike nature of any colloids that may 

have been in solution also manifests itself as the water is removed.

EFFECTS OF HEATING.

The effects of heating are so complex that the subject must be 

subdivided. Heating decreases plasticity, tensile strength, and 

shrinkage; drives off certain volatile products; induces important 

chemical reactions; causes progressive fusion,,which can be studied 

at several stages; and affects the quality of the product, including 

its color, shrinkage, toughness, hardness, and strength.

PREHEATING.

Bleininger 1 has made an exhaustive study of the effects of temperatureis up to.400° C., in the hope of finding a means for correcting the 

defects of clays that check or crack badly in drying. His results 

show that most clays after heating to 250° to 300° C. require less 

water to make them plastic and have less plasticity and air shrinkage. Subject to certain limitations, which are clearly discussed in the 

paper cited, preheating offers valuable commercial possibilities in 

Minnesota, for there are immense bodies of joint clay in the Red 

River valley. . 

EXPULSION OF VOLATILE MATTER.

Hygroscopic moisture is as a rule completely removed from the 

clay ware before it is placed in a kiln for firing. During firing a 

series of products is removed, whose nature depends somewhat on 

the impurities of the clay. The most prominent constituents driven 

out are water, hydrocarbons, carbon dioxide, and sulphur, each of 

which requires a different degree of heat for its expulsion. Oxygen 

may be driven off or combined with the clay, according to the conditions of firing. Firing at red heat increases the porosity without 

much change in the size or strength of the ware. A too rapid increase of temperature and evolution of gases may break the clay mass 

with an explosive violence that may injure the ware near by. Snapping of this sort is seldom troublesome if care is used in removing 

water. If it is really troublesome and can not be prevented by 

thorough drying, it may be lessened by preheating.

The burning of the organic matter in the clay produces heat, like 

the addition of more fuel, and may cause a sudden undesired rise 

in temperature. Iron should be oxidized at 500° to 600° C., yielding

1 Bleininger, A. V., Effects of preliminary heat treatment on the drying of clays: Bur. 

Standards Bull., vol. 7, No. 2, 1911.
PHYSICAL PKOPEETIES OF CLAY. 35

normally a red color if abundant, but the oxidation may be delayed 

if oxygen is excluded by the evolution of other gases. At a temperature somewhat higher than 600° C. the carbonates, chiefly calcium carbonate, begin to give off carbon dioxide and leave a chemically active lime residue in the clay. Sulphur may be evolved and 

oxidized from sulphides like pyrite at low temperatures but remains 

in sulphates like gypsum until very high temperatures are reached. 

If fusion begins before all these gases are evolved, the clay mass will 

swell and become vesicular or " blebby " and be ruined.

CHEMICAL REACTIONS.

The oxidation and reduction of clays are complex, depending on 

the supply of fuel and air and on the temperature of the kiln as it 

rises to the. successive fusion points of the several compounds present in 

the clay. Furthermore, reactions may produce a liquid from two 

solids which are in contact, even if the temperature is not high 

enough to melt either. The familiar example is ice and salt, which 

become liquid when mixed, at temperatures below the melting point 

of either. In clays lime and silica are examples of such substances. 

The fused material later acts as a solvent, which absorbs other minerals and which at this high temperature in fluid or semifluid condition 

is chemically more active than before. As silica is usually the chief 

acidic oxide present, the main products are silicates of indefinite 

mixed composition. After firing, these melted silicates solidify, forming the cementing material between the more solid grains and giving 

the rocklike quality to the finished ware. To them is largely due the 

character of the final product; if they are tough, the ware will be 

tough; if 'brittle, the ware will be brittle; if too scanty, the ware will 

be soft; and if too abundant, the ware will be deformed or melted. 

It is probable 1 that the chemical nature of the melt largely determines its toughness, and that magnesia, iron, and the alkalies give a 

tougher product than lime.

FUSION.

The formation of the fused silicates is progressive, increasing as 

the temperature increases. The first liquid to form, if kept at the 

temperature of formation, may dissolve some considerable portion of 

the surrounding minerals without becoming less fusible. If the temperature is raised, other minerals and combinations become fused and 

dissolve still other materials.

The fusion of the clay is therefore to be studied as a progressive 

and not as a sudden change from solid to liquid. Three stages are

1 Grout, P. F., and Brown, H. I-I., Relation of composition and properties: Am. Ceramic 

Soc. Trans., vol. 14, p. 355, 1912.
36 CLAYS AND SHALES OF MINNESOTA.

usually noted incipient fusion, vitrification, and viscosity. The

-" temperature of fusion " is usually considered to be that of viscosity

-under no load. Fusion under load 1 is a test applied only to refractory clays.

At incipient fusion only the minerals and combinations with the-, 

lowest melting points are fused. If the fused parts are abundant, the 

whole mass, when cooled, will form a steel-hard product, so that hardness of the product is the common sign of incipient fusion. This 

degree of fusion causes very little shrinkage. Common brick usually 

require no further heat, and fire clays are not often burned even to 

this stage.

At vitrification enough of the clay has fused to fill nearly all the. 

pores between the unfused grains, but unfused material is still abundant and the fused portion is so viscous that the ware keeps its shape. 

Shrinkage is usually high. A large amount of high-grade ware is 

burned to or very near vitrification. Porcelain and chinaware bodies,, 

flooring tile, paving and foundation brick, and sanitary ware are 

usually vitrified, and some also receive a glaze, which makes the ware 

quite impervious to water. Many vitrified bricks are used for ordinary building, as they are more durable and resistant than common 

brick, and some have better color.

At a still higher temperature the clay becomes viscous, its unfused 

particles being quite surrounded and suspended in the fused and 

liquid portion, and the mass flows, losing its original form. When 

brick piled in a kiln have been burned to the approach of viscosity 

they may stick together and, if not too greatly deformed, may be 

broken up into blocks of about the size and shape of brick with the 

rough, irregular surface of broken stone. Such brick can be used 

in producing many artistic effects and have become popular under 

the name " klinker brick." (See PL II, A, B.) The actual temperature of viscosity, commonly noted as the fusion temperature, varies, 

widely.

RANGE" OF VITRIFICATION.

A most important point in determining the applicability of a clay 

to different processes of manufacture is the range of temperature 

between incipient fusion and the viscous state. In firing a kiln 

.full of clay ware the combustion chambers can not be so distributed 

.as to give absolutely uniform temperature throughout. Well-made, 

expensive kilns can approach uniformity very closely, but all are 

likely to show a variation of a few degrees. If it is desired to fire 

a brick to vitrification at 1,200° C., the top or bottom courses may

' x Blcininger, A. V., and Brown, G. H., The effect of heating fire clays 'under load: Am. 

Ceramic Soc. Trans., vol. 12, p. 337, 1912.
TJ. S. GEOLOGICAL SURVEY BULLETIN" 678 PLATE II

A. SMOOTH AND CLINKER BRICK FROM 

WEST ST. PAUL.

S. SMOOTH AND ROUGHENED BRICK 

FROM COON CREEK.

C. BRICKLETS BURNED IN LABORATORY TEST.

l>. LIMY CONCRETIONS IN GRAY LAMINATED CLAY.
PHYSICAL PROPERTIES OF CLAY. 37

reach only 1,160° and the brick nearest the fire "may reach 1,240°. 

If the point of incipient fusion is only 40° below the point of vitrification, the underburned brick will not be salable. But if the 

incipient fusion is 100° to 200° below vitrification there is every 

reason to expect that all the brick fired within 40° of the point of 

vitrification will be so nearly vitrified as to be entirely satisfactory. 

On the other hand, if the viscous state is reached at 1,240°, the brick 

near the fire will be waste, but if it is not reached for 200° after 

vitrification the brick burned to 1,240° will no doubt be of good 

quality. The losses due to unclerburning and everburning may be

Cone No. 010 04. 02 

TEMPERATURE IN"CONES

FIGURE 3. Temperature-porosity curves for refractory and semirefractory clays. (After

Purdy.)

as high as 30 per cent of the kiln. Underburned brick may be 

returned to the kiln, but they never equal brick directly fired to thg> 

proper point.1

The importance of determining the range in temperature during 

fusion has led to a careful study by Purdy 2 that resulted in recommendations for tests of porosity and specific gravity as a measure 

of vitrification. The accompanying diagrams (figs. 3 and 4) give, 

a general idea of the method used in distinguishing the applicability 

of a clay from its behavior. By firing bricklets of clay to several

1 Grimsley, G. P., and Grout, F. F., Physical tests on West Virginia building and 

paving brick : West Virginia Geol. Survey, vol. 8, pp. 293-294, 1906.

2 Purdy, R. C., Pyrophysical and chemical properties of paving-brick clays: Illinois 

Geol. Survey Bull. 9, pp. 277-278, 1908.
38 CLAYS AND SHALES OF MINNESOTA.

different temperatures and determining their porosities a curve 

showing the rate of vitrification can be drawn. This curve, if com-! 

pared with Purdy's diagram, will indicate the applicability of the 

clay. In practice, however, the behavior of a clay is much more 

commonly judged by inspection of the bricklets burned to several 

different stages. A knife will easily show the steel-hard brick 

burned to the point of incipient fusion, and a glance will show the 

deformation of the bricklet burned to the viscous state. If these 

stages are widely separated in temperature, the clay can be safely

Cone No. 010

FIGURE 4. Temperature-porosity curves for brick clays. (After Purdy.)

vitrified. The temperatures to which common clay wares are burned 

are shown in the following table in terms of Seger cones:*

Cone.

022

021

020

019

018

017

016

015

014

013

012

Oil

010

09

08

°C.

590

620

650

680

710

740

770

800

830

800

890

920

950

970

990

°F.

1094

1148

1202

1256

1310

1364

1418

1472

1526

1580

1634

1688

1742

1778

1814

Cone.

07

06

05

04

03

02

01

1

2

3

4

5

6

7

8

°C.

1010

1030

1050

1070

1090

1110

1130

1150

1170

1190

1210

1230

1250

1270

1290

°F.

1850

1886

1922

1958

1994

2030

2066

2102

2138

2174

2210

2246

2282

2318

2354

Cone.

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

°C.

1310

1330

1350

1370

1390

1410

1430

1450

1470

1490

1510

1530

1550

1570

1590

°F.

2390

2426

2462

2498

2534

2570

2606

2642

2678

2714

2750

2786

2822

2858

2894

Cone.

24

25

26

27

28

27

28

29

30

31

32

33

34

35

36

°C.

1610

1630

1650

1670

1690

1670

1690

1710

1730

1750

1770

1790

1810

1830

1850

°F.

2930

2966

3002

3038

3074

3038

3074

3110

3146

3182

3218

3254

3290

3326

3362

1 Seger cones are small cones made of clay and chemicals so mixed that they soften at 

known temperatures, as indicated above. More accurate pyrometers are seldom needed 

in clay work.
PHYSICAL PKOPEKTIES OF CLAY. 39

Temperatures for burning common clay wares, vn, terms of Seger cones,

Cone.

Common brick___________________________ 012-01 

Hard-burned common brick____________________ 1-2 

Buff-faced brick_______.___________________ 5-9 

Fireproofing _____ __ ______________ 03-1

Terra cotta____:__________________________ 02-8 

White earthenware_________________________ 8-9 

Fire brick_____'.___________________________ 5-14

Porcelain _____________. 11-13 

Sewer pipe___________________________ 3-7

QUALITY OF THE PRODUCT.

The several steps in the process of heating have important effects 

on the quality of the product. Color is due largely to the content of 

iron or manganese, but in the firing it is modified by the oxidizing 

or reducing gases and by the degree of vitrification. Shrinkage becomes notable at the beginning of fusion, is complete at thorough 

vitrification, and may be replaced by swelling if gases are evolved 

after the formation of much glass. Hardness, strength, and toughness are all low until fusion begins; after that they depend on the 

quantity of glassy cement produced until vitrification is reached; 

after that they depend on the character of the glassy cement. Lime 

pebbles are causes of very serious difficulty. (See p. 23.)

MINOR PHYSICAL PROPERTIES.

Slaking is the quality by which a dry lump of clay tends to absorb 

water and fall to pieces when immersed. Clays that slake promptly 

are easily rendered plastic without fine grinding.

Bonding power is the ability of a clay to hold in suspension lessplastic material and to render the whole mass plastic and strong. It 

is usually though not invariably good if plasticity is high.

The specific gravity, porosity, fineness, feel, and color of raw ' 

clays may bear some relation to their availability for certain uses, 

but no one has yet discovered a system by which any useful property 

may be judged from these qualities.

Fineness of grain probably affects the fusibility and rate of fusion 

of impure clay3 but is less effective in high-grade clays.1 The particles in a clay range in size from less than 0.001 millimeter to the 

size of a coarse sand. In general the finest particles approach the 

composition of kaolinite, though in some clays lime and iron also concentrate in the fine portions. The coarser particles are in general 

more siliceous.2

1 Hofman, H. 0., Am. Inst. Min. Eng. Trans., vol. 28, p. 440, 1898.

2 Grout, F. F., West Virginia Geol. Survey, vol. 3, p. 61, 1906.
40 CLAYS AND SHALES OF MINNESOTA.

Homogeneity might be considered a physical property and is of 

importance in the application of clays to industries, as the variable 

clays need more careful selection and mixing.

CLASSIFICATION AND ADAPTABILITY OF CLAYS.

CLASSIFICATION. 

BASIS.

Clays have been differently classified for different purposes. Commercially, use is the basis of class names. Geologically, origin is 

most important. Technologically, the properties of the clay are the 

best points of distinction. These methods of classification are here 

.kept distinct, as the combination of several methods nearly always 

results in confusion and overlapping groups.

CLASSIFICATION BY USES.

The uses of clay are listed by Hies 1 as follows:

Domestic. Porcelain, white earthenware, stoneware, yellow ware, and Rockingham ware for table service and for cooking; majolica stoves; polishing brick, 

bath brick, fire kincllers.

Structural. Brick, common, front, pressed, ornamental, hollow, glazed; 

adobe; terra cotta; roofing tile; glazed and encaustic tile; draintile; paving 

brick; chimney flues; chimney pots; door knobs; fireproofing; terra cotta lumber; copings; fence posts.

Hygienic. Closet bowls, urinals, sinks, washtubs, bathtubs, pitchers, sewer 

pipe, ventilating flues, foundation blocks, vitrified bricks.

Decorative. Ornamental pottery, terra cotta, majolica, garden furniture, 

tombstones.

Minor uses. Food adulterant; paint fillers; paper filling; electric insulators; 

pumps; fulling cloth; scouring soap; packing for horses' feet; chemical apparatus ; condensing worms; ink bottles; ultramarine manufacture; emery wheels; 

playing marbles; battery cups; pins, stilts, and spurs for potters' use; shuttle 

eyes and thread guides; smoking pipes; umbrella stands; pedestals; filter tubes; 

caster wheels; pump wheels; electric porcelain; foot rules; plaster; alum.

Refractory wares. Crucibles and other assaying apparatus; gas retorts; fire 

bricks; glass pots; blocks for tank furnaces; saggers; stove and furnace bricks; 

blocks for fire boxes; tuyeres; cupola bricks; mold linings for steel castings.

Engineering works. Puddle; Portland cement; railroad ballast; water conduits; turbine wheels; electric conduits; road metal.

Some of these uses are of sufficient importance to give class names 

to clays, as follows:

Fire clay. 

Slip clay. 

Stoneware clay. 

Sagger clay. 

Terra cotta clay.

Brick clay. 

Glasspot clay. 

Paving-brick- clay. 

Paint clay. 

Adobe clay.

Paper clay. 

Tile clay. 

Sewer-pipe clay. 

Pottery clay. 

China clay.

1 Ries, IJeinrich, and Ktiiumel, H. B., Clays and clay industry in New Jersey : New 

Jersey State Geologist Final Kept., vol. 6, pp. 213-214, 1904.
CLASSIFICATION" AND ADAPTABILITY OF CLAYS. 41

These terms are never used in a restricted sense. The same term 

may be applied to widely different clays, and different terms may 

be applied to similar clays. It is hoped that these terms will be 

used less as the properties of the clays become better known.

CLASSIFICATION BY GEOLOGIC ORIGIN.

A classification of clays by geologic origin gives the following:

Residual:

From igneous and rnetamorphic rocks.

From sediments.

Colluvial. . 

Transported:

Marine.

Estuarine.

Lacustrine.

Alluvial (flood plains and terraces).

Glacial: 

Till.

Lacustrine. 

Alluvial.

Eolian, loess.

Metamorphosed slates.

CLASSIFICATION BY PHYSICAL PROPERTIES.

Classification by physical properties should be based primarily on 

the most important and secondarily on the less important properties. 

Plasticity, strength, and behavior in the fire are the major properties, 

and of these fusion is fundamental. If the plasticity or strength is 

insufficient it can be easily corrected by the addition of some proportion of other clay, but if the process of vitrification is unsatisfactory 

it is very difficult to remedy. Hence, the primary division should 

be based on heating behavior. The following classification, however, 

is not ideal, because there is some overlapping between the several 

grades of clay indicated:

Eefractory (fusing above cone 27) : Main uses. 

Earthy, usually residual, nonplastic China clay. 

Plastic______ iBall clay and plastic fire clay; 

Flintlike,. nonplastic______________.Hard fire clay. 

Semirefractory (fusing above cone 10) : 

Vitrifying gradually:

Red burning_____ _______.Sewer pipe, paving brick. 

Buff or cream burning___ ____Stoneware. 

Vitrifying suddenly__-__ Low-grade fire clay. 

Nonrefractory (fusing below cone 10) : 

Vitrifying gradually:

Red burning________________ Vitrified brick, foundation brick,

sewer pipe.

Buff or cream burning_________Foundation brick, sewer pipe. 

Vitrifying suddenly________ ___ Common brick.
42 CLAYS AND SHALES OF MINNESOTA.

Subdivisions of semirefractory and nonrefractory days may be 

based on their degree of plasticity.

SPECIAL. CLASSES.

In addition to the comprehensive systems of classification special 

names are used to designate certain peculiarities. " Shale," one of 

the commonest, is used to indicate an indurated and generally laminated clay. The word is not applied to surficial deposits that have 

never been buried under later sediments, for few of these are laminated. Hardening (induration) is brought about by pressure, and 

cementation is effected by precipitation of mineral matter. The extreme of the hardening process is to be found in the development of 

slates, which are metamorphic rocks. Of those not classed as metamorphic rocks, probably the " flint clays " of the coal measures represent the maximum hardening. These may be grouped with shale, 

properly enough, though they are not usually so distinctly laminated 

as typical shale. Weathering reduces shale to its soft original state, 

probably by dissolving its cement. The term " slate " is incorrectly 

but very commonly applied to shales, especially to shales of the coal 

mines. " Soapstone" is applied, also incorrectly, to a shale that 

has a soapy feeling, which is probably due to a magnesian impurity. 

" Fire clay " is a miner's term for any clay below a coal bed, but as it 

is usually supposed to mean a refractory clay, its use to connote 

position is incorrect and confusing. Joint clay is very fine grained 

plastic clay which shows so great a tendency to shrink on drying 

that it almost invariably cracks. A great many adjectives, such as 

calcareous, ferruginous, and micaceous, are used to designate conspicuous impurities. It may also be worthy of note that geologic 

age is often used as a criterion for distinction, as Archean, Cretaceous, and Pleistocene clays.

Knowledge of the qualities that are essential in the clay for the 

production of certain grades of ware is most important for one who 

is about to develop a deposit. These qualities can be only briefly 

and in some cases not very definitely stated. The relation between 

the various systems of naming a type of clay and its uses is not 

always definite. Each' system is of value, however, in its proper 

place. The physical properties are the most necessary to ascertain. 

The effects of impurities are discussed on pages 22-27. The age of a 

clay is worthy of note, chiefly as a help in finding more deposits. 

Ancient clays are much like recent ones, but in general the older 

formations are igneous or metamorphic, and the only clays they 

contain are either much altered slates or the residual products formed 

by recent decay of the old rocks.
CLASSIFICATION AND ADAPTABILITY OF CLAYS. 43

The relation between mode of origin and properties or uses is; 

equally indefinite. Residual clays formed from igneous rocks vary, 

with the completeness of alteration and the character of the original 

rock. «If thoroughly altered they contain little, if any, of the origi-t 

nal minerals except quartz; iron oxides and musoovite are abundant 

impurities. If iron oxide is lacking, the kaolinite can be washed 

clean and used for china ware, though nearly all of it requires some* 

plastic addition. Residual clays formed from sedimentary rocks 

differ somewhat from those formed from igneous rocks. Among 

transported clays the variety is great. In some parts of the country 

it is possible to find a transported clay that is suitable for almost 

any use to which clays are adapted. Estuarine, lacustrine, and glacial clays occur in similar variety. River clays are more likely to 

be sandy and impure, and will generally make nothing better than 

common brick. i

True slates are seldom used in making clay products, but it is 

believed that excellent building material can be made from some of 

the Minnesota slates.

RELATION OF PHYSICAL PROPERTIES TO USES.

Common-brick clays should be capable of being molded into brick, 

 should burn hard below cone 1 (2,100° F.), and should have a popular color. Somewhat higher plasticity is required for stiff-mud 

brick than for soft-mud brick.

Clay for front brick should be more plastic, so that the brick' 

may hold their form better and present smooth surfaces and square 

corners. Their color after burning is more important than that 

of common brick. Front brick are nearly always burned steel-hard,' 

and should have a good range of vitrification to avoid heavy losses 

from deformation.

Hollow brick and fireproofing blocks are made to attain lightness 

in weight. Other properties being equally good, the lighter and ' 

more porous product is the more desirable. The clay must be plastic 

enough to work in an auger machine with a die for the hollow' 

center. If the bonding power is good, it may be desirable to add 

sawdust to increase the porosity. The brick should have fair tensile 

strength. The color of the burned product is immaterial, but the 

red blocks are usually ferruginous and somewhat heavier than the 

lighter-colored ones. The burning must produce strength and durability in the product rather than hardness or density or beauty. 

Specifications for these products have been formulated, and published.1

iEng. News, vol. 47, p. 177, 1902.
44 CLAYS AND SHALES OF MINNESOTA.

Foundation, sewer, and sidewalk brick, which may be exposed to 

wet, freezing, and thawing, differ from common brick only in their 

degree of vitrification. They must be so well vitrified that water 

can not enter in such a way as to disrupt the brick on freezing. It 

should be possible to vitrify the brick very completely to a porosity 

of only 4 or 5 per cent without leaving many soft brick or many 

viscous, deformed brick in the kiln.

Paving bricks and blocks require material of the same type as 

foundation, sewer, and sidewalk brick, with an added toughness. 

This is even more important than completeness of vitrification and 

is attained with some clays by stopping the heat before vitrification 

is complete. As yet no way is known by which toughness of product 

can be inferred from the composition and properties of raw clays, 

and it is necessary to try them in actual practice.

Clays for draintile are similar to those used in making stiff-mud 

brick. The form of a tile is such that it tends strongly to warp 

and crack in drying. If a brick clay is free from this tendency and 

does not show auger laminations, it will probably make draintile.1

Wall and floor tile are made from buff-burning clays or white 

porcelain mixture, but more attention must be given to color,, and, for 

some purposes, a special glaze is necessary.

Terra cotta clay must be very highly plastic and very strong to 

retain the complex ornamental designs into which it is worked. It 

is usually selected with great care to obtain uniform color and freedom from cracks. It should have a good range of vitrification but 

is only partly vitrified in manufacture.

Clay for sewer pipe must be much like that for paving bricks. 

The product is not subject to the same severe abrasion, but the forms 

are so large and thin walled that high strength is necessary. Only 

a small amount of shrinkage is allowable, as warping and cracking 

are fatal defects. The dark product demanded by the market is 

usually obtained by adding a salt glaze.

Clay for porcelain, pottery, china, and other domestic and sanitary ware requires the highest degree of preparation and control. 

It must be plastic and free from sand, and it is generally washed. It 

must be strong to hold its shape and must not shrink so much that it 

warps. It must burn white or very light and must partly vitrify 

without losing its form. The range in temperature between the 

beginning of its vitrification and the point where it attains the 

viscous state should be over 200° F. The product should be tough 

and strong. Much of it should be capable of receiving a glaze without being cracked and without subsequent breaking away of the 

glaze.

1 Tests for good draintile have been formulated by the American Society for Testing 

Materials (Proc., vol. 11, p. 833, 1911).
CLASSIFICATION AND ADAPTABILITY OF CLAYS. 45

Refractory clays must primarily stand in the structure desired, 

at high temperatures, and they must withstand repeated heating 

and cooling without losing their strength and infusibility. Many 

of the refractory clays are nonplastic and few are burned to incipient vitrification. It has become a custom not to expect high plasticity of refractory clays nor much strength of the product. But if 

the brick are too weak, additions of plastic clay or bonding material must be made, even at the expensexof fusibility. Fire brick 

are sometimes wanted with very coarse grain and open texture to 

prevent the rapid conduction of heat. Such brick are produced by 

the addition of large amounts of crushed burned clay ("grog"). 

For other purposes clay is desired that burns to a very strong, 

dense body at medium temperature and weakens or softens only at 

a very high temperature.

Clays for minor uses must meet varied requirements. Paper clay 

should be white, free from sand, and of good plasticity. Slip clay 

should be fusible and so fine grained that it will remain for a long 

time in suspension in water. Paint clay is so impure with ferruginous minerals as to have a dense color, usually red or brown. Adobe 

is any clay that will dry hard in the sun. Fuller's earth is an impure clay which has the property of absorbing coloring matter from, 

oil. Deposits of several of these different types have been reported 

in Minnesota, but none have been much developed.

TESTS OF CLAYS. 

SAMPLES.

All clay deposits visited in Minnesota were carefully sampled so as 

to get representative material. Pits were sampled by cutting a 

groove from top to bottom of the working face, and undeveloped 

deposits by boring several holes with a 2-inch auger. The samples 

taken for the Bureau of Standards weighed about 100 pounds and 

those for the University of Minnesota about 25 pounds. The results 

may be accepted as good indications of quality but are not by themselves sufficiently conclusive to warrant large investments.

CHARACTER OF TESTS.

Plasticity, strength, shrinkage on drying and burning, burned 

color, and character of vitrification may all be determined in the 

laborator}^. If toughness of the burned product is essential, however, 

adequate data can not be obtained from a small laboratory sample 

and factory tests of carload lots are necessary. Factory tests should 

also be made on clays intended for glazed ware.
46 CLAYS AND SHALES OF MINNESOTA.

The following tests were made in the laboratory of the University 

of Minnesota, and the more important were checked by the United 

States Bureau of Standards with a somewhat better equipment.

Time of slaking of a half-inch dry lump was noted. The sample 

was then ground to 40-mesh, if it seemed desirable.

Plasticity was noted by feel and reported in six degrees very 

high, fairly high, high, low, very low, and sandy.

Ten bricklets, 4 by 1 by^L inch, were molded in a single brick mold, 

under a pressure of 300 pounds, one side being cut with a knife edge 

to get the proper dimensions. Volumes as made were fairly constant. Several briquets were made for tensile tests.

In measuring tensile strength no high degree of accuracy was 

attempted. Results usually differ for different operators, and as 

much as 30 per cent on different tests by the same operator. For 

this reason a test of a single briquet was sometimes considered sufficient', unless it showed exceptionally high or low results. Below 50 

pounds to the square inch is considered poor; 50 to 150 fair; above 

150 high. Correction must be made for shrinkage.

The effect of rapid drying on tensile strength was tested. The 

general effect of rapid drying is manifested by the appearance of 

cracks and checks and is commonly recorded as a personal judgment 

of the operator. Checks are supposed to indicate weakening of the 

briquet. In many of the university tests it was found by tF. M. 

Handy that rapid drying was injurious to the strength of the briquet 

even when checks did not show prominently.

An adhesion test, developed by Mr. Handy, aims to show whether 

a clay loses tensile strength when forced through an auger brick 

machine. When clay products are molded on an auger machine the 

clay is mixed very thoroughly by knives and by the auger, both of 

which cut through the clay and press it forward through a die. In 

most clays the pressure is sufficient to join firmly the parts that have 

been separated in the machine. In some clays, however, the adhesion 

is much less than in others, and in some it is very poor. In the test 

worked out by Mr. Handy a newly molded tensile briquet is cut 

transversely, and then pressed in the molds at 300 pounds to see if 

a firm union can be effected between the divided parts. This is at 

least partly analogous to the action of the auger. None of the briquets 

>so treated were of high strength, but those that showed defective 

auger structure had a tensile strength below 20 pounds to the square 

inch.

The molded bricklets were weighed when wet and again when 

oven-dried. The loss in per cent of dry weight was " water of plasticity." The use of oven-dry weights makes the reported water include hygroscopic water, and the totals are higher than the average
CLASSIFICATION AND ADAPTABILITY OF CLAYS. 47

reported by other investigators; however, this seems to be the only 

logical procedure, for the hygroscopic water is variable.

The volume of the dry bricklets was measured in a modified Seger 

volumeter, in kerosene.

Burning was conducted at several temperatures in a large gasolinefired muffle measuring about 12 by 18 by 6 inches. The colors were 

nearly as bright as in actual practice. The bricklets were stood on 

erid (see PI. II, C) and may have begun to be deformed at a somewhat lower temperature than if they had been laid on one side. The 

temperatures were very nearly uniform through the muffle. The 

rate of heating and temperature reached were shown by a recording 

pyrometer and the use of Seger cones.

The burned bricklets were tested for hardness, color, and freedom 

'from deformation.

Undeformed bricklets were weighed, boiled four hours in water, 

and weighed again, the difference showing the weight of water 

absorbed.

The volume of the saturated bricklet was measured in the volumeter, in water.

The porosity was determined by the formula

absorption in grams Porosity (per cent)= - : XlOO

volume in cubic centimeters

From these measurements it was possible to calculate or report 

slaking time; water of plasticity; plasticity; air shrinkage (volume 

shrinkage was obtained directly from measurements and linear 

shrinkage was calculated from volume shrinkage; only linear shrinkage is reported); tensile strength; effect of rapid drying; probable 

injury from auger structure; behavior at several temperatures, including fire shrinkage (volume and linear; only linear is reported), 

color, hardness, per cent of absorption and porosity, and special 

characteristics, such as checking and black coring; and range or rate 

of vitrification.

Refractory clays were made into smaller bricklets and burned 

in a Meeker (compressed-air) muffle furnace.

The large number of gray-drift clays that are rendered useless 

by limestone pebbles made necessary a modification in treatment". 

The Minnesota plant which is most successful in removing these pebbles operates at Hutchinson on material containing TO per cent of 

grains fine enough to call clay and 30 per cent sand. About 9 per 

cent of the mixture is lime. It was thought that a determination 

of these ratios in other deposits would be of more value than an 

attempt to burn brick from the pebbly clay. In conformity with 

the practice at Hutchinson, very little material coarser than 20-mesh 

was used. The sand was separated and caught on a 100-mesh sieve.
48 CLAYS AND SHALES OF MINNESOTA.

The few analyses made are of value in estimating the availability 

of fire clays and in comparing the clays of different formations. Two 

sets of vitrified brick were subjected to a rattler test by Edward 

Orton, jr., at Columbus, Ohio.

The kaolin burned white and was glazed to ascertain whether the 

color was satisfactory.

Several mechanical analyses were made by the use of a centrifuge, 

according to the methods of the United States Bureau of Soils.1 In 

most mechanical analyses it is common to class all particles smaller 

than 0.005 millimeter as " clay." In the analysis of soils this is one 

of several fractions resulting from the analysis, each of which is of 

about equal importance; but in clays these fine particles are uniformly abundant and it is advantageous to make a special classification of the finest material. Coarse sizes are not abundant in clays 

and may well be thrown together as coarse sand. The following 

groups were therefore adopted in this work, and the results were 

checked by microscopic measurements:

Mechanical classification of grains in clay.

Diameter in millimeters.

Fine clay_______________________, Less than 0. 001 

Coarse clay ______________________ 0. 001- . 005 

Silt ___________________________ . 005- . 05 

Fine sand_______________________. ..05- . 5 

Coarse sand________ ____________ Larger than .5

The samples were air dried before and after separation, and the 

total of the fractions was usually 96 to 100.7 per cent of the sample 

used to start with. The analyses were recalculated to 100 per cent.

The quality of products was tested in the engineering department 

of the University of Minnesota, and other available records were 

added.

RELATION OF TESTS TO PEACTICE.

As an example of the relation of tests to practice, comparison may 

be made of the clays of Coon Creek, West St. Paul, Red Wing, and 

Wrenshall, all of which have been largely used. All the clays slake 

promptly and develop fair plasticity. That from West St. Paul is 

the most plastic and is found to work somewhat stiff. Each has a 

tensile strength of more than 100 pounds to the square inch, which 

is usually considered necessary for ceramic work. The sandy red 

drift of Coon Creek shows the smallest shrinkage in drying (5 per 

cent), but none of the clays show more than 8 per cent, which is 

small enough to insure against danger of serious warping or cracking. Rapidly dried briquets made from these clays were just as 

strong and free from checks as those slowly dried.

1 H. S. Dept. Agr. Bur. Soils Bull. 84, Washington, 1912.
TECHNOLOGY OF CLAY. 49

In firing, these clays are typical of the groups to which they belong. 

Under vitrification (see fig. 8, p. 84), Pleistocene clays, like the laminated clay of Wrenshall and the red drift of Coon Creek, show a sudden drop in porosity, and the older shales, Cretaceous and Decorah, a 

much more gradual decrease. This rate of decrease and the relation 

of low porosity to the viscous state largely determine the uses of the 

clay. The university tests show that the clay of Wrenshall can not be 

burned to a very low porosity without danger of melting out of shape. 

The clay of Coon Creek shows unusual resistance to fire for a few degrees after a somewhat sudden drop in porosity. The shales of West 

St. Paul and Red Wing both show a very gradual falling off in porosity as the heat is increased and, though not tested in the university 

laboratory to a porosity below 5 per cent, they can easily be burned to 

a product of that density without danger of melting. The two shales 

differ most remarkably in the temperature at which the lowest 

porosity is reached, that from West St. Paul being well burned at 

about 2,150° F., and that from Red Wing requiring 2,700° F. The 

shale of West St. Paul contains so much organic matter and ferruginous fluxes that black cores and vesicular texture are likely to 

develop unless it is slowly and carefully burned. The color of the 

product is indicated very definitely for each. clay.

These results would be sufficient to warrant very definite conclusions as to the uses of the clays, which are now being used for the 

purposes for which they are best suited. The clay of Wrenshall will 

produce a porous but good common brick. The clay of Coon Creek 

will yield a much harder, denser brick, suitable for harder usage, as in 

foundations, public buildings, and even pavements. The clay of Red 

Wing is of still higher grade and will make light-colored vitrified 

ware like stoneware, as well as light-colored paving brick. It is used 

only for stoneware, and the more ferruginous A7 arieties for sewer pipe. 

A shale that vitrifies at so low a temperature as that from West St. 

Paul is usually believed to give a product that even if well burned 

will not have the resistance to abrasion required of a street pavement 

nor the strength needed for sewer pipe. The shale of West St. Paul, 

however, is eminently fitted for high-grade brick and tile.

TECHNOLOGY OF CLAY.

By E. K. SOPEB.

PBOSPECTING.

T36TJAL METHOD OF PROSPECTING.

Most of the developed deposits of clay have been found by men 

occupied in other pursuits, who had the requisite knowledge and 

64310° 19 4
50 CLAYS AND SHALES OF MINNESOTA.

skill to observe the signs about them and to investigate what others 

would pass by unheeding. One who has become familiar with the 

appearance of a clay will recognize similar material elsewhere.

There is not a farm in Minnesota that does not contain some clay, 

good, bad, or indifferent, in deposits of greater or lesser extent. 

Common brick clays are so widely distributed that it is unwise to 

prospect for them in places far from lines of transportation, except 

for local trade. In many places, however, a little prospecting for 

material to supply such local trade with better brick than are now 

made would be worth while. A plowed field, an excavation along 

a road, a well, a posthole, or the bank of a stream may reveal clays 

of a type known to be of value. The most common clays lie near 

the surface and may be found by examining any place where the 

soil has been removed. If there are no such places a dirt auger, 

with an extension handle, is the simplest means of making the necessary excavations. Some clays do not lie so near the surface and are 

not so easily discovered. Yet, if they are fire clays or kaolins, they 

may be worth some effort at prospecting and development.

STRATIGRAPHIC PROSPECTING.

The stratigraphic method of searching for clays proceeds on an 

assumption that is fairly reliable, if used with caution. Where 

sedimentary formations lie in nearly horizontal layers, as in the 

southern half of Minnesota, it may often be assumed that they are 

continuous underground, even if concealed by soil and vegetation. 

For instance, the rock formations of southeastern Minnesota are 

well exposed at many places in Ibluffs, at the top of which is a limestone containing fossils that prove it to be the Galena. Below this 

limestone come, in order, the Decorah shale, the Platteville limestone, and the St. Peter sandstone, each with a definite thickness 

and character. If near Faribault, for example, there should be 

found a number of such exposures of uniform character, and if at a 

particular place no formation except the Galena crops out, it is 

safe to conclude that under the surface at that place the Decorah 

shale lies at the same elevation as it does in other parts of the area. 

Such an assumption is useful in finding some clays.

A line of springs along a hillside also often gives evidence of clays 

underground. Barely, when conditions seem to warrant it, drill 

holes and shafts are sunk to considerable depths in search of clays.

ECONOMIC CONSIDERATIONS.

Common clays are so widely distributed in Minnesota and in most 

other States that the choice of a deposit to exploit depends princi-
TECHNOLOGY OF CLAY. 51

pally on the marketing conditions. To be valuable, clays must be 

near a market or near some line' of easy transportation. Some very 

excellent clays in Minnesota are destined to remain untouched for 

years because they are too inaccessible. At present it will not pay 

to haul fire clay or pottery clay by wagon to any distant railroad 

point for shipping. The price in 1915 for good fire clay was about 

$1.50 a ton, and the cost of a wagon haul would absorb most of the 

profit at that price. The cost of labor, fuel, and other material 

should also be considered. A few high-grade clays may sell for 

enough to overcome the handicap of unfavorable market conditions. 

After studying market conditions and finding a clay, one should 

determine before a plant is erected, first, the amount of clay; second, 

its general character; third, the conditions of working, including 

accessibility of all materials needed in the working; and finally, if 

all these are favorable, the exact and detailed character of the clay. 

Each of these items deserves the most careful attention.

CLAY PLANTS. 

LOCATION.

If a clay deposit is extensive, like the glacial clays in Minnesota, 

the success of a plant may depend on the location selected. The 

relation to transportation facilities is most important. No matter 

how fine its quality, the clay is worthless if it is inaccessible, and 

for this reason prospecting in regions remote from transportation 

facilities is useless. It is also necessary to consider the overburden 

with regard to stripping operations. Another essential consideration is the drainage, provision for which is in many places difficult and in some flat regions can be made only 'by pumping. The 

possibility of mixing different clays controls the location of many 

plants, though foreign material whose admixture will improve the 

grade of the product can often be profitably brought from a considerable distance. Some sand also must usually be available for 

mixing with the fat clays used for common brick. Most high-grade 

clay products, such as chinaware, stoneware, and terra cotta, are 

made from mixtures rather than from run of bank material.

The exact location of the buildings and yards with respect to the 

clay pit is a matter that deserves more attention than it usually 

receives. In numerous places yards and buildings have been placed 

over the best clay in the deposit and must be moved before the clay 

is excavated. The plant should be arranged so that the material 

may progress from, pit to machine, to drying racks, to kiln, and to 

shipping point in regular sequence, without any great distance between points and without retracing its route. (See fig. 5.)
52 CLAYS AND SHALES OF MINNESOTA.

MINING THE CLAY.

Open pits are most commonly used for obtaining the clay, underground work being too expensive except for kaolins and fire clays. 

The expense of mining underground is affected by the size of the 

bed, the drainage, the roof, and the depth. In Minnesota the highgrade clays are well situated except that the roof consists of shale 

or drift and is not strong.

Pick and shovel are used on most clays, and the best parts of 

variable high-grade clays may be carefully selected. Uniform clays

ELEVATION 

FIGURE 5. General arrangement of brick plant.

requiring no selection in the pit may be excavated with a plow and 

scraper or with a steam shovel, which in large plants is the most 

economical. (See PL XIII, A.) Blasting is not usually necessary. 

Any overburden is removed by similar methods. Where land is 

valuable for farming and the pits are shallow, as in the Red River 

valley, the soil of the overburden is spread on the bottom of the 

worked-out pit.
TECHNOLOGY OF CLAY. 53

 Drainage is an item of expense in some places. Ditches are most 

economical if an outlet can be found, but in many places pumping 

is necessary.

Deep pits are worked in benches, though in a deposit of firm shale 

where proper protection" can be provided, as at West St. Paul, high 

vertical faces are worked by undermining and caving. In some 

other States, where high-grade clays occur in peculiar forms, special 

methods of mining have been adopted. The southern kaolin deposits, for example, are worked by a series of circular or square pits.

TRANSPORTATION FROM PIT TO PLANT.

Where the plant and the clay bank are close together excavation 

and transportation are combined by the use of scrapers and similar 

apparatus. Horse carts and cable-dump cars are very commonly 

used. In some of the larger deposits in hilly ground aerial tramways and even chain conveyors are used. Where the clay lies along 

a navigable stream or lake, like many deposits in Minnesota and 

Wisconsin, barges can be used both for transporting the raw material 

to the factory and for shipping the finished product. There are but 

few plants in Minnesota where the raw clay has to be hauled far. 

At present it will not pay to haul even good fire clay or pottery clay 

by wagon to a distant railway shipping point. The only Minnesota 

clays extensively shipped any great distance are the Cretaceous 

clays of Goodhue County. The; raw material from these deposits 

is loaded on flat cars and hauled to Red Wing, a. distance of 12 to 

18 miles. Another part of the product is shipped to Hopkins for 

the Minneapolis sewer-pipe plant. Some high-grade clays may 

prove sufficiently valuable to warrant transportation for a considerable distance.

DRAINAGE.

Pits in clay deposits that underlie flat areas are usually drained 

by pumping, especially if they are deep. Many thin clay deposits 

can be drained by a proper system of trenches. Too little attention 

is given to drainage at many clay plants. Where the deposits are 

on steep hillsides improper drainage may cause caving.

PREPARATION OF THE CLAY. 

PRELIMINARY TREATMENT.

Some clays, after being dug and brought from the pit to the yards, 

require preliminary preparation before they are ready for the molding machines. Many clays are rendered more plastic after weathering, and in a few localities where greater plasticity is desired the
54 CLAYS AND SHALES OF MINNESOTA.

material as it comes from the pit is spread out in the sun for several 

iweeks or months. Other clays are mixed with sand or some different 

clay. Very few yards use the best clay alone; as a rule more or less 

sand is mixed with it, especially for making ordinary brick and tile. 

The most common practice is to take the fun of bank material, including a foot or two of sandy-surface soil. The sand increases the 

density of limy clays and decreases the air shrinkage and sometimes 

the fire shrinkage.

If the clay contains sticks or large pebbles or concretions they are 

sometimes picked out by hand. Hard clays and shales must be 

crushed, and if the clay contains the top layer of soil it may include 

some pebbles, which must be either crushed or removed. For some 

shales fine crushing is absolutely necessary to obtain plasticity.

GRINDING.

The commonest types of crushing and grinding machinery are 

dry pans, jaw crushers, disintegrators, and rolls. Ball mills are 

sometimes used for very fine wet grinding. Clays of ordinary hardness and toughness do not require crushers or rolls and can be 

worked up directly in wet or dry pans. Rolls are used more than 

jaw crushers because of the tendency of the clay to pack and clog 

the crusher. The commonest combination used in Minnesota consists of rolls and pug mills. The dry pan is a heavy pan supported 

and driven by a vertical shaft. Within the pan are two or more 

heavy mullers or wheels supported on a horizontal shaft. As the 

pan revolves, the mullers are rotated in the opposite direction by 

their contact with the pan, grinding the lumps of clay. (See PI. Ill, 

A-.) Several types of disintegrators are on the market, but the commonest break up the clay by impact against the bars of opposite 

revolving cages or by the impact of flying hammers attached to axles 

revolving in opposite directions. As the axles revolve the hammers 

are flung out by centrifugal force and beat the clay to pieces.

WASHING.

Many higher-grade clays, such as kaolin and stoneware clays, are 

washed after disintegration to remove sand and other impurities of 

a harmful nature. The disintegrated clay is mixed with water to a 

thin sludge and settled in a series of shallow tanks. The sand settles out rapidly in the first two tanks and the finer clay substance is 

kept in suspension longer and is recovered in the lower vats. This 

wet clay (slip) then passes through filter presses to remove the remaining water, and the resulting cakes are tempered or are dried 

for shipment. The details of tKe process now applied at Bed Wing 

are described in the Goodhue County report (pp. 165-173).
U. S. GEOLOGICAL SURVEY BULLETIN 078 PLATE III

A. DRY PAN.

S. DOUBLE 8-FOOT WET PAN.
TJ. S. GEOLOGICAL SURVEY 

SOFT-MUD L>PICK MACHINE FOBMER1Y USED AT 
I

TECHNOLOGY OF CLAY. 55 

SCREENING.

After grinding or washing it is usually necessary to use a screen to 

separate coarse or uncrushed material from that ready for molding. 

Dry pans combine the grinding and screening by means of perforations in the bottom of the pan.

OVERCOMING THE TROUBLE FROM LIMESTONE PEBBLES. 

METHODS.

Many poorer-grade clays for brick and tile are not washed, because the value of the product will not offset the extra expense. 

However, the gray drift that is so widespread over Minnesota must 

be cleaned before it can be used for the manufacture of high-grade, 

ware. Limestone pebbles are its chief defects, for after the clay is 

burned they will slake, swell, and destroy the brick. They can be 

removed or rendered harmless in several ways. If they are not too 

abundant, fine grinding may be sufficient. Fairly fine grinding and 

immersion in water after removal from the kiln will render the lime 

harmless. The addition of some salt with the water used in tempering the clay seems to prevent the swelling and slaking of the lime. 

By drying and gently grinding, so that the clay is disintegrated and 

the harder pebbles left, it is possible to catch most of the lime on a 

screen. The use of certain machines 1 will remove pebbles from 

plastic clay. Washing, however, is the most effective process and 

has been commercially successful in a plant that uses material such 

as can be found in nearly every part of the State. This plant is described below.

HUTCHINSON PROCESS.

At Hutchinson, in McLeod County, the gray drift is cleansed of 

limestone pebbles by a process that is probably not duplicated in 

America. The washing machinery occupies a space not over 20 feet 

square and 15 feet high and washes 130 yards of clay in a day. The 

clay from the bank is hauled by cable car to the washer, where it is 

mixed with an excess of'water and agitated by a series of vertical 

rods fastened to a rotating crossbeam. The harrow-like motion of 

these rods tends to throw the larger pebbles toward the center and 

leaves the fine clay and sand suspended and distributed throughout 

the washer pit. A bucket elevator of continuous operation dips into 

the pit near the center and removes the gravel. The gravel, if 

cleansed, forms a by-product of considerable value. At the sides of 

the pit a screen of proper mesh allows the escape of the fine sand and

lrrhe Diesner clay cleanser: Brick, vol. 31, No. 5, 1007.
56 CLAYS AND SHALES OF MINNESOTA.

clay to one of a series of open ponds in which they are allowed to 

settle. After a time some of the water is pumped off and the rest 

is left to sink into the ground. The sand naturally settles close to 

the intake of the pond, and the clay is carried to the farther side. 

'After partial drying the material is taken to the stiff-mud machine, 

where the clay and sand are mixed in approximately the same proportions in which they existed in the drift before the washing. 

Experiments are in progress to determine whether the clay is improved by standing in the settling ponds all winter. The gravel is 

sold for concrete. Both the clay and the sand contain a considerable amount of calcium carbonate (see analyses in report on McLeod 

County, pp. 191-193), but if care is taken to remove the coarser sand 

the lime does no harm, and it is certainly less abundant than in the 

unwashed drift. The plant at Hutchinson uses three round downdraft kilns, and plans are made to double the capacity. It has been 

found possible with this clay to produce a very good draintile and 

hollow building block, so that the production of common brick has 

become secondary. Recently most of the tile made from clay have 

been of small sizes; the gravel by-product was used with cement for 

larger tile. M. C. Madsen, of Hutchinson, has been developing this 

process for about 20 years.

A large plant of this character, shipping its product over a considerable territory, would meet the competition of plants using clay 

that is free from limestone pebbles and that is therefore more 

cheaply worked. A local plant of medium size, however, could succeed, and there is room for several such plants in the western and 

northern parts of the State.

GRINDING AND SCREENING.

If the clay is not too heavily charged with limestone .pebbles, it 

is possible that a method cheaper than washing may be applied. 

According to Binns and Coates: A

Lime grains as large as would be rejected by a 12-mesh sieve are objectionable even in small quantities, for though the brick may not be ruptured there 

is apt to be an unsightly spalling of the surface. To be entirely safe, lime 

grains,must be ground to pass a 36-mesh sieve. Lime as fine as this may be 

present in a proportion as high as 12 per cent. 'The danger of rupture from 

lime grains may be almost completely avoided by a saturation of the brick 

on being drawn from the kiln.

SATURATION OF THE BURNED BRICKS.

Saturation of the freshly burned and cooled brick is especially 

effective if the brick are very porous. Clays that burn to a very 

dense body would probably be more affected by the lime content than 

those making soft, porous building brick. This treatment has been

1 Binns, C. P., and Coates, M. A., Am. Ceramic Soc. Trans., vol. 14, p. 22, 1912.
TECHNOLOGY OF CLAY. 57

tried at several places on the gray drift and, though partly successful, has not yielded so high grade a product as that obtained by the

washing.

COLORING.

Special colors are most commonly obtained by adding compounds 

of manganese or of iron. At Preston the .red color of the brick is 

improved by the use of " mortar-color " red in the molding sand. A 

similar process is reported from Menomonie, .Wis., and Winona, 

Minn., and may give satisfactory results elsewhere in Minnesota. 

At other places a glaze or slip is used to impart the desired color. A 

salt glaze is common, especially on sewer pipe. Pottery, stoneware, 

and fancy face brick may be covered with a thin layer of some slip 

clay that is known to burn to the desired color. Where a slip is used 

special care must be taken that the difference in shrinkage between 

the slip and the body of the ware is not too great, for uneven shrinkage may cause the slip to peel or crack.

MIXING.

Many of the best plants in the United States mix clays from two 

sources. Very little of such mixing is done in Minnesota, though 

tests show that it would much improve some of the products, especially those made from slate and red clay near Duluth. Careful 

mixing is practiced at West St. Paul, where the upper and lower parts 

of the Decorah shale are unlike. At most clay banks, however, mixing is effected merely by running the scraper from the top to the bottom of the bank.

PREHEATING.

Some defective clays may be greatly improved by preliminary 

heating to 200° to 300° C. (see p. 34), particularly joint clays, which 

are too plastic to work easily and which crack badly on drying. 

The process will probably be used in certain parts of Minnesota, 

where the only clays available are joint clays. The expense is not 

great, but in most places clays that do not require such treatment are 

available.

TEMPERING.

Before the clay is molded it must be thoroughly mixed Avith water 

until it attains the required degree of plasticity. This process, 

which is called tempering, may be carried out in the soak pit, the 

ring pit, the wet pan, or the pug mill.
58 CLAYS AND SHALES OF MINNESOTA.

SOAK PIT.

The soak pit is a square or circular pit in .which the clay is m ed 

by hand or by horsepower. As a rule the sides of the pit ai of 

natural earth, unbearded, though planks or stones may be pi ed 

on the bottom. The clay is dumped in, usually without any % eliminary crushing, and is mixed with water. Many pits ha^ \ a 

vertical post in the center with a rod so attached that a horse may 

rotate it and thereby mix the clay. The soak-pit method is applicable only to the soft-mud process. (See p. 59.)

RING PIT.

The ring pit is similar to the soak pit, except that it is invariably 

circular, has permanent walls, and has a post in the center, to which 

is attached a long horizontal rod which carries a wheel. As the 

horizontal rod is revolved about the vertical post the wheel travels 

back and forth along the rod, from the center to the outside of the 

pit and back again, thoroughly mixing the clay and water. The ordinary ring pit has a capacity of 3,000 to 8,000 brick a day.

WET PAN.

The wet pan is similar to the dry pan (see p. 54), except that it 

has a solid instead of a perforated bottom and can ordinarily be 

emptied only when it is stopped. Some lumps of clay, therefore, always remain in the bottom. Its chief advantage is that it grinds 

and mixes at one operation. (See PI. Ill, B.) It is used in making 

sewer pipe, fire brick, and paving brick.

PUG MILL.

The most common method of tempering in use at the larger plants 

is that employing the pug mill. This mill consists of a cylindrical 

trough in which revolves a shaft carrying arms or knives set at an 

angle. The clay, with water in proper amount, is fed into the 

upper end of the mill and is forced by the revolving arms toward the 

lower end. On the way it is thoroughly mixed, all lumps are broken 

down, and the whole is kneaded into a plastic mass. The method 

and rate of feeding the clay to the mill will differ at different plants 

but are usually controlled by some mechanical device. Pug mills are 

made in different lengths, and as the thoroughness with which the 

clay is mixed depends chiefly oil the length of the trough, the machine must not be too short for the clay to be used. Many machines are not long enough and do poor mixing, and poor mixing 

invariably results in a poor grade of brick. When the pug mill is 

used in conjunction with the stiff-mud method of molding (p. 60), a
TECHNOLOGY OF CLAY. 59

special combination of pug mill and auger machine is usually 

employed, by which the clay, after being mixed by the revolving 

arms, is forced out at the lower end through a die in the shape of a1 

long bar or ribbon.

In Minnesota numerous pug mills and combination pug and auger 

machines are used. At the smaller plants ring pits are nearly always 

employed. At some brickyards, as the result of improper mixing/ 

many lumps of clay half an inch or less in diameter are allowed to 

get into the brick without being crushed. This is undesirable and 

causes the splitting or breaking of the brick.

WEDGING.

Ill many pottery plants the washed clay, after it comes from the 

pug mills, is given an additional tempering by kneading by hand or j 

in rolls. This treatment is called wedging.

MOLDING.

BRICK HOLDING.

There are three methods of molding brick the soft-mud process,' 

the stiff-mud process, and the dry-press process.

SOFT-MOD PROCESS.

Bricks may be manufactured by the soft-mud process either by,' 

hand labor or machine. Hand-molded brick made in this manner 

are known as slop brick and are now made only at the small yards. 

The molds, which contain compartments for six brick, are first wet 

and sanded. Into these the molder flings the wet clay from the 

soak pit with some force, so as to fill all the corners. The tops are 

cut off by a wire stretched between two-sticks, and the brick are 

taken to the drying floor, which is usually only a leA7 el place in the 

yard, and are turned out of the mold on a sanded surface. When 

part dried they are turned on edge. A good molder can turn out 

several thousand bricks a day by this method. '»

For machine-molded soft-mud brick the clay is put into a pug 

mill that pushes it into a hopper from which it is forced by a plunger 

into molds beneath. These molds have been sanded by hand or by a 

special mechanical device. As the plunger is withdrawn the hopper 

is again filled with clay from the pug mill. The filled mold is removed by a lever-operated mechanism and an empty mold put in 

its place. (See PL IV.) Brick molded by the soft-mud process have 

fine sanded surfaces. The machines have a capacity of 8,000 to 

15,000 brick a day when driven by horsepower, and 20.000 to 35,000
60 CLAYS AND SHALES OF MINNESOTA.

 when driven lay electric or steam power. The soft-mud process is 

adapted to clays of low or medium plasticity and is the one most 

commonly used.

STIFF-M0D PROCESS.

Stiff-mud molding is almost never done by hand. Clays of moderate plasticity are mixed with considerably less water than is used 

in the soft-mud process to a sufficient stiffness for the wet ware to 

be handled without danger of deforming it. There are two types 

of stiff-mud machine plunger and auger. The plunger machines 

are essentially the same as those employed in the soft-mud process, 

but their use has been rapidly diminishing and is now restricted to 

the manufacture of sewer pipe. Practically all stiff-mud brick are 

now made by the auger machine, which consists essentially of a pug

FIGURE 6. Auger machine and wire cutter. Sketch from catalogue of American Machinery Co.

mill, in which an auger is placed at the end of the shaft. After the 

clay and water are mixed by the blades on the revolving shaft the 

plastic mass is taken up by the auger and forced from the lower end 

of the machine through a die, in the form of a continuous ribbon or 

bar of clay. By changing the die, common brick, cylindrical draintile, hollow building blocks, fireproofing, and other shapes can be 

made in the same machine. As the ribbon of clay comes through the 

die it passes on a traveling belt to a cutter, which may be operated 

automatically or by hand. Nearly all stiff-mud brick are now cut 

automatically, by wires placed on a revolving wheel or on a bar 

operated by a lever. (See fig. 6.) The brick may be side cut or end 

cut, and they have smoother surfaces than the sand-molded brick. 

[Any pebbles in the clay may cause difficulty in the cutting, though 

.usually the difficulty is not serious." (See PI. V, A.) Auger machines 

tend to produce a laminated structure in some clay, which weak-
IT. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE V

A. WIRE-CUT BRICK MADE FROM PEBBLY CLAY.

B. AUGER STRUCTURE IN AN OVERBUHNED BRICK.

C. BRICK DRYING IN OPEN SHEDS.
S. GEOLOGICAL SURVEY BULLETIN 678 PLATE VI

A. SEWER-PIPE PRESS.

E. FOUR-MOLD DRY PRESS BRICK MACHINE.
TECHNOLOGY OF CLAY. - 61

ens the brick and renders them practically worthless. (See PL V, 

B.) Unless the dies are well lubricated the soft clay may stick to 

the corners and tear, producing rough, ragged edges. Generalization 

as to the behavior of any type of clay is not possible.1 The-form of 

the die can usually be adjusted to remove the worst trouble. The 

only other factor capable of control is the tempering, and this requires personal and careful attention. By proper adjustment the 

process can be made to roughen all sides of a brick and produce an 

imitation of the popular " klinker" brick. The capacity of a stiffmud auger machine ranges from 45,000 to 60,000 brick in 10 hours. 

In some machines double or triple dies are used and the output is. 

correspondingly increased.

RE-PBESSING.

It is often desirable to re-press brick that have been molded wet. 

Soft-mud brick are likely to be somewhat irregular in size and to come 

from the machine with comparatively ro'ugh edges. Ke-pressing improves the shape, increases the density, and makes better face or front 

brick. Stiff-mud brick are also sometimes re-pressed in order to 

remedy the laminated structure produced by the stiff-mud auger machines (p. 60), which considerably lessens the tensile and crushing 

strength. " The additional pressure, however, does not 'always obliterate the lamination. In general, where different shape is desired, 

where rounded corners or smoother surfaces are wanted, or where 

there is a tendency toward lamination re-pressing is beneficial. The 

re-pressing is done in a plunger machine. The brick are placed in the 

mold^ iiitomatically and are pressed to any desired shape for which 

a. mold can be made. This process is used in making complex forms 

such as interlocking roofing tile.

DlOr-l'HESS rilOCESS.

The dry-press process is so named from the fact that the ground 

clay is molded into brick in its natural dry state without being mixed 

with water to a plastic mass. It is not, however, strictly a dry 

method, for there is usually 5 to 15 per cent of water in the clay as it 

comes from the dry pan. The process is best adapted for the production of fancy and front brick, but at many of the larger plants common brick are now molded by this method. The clay should be 

ground to pass a 16-mesh screen. The dry-press machines are of the 

plunger type and the clay is fed from the charger into the molds. 

The plungers descend upon the powdered clay, and at the same time

1 Artz, W. H., Flow of plastic clay through dies: Am. Ceramic Soc. Trans., vol. 11, 

p. 411, 1909.
62 CLAYS AND SHALES OF MINNESOTA.

the bottoms of the molds are forced upward, so that the brick are subjected to pressure from both sides. The pressure is considerably 

.greater than is applied in any other process. The bottom of the 

mold continues to move upward after the upper mold is withdrawn, 

so that the brick is forced up and out onto the dry table. (See PL 

VI, B.) The molds are heated by steam to prevent the clay from 

sticking to them. As the air contained in the ground clay is compressed and imprisoned in the brick and, unless given an opportunity 

to escape, would expand and spoil the brick on the release of pressure, 

the faces of the molds are provided with minute air holes. This precaution is not necessary in any of the other processes. Brick molded 

by the dry-press process are ready for the kilns directly after molding and do not need to be subjected to preliminary drying. The 

advantage of dry pressing is chiefly that smooth brick with sharp, 

true edges are produced by a single molding process. Two, four, and 

six mold machines are on the market. The capacity of the six-mold 

machine is about the same as that of the soft-mud machine.

HOLLOW WAKE AND TILE.

Draintile, hollow brick, hollow tile, fireproofing, and terra cotta 

are molded by a stiff-mud process not essentially different from that 

employed for molding stiff-mud brick. Products of almost any shape 

can be made by the stiff-mud method by changing the form of the 

dies, but different clays are necessary for the different kinds of ware. 

Almost any good plastic clay that has a moderately high tensile 

strength and not too much shrinkage and that would make a good 

common brick can be used for cylindrical draintile.

SEWER PIPE.

Sewer pipe are molded in stiff-mud machines of the plunger type. 

The essential parts of the machine are two cylinders connected by a 

piston an upper steam cylinder and a lower cylinder into which 

the clay is fed. As the steam enters the upper cylinder, the piston 

is forced down on to the clay and presses it through a die at the 

bottom. At the end of the stroke the pipe thus molded is cut and 

the piston is raised to allow more clay to enter. (See PI. VI, A.) 

Elbows, turns, and combined shapes are molded in plaster casts, each 

half of the pipe being molded separately, and the two being cemented 

by slip clay. As the clay dries the air shrinkage loosens the pipe in 

the mold and permits its removal.

POTTERY.

The processes used in the manufacture of pottery and chinaware 

are so complex and require so much specialized skill that detailed
TJ. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE VII

A. BRICK DRYING ON CARS IN TUNNELS.

B. HOLLOW WARE DRYING ON A FLOOR.
TJ. S. GEOLOGICAL SURVEY BULLETIN 078 PLATE VIII

* i

JL. SCOVE KILN, SHOWING HOW BRICK ARE PILED.

B. ROUND DOWNDRAFT KILN AT HOPKINS.
TECHNOLOGY OF CLAY. 63

discussion is not warranted in a report of this nature. Certain shapes 

are hand molded, but machine molding on wheels is most common. 

Eound ware is generally molded by jolly wheels and lathes. Some 

forms are pressed or poured into plaster molds. All pottery is dried 

in rooms where the moisture and temperature are carefully controlled.

GLAZING.

Little cheap earthenware is glazed, but the higher grades of stoneware are either slip or salt glazed.1

DRYING. 

METHODS.

All brick and other ceramic products except those molded -by the 

dry-press method have to be dried before burning in order to free 

them from the excess of water of tempering. If the clay shrinks 

greatly or if the products are complex in form, the process requires 

great care. It may even be necessary to place the wares first in a 

room in which the air is not very dry, and it is often best not to 

apply heat until drying is well advanced. Drying may be effected 

in open yards, sheds, and pallets, or drying floors and tunnels.

Bricks are commonly dried in pallet dryers long, low, narrow 

sheds with open sides and movable roofs. The wet brick from the 

molding machine are placed on small boards called pallets, which 

hold about six bricks each,'and are carried on trucks or on a traveling belt along alleys between the drying sheds, where they are placed 

on shelves in the open air. (See PL V, C.) In the smaller yards 

and at most soft-mud brick plants the brick are placed on ground 

that has been smoothed off and are allowed to dry in the sun with 

only boards ("hacks") to protect them against rain.

Drying floors are similar to open-yard dryers, except that they 

are permanent and that at some plants they are partly covered by 

a roof. (See PL VII, B.}

Drying tunnels are cylinders or tunnels artificially heated to about 

120° C. by the waste heat from the kilns or the power plant. The 

wet brick from the molds are loaded on cars, which are run through 

these tunnels very slowly (see PL VII, 4), remaining in them for a 

length of time that depends on the amount of moisture in the clay, 

the quality of the clay, and the behavior of the clay on rapid drying.

1 For a detailed description of the manufacture of pottery and other ceramic products 

see Hies. Heinrich, Clays, their occurrence, uses, and properties, 1906.
64 CLAYS AND SHALES OF MINNESOTA.

EFIXORESCEN CE.

Brick made from some clays become covered during the process of 

drying by an efflorescence, the water in the clay dissolving out soluble 

salts and depositing them on the surface of the brick as it evaporates. 

Calcium sulphate is the most common salt thus formed; others are 

sulphates of magnesium, potassium, sodium, iron, and aluminum. 

Occasionally carbonates and rarely silicates are formed in this way. 

Efflorescence during the drying process can be prevented by leaching the clay to dissolve out the soluble salts, by adding barium salts, 

by using pure water in tempering the clay, or by careful drying. 

A simple test to determine the approximate quantity of soluble salts 

in the clay will often indicate which process would be best to use.1

BURNING THE CLAY. 

KILNS.

The numerous types of kilns in use have been described and classified by Beyer and Williams.2

UPDHAFT KILNS.

The most common type of kiln is the temporary updraft scove 

kiln (PL VIII, A), which is used at nearly all the smaller brick-' 

yards. The bricks are built up into a rectangular open-work mass, 

under which are left a series of parallel arches running through the 

pile and spaced about 2 feet apart. After the pile is built up it is 

surrounded by a closely built two-brick course wall, daubed over 

with wet clay. It may be covered with a board roof supported on 

a frame outside the kiln. The kilns are only temporary and must 

be rebuilt for each new batch of brick. They are used only for 

common brick and can not be heated to high temperatures. Their 

use necessarily involves a high percentage of loss around the arches 

from overburned brick and probably another serious loss around the 

outer wall from underburned brick.

Another type of updraft kiln is the permanent scove kiln, which 

is similar in principle to the temporary scove kiln except that it 

has permanent walls on two or three sides but no roof.

Pottery may be burned in updraft kilns that have compartments, 

chambers, muffles, or saggers to keep the ware from direct contact 

with the flames.

iJour. Ind. and Eng. Chemistry, vol. 2, p. 373, 1910. ,

2 Beyer, S. W., and Williams, I. A., Technology of clays : Iowa Geol. Survey Ann. Kept, 

vol. 14, p. 288, 1904. See also Snyder, L. C., Clays and clay industries of Oklahoma: 

Oklahoma Geol. Survey Bull. 7, p. 81, 1911.
TECHNOLOGY OF CLAY. 65

DOWNDKAFT KILNS.

Downdraft kilns may be either round (PL VIII, -B) or rectangular and are provided with permanent fire boxes along the outer 

walls. The hot gases pass through flues to the top of the kilns, 

down through the spaces between the clay ware, out from the bottom of the kilns through the flues, and upward through the stack. 

Downdraft kilns have distinct advantages over those of the updraft type, although they cost considerably more. Their temperature can be more exactly controlled and can be raised higher, and 

they waste less in overburned and underburned' products. In tha 

updraft kiln, if the lower brick become overheated, the entire mass 

may melt and sink -down, a danger that is obviated in the downdraft kiln.

CONTINUOUS XILNS.

A continuous kiln consists of several chambers connected with 

one another and with a central stack. The heated gases pass from 

one chamber to another and finally out the stack, the waste heat 

from one chamber, being utilized in preheating the next. In a^ properly operated continuous kiln the clay ware in some of the chambers is being cooled; in others it is being burned at maximum.temperature; and in still others it is just being placed in position all 

at the same time. The continuous-kiln system is especially adapted 

to larger plants; and, though it is chiefly used for products of the 

better grade, it is employed in many plants for burning common, 

brick. The first cost of the continuous-kiln system is greater than 

that of other kilns, but many advantages are claimed by the manufacturers, as follows: Saving of fuel (only one-third of the" fuel is. 

required) ; better, more uniform burning, and consequently a more 

uniform color; fewer seconds and culls; less labor for firing; longer 

life; less cost for maintenance and repairs; no smoke; less ground 

space for a given daily capacity; less handling of fine ware; superiorarrangement for water smoking; and easier supervision and control.. 

The greatest disadvantage of the continuous kiln is that it can be 

used only by the larger plants, its high first cost being prohibitive-, 

to smaller companies.

FUELS.

The fuels that can be used in burning clay products are wood,, 

crude oil, coal, and! natural gas. Tn Minnesota the fuel is usually 

wood or coal. A producer-gas plant is installed at one of the continuous kilns. The smaller plants nearly all use wood. Crude oil 

and natural gas are used only in regions where these materials arecheap or where wood and coal are not to be obtained. Natural gas, 

is, however, the ideal fuel.

. 64310° 19 -5
66 CLAYS AND SHALES OF MINNESOTA. 

BURNING PROCESS.

No matter what type of kiln is used, great care should be exercised 

in burning', and the temperature should be kept under constant control. Unfortunately, few of the smaller plants make any effort to 

measure the temperature obtained in the kiln. In the common scove 

kiln accurate measurements are impractical, but in the permanent 

downdraft kilns measurements could easily be taken, and the more 

frequent use of Seger cones or some other form of measurement is 

urged. (See PL XI, 4, p. 88.) The practice of estimating the temperature from the settling of the upper corners of the ware or from 

simple inspection is not much better than a guess and is the cause of 

much waste. 

The physical and chemical changes that take place in burning are 

dehydration (p. 34), oxidation, and vitrification (p. 36).1

Some weathered glacial elays

River clay

Archean residual clay

Buff-burning Cretaceous clay 

Red drift

Oxidized gray drift

Recent swamp and lake clays

Decorah shale 

Some Cretaceous clays 

, Fresh gray drift

Red burning- Cretaceous clay

30 120 150 180 

Minutes

210 240 270

FIGDKE 7. Diagram showing the gradual oxidation, and disappearance of black cores due 

to organic matter, when, brick are kept at red heat.

Oxidation affects only clay that contains organic matter or iron. 

All common ware must be oxidized before being vitrified. More 

losses and trouble in burning are due to mismanagement at this stage 

than at any other, for if the clay begins to melt before oxidation is 

complete the evolution of gases usually puffs the ware out of shape. 

A black core or an appearance called " blue stoning" often results, 

even when no swelling occurs. (See fig. 7.) Lack of complete oxidation may be due to the density of the fine clay, the evolution of 

gases from the clay, an excess of fuel and gases, or too great thickness of pieces of clay to be oxidized. Vitrification is discussed on 

pages 35-37.

The rate of cooling should be carefully controlled. There is often 

as much danger from too rapid cooling -as from too rapid heating. 

The percentage of loss from underburned, overbumed, or broken.

iOrton, Edward, Am. Ceramic Soc. Trans., vol. 5, p. 377,. 1903.
USE OF CLAY PRODUCTS. 67

products varies in kilns of different types but is directly dependent 

on the care exercised in burning. Overburned brick may at some 

plants be sold as the popular *' klinker " brick and are even imitated 

-by ;an artificial roughening process. (See PL II, J., B.)

Minor points in connection with burning .are glazing, flashing, 

and efflorescence. Glazing is sometimes accomplished by throwing 

salt -on the fire when the kiln is at its hottest. Flashing is 'a process 

by which the color of the products containing iron can be brightened 

and 'Changed; it depends on the regulation of the supply of fuel and 

air. Efflorescences may form in the kiln quite independently of any 

action of the .soluble salts in drying, apparently as a result of the 

action of combustion gases in the kiln.

TECHNOLOGIC SUGGESTIONS.

The clay products shipped into Minnesota at present include much 

.brick and tile of grades no better than those produced within the 

State. This seems to be the result of lack of equipment for producing 

large quantities and consequent inability to accept large contracts. 

Good-sized plants should install numerous labor-saving devices and 

better and more economical machinery. Special attention should be 

directed to washing, or to any other process that might make the 

widespread gray drift available for draintile. Experiments in mixing clays should be made for they may result in the development of 

some high-grade products. Other detailed suggestions are made in 

the county descriptions (pp. 111-251).

USE OF CLAY PRODUCTS.

Whether or not a brick or tile is satisfactory in practice depends 

not only on the method of manufacture and on the qualities of the 

raw material, but also largely on the skill with which it is used in 

construction. If brick are laid in poor mortar or in such a position 

that they are subjected to constant wetting and drying out again 

efflorescences are almost certain to appear. If tile are laid haphazard, without calculating the necessary grade and efficiency, they 

can not be expected to be satisfactory. If the best of brick are laid 

in a street without a proper foundation the pavement will not stand 

well. For these reasons the following notes may be of value to the 

users of clay products.

PAVING BRICK.

Brick and paving blocks of different sizes are probably more used 

in paving work than asphalt, stone, and wood blocks combined. 

They have many advantages, among which are ease of traction, 

good foothold for horses, minimum dust and mud, adaptation to all.
68 CLAYS AND SHALES OF MINNESOTA.

street grades, ease in repairing, ease in cleaning, slightness of absorption, pleasing appearance, and ease of laying.

Many towns in Minnesota use paving brick on their streets, but 

their general use has been greatly delayed because there are comparatively few localities in the State where such brick are manufactured. Clay suitable for paving brick is widespread in Minnesota, 

and no doubt when these deposits are developed the use of brick for 

paving will become much more common.

In some States, notably Ohio and Pennsylvania, paving brick are 

used for country highways, but it is unlikely that they will soon be 

put to that use in Minnesota, although' there is sufficient clay in the 

State to insure a good supply.

The cost of brick pavement varies with the local conditions, but 

until recent years has been $1.50 to $2 a square yard, including a concrete foundation. The cost of maintenance can be kept down to the 

minimum by prompt, repairs. When a soft brick shows signs of wear 

it should promptly be replaced by a good one, for a hole once started 

is rapidly enlarged by the wheels of passing vehicles, which break the 

surrounding bricks. The life of a good brick pavement is stated to 

be 15 to 20 years under moderate traffic. The brick are usually laid 

upon a 6-inch layer of Portland cement concrete covered by a 1-inch 

cushion of rolled sand. The brick are laid with their long dimensions 

at right angles to the curb, and either cement or asphalt is poured in 

the joints. They are then rolled to insure, a firm setting, and are 

allowed to remain undisturbed till the cement has set.

DRAINTILE.

Soils which are not readily freed from an excess of water and which 

are suitable for agriculture should be drained. A closed drain is 

better than a ditch, for it is permanent and wastes no land. If the 

ground-water level is less than 4 feet below the surface for any length 

of time, the soil will have too much water and should be underdrained. 

Underdraining improves wet soils by permitting earlier working after 

rain, by permitting the deeper growth of plant roots, with corresponding increase of the portion of the plant above ground, by furthering the circulation of the air through the soil, producing chemical 

changes necessary to plant growth, and by permanently loosening the 

surface soil, with consequent attraction (by capillary power) of the 

deeper-seated ground water.

Tile drainage may be extended on land adapted to profitable farming until water from an ordinary rainfall is all passed down into the 

soil and the excess is carried away through the underdrains without 

injury to the growing crops and without surface washing of the land. 

This, of course, would involve a very considerable enlargement of the 

work, much more than has been contemplated by many farmers. In
USE OF CLAY PRODUCTS. . 69

the early days of tile drainage the opinion was entertained by some 

that only the low, wet places, sloughs, or ponds needed this improvement of soil conditions, and a few people may be still of the same 

opinion; but the change among intelligent farmers and other landowners has been radical.

Thorough work in drainage involves the construction of underclrains in parallel lines, near enough together to affect the soil and the 

subsoil about alike, and to lower the water level to a point where it 

will not injuriously affect the growing crops and will permit the circulation of air through the soil and subsoil above the water level. 

The following suggestions are taken largely from an article by 

Billingsley:*

In planning to drain a field or any given,area of land, the general 

surface configuration of the land should be carefully studied and 

levels taken. It is important to know definitely where the best outlet 

should be located to afford a free flow of water, and where the main 

and subordinate drains should be placed to insure the most efficient 

drainage. It is also important to know what fall can be.had in the 

several drains, including the main and lateral drains, for the reason 

that drains having considerable fall do not require as large a tile 

as those having slight fall.

Again.it is important to know the character of the soil and subsoil. If they are open, the lateral drains may be laid from 60 to 

.100 feet apart; if the soil or, more particularly, the subsoil is retentive or close, allowing the water to percolate only slowly through 

it, the drains need to be closer together (from 30 to 50 feet apart).

Still another important factor to be considered in the general plan 

is the amount of water that flows on to the land to be drained from 

land adjoining. This flow of water, if considerable, must be provided for by using larger tile for the drains that 'will necessarily 

carry it from the neighboring land.

After determining all these factors the entire system should be 

outlined on paper, including the levels, mains, submains, and lateral 

drains, the sizes of tile to be used, and the depth of the drains.

The work of construction properly begins at the outlet, which 

should be so placed as to give the greatest fall and most direct outflow of water. The main drain at the outlet should be as deep as 

conditions will allow or the perfect working of the system requires^ 

not exceeding ordinarily 4 or 5 feet.

The size of the tile to be used depends upon the area to be drained, 

the inclination, or fall, the depth of the drains, and the character of 

the soil and subsoil. Prof. E. C. Carpenter has prepared the following estimate of the number of acres drained by tile of different sizes :

1 Billingsley, J. J. W., Clay Worker, October, 1908, p. 386.
70 CLAYS AND SHALES OF MINNESOTA. 

Number of acres drained by tile of specified sizes.

Inclination.

One foot in 

50.................................................

100................................................

150................................................

200 ..................:.............................

250................................................

300. ...............................................

400................................................

500. ...............................................

600. ...............................................

800................................................

1,000..............................................

3-inch.

8.4

5.7

4.5

3.9

3.5

4-inch.

17.0

11.9

9.5

8.2

7.5

6.9

5.9

5.2

4.8

4.1

6-inch.

47.7

33.1

26.6

22.8

20.4

18.4

16.5

14.8

13.3

11.4

10.2

8-inch.

"98.0

69.2

56.0

48.0

42.4

38.2

34.6

30.1

28.0

24.0

21.2

10-inch.

170.4

120.6

97.3

83.9

74.4

65.5

60.3

54.0

48.6

41.9

37.2

12-inch,

298.0

190.5

154.4

132.5

H7. 0

107.0

90.7

81.6

74.0

65.0

56.0

To insure sufficient capacity to carry the water from 10 acres the 

use of tile at least 4 inches in diameter is recommended. Besides, it 

is claimed that larger tile give better aeration of the soil.

The depth of the drain also affects the size of the tile. Other conditions being equal, the greater the depth the smaller the tile required. Drains laid at the depth of 3 feet and 80 feet apart would 

afford very little drainage to the soil midway between the drains in a 

close, retentive clay soil but would probably be satisfactory in an 

open soil.

Ditches should be only wide enough to work in conveniently and at 

the bottom should be only wide enough to lay the tile. Tile laying 

is begun at the outlet and is continued up grade. Unevenness at 

the joints is to be avoided.

Lateral or side drains should enter the main drain at an acute 

angle, so that the water they carry will not interfere with the current of the main drain.

Minnesota has large areas of swamp land which when once drained 

raise excellent crops. Drainage with cylindrical clay tile has many 

advantages, and the manufacture of draintile should become of much 

greater importance in the next few years. Fortunately the State 

possesses an abundant supply of raw clays from which good tile 

can be made.

GEOLOGY OF MINNESOTA.*

By FKANK F. GROUT and E. K. SOPEB.

PHYSIOGRAPHY.

Minnesota is made up largely of gently undulating plains underlain by glacial drift alternating with belts where the surface is 

rougher, owing to the irregular heaping up of glacial drift as termi1 For the main features of <the discussion of the geology, credit is due to Winchell, 

N. H., and Upham, Warren, Minnesota Geol. and Nat. Hist. Survey Final Repts., 1884, 

1888, 1899, 1900; and to Hall, C. W., and Meinzer, 0. E., Geology and underground waters 

of southern Minnesota : U. S. Geol. Survey Water-Supply Paper 256, 1911.
GEOLOGY OF MINNESOTA. 71

nal moraines. In many places these moraines are bordered by nearly 

flat tracts underlain by sand and gravel deposited by glacial waters. 

Both these flatter areas and the moraines are pitted with abundant 

depressions, known as kettleholes. The hollows and many larger 

low areas are poorly drained, and in consequence lakes and swamps 

are very numerous, particularly in the north-central part of the 

State. In the northwestern part there is an extensive flat plain which 

was at one time covered by the waters of a great lake, known as 

glacial Lake Agassiz, and a much narrower area bordering Lake 

Superior was also flooded by the waters of a succession of temporary 

glacial lakes known as Lakes Duluth, Algonquin, and Nipissing. 

Though the mantle of glacial drift is generally thick there are numerous, places, especially in the eastern part of the State, where the 

bedrock is exposed or but thinly covered.

Southern Minnesota, considered broadly, is a low plateau, the 

southwestern part of which reaches 1,900 feet above sea level, or 500 

feet above the rest. This higher part extends into South Dakota 

and has been named the Coteau des Prairies. The next highest part 

of the plateau is in the southeastern part of the State, in Mower 

County, where the elevation is 1,400 feet above sea level.

In the southeastern, counties the streams have cut deep gorges with 

precipitous walls. In much of this district the glacial drift is thin, 

and in the eastern parts of Winona and Houston counties there is no 

drift at all, this being part of the great Driftless Area of the upper 

Mississippi Valley. In these deeply dissected areas rock outcrops 

are numerous, and here and there are flat-topped mesa-like erosion 

remnants and rock towers like ancient castles. Most of the Driftless 

Area and some of the adjacent drift-covered tracts are covered by a 

thin veneer of dustlike clay, or loess, which ranges from. 1 to 12 feet 

thick, averaging 4 or 5, feet. This loess tends to smooth over any 

small irregularities in the surface. It reaches its maximum thickness in stream valJeys and depressions, and is absent from many of 

the higher knolls and rolling prairies.

Northern Minnesota possesses a more varied topography. The 

northwestern part, which was covered by glacial Lake Agassiz, is as 

flat as a floor, except for a series of low gravel ridges that represent former beaches of the lake. The north central and the northeastern parts are more undulating and contain numerous morainic 

belts. In the southern part of Otter Tail County three morainic 

belts converge to form the Leaf Hills, which rise 250 to 300 feet 

above the general elevation of the surrounding land. Otter Tail 

County also contains 430 lakes,1 not including swamps and ponds 

a greater number than any other county in the State. The extreme

1 Terry, C. M., Minnesota Geol. and Nat. Hist. Survey Final Rept, vol. 2, p. 535, 1888.
72 CLAYS AND SHALES OF MINNESOTA.

northeastern part of the State has a rather rough topography and it 

includes the highest point in Minnesota. Here several low " ranges " 

of. pre-Cambrian rock trend approximately N. 70° E. and rise from 

1,800 to 2,000 feet above sea level.

The principal drainage system is that of Mississippi River and 

its intricate net of tributaries. In the northwestern part of the State 

Red River is the main stream; and in the northeastern part a considerable area drains to Lake Superior.

GEOLOGIC HISTORY.

The rocks of Minnesota range in age from the earliest Archean 

granites and schists to the Recent alluvium. The columnar section 

(PL IX) shows the principal formations in the State, arranged in 

ths order of age, with the oldest at the bottom.

ARCHEAN PERIOD.

The Keewatin epoch was largely a time of volcanic activity. The 

basalt lava flows, which were both subaqueous and subaerial, were 

profoundly metamorphosed and softened to the so-called green 

schists over much of the area, both before and after the deposition 

of the Algonkian sediments. Small amounts of sediments were deposited, especially near the end of Keewatin time.

In Laurentian time acidic granitoid and gneissic masses were intruded into the Keewatin, mostly as great granite batholiths. Their 

relation to the Keewatin is complex, and some outcrops show evidence that the granite magma stoped and absorbed parts of the basic 

rock. North and northwest of Lake Superior the granite intrusions 

are enormous. The age of the granite on the southwest along Minnesota River is less certain. «

After the Archean period closed erosion was long continued, the 

region was subjected to notable earth movements, and the rocks were 

metamorphosed.

ALGONKIAN PERIOD.

As a whole the Algonkian was a period of sedimentation, as contrasted with the Archean, though marked igneous action occurred 

at intervals. Two main divisions of Algonkian rocks, each of .considerable thickness are represented in Minnesota the Huronian 

series below and the Keweenawan series above.

The earlier Huronian sediments, which have been called lowermiddle Huronian, were clays and graywacke sands. Some igneous 

action also occurred at this time, yielding a variety of products. Deposition extended from northeastern Minnesota westward, and the
U. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE IX

ERA.

Cenozoic.

o 

o

I '

«n

Protefozoic.

SYSTEM AND 

SERIES.

Quaternary.

Recent.

Pleistocene.

Cretaceous. 

Upper Cretaceous).

Ordovician.

Cambrian.

Algonkian (?).

!Algonkian. 

1Archean. 

Keweenawan.

Huronian.

Laurentian.

.g'

'-£> 

1M

GROUP AND FORMATION.

Bentoi 

Dakot 

Basal

i shale.

i sandstone. 

Cretaceous clay.

Maquoketa shale.

Galena limes tone. 

Decorah shale. 

Platteville limestone.

St. Peter sandstone.

Oneota dolomite.

Jordan sandstone.

St. Lawrence formation.

Franconia sandstone.

Dresbach sandstone and 

underlying shales and 

sandstones.

Red clastic series.

Conglomerate and sandstone.

Eruptives.

Huronian). Animikie (uppr group 

Lower-middle Huronian.

Acidic and basic intrusives.

Virginia and other slates.

Biwabic and gunflint format ions.

Pokegama quartzite.

Giants Range and other intrusive granites, granite 

porphyry, and dolerites.

Slates, graywackes, and con 

glomerates.

Residual clay.

Intrusive granites, gneisses, and 

porphyries.

Soudan formation.

Green schists, porphyries, Ely 

and other green stones.

SECTION.

^T^. . ^ .'Tr^'.«"r^.»"'

oSl§u>6!iSj

 

_^_ ^ L- - 

 

-^ii^Uv^i

i 1 !..._! 1_

 ' . 77.' ' ' TT.

i ' i 'i 'i V

rrrr.-::^i.v:::

 * ....." ' ' '

"7=-=r?-:=r^>'.

- n . 

: ::::-~~- : :. /

........ _ - - 

. O O ; O * b o . . . O.

. o o ° 'o o'o o.o

 . . .0 . - -o , o ... £?''o .O'.o.- O'.'o'.o 

.O 'O 'O O -O' o '.o

V >^V<A1-7V/ 

1 L/1 ^ /) ^ V

~~ ~-'T.^""^^.~

'.-rr: I '.'.'

OOO O»OOo Oo

x^ / v <-^ / r*' \

. C^ C> o b ° C? o

 <? . o'.o . O/ o. O

. ?. °.O o O o

 9 P.V -Q-b -o o

<?'°. o'o ;o cf? o

O O 6 O O.Q O

 9-O.O.o'o'oi;

 /'- : «'. : ' ' *:

 .* i * *. -*.

»*,* * » ^ 

: :V-' ' '/: ' . : 

^^=

Hi

"C" ^^ ^ ^-^

> x X X X x

X X K X x

» -« X X X, X 

X1 X )> X X X

, Vv\V*

CHARACTER OF FORMATION.

Alluvium, etc.

Glacial drift, boulder clay, sand, 

gravel, associated lake and river 

clays and loess.

Soft blue and gray shale and incoherent sands, white sandstone, 

and white clay.

Shale, dolomite, and sandstone.

Limestone and shale.

Wiite and yellow sandstone and 

some shale.

Buff to reddish dolomite.

Coarse-grained white sandstone.

Dolomite, shale, and sandstone.

Micaceous sandstone with green sand 

at base.

Fine-grained white sandstone and 

shale; limestone beds toward 

base.

Red sandstone and shale.

Conglomerate and sandstone.

Gabbro, diabase, and granite.

Black to dark-gray carbonaceous 

slates.

Taconite, iron ore, ferruginous 

chert, and paint rock.

Quartzite and quartz slate, conglomerate base.

Gray and pink granite, granite 

porphyry, dolerites, and lamprophyres.

Green to gray slates, graywackes, 

and conglomerates.

White residual clay; decomposition product.

Granites and porphyries in part 

altered to schists.

Banded slates, cherts, and red jaspers; iron bearing.

Greenstones, green schists, porAPPROXIMATE 

MAXIMUM 

THICKNESS

(FEET).

500

500 

100

100

230

200 

100

200

200

200

100

450

1,750

500

Unknown.

Unknown.

3,000

800

200

Unknown.

5,000

Unknown.

Unknown.

CLAY-BEARING VALUE.

Contains alluvial clays.

Contains largo amounts of good clay.

Contains much high-grade clay. 

Fire clay.

Contains but little clay shale.

Contains but little clay shale. 

Contains much good clay shale. 

Contains no clay.

Contains no clay.

Contains no clay.

Contains no clay.

Contains small amount of shale.

Contains no clay.

Contains some sandy shales.

Contains but little available clay or shale.

Contains very little clay.

Contains no clay of value.

Contains no clay.

Contains no clay except residuals. 

Slates may be used after crushing.

Contains very little clay.

Contains no clay.

Contains no clay.

Contains much slate but no clay.

Contains large amounts of residual clay am 

kaolin beneath the drift.

Contains no clay.

Contains no available clay.

GENERAL GEOLOGIC SECTION OF MINNESOTA.
GEOLOGY OF MINNESOTA. 73

beds may have covered meet of the Ar:-hean area in the State, but 

they were later removed by erosion from, much of the northern 

area. Further earth movement and metamorphism occurred. :

The upper Huronian sediments (Animikie group) were deposited 

over a relatively plane, eroded surface of Archean and lower-middle 

Huronian rocks. The advance of the sea was marked by the deposition of thin conglomerate and sandstone, above which were laid 

down the iron-bearing formations of the Mesabi range, and above 

these some other slates. The abrupt change from sand to ironbearing formation indicates a sudden change of conditions, probabty 

to be explained by basic eruptions rather than by topographic or 

climatic changes.

The upper Huronian rocks are much less altered than the earlier 

rocks, but in central Minnesota were rendered schistose by the heat 

and pressure attending the intrusion of large volcanic masses, probably for the most part Keweenawan. The quartzite of the Minnesota 

River valley may have been deposited as sand at this time.

The Keweenawan epoch began and. ended with normal sedimentation but included vigorous igneous action, both intrusive and extrusive. The sediments of this age are relatively thin, and most of 

them, from their red color, poor assortment, and alternation with 

lava flows, may be considered probably land deposits. Most of the 

material of the middle and upper Keweenawan sediments was derived from the dominantly basic Keweenawan igneous rocks. These 

sediments lie unconformably above the Huronian, but their exact 

relation to the Cambrian is not a simple problem. No profound 

metamorphism has occurred since the beginning of the Keweenawan 

epoch.

The Lake Superior basin was developed partly in Keweenawan 

time, and lavas now dip under the lake on each side. The large 

area on the north shore is of special interest on account of the great 

gabbro mass (Duluth gabbro) and the series of flows and intrusions easily studied in the shore cliffs. Granites and diabases, 

probably of the same age, extend southwestward to central Minnesota near Little Falls, and diabase dikes as far as the Minnesota 

River valley.

The red clastic series shown in the well records of the region 

around Minneapolis and St. Paul is regarded as probably Algonkian, though it may be Cambrian.

CAMBRIAN PERIOD.

Prolonged erosion at the end of Keweenawan time was followed 

by the deposition of a sandstone on the eroded slopes of all the earlier 

formations. Above the profound unconformity thus produced the
74 CLAYS AND SHALES OF MINNESOTA.

strata vary little from the horizontal, furnishing a strong contrast 

with the earlier rocks. In some places, as at Taylors Falls, a sandstone in contact with tilted Keweenawan lavas contains marine fossils and is well up in the Cambrian. On the other hand, from Mora 

to Fond du Lac there is a sandstone with some shaly layers near 

the base that is nonfossiliferous and may be continuous with the 

upper Keweenawan sandstone. With this exception the sediments 

seem to be marine. A great basin in the southeast quarter of the 

State contains a series of Paleozoic rocks from the Cambrian up. 

In the middle of the Cambrian period some minor change of conditions caused the deposition of shale and magnesian limestone (the 

St. Lawrence formation), after which sandstone (the Jordan) was 

again deposited.

ORDOVICIAN PERIOD.

Without any apparent unconformity the deposition of sediments 

continued after the Cambrian. The lowest formations included in 

the Ordovician system are the Oneota and Shakopee dolomites, made 

up mostly of dolomite, with a few sandy layers and lenses.

Above these dolomites lies the St. Peter sandstone, 80 to 200 feet 

in thickness and consisting of very pure quartz in well-rounded 

grains. Locally a thin, shaly bed appears about 40 feet above the 

base, and another thin shale is very persistent between the sand 

and the overlying Platteville limestone.

The Platteville, usually 12 to 20 feet, but in places 30 feet thick, is 

a shaly magnesian limestone of variable quality.

Upon the Platteville was laid down the Decorah shale, which now 

crops out in places from the Twin Cities southeastward. The period 

of its formation favored alternately the deposition of shale and that 

of limestone, and the resulting rocks show variable alternating materials in layers from an inch to several feet in thickness. At St. 

Paul the exposed shaly beds are 80 feet thick, but farther southeast 

they thin considerably. With included limestone layers the maximum thickness of the formation is about 100 feet. The shales are 

green but weather brown from original pyrite. Fossils are numerous.

After the deposition of the shale with limestone layers there was a 

gradual increase in the proportion of limestone. The Galena limestone in Minnesota (including some shale layers) makes up 50 to 

100 feet or more of the section. Because of absence of exposures its 

maximum thickness is unknown. Careful paleontologic work is 

needed to locate accurately the boundary between the Galena and 

the Decorah. However, no shales of value have been found much 

above the base of the Galena.
GEOLOGY OF MINNESOTA. 75'

The Maquoketa shale is variable both vertically and horizontally,.; 

being full of sandy and calcareous Iense3 and irregular beds. It has 

a thickness of about 100 feet.

DEVONIAN PERIOD.

After a period of erosion 50 to 100 feet of Devonian sediments 

 were deposited. .These constitute the northern part of a large .mass 

in Iowa. In Minnesota the main portion of the rock is sand and limestone, but it includes some shaly bands, and by long weathering has 

formed residual clays, as at Austin.

PRE-CRETACEOTTS EROSION INTERVAL.

.The period of erosion that followed the deposition of the Devonian, 

rocks must have been long. Weathering was widespread and profound. No rocks are known which indicate any deposition of sediments in Minnesota until Upper Cretaceous time. No important 

diastrophic movements are indicated, and it is not probable that the 

elevation above sea level was great or that the topography was rough. 

In many places the Cretaceous arid glacial deposits rest on earlier 

rocks which have been very deeply weathered. Archean granites, 

and gneisses, extending over many counties, have been kaolinized' 

to depths of 10 to 100 feet. If any considerable relief had existed 

when or after the weathering took place, erosion of these softened 

rocks would have been very rapid. The period of weathering is also 

indicated by the decay of Paleozoic sediments, yielding residual 

clays.

CRETACEOUS PERIOD.

The Cretaceous sea encroached upon Minnesota from the west and 

southwest, and Cretaceous clays and sands and in a few places limestone now unconformably overlie Archean, Algonkian, and Paleozoic rocks. The clays contain marine fossils of Benton age. The 

southwest quarter of Minnesota is almost entirely covered with such 

sediments, except for the prominent quartzite knobs which probably, 

represent islands in the Cretaceous sea.

Occurrences in North Dakota and some thin deposits extending as 

far east as the Mesabi range have been thought to indicate that 

similar Cretaceous deposits underlie the drift in the northwest quarter of Minnesota. However, it is .known from recent wofk of Frank 

Leverett 1 that Paleozoic sediments underlie the drift in this part of 

the State, and hence that any Cretaceous sediments that were de1 Personal communication.
76 CLAYS AND SHALES OF MINNESOTA.

posited between the Mesabi and Dakota areas have been removed by 

erosion. From the Mesabi range along a belt extending through 

southwestern Minnesota, however, outcrops' of Cretaceous beds are 

sufficiently numerous to justify mapping the formations as continuous, and well records and the drilling on the Cuyuna range confirm 

the connection.

Toward the southwest were accumulated as much as 500 feet of 

sediments that consist chiefly of impalpable clay and fine sand, such 

us would be derived from thoroughly weathered granites. Since the 

recession of the sea in late Cretaceous time the region has not been 

again submerged. Probably there was extensive erosion before Pleistocene time and during the ice invasions and the interglacial stages.

QUATERNARY PERIOD. 

PLEISTOCENE EPOCH.

By FRANK LEVERETT.

Just before the Pleistocene epoch began the larger features of the 

topography of Minnesota were much the same as now. The advance 

of the ice, however, scoured out some valleys, filled in others, and deposited drift over large areas, entirely changing the details of topography and drainage. The drift deposits over a large part of Minnesota west of Mississippi River above the mouth of the Minnesota are 

200 to 300 feet thick and in places reach 500 to 600 feet. They are 

much thinner in the eastern and southern parts of the State, where 

over large areas there is only a mere trace of drift and in but few 

places does it exceed 100 feet. The retreat of the ice, by melting, 

formed marginal lakes and swollen, heavily silted streams, with further deposition and modification of topography.

The' Pleistocene deposits show a peculiarly complex history, recording not only recurring stages of glaciation separated by long 

stages of deglaciation but also a complexity of ice movement within 

a single glacial stage. In the latest stage (known as the Wisconsin 

stage) there was one movement into Minnesota from the northwest, 

another from the north, and a third from the northeast; and possibly there was similar complexity in earlier stages. These movements were not synchronous in their advance, culmination, and waning, but each had its time of waxing and waning. The interpretations of these complex conditions as yet are incomplete, and the 

relations of ice lobes are at best only approximately known.

The oldest glacial deposit, known as the pre-Kansan or Nebraskan drift, is almost completely buried beneath later deposits. The
GEOLOGY OF MINNESOTA. 77

attenuated edge of this drift may be exposed outside the Kansan 

drift in the southeastern counties.

Clayey and silty deposits found in a few places under the Kansan 

drift may represent accumulation in the Aftonian interglacial stage. 

They are, however, thin and of small extent and are rarely seen in. 

either natural or artificial cuts.

The Kansan drift is extensively exposed in the southeastern part 

of Minnesota and in Pipestone and Eock counties in the southwestern part. It is generally of clayey texture, but as a rule carries 

limestone pebbles. It contains local pockets or lenses of marly 

pebbleless clay.

Weathering has somewhat modified the character of the upper 

part of the Kansan .drift, and wind has coated much of the surface 

in the southwest corner of the State and some of it in the southeast 

part with several feet of loess, a pebbleless deposit of fine dust. 

Recent wash has moved some loess and some drift down sloping 

hillsides and so mixed them that the precise mode of origin of some 

particular clay banks may not be easily determined. The possibility 

that some of the glacial clay may have been deposited at the lowan 

or Illinoian stages of glaciation need not be considered in this connection.

 The Wisconsin gray drift, which was deposited by an ice sheet 

moving from Manitoba across western and southern Minnesota, is 

largely of clayey texture, but, like the Kansan drift, contains many 

pebbles, a large part of which are limestone. In places some lenses 

and pockets of pebbleless clayey material are included in the stony 

clay.

The Wisconsin drift that was deposited by glaciers invading 

eastern and central Minnesota from the north and northeast is. in 

large part stony and sandy and contains very few bodies of silt or 

clay.

Locally streams of water from the melting ice spread fine sandy 

clays over what are called outwash plains.

The lake silts laid down in bodies of water in the western part of 

the Lake Superior basin and in the Red River basin are in places 

very thick, as at Wrenshall, but generally there is only a thin deposit of lacustrine sediment in the deep pools of these old lake beds, 

and in certain localities there is only sand.

On the borders of the Lake Superior basin red boulder clay 

was deposited in large quantities; it is now dissected by steep gorges.

In addition to the great glacial lakes of the Lake Superior and 

Red River basins, there were numerous small lakes or ponded areas 

along the border of the ice, in which silt was deposited. Such an 

area lies north of Princeton at the large plants of Brickton, and
78 CLAYS AND .SHALES OF MINNESOTA.

similar areas lie farther east along the northern border of % a district 

which was occupied by a lobe of -ice that extended northeastward 

from the Mississippi to the 'St. Croix Valley, above the Twin Cities. 

These clays were, in places, overridden by the later advances of 

the ice.

RECENT EPOCH.

Since the final disappearance of the Pleistocene glaciers there have 

been only slight modifications of the surface and very little accumulation of material or removal by erosion. A few lakes and swamps 

have been1 drained, and a few have been filled. The large river channels have been silted up.

GEOLOGIC FORMATIONS AND THEIR CLAY DEPOSITS.

ARCHEAN SYSTEM.

The rocks belonging to the Archean system in Minnesota consist of 

greenstones, granites, gneisses, schists, and small amounts of altered 

sediments (slate, jaspilite, and dolomite), which underlie all other 

formations and constitute the base upon which all subsequent strata 

were laid down. In northern Minnesota these Archean greenstones 

and granites crop out at many points .and include the productive 

iron-bearing formations of the Vermilion iron range. In the western 

part of the State hornblende and biotite schists and granites underlie the Cretaceous formations in many localities, where they crop 

out or have been reached by deep wells. Granite and gneiss crop 

out in central Minnesota and are known by well records to underlie 

the greater part of southern Minnesota.

In the southwestern part of the State the upper portions of the 

Archean rocks that are covered by Cretaceous sediments are invariably decomposed to white clay, as is clearly shown in the numerous wells throughout the region and in the few outcrops. The clay 

is in places 50 feet thick and grades downward into rotten granite 

of various shades. Its upper portion grades upward into the Cretaceous sedimentary clays, and the dividing line between the two has 

rarely been determined. It is more than probable that the upper 

parts of some of the very thick bodies of white kaolin that have been 

reported are residual clays reworked into the Cretaceous sediments. 

The clay in these deposits was formed long after the Archean period, 

but the exact time is uncertain, and they will be referred to in this 

report as clays residual from the Archean.

Much of the residual clay is of excellent quality. Outcrops are 

known chiefly along the Minnesota Valley from New Ulm up to 

the vicinity of Montevideo. Well records show these clays in Big 

Stone County at a depth of 250 to. 600 feet, in Chippewa County
GEOLOGY'OF MINNESOTA. 79

at about 700 feet, and in Lac qui Parle County at 150 feet. Probably the clays are very extensive and continuous in the counties north 

and west, where well records are not available. However, if the 

pre-Cretaceous weathering affected the granites in the northern 

part of the State, erosion by ice probably removed all traces of the 

products.

The following analyses of the clay as mined and one of the clay 

after washing are available. (See also analysis of a decomposed 

gneiss, p. 17.)

Analyses of residual clays.

Silica........:..................

Soda............................

Potash. .........................

Water...........................

1

43.86

1 41.82

> -Very small.

Not det.

Not det.

14.65

2

45. 92

39.84

Not det.

Not det.

14.12

3

41.71

f 34. 01

\ 4.58

6.88

/ .22

\ 1.16

.11

Tra-e.

12. 69

4

62.04

25.54

| 1.89

}.........

5

37.88

26.96

15. /o

1.74

 jtj

15.88

G

60. 05

27.55

1.30

.77

.38

/ .31

\ 4.26

5.30

.11

1. Clay from Morton; F. F. Grout, analyst. U. S. Geol. Survey Water-Supply Paper 256, p. 310,1911.

2. Clay washed from a decomposed granite, Redwood Falls; F. F. Grout, analyst. U. S. Geol. Survey 

Water-Supply Paper 256, .p. 310,1911.

3. Clay from decomposed gneiss, Birch Cooley, near Morton; A. D. Meade, analyst.

4. Clay, partly analyzed by L. B. Pease.

5. " Fahlunite." Average of three analyses by S. F. Peckham. Minnesota Geol. and Nat. Hist. Survey, 

vol. 2. p. 196,1888.

6. ''Kaolin (Archean), green or pink to white decayed schist." Minnesota Geol. and Nat. Hist. Survey, 

vol. 5, p. 730,1900;

This widespread residual clay can probably be used after washing 

for making porcelain and chinaware. A rough washing test in the 

laboratory on a few samples from widely separated localities shows 

that about 50 per cent of the crude product can be washed through a 

100-mesh sieve. This finer fraction of the clay burns to a clear 

white, which even after being glazed darkens very little. These 

clays are the most refractory in Minnesota and are capable of being 

used for the highest grade of clay products. Their plasticity and 

tensile strength are low, and even if they are used only for brick 

they need a plastic bond. In firing they become hard at about cone 3 

(2,200° F.), though in this respect they vary rather widely, and the 

temperature of viscosity is much higher. They remain porous to 

high temperatures.

ALG03STKIAN SYSTEM. 

HURONIAN SERIES.

In Minnesota two divisions of the Huronian series have been recognized the lower-middle Huronian and the Animikie group or
80 CLAYS AND SHALES OF MINNESOTA.

upper Huronian. These two divisions are separated by an unconformity, and the Huronian as a whole is separated by unconformities 

from the overlying Keweenawan and the underlying Archean.

The lower-middle Huronian includes no clays but consists of 

granites, granite porphyries, dolerites, slates, graywackes, and conglomerates and their metamorphosed equivalents. The sedimentary, 

series attains a thickness of 5,000 feet in the northern part of the 

State. It lies unconformably upon the Archean and crops out in, 

general in a belt around the Archean area, except where concealed 

under drift.

A number of distinct formations belong to the Animikie group or 

upper Huronian. Among these are the acidic and basic intrusive 

rocks, the Virginia and other slates and schists, the iron-bearing 

Biwabik and Gunflint formations, and the Pokegama quartzite. 

The Sioux quartzite is thought by some to be equivalent to the Pokegama quartzite and by others to belong in .the lower-middle Huronian.

The Huronian rocks crop out only in the central and northeastern 

part of the State, except the Sioux quartzite, which occurs in the 

southwestern part. The slates, cover the largest area and attain great 

thickness. Their mineral composition is very different from that of 

an average shale or slate.1

None of these Huronian rocks contain any clay deposits of importance, but experiments made in connection with the preparation 

of this report show that some of the slates exposed in Carlton 

County, when mixed with a small amount of common clay from the 

drift, will make a handsome fancy brick of high quality. They 

must be crushed, as they do not slake nor become plastic. The Sioux 

quartzite contains some layers of a silicified shale known as pipestone, but as none of them are more than 4 feet thick they are of no 

importance in the ceramic industries. Some layers of clay in the 

iron-bearing Biwabik formation are so ferruginous that they are 

called paint rock. This paint rock does not melt at, a temperature as 

low as might be expected from its high content of iron. Where 

necessarily removed in the course of iron mining it can be used in 

brickmaking, though it is not especially desirable. An analysis 

may be found in the report on St. Louis County (pp. 225-230). Residual clays from mica schist crop out along Mississippi River in 

Morrison County, and though they are not so refractory as those from 

the Archean they fuse at a relatively high temperature. An analysis 

may be found in the report on Morrison County (pp. 197-200).

1 Van Hise, C. R., and Leith, C. K., The geology of the Lake Superior region : U. S. 

Geol. Survey Mon. 52, p. 612, 1911.
GEOLOGY OF MINNESOTA. 81

KEWEENAWAN SERIES.

The Keweenawan series in the eastern and northeastern parts of 

the State is made up largely of flows of basic igneous rocks and includes no clays. Some of these flows alternate with sediments, which, 

however, were in large part derived from the flows and are highly 

ferruginous and feldspathic and not suitable for use as clay. At 

Two Harbors, on the north shore of Lake Superior, lenses of these 

sediments a few feet in length and a few inches in thickness were 

sampled to determine their exact character. An analysis of shaly 

sand rock, probably Keweenawan, is given in the report on Lake 

County (pp. 186-187). Along Snake Eiver, just below Pine City, a 

larger bed of essentially the same material occurs. The clay from 

these deposits does not slake or become plastic, and it remains sandy 

and soft to a temperature of 2,300° F.

ALGONKIAN ( ?) SYSTEM. 

RED CLASTIC SERIES.

Sediments known as the red clastic series, probably of the same 

age as the Keweenawan igneous rocks, are known in the eastern 

and southeastern parts of Minnesota and have been provisionally 

assigned to the Algonkian (?) system. In the south they underlie 

Upper Cambrian sediments and are known only from well records. 

They are probably of the same age as the red sandstone and shale 

(locally called Hinckley sandstone) that crop out unconformably 

above the Huronian from Lake Superior southwest to Mora. Shaly 

layers are especially abundant near the base of the red clastic series. 

An analysis of this shale from the vicinity of Fond du Lac is given 

in the report on Carlton County (pp. 134-140).

CAMBRIAN SYSTEM.

The Cambrian system embraces, in order of age (the oldest being 

named first), shales and white sandstones, the Dresbach sandstone, 

the Franconia sandstone, the St. Lawrence formation, and the Jordan, 

sandstone.

LOWER FORMATIONS.

The lower formations, including the older sandstones and shales, 

and the Dresbach and Franconia sandstones, are made up of 550 

feet or more of fine-grained white sand with shaly beds and sandy 

shales and thin layers of limestone toward the base. The best exposures are along St. Croix Eiver north of Stillwater and at Dresbach, on Mississippi Eiver just north of the Iowa line. Siliceous

64310° 19 6
82 CLAYS AND SHALES Otf MINNESOTA.

shales of variable character occur at these places, but the deposits are 

not likely to be of importance as clays because of their small size and 

inaccessible position in river bluffs. Their behavior under firing is, 

however, not unfavorable.

ST. LAWRENCE FORMATION.

Overlying the Franconia sandstone is the St. Lawrence formation, 

which consists of buff-colored dolomite interbedded with shale and 

sandstone. The shale is greenish, and toward the top of the formation there are several thin layers of greensand. The total thickness 

of the formation is about 130 feet. The best outcrops are found 

along Mississippi and Root rivers, north of the Iowa line, but the 

formation underlies practically all of southeastern Minnesota, extending as far north as northern Washington County and westward 

to a point beyond Mankato, where it crops out in the Minnesota River 

valley. The shales are too thin to be of value as brick material. 

They are so sandy that they shrink very little up to the point of 

viscosity. The porosity can not be reduced below about 20 per cent.

JORDAN SANDSTONE.

The Jordan sandstone, the uppermost formation of the Cambrian 

system in Minnesota, consists of 75 to 200 feet of white to brown 

sandstone, without any clay. It is confined chiefly to the southeast 

corner «f Minnesota, and its outcrops are best seen in the Minnesota 

River valley north of Mankato and in the bluffs along the Mississippi 

from Hastings to the Iowa line.

ORDOVIGIAN SYSTEM.

The Ordovician system in Minnesota is composed of the following 

formations, named in order from oldest to youngest: Oneota dolomite, Shakopee dolomite, St. Peter sandstone, Platteville limestone, 

Decorah shale, Galena limestone, and Maquoketa shale.

The Ordovician rocks are confined to the central and southern 

parts of the State, where they rest conformably upon the Cambrian. 

They have a very slight general dip to the south.

ONEOTA DOLOMITE.

The Oneota dolomite is a buff to reddish dolomite that crops out 

in numerous localities along valleys and river bluffs in southern 

Minnesota. The texture of the rock ranges from compact to crystalline, but the crystalline variety is the more typical. The formation is from 75 to 200 feet thick. It contains no clay.
U. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE X

loraen 1 (1

MAP OF

MINNESOTA

SHOWING THE DISTRIBUTION 

OF CLAY MATERIALS

By FrankF. Grout and Edgar K.Soper

Scale 2,000,000 

o 25

EXPLANATION

Approximate eastern boundary of gray drift clay brought 

from the northwest by glaciers of the Wisconsin and or< 

Wisconsin stages of glaciation

Approximate western boundary of red drift clay brought 

from the north and northeast by glaciers of the Wisconsin 

stage of glaciation; partly covered by gray drift clay

(Drift and lake boundaries mostlyfrom maps by Leverett and Sardeson 

(Minnesota Geol. Survey Bulls. 12,13,and 14.) For areas of loess, etc. in 

southeastern and southwestern counties see figs. 9 and 10.)

Eastern border of the material worked 

over by Lake Agassiz and Red River 

and its tributaries

Area of Decorah shale

Large deposits of gray laminated glacial clay

Large deposits of red laminated glacial clay

Pit worked for Archean residual and Cretaceous clays

Pit worked for Decorah shale

Pit worked for Pleistocene cream-burning clays

Pit worked for Pleistocene red-burning clays

Pit worked for Recent river and lake clays
GEOLOGY OF MINNESOTA. 83

SHAKOPEE DOLOMITE.

The Shakopee dolomite also contains no clays. It consists of a 

maximum of 100 feet of yellow, buff, or red magnesian limestone, 

which differs from the Oneota in color and in its finer grain and 

greater sand content. The Shakopee crops out along the Mississippi 

and Minnesota river bluffs. In much of south-central Minnesota it 

forms the surface upon which the drift has been deposited.

ST. PETER SANDSTONE.

The St. Peter sandstone consists in the main of a fine-grained, 

loosely consolidated white sandstone, which weathers yellow. It 

ranges from 80 to 200 feet in thickness, but the average is somewhat ^over 100 feet. In most parts of southern Minnesota the St. 

Peter is covered by either late Ordovician sediments or drift or by 

both, but it crops out along the Mississippi and its tributaries from 

Minneapolis south.

There is a 2-foot bed of shale at the top of the St. Peter sandstone, 

but it is of too small extent to be of value.

PLATTEVILLE LIMESTONE.

The Platteville limestone has an average thickness of 12 or 15 

feet and reaches a maximum of 30 feet. The rock is a magnesian 

limestone that ranges in texture from compact to thoroughly crystalline and in color from buff to blue-gray. It crops out over large 

areas in southern Minnesota from the Twin Cities southeast. It contains no clay of value.

DECORAH SHALE.

Lying on top of the Platteville limestone is a series of green shales 

with a maximum thickness of more than 100 feet, though the common thickness is much less than this probably not more than 50 

feet. Interbedded with these shales are numerous layers and lenses 

of hard granular limestone, some of which are composed almost 

entirely of fossils. In places these limestone layers constitute more 

than one-half of the total thickness of the formation. They range 

in thickness from 1 inch to several feet, but most of them are less 

than a foot thick. At the base is usually a thick shale (about 10 

feet), above which the shale and limestone alternate in similar layers. 

The shale is fissile and crumbles easily. The map (PI. X) shows the 

area of workable Decorah shale but not the total extent of the 

formation. The upper part of the shale grades on the south into 

limestone. 1 The northern and eastern limits shown on the map are

1 Sardeson, F. W., Galena series: Geol. Soc. America Bull., vol. 18, pp. 179-194, 1907.
84 CLAYS AND SHALES OF MINNESOTA.

eroded' outcrops. On the west and south the Cretaceous and Devonian rocks overlap the Decorah and make it inaccessible, and even 

in the area where it is mapped the glacial drift covers some of it so 

deeply that it is quite beyond reach. In the extreme southern part 

of Minnesota the formation thins to about 30 feet. At Cannon 

Falls, as at St. Paul, it reaches a maximum thickness, but north of 

St. Paul it is entirely eroded away. Throughout the southern part 

of the State it is very gently folded, and its elevation above sea level 

ranges from 1,000 to 1,300 feet.

The Decorah is one of the most valuable clay formations in Minnesota. The shales, when crushed and pulverized and mixed with

CONE NO. OI4> 010 08 06 04 02 "'1.000° 1,100" 

TEMPERATURE IN "DEGREES tt

3 

1200s 1.300°

FIGURES. Diagram showing the decrease in porosity with increasing temperature exhibited by average clays of the several geologic formations in Minnesota. (Compare 

with figs. 3 and 4.)

water, yield a greenish plastic clay that is used extensively near 

St. Paul and in Goodhue County for the manufacture of pressed 

brick, fancy brick, hollow ware, draintile, and common brick. The 

St. Paul plants are the most favorably situated in respect to markets, but others might be developed at Faribault, Rochester, and 

Cannon Falls. The high grade of the product eliminates most of 

the competition with common brick.

The plasticity of the Decorah shale is very high, but its shrinkage 

is not excessive. The tensile strength of the dry clay is about 125 

pounds to the square inch, and the linear air shrinkage is 8 per cent. 

In general the shale burns red, but it can be burned green and brown 

or mottled by reduction during firing. It requires a much lower
GEOLOGY OF MINNESOTA. 85

temperature for vitrification than most clays, about 1,800° F., but 

has a good range between incipient fusion and viscosity (see fig. 8), 

and therefore can be easily vitrified without loss.

The fire shrinkage is not excessive. Paving brick have not been 

produced from the Decorah, but they may yet be made from it. 

When burned at a little over 2,000° F. it produces klinker brick. The 

upper layers of the Decorah differ slightly in color and behavior 

from the lower ones. In many outcrops this shale contains so much 

organic matter that careless burning of it will result in "black 

cores." Care must be used to attain complete oxidation. Even if oxidation is long continued and thorough, gases are evolved at high 

temperatures (probably from the reactions of sulphur and iron), 

which cause swelling and deformation. These can be avoided by 

careful control of the burning. An unsightly efflorescence (kilnwhite) also appears on some products, but it is seldom of great extent and was not seen in any brick burned to a high temperature. 

Analyses of the Decorah shale are reported in the discussion of 

Dakota County (pp. 149-153).

The shale is exposed in only a few places and should be sought by 

the stratigraphic method of prospecting. (See p. 50.) The top of 

the shale is likely to be marked by series of springs on grass-covered 

hillsides. Tests made at the University of Minnesota show that 

bricks made from the Decorah shale are of excellent quality. Soft 

red brick, not burned to vitrification, have a strength of 1,500 pounds 

to the square inch, and partly vitrified bricks with a rather high 

porosity still evident have a strength of over 3,100 pounds to the 

square inch.

GALENA LIMESTONE.

The Galena limestone overlies the Decorah shale or in part grades 

into it. (See fig. 33, p. 207.) It consists of granular or massive limestone that caps the hills in the southeastern part of Minnesota but 

is exposed in few places, owing to the loess and drift covering. In 

typical outcrops, as in Fillmore County, it contains only a few beds 

of shale, which are of no value, as they are but a few inches thick 

and shale free from limestone could hardly be obtained from them. 

Fragments of the dry shale slaked in three minutes to small lumps. 

The plasticity and tensile strength of the shale are fairly high. 

It requires 22 per cent of water for molding. Its air shrinkage is 

5 per cent. At low temperatures the burning results in a salmoncolored product without any fire shrinkage and with an absorption 

of about 28 per cent. It becomes buff and hard at cone 4 (2,210° F.) 

and turns gray at cone 6 (2,282° F.) but is still undeformed at even 

higher temperatures, though wholly melted at cone 12. The lime 

in the soft-burned bricks slakes and destroys the product.
'86 CLAYS AND SHALES OF MINNESOTA.

MAQUOKETA SHALE.

The Maquoketa shale in Minnesota is an alternation of dolomitic 

shale and limestone, with shales too thin to be of value. Outcrops 

are known only in Fillmore County, where it has a maximum thickness of 80 feet. The dry clay slakes in 10 minutes. Its plasticity is 

fairly high, and it requires only 15 per cent of water for molding. 

Its tensile strength is about 100 pounds and its air shrinkage less 

than 3 per cent. It can safely be dried with artificial heat. Several 

samples burned to the temperature of cone 2 were buff in color, 

showed no fire shrinkage, and had an absorption of 27 per cent. The 

clay does not become hard at cone 3 (2,174° F.), and it becomes 

viscous at cone 6 (2,282° F.) and therefore can not possibly be burned 

to a hardness approaching vitrification. Only one sample of the 

Maquoketa shale was available.

DEVONIAN SYSTEM.

The Devonian rocks in Minnesota, which consist of not more than 

100 feet of sandstone and limestone with some shale, overlie the Ordovician unconformably. They are confined to the extreme southern 

part of the State (Mower, Fillmore, and Faribault counties), into 

which they extend from Iowa. The shales are not of specially high 

quality and are too thin to be of much importance as a source of clay. 

In the vicinity of Austin marly layers of the Devonian have been 

used to mix with an overlying plastic clay, which has been described 

as Cretaceous but which may be residual from Devonian rocks.1 . The 

effect of the added lime is to improve the working quality and 

lighten the color.

Where Bear Creek crosses the line between Fillmore and Mower 

counties the shale beds were found to be as much as 1 foot thick and 

to show every indication of extending over considerable territory. 

They are yellow to buff in color, are very sandy and lean, and, of 

course, could not be separated commercially .from the interbedded 

limestone. The shales slake in about four minutes and develop 

surprising plasticity, considering their sandy appearance. They 

require about 20 per cent of water for molding. Their tensile 

strength is nearly 100 pounds to the square inch. They can be 

dried rapidly without danger of cracking, and they retain their 

tensile strength even after being cut apart and pressed together. 

Their air shrinkage is about 3 per cent. At very low temperatures 

the burning tests yield a salmon-colored product, but at the higher 

temperatures buff colors prevail, as indicated in the table.

1 Sardeson, F. W., The so-caUed Cretaceous deposits in southeastern Minnesota : Jour. 

Geology, vol. 6, p. 679, 1898.
GEOLOGY OF MINNESOTA. 87

Cone No.

06

2

5

Color.

Buff...........................

.....do.........................

.....do.........................

Shrinkage.

Per cent.

I

Absorption.

Per cent. 

27

23

The clay becomes hard at cone 03 (1,994° F.) and viscous at cone 6 

(2,282° F.).

CRETACEOUS SYSTEM. 

GENERAL CHARACTER.

The Cretaceous rocks found in Minnesota consist of soft sandstones, shales, and clays and locally have thin beds of conglomerate 

at the base. They lie immediately below the drift in much of the 

western part of the State and also in numerous scattered areas in the 

southern, central, and northern parts. Outcrops are few on account 

of the drift cover, but numerous well records have helped to show 

their general distribution. Their maximum thickness in Minnesota 

is about 550 feet. Their upper portion is composed chiefly of soft 

blue or gray shales and clay (Benton shale); lower down they conisist of white sandstone and kaolins (representing the Dakota sandstone) . In a few places in the northern part of Minnesota a Cretaceous conglomerate containing pebbles of hard hematite lies at 

the base of the shale overlying beds of iron ore. In the western part 

of the State the Cretaceous rocks rest upon the decomposed Archean 

granites and gneisses; the base of the shale is white clay of conglomeratic or concretionary texture that contains quartz pebbles. 

In a few places where the Cretaceous lies in contact with Paleozoic 

sediments the conglomerate is not prominent, but the clays are 

similar to those just mentioned. The variation of the conglomerate 

with variations in the bedrock indicates that the white clay is colluvial.

The Cretaceous beds contain the highest-grade clays found in 

Minnesota. Some of these clays are used for stoneware, pottery, 

sewer pipe, and fire brick. At present few good bodies of Cretaceous clays that lie close enough to the surface to be profitably 

excavated are known, but it is very probable that more detailed 

prospecting in the drift in the vicinity of Cretaceous areas would result in the discovery of other deposits of valuable clay. For convenience in discussion the pebbly or concretionary basal clays of 

the Cretaceous will be treated separately, and many references will 

be made to the residual clays from the Archean, from which the bagal 

clays can not'always be sharply distinguished. The higher formations are shales of much more ordinary appearance.
88 CLAYS AND SHALES OF MINNESOTA.

BASAL CRETACEOUS CLAYS.

The basal Cretaceous clays are most prominently exposed in the 

bluffs on both sides of Minnesota River from Granite Falls to New 

Ulm and probably to Mankato. Apparently similar white clays are 

found under the drift in several counties on either side of this strip 

along the river. Their great extent under the drift is thus further 

confirmed, and the certainty that they are not entirely Archean 

residual clays is shown by their stratified character and their development from Huronian schists near Richmond, in Stearns County, and 

near Bowlus, in Morrison County.

There is a general variation in the character of these basal Cretaceous clays as traced through these outcrops and farther north. 

Where the Archean or other bedrock formations are feldspathic, 

the basal conglomerate consists largely of clay. At Bowlus, farther 

north, the basal Cretaceous has the appearance of an iron-stained 

clay and is shown by analysis to be high in iron. Still farther north, 

on the iron ranges, the Cretaceous basal conglomerate immediately 

overlying the Huronian iron-ore deposits is good iron ore. This 

gradation, evident from the study of a series of scattered outcrops, 

may be taken as some slight indication of the continuity and contemporaneous formation of the various materials.

The clays that crop out in the Minnesota Valley, however, are not 

wholly conglomeratic but appear to be concretionary. (See PI. 

XI, B.) The.ro.unded spots show only a little concentric structure and 

are at some places more highly colored than the matrix and at others 

less highly colored. In a very few instructive outcrops these rounded 

spots, which appear to have the same composition as the matrix, are 

associated with, rounded quartz pebbles. It is therefore concluded 

that not all of them are concretionary. Part of them may be waterworn fragments. Possibly the original pebbles were quartz and feldspar, and the feldspar was subsequently altered, as the bedrock below 

was altered. Analyses of several samples show high alumina. The 

sample from Bowlus (see section on Morrison County, pp. 197-200) 

certainly contained too much alumina for the mineral kaolinite and 

may have contained concretionary bauxite' that originated during or 

after the formation of the basal Cretaceous conglomerates. The later 

Cretaceous shales overlie these beds with a very abrupt change in 

lithologic character.

Most of the basal Cretaceous clays are highly refractory, fine 

grained, and rather siliceous, and some of them are greatly contaminated with hematite. Their plasticity is low, and their tensile strength 

in the dry state is generally not over 50 pounds to the square inch. 

Their shrinkage both in drying and burning is very small. They 

become steel-hard at temperatures ranging from cone 06 to cone 35,
TJ. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE XI

A. SEGER CONES AFTER HEATING TO THE TEMPERATURE OF THE THIRD 

CONE OF THE SET.

B. CONCRETIONARY OR PEHBLY CRETACEOUS CLAY.
GEOLOGY OF MINNESOTA. 89

Analyses are given in the descriptions of Morrison, Redwood, and 

Stearns counties (pp. 197-200, 216-220, 233-237). The whiter clays 

could probably be washed to produce a kaolin fit for chinaware.

LATER CRETACEOUS SHALES.

The later Cretaceous shales are thought to underlie much of the 

western part of Minnesota, but are covered with a thick mantle of 

drift over most of the area. Beyond their eastern border, which can 

not be accurately mapped on account of the drift cover, there are 

many outliers and patches that have been transported bodily by ice.1 

These include some of the most valuable deposits in the State. In 

places the shales are interbedded with sandstone and less commonly 

with limestone. Nearly all the shales are light to dark gray, but some 

have a greenish tint. They are exceedingly plastic and have a peculiar waxy feel, apparently related to the occurrence of some mica 

scales in the clay.. They overlie the basal conglomerate with an 

abrupt change in structure and color. Many of them are cont^minated with organic matter and many are somewhat ferruginous. 

Their thickness in any place depends on the depth to which they 

have been eroded. Outcrops show vertical banks ranging from 1 to 

50 feet in height and well records reveal much greater thicknesses. In 

the southern and southeastern parts of the State the shales are semirefractory, but in the western and northern parts they are more 

uniformly ferruginous and are not so valuable. Nearly all the 

Cretaceous shales have a good range of vitrification and can be 

burned hard without danger of fusion.

The buff-burning Cretaceous clays require 27 per cent of water 

for molding. Their air shrinkage is less than 7 per cent, their plasticity is fair, and their tensile strength is 170 pounds to the square' 

inch, high enough for the production of the most elaborate and 

complex forms constructed in Minnesota. On burning many of the 

clays become dense and hard below 1,900° F. Their shrinkage on 

burning to thorough vitrification is only about 5 per cent. The 

absorption is 5 per cent after the clay becomes hard. Several of the 

clays, though burning very dense, give indications of withstanding 

high temperatures without losing any of their strength, the range 

of vitrification being over 500° F., probably higher than that of any 

other of the common clays of Minnesota. (See fig. 8, p. 84.)

These shales are utilized in Goodhue and Le Sueur counties (pp. 

165-173,187-191), and their quality is shown by the reputation of the 

stoneware made at Red Wing. Tests show that some clays not now

1 Sardeson, F. W., The so-called Cretaceous deposits in southeastern Minnesota: Jour. 

Geology, vol. 6, p. 679, 1898.
90 CLAYS AND SHALES OF MINNESOTA.

used are similar in properties to some that are used with excellent 

results. The following analyses are typical:

Analyses of buff to white burning Cretaceous shales.

Ferric oxide- .........................

Ferrous oxide ........................

Sulphur trioxide. ....................

Titanium ............................

1

69.92 

17.39

} 1.68

.60 

1.11 

.07 

2.25

.63

1.10 

5.45

100.20

2

69.84 

23.07

.48

.11

' .14

JTrace.

6.35

99.99

3

68.298 

18.266

2.867

.719 

.802 

f .81 

\ .60

1.29 

6.155

99.807

4

69.050 

18.830

2.607

.296 

.622 

1.066 

1.461

.898 

4.912

99. 742

5

59.72 

30.00

.82 

.51

10.34

101.39

0

70.10 

16.99

Trace.

10.69

.23

1.98

99.99

7

87.70 

7.24

Trace.

.67 

.07 

3.17 

.49

Trace. 

Trace.

99.34

8

68.70 

18.04

1.53 

1.24 

.56 

.24 

5.28 

.09

1.40

97.08

1. Red Wing, Goodhuo County. Clay sampled at stoneware plant. F. F. Grout, analyst.

2. Red Wing, Goodhue County. Analysis reported by J. H. Rich to Heinrich Ries.

3. Red Wing clay. Sample from Minnesota Stoneware Co., Red Wing, Apr. 22, 1902. C. P. Berkey, 

analyst.

4. lied Wing stoneware clay, air dried. C. P. Berkey, analyst.

5. Ottawa. Ottawa Brick Co. Ries. Heinrich, Clays; their occurrence, properties, and uses, 1906.

6. 7/and 8. Minnesota Geol. and Nat. Hist. Survey Final Rept., vol. 1, p. 438, 1884.

6. Near Mankato. Clay filling hollows in Shakopee dolomite.

7. Near Mankato (sec. 20). White clayey bed of considerable extent.

8. Near Mankato. Clay or shale between Shakopee dolomite and Jordan sandstone in L'Huillier Mound.

The red-burning Cretaceous shales are approximately the same as 

the buff-burning shales in slaking, tensile strength, and air shrinkage. Their plasticity is high. The water of plasticity is 29 per cent. 

They burn hard at about 1,800° F., with a linear fire shrinkage of -2 

per cent and an absorption of 15 per cent. They reach viscosity at 

a temperature of about 2,200° F., thus having a range of vitrification of nearly 400° F. (See fig. 8, p. 84.) The absorption of wellburned brick can be reduced below 5 per cent, and the linear fire 

shrinkage is then about 7 per cent. Care must be used in oxidation 

to avoid black cores and swelling. This description applies to clays 

not now used as well as to'several from which excellent brick are 

made.

Bricks are made from these Cretaceous shales by both soft-mud 

and stiff-mud methods. Soft-mud solid red brick show a compressive strength of 3,600 pounds to the square inch. Stiff-mud hollow 

brick, made light in weight for shipping, show compressive strengths 

of 900 to 1,600 pounds to the square inch, the strength depending on 

the degree of vitrification. The modulus of rupture is from 500 to 

1,500 pounds to the square inch. Typical analyses are given below. 

Plants making use of these clays are described in the reports on 

Brown and Goodhue counties (pp. 126-134, 165-173).
GEOLOGY OF MINNESOTA. 

Analyses of red-burning Cretaceous shales.

91

1

63.65

17.27

4.75

1.21

.06

.91

.2.47

fi9

9 fi^

7.36

100.33

2

61.32

12.27

3.62

4.18

.99

1.76

.42

3.59

.05

.27

.27

.19

.66

10.73

100.32

3

58.14

19.40

5.52

.79

1.52

.54

2.09

.68

2 jo

8

01

99.59

4

73.34

14.75

} 5.45

.28

.05

TVapA

4.71

98.58

1. Gray shale, west of Springfield. F. F. Grout, analyst.

2. New Ulm. Minn. Brick clay. U. S. Geol. Survey Bull. 60, p. 151, 1890. T. M. Chatard, analvsfc. 

A brick made from this clay is reddish brown, strongly sintered, somewhat fractured. Sample taken by 

John Lind on south bank of Cottonwood Eiver on section line at river crossing, east of wagon-road cross* 

ing, south of New Ulrn.

3. Clay sampled by A. Parker, of Brown Valley, Minn., just beyond the State lino in South Dakota. 

F. F. Grout, analyst.

4. Eed ocliery clay, near Mankato. Minnesota Geol. and Nat. Hist. Survey Final Kept., vol. 1, p. 438;

TERTIARY SYSTEM.

Rocks of Tertiary age have not been certainly recognized in Minnesota. Numerous thin stream deposits that are probably of this 

age can not be differentiated from the more recent surficial deposits.: 

Most of them have been worked over by streams or by the ice and 

have been mixed with the material of the drift.

QUATERNARY SYSTEM.

PLEISTOCENE DEPOSITS. 

GENERAL CHARACTER.

With reference to their ceramic value, the Pleistocene deposits 

of Minnesota, may be subdivided as follows: Nebraskan drift (no 

clay); Aftonian (?) interglacial deposits (only thin clays); Kansan 

and Wisconsin drift from the northwest (the gray drift); Wisconsin 

drift from the north and northeast (the red drift, including as a 

special phase some red boulder clay deposited west of Lake Superior 

by the combined action of ice and water); laminated lake and river 

clays (including earlier gray or yellow weathered clays and later 

red clays); outwash; and loess. These subdivisions are based on 

differences in character, and a single subdivision (as the gray drift) 

may include material deposited by two or three separate invasions 

of the ice. The red drift from the north differs somewhat from that 

from the northeast, but the associated clays are so much alike that no 

distinction is made between them.
92 CLAYS AND SHALES OF MINNESOTA.

AFTONIAN (?) INTERGLACIAL DEPOSITS.

After the early or Nebraskan ice invasion vegetation apparently 

spread over the southern part of Minnesota and formed a dark-gray 

soil from 1 to 4 feet thick, which has been buried under more recent 

deposits of gray drift. Though too thin to be of economic value, 

the soil could easily be traced for perhaps 20 rods in a clearly defined 

outcrop along the Chicago, Rock Island & Pacific Railway about 2 

miles southeast of Faribault. Two analyses of it were made in 

1906 by F. F. Grout, as follows:

Analyses of Aftonian (?) soils.

Silica ...............................................................................

1

65.10

10.42

4.74

2.06

4.52

1.05

8.10

.82

3.19

2

55.10

10.60

4.47

2.06

7.26

1.58

15.32

.60

3.01

GEAY DRIFT CLAYS.

. Glacial drift, consisting largely of clay, generally gray, with a 

surficial alteration to yellow, covers more than half of Minnesota, 

Apparently it was brought from the northwest by glaciers, which in 

a. few places reached the eastern border of the State. The map 

(PI. X) shows its general distribution, but the area delineated includes some local sandy areas in which there is little or no clay. The 

gray drift may be the product of more than one ice invasion, but the 

clays do not differ sufficiently to permit correlation of the type, with 

.the age. Several samples of Kansan drift gave much the same results as the more abundant material of Wisconsin age.

Most of the gray drift contains abundant limestone pebbles, which 

were probably derived from the Devonian limestone far to the northwest. In most places the drift is covered only by a few inches of 

soil. Loess may have accumulated over much of the area, but' on 

hillsides it is in many places mixed with surface wash and is not 

readily differentiated. Loess mixed with pebbles is not distinguished 

from the gray drift in this discussion. The methods by which such 

clay with limestone pebbles can be used are described on pages 55-56.

In general clays found in the gray- drift slake in two minutes and 

require^ 24 per cent of water for molding. Their plasticity is high 

and their tensile strength is 150 pounds to the square inch. They 

can be rapidly dried without serious injury. Their air shrinkage
GEOLOGY OF MINNESOTA. 93'

is 5 per cent, and their fire shrinkage is only 1 per cent at the time 

the clay becomes steel hard and about 6 per cent before it becomes 

viscous. The absorption meanwhile ranges from about 21 per cent, 

down to 6 per cent. The average clay becomes steel-hard at cone 

02 (2,030° F.), and viscous a little above cone 3 -(2,174° F.). The. 

range of vitrification is therefore less than 150° F., and it is usually 

unsafe to burn the clays very hard. (See fig. 8, p. 84.) On .the 

other hand, after the clay has been burned at moderate temperatures 

the lime pebbles it contains slake and destroy the product. The unoxidized gray clay is essentially like the surface yellow clay but may 

shrink a little more and requires more care during oxidation. The 

properties of the clay can be greatly improved by the removal of the 

limestone the washing or " slumming " process used at Hutchinson 

and the dry-cleaning process used at Jackson are recommended for 

careful investigation by all who desire to utilize the gray drift. 

For some clays simple grinding will be sufficient, but washing is 

much more certain and of much wider application. Analyses of 

the drift and washed drift are given in the report on McLeod 

County (pp. 191-193). Brick and tile made from this drift are 

salmon-colored at low temperatures and buff at higher temperatures. 

Crushing tests made by the experimental engineeering department 

of the University of Minnesota show an average strength of over 

2,400 pounds to the square inch. Draintile made from washed gray 

drift is exceptionally resistant to frost.

As the northern part of Minnesota becomes more settled, and as 

the farms in all parts of the State find tile drainage desirable, the 

increasing local demand for a good quality of tile such as can be 

produced from this gray drift will warrant the construction of 

several plants with half a dozen dqwndraft kilns each. The marketing radius of such a plant would be rarely over 50 miles. Nearly 

every region in the western half of the State in which the demand 

is at all favorable will undoubtedly be found to be supplied with 

gray drift of the proper quality. Burning tests without cleaning, 

made at a dozen widely separated points in the State, were not at 

all conclusive; and more information was obtained by washing the. 

drift through sieves and determining the proportion of sand to 

clay and the percentage of lime in the clay, these being the important factors. The sand caught on the 100-mesh sieve at these 

points ranged from 23 to 33 per cent; at Hutchinson it was 30 per 

cent. The lime (CaO) ranged from 6 to 11 per cent; at Hutchinson 

it was 9 per cent. Most of the samples were closely similar to the. 

Hutchinson material. Some of the washed clays burned salmon and 

some buff, but all were hard at cone 02. It is therefore safe to say 

that throughout about half of Minnesota this drift material is.
94 CLAYS AND SHALES OF MINNESOTA.

available for the production of high-class draintile at a commercial 

profit unless it has to meet the local competition of some purer clay. 

Locally drift clays may be largely affected by the character of 

the bedrock passed over by the ice just before it deposited its load. 

An example is found near Goodhue, in Goodhue County, where much 

Cretaceous clay is incorporated in the drift.

GRAY LAMINATED LAKE AND RIVER CLAYS.

In many parts of Minnesota, chiefly along the valleys of Minnesota and Mississippi rivers and their tributaries, there are beds of 

glacial clay which are stratified in distinct, nearly horizontal layers 

from a fraction of an inch to 8 inches in thickness. These layers are 

dark blue-gray where fresh and yellow where they have been exposed to oxidation. In many places these beds are interlaminated 

with thin layers of fine sand. They tend to split along the darker 

partings, which extend continuously without grading into one another. The beds are nearly level but may dip a few degrees in either 

direction or may even be locally folded into arches or basins. Some 

clean exposures show 60 layers, all similar, in a depth of 5 feet. It is 

evident that these were produced by varying conditions. Deposition 

of sand alternated with deposition of clay a great many times, the 

changes in sedimentation being due possibly to seasonal variations in 

the water of the glacial streams. Along the flood plain of an ordinary river clay settles only in hollows outside the path of the main 

current. The structure of this clay and its occurrence only in glaciated regions, or valleys drained from glacial drift, indicate that it 

was formed by large streams probably coming from a melting ice 

sheet.1 Such streams flow in greater volume and carry coarser sediments in summer than in winter and might thus have produced the 

alternating layers.

Such clays have long been known and used along Minnesota River 

at Chaska and Jordan and along Mississippi River from Minneapolis 

to Brainerd. They are calcareous and are suitable mainly for common brick and for fireproofing. The clay of Wrenshall is similarly 

laminated. (See PL I, p. 20.) The present investigation shows a 

much wider distribution than has heretofore been reported, and there 

is every reason to expect that still other deposits will be developed.

In general the gray laminated clays hav^ fair plasticity and require 

27 per cent of water for molding. Their tensile strength is about 120 

pounds to the square inch and is not seriously affected by rapid dry1 Winchell, N. H., The geology of Minnesota: Minnesota Geol. and Nat. Hist. Survey 

Final Rept., vol. 1, p. 467, 1844 ; vol. 2, p. 132, 1888. Berkey, C. P., Laminated interglacial clays<: Jour. Geology, vol. 13, p. 35, 1905.
GEOLOGY OF MINNESOTA. 95

ing. Their air shrinkage was shown by the tests to be about 5 per 

cent, but this average figure is too high, for the samples include some 

of the underlying blue joint clays^ which are not used in manufacturing. When the clay is first burned hard the fire shrinkage is only 

a little over 1 per cent, but the maximum shrinkage observed before 

viscosity averages about 8 per cent. The absorption at the temperature at which the clay becomes hard is about 25 per cent, and 

this drops to 7 per cent before the product is in danger of melting. 

The average clay burns hard at cone 02 (1,994° F.) and becomes 

viscous at cojie 3 (2,174° F.). These figures, though better than those 

for the gray drift, show a rapid fusion and the clay should not be 

used in attempts to make vitrified products. (See fig. 8, p. 84.) An 

analysis is given in the discussion of Anoka County (pp. 113-118). 

The clay is suitable for common brick and hollow ware, usually of 

cream color, and makes fireproofmg of excellent quality.

In the northern part of Minnesota large bodies of similar laminated 

clays occur in less accessible localities, as along the Bigfork and 

Littlefork rivers in and near Koochiching County. Samples from 

widely separated outcrops show surprising uniformity, though some 

laminated deposits are more sandy than those sampled. The clays 

are ,a little better in quality than those farther south, and they constitute a natural resource of future importance. They were formerly 

mapped as Cretaceous, but the present field studies show clearly 

that they are Pleistocene. This determination is corroborated by the 

character of the clay, which shows a much more rapid vitrification 

than any Cretaceous samples tested. The analysis also furnishes evidence of closer relation to glacial clays than to Cretaceous clays in 

other parts of the State.

The clays slake in a few minutes and yield with 33 per cent of 

water, a mass of high plasticity. The air shrinkage is 9 per cent and 

the tensile strength 160 pounds to the square inch. They become 

hard at cone 04 (1,958° F.) and reach viscosity at cone 3 (2,174° F-), 

having thus a range of vitrification of over 200° F. The absorption 

can be reduced from 20 per cent nearly to 1 per cent, and the fire 

shrinkage is then 8 per cent. A sample from Net Lake Rapids, on 

Littlefork River, was analyzed by A. W. Gauger with the following 

results:

Analyses of gray laminated, clay of northern Minnesota.

'Silica 1 _________________ 47.70 

Alumina ___ __________________._______ 13.58 

Iron oxides____________________________ 6. 51 

Magnesia ___________^__________________ 3.13 

Lime __ ____. _________________ 11. 70 

Soda _ _______________________ . i. 05
96 CLAYS AND SHALES OF MINNESOTA.

Potash________________________________ 2. 34

ignition_________________________________ IS. 23

Moisture______________________________;__ 1.79

Titanium oxicle_________Q_________________________ .31

101.34

RED DRIFT CI.AIS.

The red drift lies generally in the eastern part of Minnesota, from 

Dakota County on the south to Lake County on the north. It is 

most conspicuous in counties that touch the border, and in the region 

of Mille Lacs, Brainerd, and St. Cloud, in Morrison and adjacent 

counties it extends westward to and beyond Mississippi River.

In the areas shown on the map (PI. X) between the western 

boundary of the red drift and the eastern boundary of the gray drift, 

the red drift is overlain by a thin layer of gray drift. Much the 

larger part of the red drift is sandy and gravelly, but it contains 

locally valuable deposits of clay.

In general, the red drift, even where not pebbly, is more sandy 

and not so plastic as the gray drift but is still satisfactory. .It requires 20 per cent of water for molding. The tensile strength is 

over 140 pounds to the square inch and is only slightly decreased by 

rapid drying: Shrinkage on drying is 4 per cent, and fire shrinkage 

ranges from 1 per cent at the time the clay becomes hard-to 6 per 

cent at complete vitrification. The absorption is only 15 per cent 

when the clay is burned hard and can be reduced to 4 per cent or 

less. The average clay begins to vitrify at cone 04 (1,958° F.) and 

reaches viscosity at cone 3 (2.174° F.) It has thus a range of over 

200° and can safely be burned to a vitrified brick, as has long been 

done at Coon Creek. (See fig. 8, p. 84.) Other deposits farther north 

are similar to that at Coon Creek. The excellence of the products is 

demonstrated by the tests made in the experimental engineering department of the University of Minnesota, which show the brick to 

have a crushing strength of over 7,000 pounds to the square inch. 

Rattler tests indicate that they would be satisfactory for paving. 

(See the report .on Anoka County, pp. 113-118.)

RED LAMINATED LAKE AND RIVER CLAXS.

Along the eastern border of Minnesota and extending a considerable distance into Wisconsin are a series of deposits of laminated 

clay that have a striking red color, though otherwise similar to the 

gray laminated clays previously described. There can be very little 

doubt that their origin was dependent on the same seasonal alteration 

of sand and clay deposits brought by water from the melting ice 

sheet.1

i Berkey, C. P., Laminated clays: Jour. Geology* vol. 13, p. 35, 1905.
GEOLOGY OF MINNESOTA. 97

In general, the red glacial lake and river clays have low plasticity, 

which is developed by 21 per cent of water. Their tensile strength is 

less than 100 pounds to the square inch, but they can be safely dried 

with artificial heat. The air shrinkage is 4 per cent. The clays become steel-hard at cone 04 (1,958° F.) and reach viscosity at cone 2 

(2,138° F.). At 1,958° F. the fire shrinkage is 1 per cent and the 

absorption 20 per cent. Before they reach viscosity the fire shrinkage 

may increase to 8 per cent and absorption may be reduced to less than 

2 per cent. These red-burning clays should be exploited sufficiently 

to do away at least partly with the need of importing material of this 

type from Wisconsin. The extensive brick works at Menomoniej 

Wis., from which the Twin Cities and other parts of Minnesota receive large quantities of red brick, use laminated red clays exactly 

like those found in eastern Minnesota. The clays may also be used as 

a slip or glaze for colored semirefractory stoneware.

The following analyses, mostly of Minnesota material, show the 

general character of the clays:

Analyses of red laminated lake and river clays.

Silica...............

Potash..............

1

57.79

12.63

.82

4.11

3.33

1.75

2.71

2.50

6.10

2

53. 52

14. 98

3.39

5.26

7.92

3

64.76

15.45

4.02

4.22

5.96

4

77.7

3.4

3.5

8.2

7.2

5

77.00

1.50

7.00

012.00

2.50

6

82.50

7.50

o7.75

2.25

7

77.00

9.00

a 10. 75

2.75

8

77.00

8.50

a 12. 00

2.50

9

77.00

9.00

all.50

2.50

10

77.00

9.00

a 10. 75

2.75

a Determined by difference; includes trace of magnesia.

1.. Rod laminated clay, Pine County. F. F. Grout, analyst.

2 and 3. Laminated clay, Grantsburg, Wis. Berkeley, C. P., Jour. Geology, vol. 13, p. 38, 1905; 2, 

Mixture of layers worked, fairly representative: 3, from uppermost layers.

4 to 10. Frombedoftripoliat Stillwater. Analyses by J. E. Eckfeldt at United States Mint, Philadelphia. Minnesota Geol. and Nat. Hist. Survey Final Kept., vol. 2. pp. 394-396,1888. 4, Position in bed 

not given; 5, upper stratum of lower bed; 6, small shaft at lower bed; 7, dark seam through lower bed; 8r 

middle of 20-foot exposure; 9, water line of 20-foot exposure; 10, upper exposure on the creek.

RED CLAYS OF LAKE DULOTH.

The retreat of glacial ice fronts toward the north and northeast 

probably occupied thousands of years. When the ice had vacated 

the western part of the basin of Lake Superior and the southern part 

of the Red River valley and while it still blocked the former, the 

obstructions caused the accumulation of immense lakes. Around the 

west end of Lake Superior are large deposits of a very sticky plastic 

red clay, with some sand grains and pebbles, apparently formed during one of the high stages of the lake known as Lake Duluth. Frank 

Leverett 1 says that the deposits accumulated as moraines laid down

1 Personal communication.

64310° 
98 CLAYS AND SHALES OF MINNESOTA.

in water, a mode of origin somewhat different from that of the 

laminated clays. Such red clay was formerly used for brick at West 

Duluth and for a short time at Superior, Wis. It appears from the 

bricks now to be seen in the old buildings that the clay was not burned 

at sufficiently high temperature to make hard brick. Some of the 

deposits require more water to make them plastic (50 per cent) and 

show greater air shrinkage (12 per cent) than any other Minnesota 

clays tested. They burn hard at cone 08 (1,814° F.) and become 

viscous at cone 1 (2,102° F.), which means that they can be vitrified 

with reasonable safety. Absorption can be reduced to less than 2 

per cent. The immense shrinkage is the main defect, but this can be 

partly corrected by additions of sand or slate. (See description of 

Carlton County, pp. 134^-140). The clays are sufficiently fine grained 

and fusible to make satisfactory slip glazes.

Analyses of the reel clay of^ Lake Duluth.

Silica ...............................................................................

Lime. ...............................................................................

1

53. 390 

14. 259 

13. 706 

3.033 

1.740

JNot det .

14. 273

100. 451

2

50.51 

15.89 

8.21 

7.10 

5.14 

( 1.87 

\ 1.66 

.26 

7.35 

2.44

100.43

1. Cook County, C. P. Berkey, analyst.

2. Carlton County, A. W. Gauger, analyst.

O-JTWASH CLAYS.

In some parts of Minnesota, .especially in the area of the red drift, 

there are glacial out wash plains that contain sandy but valuable 

clays. Few of these clays have been developed, but they are of fine 

quality. They slake at once, and with 25 per cent of water they 

show low plasticity. Their air shrinkage is 4 per cent, and their dry 

tensile strength is 120 pounds to the square inch. The range of 

vitrification is from cone 02 (2,030° F.),.where they become hard, 

to cone 5 (2,246° F.), where they become viscous. The absorption 

can be reduced from 20 to 4 per cent with an accompanying fire 

shrinkage of 8 per cent.

LOESS.

The loess of Minnesota is generally considered a wind-blown deposit. It is composed of mineral derived chiefly from the glacial 

drift. Its origin appears to be similar to that of sand dunes, but 

loess, being finer grained than sand, is carried farther by the wind.
GEOLOGY OF MINNESOTA. 99

In Minnesota the largest deposits of loess occur in the southeastern 

counties near the Driftless Area. It also occurs in the southwestern 

corner of the State (figs. 9 and 10). Over the uplands the loess 

ranges from 2 to 4 feet in thickness, but in the valleys and especially 

on the terraces along the sides of the valleys it is much thicker. At 

a great many of the small brick plants in the State the main 

deposit of clay is overlain by loess, and the two^ are mixed for the 

manufacture of brick.

FIGURE 9. Map of southeastern Minnesota showing an area (dotted) in which the drift is 

largely'covered with loess. Data by Frank Leverett. The loess mantle is aearly continuous except along the larger valleys.

In general the loess clay is very uniform. The plasticity is low, 

and the water required for molding is 23 per cent. The tensile 

strength is over 100 pounds to the square inch. The air shrinkage is 

3 per cent. The fire shrinkage during vitrification increases from 1 

to 7 per cent, and the absorption decreases from 20 to 3 per cent. The 

range of vitrification is over 200° F., from cone 02 to cone 5. (See 

fig. 8, p. 84.) An analysis is reported in the discussion of Fillmore 

County (pp. 158-162),
100 CLAYS AND SHALES OF .MINNESOTA.

Tests were made on loess clay bricks by the engineering department 

of the University of Minnesota. The crushing strength was not uniFIGURB 10. Sketch map of the southwest corner of Minnesota showing an area (dotted), 

of old gray drift outside the young gray drift; part of this is loess covered. From 

map of southern Minnesota by Leverett and Sardeson.

form and was apparently'greater in wet than in dry bricks; the minimum strength is 1,300 and the maximum 3,800 pounds to the square
GEOLOGY OF MINNESOTA. 101

inch. The average absorption is 15.6 per cent, and the modulus of 

rupture is 582 pounds to the square inch.

CLAYS OF RED UIVEB VALLEY.

The lake formed when the receding ice front dammed the northern 

outlet of the Red River basin is known as Lake Agassiz; its shore 

lines are marked by beach ridges and to some extent by the delta deposits formed by the incoming streams. (See PL X.) The deposits 

of Lake Agassiz do not seem to consist as largely of clay as those 

formed in the Lake Superior basin. The drift on each side of the 

Lake Agassiz basin has a moderately rolling surface. Within the 

area covered by the lake the plain is very smooth and nearly flat, yet 

the drift shows only slight traces of stratification. Wave action piled 

up ridges of sand and gravel along the shores and washed away the 

finer-grained material, depositing it as clay farther from the shore. 

These clay deposits were evidently small, as they are hardly perceptible over most of the area. Very thick beds of stratified clay,' 

however, occur in the central portion of the Red River valley, and 

their position shows that they were not deposited by the waters of the 

lake, which must have spread over the entire valley. At the present 

time much of the area of stratified clay is covered by the higher floods 

of Red River, and probably no part of it is more than 10 feet above 

the high-water line of Red River or its tributaries. As the river may 

have been much larger about the end of the glacial epoch, it seems 

clear that the clays were deposited as alluvium, partly in glacial and 

partly in recent time.

The thickness and width of the clays of Red River increase northward. At McCauleyville the deposit is about 2 miles wide and 50 

feet deep, and at Moorhead and Fargo it is many miles wide and 100 

feet deep. In general the clay is rather sandy and contains considerable carbonaceous material. It is colored yellow by oxidation near 

the surface and is highly calcareous, containing both finely disseminated lime and medium-sized pebbles and concretions, except in the 

upper part, where, throughout most of the valley, it is leached to 

depths of 1 to 10 feet; the deepest leaching is in the northern part of 

the valley. Over the clay is a thin layer of black loam.

Only the yellow subsoil has been employed for the manufacture of 

brick. Most of this leached portion is quite free from the limestone 

pebbles, is less plastic, and dries more safely than the lower portion. 

On account of its tendency to crack in drying the lower clay is spoken 

of as a joint clay and is very little used, though it forms much the 

largest portion of the whole mass. Across the line in North Dakota, 

where the material is of exactly the same quality as in Minnesota, a
10.2 CLAYS = SHA1LES OF MINNESOTA.

sample of joint clay was- taken and tested by the North Dakota Geological Survey, with the following result:1

It contains more clay substance than the yellow clay, although considerable 

fine sand is still, present. It takes 29.6 per cent of tempering water for the best 

plasticity, whi«h is good. The tensile strength is 255 pounds, and the air shrinkage is 5.3 per cent. In burning i-ts behavior was as follows:

Cone. No.

010

05

03

01

Color.

....do...........................

Shrinkage;

0

0:3

0

(a)

Absorption.

30.3

30.9

30.3

10.1

a Failed by cracking.

Incipient fusion occurred at cone 02,. vitrification- at cone 1, and. viscosity at 

cone 2. The bricklets were all strong. This clay alone would probably be 

valueless, but because of its good plasticity and high binding power it could 

be mixed with a sand or a sandy clay and worked by the stiff-mud process for 

the manufacture of common brick. Several, tests have been made for the use 

of this clay as a paving material. In some cases, with a correct mixture, fair 

results are obtained.

In general the clays of the Bed River valley developed high plasticity with 30 per cent of water. Their tensile strength is 120 pounds 

to the square inch but is somewhat reduced by rapid drying. The air 

shrinkage is 8 per cent, and the- fire shrinkage increases from 1 to 8 

per cent during vitrification. The absorption, meanwhile, decreases 

from 24 to 8 per cent. Vitrification begins at cone 03 (1,994° F.), 

and viscosity is reached at cone 3 (2,174° F.). Analyses are given 

in the report on- Polk County (pp. 211-214).

Strength tests have been conducted on brick from these Lake Agassiz deposits by E. B. Jack, of Winnipeg. They have an average 

crushing of 2,860 pounds to the square inch, a minimum of 2,365 

pounds, and a maximum of 3,760 pounds on five bricks tested. Five 

hollow bricks gave an average of 706 pounds to the square inch. Surfaces of the brick were planed off and pressed between blotting 

paper. Bricks manufactured from the silts of Eed Elver, when, 

tested in the laboratory of the University of Minnesota, showed a 

crushing strength of 1,300 pounds to the square inch, an absorption 

of 33.3 per cent, and a modulus of rupture of 364 pounds to the 

square inch.

EECENT DEPOSITS. 

RIVER CLAYS.

The chief deposits of river clay in Minnesota lie along Minnesota 

Eiver, but Mississippi and St. Louis rivers also have a number of

1 North Dakota Geol. Survey Fourth Bienn. Kept, p. 186, 1906.
GEOLOGY OF MINNESOTA. 103

these deposits, and many of the smaller streams contribute smaller 

amounts. The deposits along the Red River valley are discussed 

under a separate heading (pp. 101-102).

In general, the alluvial clays in Minnesota have fair plasticity, 

though nearly all of them are sandy. The average clay requires 25 

per cent of water for molding, and its tensile strength is about 130 

pounds to the square inch, even if rapidly dried. The air shrinkage 

is 5 per cent and the fire shrinkage from 1 to 7 per cent during vitrification. The absorption of the brick is about 21 per cent when it 

first becomes very hard at about cone 02 (2,030° F.). Viscosity is 

reached at cone 4 (2,210° F.), with absorption reduced to 6 per cent. 

The composition of the alluvial clay is probably represented by an 

analysis of the clay at Le Sueur, made by A. W. Gauger, and a mechanical analysis by Mark Bray. This clay is in the middle of a 

series of brickyards along the river.

Analyses of all-uwal clay of Le Sueur.

Chemical analysis.

Silica ________________ 62. 20

Alumina _____________ 7.77

Iron oxide ____________ 4. 53

Magnesia ____________ 3.18

Lime _______________ 7,21

Soda _______________ 3.58

Potash _______________ 1. 63

Ignition _______________ 9.27

Moisture ___________:__ 2.15

Titanium oxide _________ . 41

Mechanical analysis.

Total clay ____________ 24.90 

Silt _________________ 38. 00 

Total sand _________._____ 37.10

100.00

101. 93

Mr. Bray made some chemical tests also on the fractions obtained 

by his mechanical analysis. The most noteworthy discoveries were 

that the coarser material contained more silica (sand), and the finer 

material more iron and aluminum. The finer portion also had the 

most alkalies, but this variation was not regular nor marked.

A fairly representative sample of bricks made from the alluvial 

clays of Minnesota River, when tested at the engineering laboratory 

of the University of Minnesota, showed a crushing strength of more 

than 1,300 pounds to the square inch, even when wet. The absorption is 20.8 per cent. Tests of similar material by the city building 

inspector of Minneapolis gave the following figures: Wire-cut common brick, 1,497 pounds to the square inch; sand-mold common 

brick, 1,560 pounds to the square inch; wire-cut hard-burned brick, 

0,010 pounds to the square inch.
104 CLAYS AND SHALES OF MINNESOTA.

LAKE' AND SWAMP CLAYS.

For the most part the sedimentary deposits of the recent lakes do 

not differ very greatly from those of the lakes of glacial time. The 

surface of the surrounding country still consists of the red and 

gray drift which furnished the sediments when the glaciers were 

melting away. Some slight differences, however, may appear, for 

during glacial time the melting ice furnished immense volumes of 

water that have not been duplicated since. Erosion and filling of 

the lake beds have also tended to decrease the size of the bodies of 

water.

In general, the recent lake clays slake at once and become highly 

plastic. The water required for molding is 28 per cent. The tensile strength is 140 pounds to the square inch and only slightly less 

if rapidly dried. The shrinkage on drying is 6 per cent, and the 

fire shrinkage from 1 to 7 per cent during vitrification. The absorption at the beginning of vitrification is 20 per cent. Vitrification occurs between cone 04 and cone 3, a range of over 200°, and 

absorption decreases to 3 per cent. An analysis is given in the report 

on St. Louis County (pp. 225-230). The city building inspector of 

Minneapolis has made tests on hollow brick and tile made from a 

lake clay that burns salmon at low temperature, and cream color at 

steel hardness. The hollow tile have an average crushing strength 

of 230 pounds to the square inch, and the hollow brick an average 

strength of about 260 pounds to the square inch. A test by the 

experimental engineering department of the University of Minnesota on some brick made with three vertical holes to decrease 

weight showed an average strength of 3,000 pounds to the square 

inch. The modulus of rupture was 374 pounds to the square inch 

and the absorption 31.4 per cent.

GEOLOGIC AND ECONOMIC SUMMARY OF CLAY DEPOSITS.

The geologic succession of the clays of Minnesota and their 

economic characteristics are set forth in the following table. Their 

behavior under vitrification is concisely shown in figure 8 (p. 84). 

The distribution of the geologic types of clay is shown in part on. 

the map (PL X).
Approximate average results of tests of the clays of the principal ge

Cretaceous:

Pleistocene:

Recent:

Number of 

tests.

4 

6 

15

10 

10 

15

50 

10 

10 

7 

5 

5 

5 

5

10 

20

Time required for 

slaking.

Minutes. 

2 

Many. 

5

Manv. "4 

3

2 

2 

6 

3 

2 

1 

2 

1 

1

1 

2

Plasticity.

....do.............

Fair..............

High..............

.....do............

High..............

.....do............ 

Fair..............

.....do............

High..............

Water 

of 

plasticity.

Per 

cent.

IS 

30

26 

22 

29

24 

27 

33 

32 

20 

21 

40 

25 

23

25 

28

Tensile 

strength.

Pounds 

jter 

square 

inch. 

30 

40 

125

50 

170 

160

150 

120 

160 

120 

140 

SO 

60+ 

120+ 

170+

130+ 

140+

Linear 

air 

shrinkage.

Per 

cent. 

4 

3 

S

4 

6 

8

S 

5 

9 

8 

4 

4 

10 

4 

3

5 

6

Inc
CLAYS AND SHALES OF MINNESOTA.

STATISTICS OF CLAY PRODUCTS;1

The value of Minnesota's clay products, exclusive of pottery, in 

1917 was $2,197,664. The principal clay product of the State is common brick, and during 1917 the manufacture of 86,606,000, valued at 

$656,247, was reported. This output constituted 30 per cent of the 

value of all of Minnesota's brick and tile products. Draintile was 

second among the State's clay products and was valued at $579,461. 

Carver County was the largest producer of common brick in 1917, 

Carlton County second, and Hennepin County third. Goodhue 

County was the leading clay-working county of the State, Hennepin 

County second, and Carver County third.

Clay products of Minnesota, 1911-1917.

Product.

Brick: 

CommonAverage per M... 

Vitrified 

Average per M... 

FrontAverage per M... 

Fire.......... value.. 

Draintile. ........ .do. . . .

Fireproonng. ..... .do. . . . 

Tile, not drain . . . .do. . . .

Stove lining. . ...........

Pottery (earthenware 

and stoneware), value . . Miscellaneous .... .do. . . .

Number of operating

Rank of State. ..........

1911

153,015,000

$868,037 

$5.67

(a) 

(a> 

$13. 16

10,853,000 

$135, 085 

$12. 45 

(a) 

3121,965 

(J) 

$109,812 

(-}

(6):

. $458,579

$1,693,478

81 

21

1912

129,604,000 

$760,983

$5.87

rav (°)

$16.34

11,555,000 

$144, 125 

$12. 47 

(a) 

$126,690 

(a) 

$160,804

( 6 )

$418,438

$1,611,040

79 

21

1913

129,261,000 

8800,441 

$6.19

( )

(a)

$15.85

13,392,000 

$163,380 

$12. 20 

(a) 

$110.543 

(a 

$170,214

i (<o

 $536,439

$1,781,017

69 

20

1914

132,688,000

$883 ,,791 

$6. 67

(a) 

(a) 

$16. 12

16,413,000 

$208, 624 

$12: 71 

(a). 

$143, 194 

(a) 

$123,911 

(a]

(5) 

$585,366

$1,94.4,886

65 

15

1915

107,473,000 

$675, 146 

$6.28

8S14. 18

17,157,000 

$205,519 

$11.98 

(a) 

$255.347 

(°) 

$125,595

(6) 

$384,306

$1,645,913

66 

16

1916'

118,.090,000 

$772,696 

$6.54

(a)

(a)

§8.87

19,014,000 

$243,246 

$12. 79 

(a) 

$422,809 

(a) 

$153,486

(»)

$472, 125

$2,064,362

55 

16

1917

86,606,000 

$656, 247 

$7-58

(aY 

(a) 

$14,00

13,600,000 

$194,800 

$14.32 

(a) 

3579,,461 

(«) 

$233,851

(a)

(&) 

$466, 382

$2,197,664

52 

18

a Included in "Miscellaneous."

6 The value of pottery products for Minnesota could not be included in the State totals without disclosing 

the operations of individual establishments.

DISTRIBUTION OF TYPES OF CLAY.

BEFRACTORY CLAYS.

AECHEAN CLAYS.

Refractory Archean residual clays crop out in the neighborhood of 

Redwood Falls, Redwood County, and at Richmond, Stearns County, 

and probably extend under the drift from one locality to the other 

and also widely on the west to many points where well records show 

white clay. They may reach 50 or 100 feet in thickness. Some begin

1 Middleton, Jefferson, Clay-worKing industries: U.. S. Geol. Survey Mineral Resources, 

1916, pt. 2, p. 551, 1918.
DISTRIBUTION OF TYPES OF CLAY. 107

to vitrify below cone 10 but are undeformed to cone 32. Washing 

would improve the color and raise the melting point of most of them..

CRETACEOUS CLAYS.

The basal Cretaceous clays occurring from Bowlus, Morrison 

County, to Redwood Falls, Redwood County, are the best refractory 

clays known in Minnesota. As they crop out at Richmond, Mankato, 

and elsewhere, they must extensively underlie the. drift. The white 

clays shown by the well records mentioned above are no doubt at 

least in part Cretaceous. The greatest thickness exposed at the surface is 18 feet at Birch Cooley, near Morton, Renville County. The 

best material is that near Redwood Falls; the clay farther north is 

more ferruginous but is nevertheless refractory.

The higher Cretaceous clays at several points in Brown County 

and thence to Ottawa, in Le Sueur County, where an attempt was 

once made to use them, are also highly refractory. Along Cottonwood River in Brown County, notably in sec. 36, T. 110 N., R. 31 W., 

the clay is of especially high quality. Much of the country between, 

and around these places may deserve more careful prospecting than, 

it has received.

SEMIREFRACTORY CLAYS, 

VITRIFYING LIGHT-BURNING Cl/AYS.

Cretaceous shales are the only semirefractory light-burning clays 

in Minnesota. Those mined for the stoneware and sewer-pipe works 

at Red Wing are the best known. Their vitrifying behavior is exceptionally good, but they fuse at temperatures so low as to leave 

them very near the nonrefractory class. The deposits worked at 

Clay Bank and Belle Chester are disturbed and apparently transported remnants of a larger formation some distance to the northwest, which, if it still exists, is'covered with drift. Careful observations should be made and records kept of all drilling in the region. 

The deposit at Belle Chester was discovered a relatively short time 

ago by drilling where the drift gave evidence of some included clay 

brought from the same direction as that at Clay Bank, and the 

method should be applied in further work in both directions, though 

it is likely that the main sources of the clay may now be more deeply 

drift covered than the transported masses. These clays are the most 

valuable yet developed in Minnesota.

West of these points much of the Cretaceous shale is nonrefrac% 

tory, but the character of the deposits at Austin, in Mower County, 

and near Essig, in Brown County, shows that the conditions for the 

development of the semirefractory type were widespread and that 

there is every reason to expect similar clays to be discovered under
108 CLAYS AND SHALES OF MINNESOTA.

the drift in the intervening counties. The clay at Austin has been 

.only partly explored by drilling; that near Essig is excellent but at 

present somewhat inaccessible and of uncertain quantity.

CLAYS THAT MELT SUDDENLY.

The Huronian residual clays near Bowlus, in Morrison County, 

and the Huronian paint rock on the Mesabi range are semiref ractory, 

but they melt suddenly and are not likely to become important.

NONREFHACTORY CLAYS. 

VITRIFYING CLAYS.

The great formations that yield honrefractory vitrifying clays are 

the Decorah shale, the Cretaceous shales, and the Pleistocene red 

drift. These clays, without exception, have a good range of vitrification. Recent lake clays also show a fairly good range. Some other 

Pleistocene and Eecent clays have a good range, but most of them do 

not. The Huronian slates when mixed with a small amount of red 

drift clay show a range of vitrification that makes it possible to 

burn them into excellent fancy brick. These slates crop out conveniently near Duluth along St. Louis River.

The shales of the great red sandstone of Keweenawan or Cambrian 

age crop out in so few places and are so thin that they are not 

likely to be developed, though their quality seems to be excellent.

The Decorah shale of Ordovician age uniformly gave favorable results. All the ground samples had a range of more than 200° F. during vitrification, and some had a range of 400° F. This is somewhat 

surprising, as the temperature of fusion is low and the shales contain 

limestone impurities. The distribution of these shales has been very 

carefully mapped. (See figs. 19, 22, and 32.) The western and southern limits shown do not indicate the farthest extension of the shales 

but the approximate limits of accessibility where the shales dip 

under Cretaceous or Devonian rocks. Even within these limits the 

drift cover may be so great as to render some parts of no value, but 

the main border is almost everywhere well situated for development.

The Cretaceous shales are known to underlie the surface over much 

of the western half of Minnesota, though they are concealed by a 

thick covering of drift except in scattered places. They extend as far 

east as St. Louis, Stearns, and Goodhue counties. All of them vitrify gradually to a low porosity.

Associated with the semirefractory clays at the Red Wing pits 

are some nonrefractory clays of about equally good range. Still 

less refractory clays are found a little farther west in Mower County 

at Austin and along the line between Mower and Fillmore coun-
DISTRIBUTION OF TYPES OF CLAY. 109

ties. The most numerous outcrops of such shales are near New Ulm, 

where a few sernirefractory shales also occur. Along the bluffs of 

Minnesota and Cottonwood rivers, from New Ulm to Springfield, 

many large bodies of shale crop out and will no doubt be developed. 

The overburden may delay the exploitation of some of this shale, but 

that which is free from overburden, as at Springfield, would make 

excellent vitrified ware. The color of the product is much lighter for 

some clays than for others and in well-vitrified ware ranges from buff 

to reddish bnywn.

A large body of similar shale crops out at several points near 

Eichmond, Stearns County, and might easily be developed. The 

presence of a thin lignite bad has diverted attention from the clay 

to prospects of coal.

Similar clays are reported in well records from the southwestern 

counties. Their character can be judged by a sample from Browns 

Valley, Traverse County, which burns red with an excellent range 

of vitrification.

The Pleistocene red drift has been used with remarkably good results at Coon Creek, north of Minneapolis, and with less favorable 

results at Forest Lake, Barnum, and Wahkon. The outwash of the 

red drift has been used at Rush City, West St. Paul, and Burtrum, 

where its range of vitrification makes it possible to get a hard, wellburned product. The distribution of such drift is shown on the map 

in a general way, and the fact that at Coon Creek red drift is covered with gray drift shows that overburden is not an insurmountable 

difficulty. Much of the red drift is too sandy for clay products, but 

where there is not too much sand and the pebbles are not too numerous it warrants more extensive development. Points on the Soo 

Line east of Aitkin are worthy of consideration. All samples tested 

have a satisfactory range of vitrification.

The map makes no distinction between the red drift from the 

north and that from the northeast. The latter, which occurs mostly 

in Pine and Carlton counties, is equally good where it consists largely 

of clay. The water-laid drift in Carlton County has an excellent, 

range of vitrification, but its temperature of fusion is low and it 

requires some sand for molding.

Gray drift is rarely suitable for hard .brick until purified by removal of the pebbles.

A very few gray laminated clays fall in the nonrefractory vitrifying class. A few samples burned red instead of the common cream 

color and had a fairly good range of vitrification. Among these are 

the clays near Aitkin and one or two that were so much weathered 

that the lime may have been leached out. A larger body of laminated 

clay with a fair range of vitrification is represented by many outcrops along Littlefork and Bigfork rivers in inaccessible parts of
110 CLAYS AND SHALES OF MINNESOTA.

Koocliiching County. These deposits constitute a valuable future 

source for northern Minnesota.

The loess at a few places in the southeastern counties shows a satisfactory range of vitrification, but it can not be recommended for 

vitrified brick.

Clays occupying recent lakes and swamps, in areas of both the gray 

drift and the red drift, have a satisfactory range of vitrification. 

In any part of Minnesota the clays of swamps or lake shores are 

worthy of attention, especially if the deposits can be easily drained.

CLAYS THAT MELT SUDDENLY.

Nonrefractory clays that melt suddenly are good only for common 

brick, draintile, fireproofing, or slip glazing. Besides minor formations too thin to be of economic value, this class includes nearly all 

the gray drift clays and about seven-eighths of the gray laminated 

clays and silts of Lake Agassiz and of the river silts. A few silts, 

which burn red, have a better range of vitrification. All the red 

laminated clays and some of the loess and the river alluvium are of 

this class.

The area of the gray drift is shown on the map (PL X). It is 

not to be expected that pebbly clay in this area will make good common brick unless treated. (See p. 55.) After treatment it may make 

not only brick but excellent draintile.

The gray laminated clays occur within the area of gray drift as 

mapped and at a few places outside that area, where a stream 

crosses from the gray drift to the red. For example, there are gray 

clays along Mississippi River from Brainerd to St. Cloud and at 

Wrenshall and vicinity, although in both the areas red drift is the 

main deposit.

Red laminated clays occur mostly along St. Croix River but are 

known in St. Paul near Mississippi River and in Floodwood, St. 

Louis County, near St. Louis River, and are probably extensive in the 

red drift area. Several are very fusible and will make an excellent 

glaze at cone.7.

The loess is most abundant in southeastern Minnesota, and is 

rather widespread in the southwestern part also, though so mixed 

with surface wash as not to be clearly identified everywhere.

The deposits of Lake Agassiz and Red River occupy a strip along 

the river extending northward from Traverse County. They increase both in width and depth toward the north.

Recent alluvium of the rivers (but not of the lakes and swamps) 

is largely of this type. Many deposits along Minnesota River and 

some along Mississippi and St. Louis rivers yield clay for common 

brick.
AITKIN COUNTY. Ill

CLAYS OF MINNESOTA, BY COUNTIES. 

AITKIN COUNTY.

Clay-bearing formations,

r Recent:

Alluvium.

Lake and swamp clay. 

Pleistocene:

Gray laminated clay.

Red drift.

At Aitkin there apparently existed a large depression into which 

Mississippi Eiver and its glacial predecessor have brought great 

quantities of fine-grained clay. The surface for many miles is praccally a flat swamp and for considerable distances on both sides of the 

Mississippi is subject to occasional floods. The river and its tributaries have cut their channels only a few feet below the general level, 

and at low water as much as 8 feet of laminated clay may be seen in 

these shallow gorges. The deposits exposed are somewhat sandy, 

are yellowish gray, and. have probably been formed in part by the 

present river. Well records show that the deposits extend to great 

depth and contain only a few sand}- layers.

In sees. 24, T. 46 N., R. 27 W., at the northeast edge of Aitkin, 

a brickyard was started about 1890 and the company was reorganized in 1900, but the production has been small. The pit is so close 

to the banks of the river that probably a considerable proportion of 

the clay used was alluvium, but the deposit extends so far in all 

directions that most of it must be classed as a lake deposit. The 

former shore lines can be traced by beach ridges, one of which passes 

directly through Aitkin.

Several samples of the clays were taken. They slake at once and 

have only medium plasticity, requiring 22 per cent of water for 

molding. Their air shrinkage is 4 per cent; their average tensile 

strength is 150 pounds to the square inch; and they could be dried 

with artificial heat without checking. As burned at the Minnesota 

School of Mines experiment station at the university they gave the 

following results:

Cone No.

05

02

1

3

5

6

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0.5

3.0

7.0

8.0

8.0

9.0

Absorption.

Per cent. 

18

16

7

5

4

3

The clay becomes steel-hard at cone 03 (1,994° F.) and does not become viscous at cone 6 (2,282° F.), thus showing the very excellent 

range of vitrification of nearly 300°. Samples at different places
112 CLAYS AND SHALES OF MINNESOTA.

from the east end of the deposits along Eice River to the exposures 

in the ditches near Aitkin show great uniformity. It should be safe 

to burn these clays thoroughly hard and perhaps to vitrification, 

though the presence of some organic matter makes it necessary to 

use care in oxidation during firing. So far they have been used 

only for common brick, but their great extent and easy accessibility 

make- them worthy of further experiment. The fact that they are 

gray laminated clays but burn red indicates a high content of iron 

and low content of lime. Such a clay might originate by the leaching of lime from gray drift, or by a mixture of red and gray drift 

worked over by water.

East of Aitkin the red drift is more largely clay than at most 

other places. In a 25-foot exposure at the intersection of the Minneapolis, St. Paul & Sault Ste. Marie and Northern Pacific railways 

the clay is intensely red and contains very few pebbles, all of which 

could easily be removed by rolls. The clay slakes in two minutes 

and becomes highly plastic with 26 per cent of water. Its tensile 

strength is about 200 pounds to the square inch but is considerably 

reduced by rapid drying. Its air shrinkage is about 8 per cent. A 

burning test resulted as follows:

Cone No.

06

03

1

Color.

Salmon. ........................

Bed............................

.....do..........................

.....do..........................

Shrinkage.

Percent. 

1

2

8

8

Absorption.

Per cent. 

17

15

3

2

The clay becomes thoroughly hard at cone 03 (1,994° F.) and reaches 

viscosity at cone 3 (2,174° F.), having a range of vitrification of 

nearly 200° F., with low porosity for several degrees before fusion. 

It resembles in nearly every way the material used with great success 

at Coon Creek, in Anoka County.

Similar clay is exposed at several places on the Cuyuna iron range 

and might be developed for building material at some of the growing 

towns. For example, in the northern part of Deerwood, near the 

shore of the lake, red drift comparatively free from pebbles has been 

exposed over a large area in grading the city streets. (See Crow 

Wing County, pp. 147-149.)

An irregularly laminated sandy clay south of the lake at the railway station at Deerwood may be partly glacial outwash but probably 

is.partly a lake deposit. The Northern Pacific Railway spur .to the 

iron mines cut through it for about 100 yards to a depth of 10 feet. 

Burning tests gave well-vitrified red brick, which were of best grade 

when the sandy and plastic layers were mixed and burned to a temperature about cone 1.
ANOKA COUNTY. 113

Lake and swamp clays that have accumulated at several places on 

the Cuyuna range make excellent common and hard-burned brick. 

No very large deposit has been explored, but the iron exploration has 

cut through bog deposits at the Eowe mine at Eiverton on the socalled north range. Clay is reported in a swamp near the southeast 

corner of sec. 20, T. 46 N., R. 28 W. Several samples have been sent 

in by mine operators, and probably came from material that was 

Sbeing moved in stripping the ore at the mines. (See Crow Wing 

County.)

ANOKA COUNTY.

Clay-bearing formations

Recent: Lake clay. 

Pleistocene:

Gray laminated clay.

Red drift.

Gray drift.

At the south end of the panhandle of Anoka County, where it adjoins Minneapolis, there is a very extensive deposit of laminated 

gray clays that extends along both banks of the river well down

FIGURE 11. Geologic section of the laminated clay in North Minneapolis. (After N. H.

Winchell.)

into the city. The value of the land within the city limits, however, tends to crowd the brick industries northward into Anoka 

County. The detailed description of the clay of this vicinity is 

therefore given here rather than in the discussion of Hennepin 

County.

The bedrock formations along Mississippi River north of Minneapolis are the St. Peter sandstone and the overlying Platteville 

limestone. Above these the hillsides show first the red drift and 

over that the gray drift. Both the drift and the bedrock were evidently eroded by the glacial Mississippi River, a wide channel being 

thus formed in which the gray laminated clays were later deposited. 

(See fig. 11.) The entire mass of stratified clay undulates at angles 

64310° 19 8 * 
114 CLAYS AND SHALES OF MINNESOTA.

of 10° to 20°. The clay is worked from top to bottom, having been 

opened to a depth of more than 30 feet at several brickyards. The 

curious internal structure (see PI. XII) seems to have been caused 

by eddying motions in the periodic flood waters. A few 'concretions 

have been noted; one that was tested by the Minnesota- Geological 

Survey was highly calcareous, containing 94.83 per cent of calcium 

carbonate. The sandiness of the deposit varies erratically, in some 

places being greatest at the top and in others at the bottom. Most 

of the pits opened are said to be pockety. Uniformity in the products manufactured is easily attained, however, by mixing clay from, 

several parts of a fairly large exposure. A similar clay, probably 

of like origin, occurs in a less desirable situation in the southeastern 

part of Minneapolis.

The clay slakes at once arid is highly plastic, requiring 24 per 

cent of water for molding. Its tensile strength is about 200 pounds 

to the square inch and its air shrinkage 3.7 per cent. The United 

States Bureau of Standards reports that it works well in the auger 

machine without much lamination. The following results of burning tests at the University of Minnesota agree closely with those 

of tests made by the Bureau of Standards:

 Cone No.

04

02

01

1

2

3"

Color.

....Ao...:......... .............

.....do..........................

.....do..........................

Buff............................

Shrinkage.

Per cent. 

0

1

2

3

8

 13

Absorption.

Per cent. 

31

31

23

25

13

4

The bricklets became hard at cone 01 (2,066° F.) and viscous at cone 

3 (2,174° F.). The small range and .sudden fusion of the clay make 

it difficult to burn the products to a low porosity. This clay is to be 

recommended for common brick and fireproofing.

Analyses of the clay at North Minneapolis have been made by 

F. F. Grout as follows:

Analyses of gray laminated

Chemical analysis.

Silica _______________ 50.65 

Alumina ______________ 10. 25 

Iron oxides____________ 4. 00 

Magnesia ____________ 4.68 

Lime _________-i_____ 10. 65 

Soda ________________ 1. 44 

Potash _______________ 1.96 

Ignition _______________ 14. 40 

Moisture _____________ 1.20 

Titanium oxide__________ -52

99. 75

clay of Nortli Minneapolis.

Mechanical analysis.

Fine clay _^___ __. 

Coarse clay _________. 

Silt ______________. 

Sand .(total)______*___.

9.1

10.9

79.5

.5

100.0
U. S. GEOLOGICAL SURVEY BULLETIN" 078 PLATE XII

VIEWS SHOWING EXAMPLES OF IRREGULARITY IN THE STRUCTURE 

OF LAMINATED CLAYS IN NORTH MINNEAPOLIS.
U. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE XIII

A. CLAY BANK AT COON CREEK. 

Steam shovel at work on gray drift overburden; lower clay is red drift.

B. SLATE OF CARLTON COUNTY, SHOWING CLEAVAGE.
ANOKA COUNTY. 115

Work began on this clay in 1875, and since then eleven plants have 

been built and worked. Most of them produce cream-colored brick, 

for which there is considerable demand in the Twin Cities for backing 

brick walls ,and for interior work. At most of. the plants the brick 

are not burned very hard, but .they serve ordinary purposes well. 

Most of. the plants have a capacity of approximately 40,000 brick a 

day and operate till, the frost. Probably nine-tenths of the brick are 

burned in large scove kilns. To decrease costs of labor and fuel the 

Minneapolis Brick & Tile Co. installed a continuous kiln, with a 

gas producer, for firing at its plant on the west side of the river. 

Thus far the saving is not sufficient to recommend it in preference to 

the scove kilns operated by the same company on the east side of the 

river. Most of the plants at North Minneapolis have now been bought 

up by C. H. Klein, who owns the similar deposits at Chaska.

Hollow ware is produced by two companies. The Swansoh Brick 

& Tile Co. has practically abandoned the production of common 

brick and devoted its energies to the production of hollow ware, 

with great success. The Minneapolis sawmills furnish a convenient 

supply of sawdust for mixing with the clay to render the finished 

product much lighter. The company now has a stock pile of sawdust 

and a thoroughly explored bank of clay sufficient to assure successful 

operation for many years. It has six oblong downdraft kilns and can 

turn out 40,000 brick a day. Work was begun at this plant in 1875.

The quality of the products made from this clay is indicated by the 

following results of tests. The Minneapolis building inspector reports that ten bricks from one plant showed an average crushing 

strength of 2,968 pounds to the square inch, a minimum of 1,600 

pounds and a maximum (in a brick from the center of the kiln) of 

5,080 pounds. Three other series of tests gave an average strength of 

1,560 pounds to the square inch, a minimum of 631 pounds and a 

maximum of 2,770 pounds. Another series of five bricks from one 

plant had an average strength of 2,588 pounds. The general average 

of all the brick from the North Minneapolis deposits tested in this 

investigation is over 2,000 pounds. One test by the Minneapolis 

building inspector on a hollow tile about 4 by 8 by 17 inches, with 

six openings through it lengthwise, gave a strength of 604 pounds to 

the square inch.

The engineering department of the University of Minnesota reports 

that five dry bricks from North Minneapolis had an average crushing strength of 1,940 pounds to the square inch and that wet bricks 

were only slightly weaker. The modulus of rupture is 411, and the 

absorption 29.7 per cent. The product varies somewhat at different 

yards.

The Minnesota Paving Brick Co. (Hydraulic Press Brick Co.) 

formerly had an extensive plant at Coon Creek, but this plant is now
116 CLAYS AND SHALES OF MINNESOTA.

closed. The red drift is 40 feet or more thick and has been explored 

over 200 acres. The overburden is 20 feet of gray drift. (See PL 

XIII, A.) As dug from the ground the red drift contains some 

pebbles and boulders, which necessitate treatment by rolls 'OrTgrinding 

machinery, but these are not as numerous as in the average of the 

red drift throughout the State. None of the pebbles are limestone 

except in the overlying gray drift, which is discarded because it is 

not available without cleaning. At the plant all the red clay dug is 

put through a double series of conical rolls by which many of the 

pebbles are removed and the rest crushed to a size that renders them 

practically harmless. A sample of the clay that had passed through 

these rolls slaked promptly and showed fairly high plasticity, requiring 24 per cent of water for molding. Its shrinkage was 5 per 

cent and its tensile strength nearly 100 pounds to the square inch, 

though somewhat less if rapidly dried. The United States Bureau 

of Standards reports that the clay has fairly good vitrification behavior, its porosity being less than 5 per cent through a range of 

about 100° F. Enough organic matter is present to make the texture 

frothy and blebby if the clay is heated suddenly, but this is easily, 

avoided by care at the plant. Burning tests resulted as follows: .

Cone No.

06

05

03

02

1

Color. '<-

Salmon. ........................

.....do..........................

Bed............................

.....do..........................

.Shrinkage.

Per cent. 

2

3

5

8

9

Absorption.

Per cent. 

17

16

10

5

4

The following analyses were made by F. F. Grout on the clay as 

used at Coon Creek:

Analyses of red drift from Coon Creek.

Chemical analysis.

Silica ________________ 60.49

Alumina _____________ 12. 62

Iron oxides_____ _ 7. 80

Magnesia...__________ 3,68

Lime _______________ 3. 87

Soda_______________ 2.17

Potash ______________ .2. 53

Titanium oxide __:. ___ . 42

Ignition _____________ 5. 90

Moisture _-_____ _ 1. 94

101. 42

Mechanical analysis.

Fine clay_____________ 17.3

Coarse clay ___________ 24. 6

Silt __________________ 47. 5

Fine sand ____________ 5.1

Coarse sand ___________ 5. 5

100.0

The Coon Creek company had a steam shovel and six large oblong 

downdraft kilns with a total capacity of about 40,000 brick a day.
ANOKA COUNTY. 117

Its product was largely used by the Great Northern Railway in the 

construction of station buildings and paving station platforms. 

Some well-vitrified brick were roughened in imitation of klinker brick 

for; fancy] building material, and some were kept smooth for paving. 

At Minot a platform built partly with these brick and partly with 

the famous Purington brick from Galesburg, 111., showed in practical 

service results very much in favor of the Coon Creek product. For 

harder use, as paving for city streets, the Coon Creek brick do not 

seem to have become as popular as they deserve. The city engineer 

of Minneapolis has tested them in comparison with the cobblestone 

paving produced in Minnesota and with the several types of paving 

brick now imported into the State. The average breaking load of 

Coon Creek brick was 16,000 pounds, the modulus of rupture was 

over 4,000 pounds, and the average crushing load was over 17,900 

pounds, all three being greater than those of any other material

'jo «o so /»a SO

OURATIpN OF'TEST IN MINUTES. .

FIGUBE 12. Rattler test on paving brick from Coon Creek.

tested. The percentage, of absorption was zero. The percentage 

of abrasion was 7.18, which was as low as that of the best imported 

paving brick, though higher than that of the granite of St. Cloud. 

A sample of vitrified brick from the Coon Creek plant was purchased in the open market and shipped to Edward Orton, jr., of 

Columbus, Ohio, to be tested as paving material. He reports, " The 

brick did very well, and I think full-sized pavers of the same quality 

would have easily met the requirements of the American Society for 

Testing Materials." The' total loss after an hour in the rattler was 

36.05 per cent.. (See fig. 12.) The loss of the best grades of Illinois 

paving brick may be as low as 20 per cent on similar treatment; that 

of Iowa paving brick is 25 to 40 per cent.1

The high quality shown in all these tests indicates that the clays of 

the red drift of Minnesota are suitable for more extensive use. 

However, care must be used to select the less sandy deposits. (See 

Aitkin County, pp. 111-113.) At Elk River, only a short distance 

from the deposits just described, the material in numerous exposures

Tests of clay products: Iowa Geol. Survey Ann. Kept., vol. 14, p. 620, 1903.
118 CLAYS AND SHALES OF MINNESOTA.

has very different properties, though still burning red with a fair 

range of vitrification. The shrinkage of the sandy clays is very 

slight.

Clays of fair quality have accumulated in glacial and recent lakes 

in other parts of Anoka County. Such a deposit was developed 

about 25 years ago by P. P. Kelsey, 2£ miles north of Anoka, near 

the shores of Round Lake. At this locality smooth yellow clay 

covers many acres, but the deposit lies near the water level, and it 

would not be easy to get the products to the large markets. The 

clay slakes in three minutes and becomes highly plastic, requiring 

32 per cent of water for molding. Its tensile strength is 150 pounds 

to the square inch and its air shrinkage 10 per cent. A burning test 

resulted as follows:

Cone No.

06

03

1

2

3

4

Color.

Buff....... .....................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

1

6

7

8

Absorption.

Per cent. 

25

21

13

10

9

4

' I

The bricklets became very hard after heating to cone 03 (1,994° ]?.), 

and reached viscosity at cone 4 (2,210° F.). Probably many of the. 

lakes and swamps would reveal clays.of this general character.

BECKEB COUNTY.

Clay-bearing formations Recent : Lake clay.

Pleistocene : Gray drift.

Along the Minneapolis, St. Paul & Sault Ste. Marie Railway^ 

about a mile south of the station at Detroit, is a massive deposit of 

gray drift that is full of pebbles and very sticky though not very 

plastic. The clay slakes in one minute and requires 30 per cent of 

water for molding. Its tensile strength is about 60 pounds to the 

square inch, even when rapidly dried- Its air shrinkage is 8 per cent. 

A burning test resulted as follows :

Cone No.

04

03

01

2

3

4

Color.

.....do...........:.............

Buff............................

.....do..........................

Greanish buff. ..................

Shrinkage.

Per cent. 

3

3

5

13

13

Absorption.

Per cent,. 

28

25

20

3

2

The clay becomes hard after heating at cone 03 (1,994° F.), and 

is viscous above cone 3 (2,174° F.). A good plant for the production
BELTRAMI COUNTY. 119

of brick and tile was erected at this deposit, but the difficulty of 

using a clay containing so many limestone pebbles caused the failure 

of the undertaking and the loss of considerable money. Crushing 

and washing were tried to obviate the difficulty, but without success. 

Some of the gray drift in the vicinity contains much fewer pebbles, 

but none of it is entirely satisfactory.

Several swamps and lakes in the neighborhood of White Earth 

and Ogema contain clays that were used to make brick for the construction of the Government industrial school for the Indians and 

for St. Benedict's Mission. Very attractive and durable brick were 

made, though they show a few lime pebbles. If the market warrants 

it numerous deposits of such clay in this neighborhood will no doubt 

be developed.

BELTRAMI COUNTY.

Recent: Lake and river clays.

 . .. Pleistocene: Clay-bearing formations .. ,. .,,,. ., Silt of the Red River valley.

Gray drift.

The gray drift is thick over most of Beltrami County, and in part 

of the area the silts of the Red River valley have smoothed the 

topography by filling up the depressions of the drift sheet. These 

silts increase in thickness toward the northwest. Both silts and drift 

require the removal of limestone pebbles to yield workable clay.

At South Bemidji, in a very favorable situation as regards shipping facilities, the south shore of the lake at the level of Mississippi' 

River, contains blue and yellow clay of a common laminated type, 

which has been used at a medium-sized brickyard for common brick. 

The deposit covers many acres and is exposed to a depth of 20 feet 

but is covered more or less deeply with sandy overburden. At the 

brickyard 1 to 8 feet of sand is being removed. Some sand is used 

in tempering the clay. An attempt has been made to mix the yellow 

clay, which is the chief body exposed, with the underlying blue clay. 

Th& blue clay appears to have been very plastic and was dug in a 

moist though solid condition, but it did not mix well and the brick 

were badly cracked, showing a most decided auger structure. Possibly more thorough mixing or the addition of sand would help. 

The two kinds of clay should be tried separately. It should be possible to make excellent products from this deposit. The average clay 

slakes promptly and the addition of 30 per cent of water develops a 

very high plasticity, which is easily reduced for better working by 

the addition of some of the sandy overburden. The air shrinkage 

of the clay is about 14 per cent, but with one part sand to two of clay 

this is reduced to 9 per cent, and the drying.is much safer. The clay 

by itself develops cracks which reduce its strength, but the mixture
120 CLAYS AND SHALES OF MINNESOTA.

of sand and clay has a strength of about 300 pounds to the square 

inch. Burning tests resulted as follows:

Clay alone.

Cone No.

03

02

1

4

Color.

.....do.........................

.....do..........................

Shrinkage.

Per cent. 

1

3

7

8

Absorption.

Per cent. 

18

18

6

3

Two parts clay and one part sand.

06

04

02

1

.....do..........................

.....do...... .... ................

Red............................

1

2

3

4

1&

17

13

3

The clay alone has the better range of vitrification (216° F.) and 

reaches viscosity at cone 4 (2',210° F.). The.mixture of clay and sand 

has a range of 180° F. and reaches viscosity at a lower temperature 

(2,102° F.). A greater proportion of sand greatly decreases the range 

of vitrification and is therefore undesirable, but 20 to 30 per cent of 

sand improves the working qualities and is very desirable for brickmaking.

North of Bemidji the shores of Bemidji.Lake consist of a more 

recent lake deposit which has been exposed by the gradual lowering 

of the lake level as its outlet has been eroded. The deposit is highly 

calcareous and was tested to ascertain whether it might be used for 

cement material. A partial analysis resulted as follows:

Partial analysis of calcareous clay from shores of Bemidji Lake.

Per cent.

Insoluble iron and aluminum oxides_______________ 65. 90 

Magnesia __ 5.10 

Lime _________________________________ 12. 20

The lime and magnesia existing in the form of carbonates make up 

about one-third of the material but are not sufficient to justify itsuse for cement, especially as the percentage of magnesia is too large* 

The material would probably burn to a cream-colored brick.

BENTON COUNTY.

("Pleistocene: 

Clay-bearing formations: | Gray laminated clays.

I Red drift.

The surface formation over most of Benton County is red glacial 

drift and glacial outwash, most of which is sandy. No clay pockets 

were noticed in it, but along Elk and Mississippi rivers are deposits
BLUE EAKTH COUNTY.

of laminated clays, some of which may be of value. One was developed in a small way on a farm now owned by Mr. Harshman, at 

the crossing of the State road, over Elk River. Although it lies in 

an area of. red drift the clay burns buff at high temperatures and 

has probably been transported by glacial streams from the area of 

gray, drift farther north. It slakes at once and with 25 per cent of 

water becomes highly plastic. It shrinks 5 per cent on drying and 

develops a strength of about 150 pounds to the square inch, even 

when rapidly dried. A burning test resulted as follows:

Cone No.

05

03

02

2

3

Color.

Pinkish buff.. . ...... '. ..........

.....do..........................

Buff............................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

,1

1

1

8

Absorption.

Per cent. 

27

of)

10

6

The clay is hard after burning at cone 02 (2,030° F.) and reaches 

viscosity at cone 4 (2,210° F.).

! BIG STONE COUNTY.

In Big Stone County the only clays known are in the gray drift 

and are of the usual type, needing cleaning before use. Archean 

residual material is found at a depth of 250 feet in a well near 

Johnson.

BLUE EARTH COUNTY.

Clay-bearing formations

Recent:

River clays.

Lake and swamp clays. 

Pleistocene: Gray drift. 

Cretaceous: Sliales and clays.

The Cretaceous clays seem to be widely distributed in Blue Earth 

County,.but in .most places they are deeply covered with gray drift 

of the common type. Exposures occur chiefly along the larger 

streams.

Five miles south of Mankato, in sec. 35, T. 108 N., R. 27 W., 

30 to 40 feet of the Cretaceous overlies the Jordan sandstone and 

underlies 10 to 20 feet of drift along the banks of Le Sueur River. 

The Cretaceous outcrops are from a quarter to half a mile above the 

Red Jacket Bridge. The deposits are crumpled in complex fashion 

and the clay occurs in irregular lenses in beds of ferruginous sands 

and conglomerates, indicating that the whole series was probably 

distorted by the crowding of the glacial ice. Samples taken from 

some of the smaller clay lenses, rarely over 1 foot thick, that crop
122 CLAYS AND SHALES,OF MINNESOTA.

out for several hundred yards along the cliffs show very fine grained 

and chalky material, stained with iron in a. few places. It does not 

slake when dropped into water. It is very lean, but it requires 

27 per cent of water for molding. Its air shrinkage is about 1 per 

cent. It becomes steel-hard at about cone 3 (2,174° F.). It is highly

- .^. . :..

§|^piiij|gSSg|J;=g;|-y <_~2T

1JTT

FIGURE 13. Section of Cretaceous clay at South Bend, a, Shakopee dolomite; l»,. Cretaceous clay; c, drift. (After N. H. Winchell.)

refractory, and some samples will stand a temperature of cone 33 

(3,254° F.) without deformation. In color the product ranges from 

buff to creamy brown. About 20 years ago the Pauline Pottery Co., 

of Chicago, tested the clay for use in the manufacture of fancy pot-

~- ' J r-,

1 - ( ^jr^5^^^'?-r^:.^b°^---^^!^ -Y i * !- ,-~j *3zQ££-|i£^^:r^r*T7pri-^

FIGOKB 14. Section of Cretaceous clay near railroad bridge, Mankato. a, Shakopee 

dolomite; 6, weathered surface of same; c, Cretaceous clay; d, drift. (After N. H. 

Winchell.)

tery. Joseph Kern, of Mankato, who owns the property, has some 

beautiful but very fragile vases that were made in the experiment. 

A portion of the deposit, which appears concretionary, has 47.4 per 

cent silica and 14.5 per cent water and would be a valuable refractory clay if large amounts were available. Other outcrops near Mankato are considered to be Cretaceous shales.
BLUE EARTH COUNTY.

Above the basal Cretaceous clays just described are a great many 

outcrops of alternating shale and sandstone and here and there one 

of ferruginous craggy conglomerate, which have been described by 

Upham.1 Most of the clay beds are thin, and their extent is not well 

determined. (For analyses see p. 90.) Their physical character is 

indicated by a sample from Le Sueur County. (See pp. 187-191.) 

They are worthy of further exploration. (See figs. 13 and 14.)

The gray drift of most of the county shows the common characteristics. A sample was taken just southwest of Lake Crystal on the 

Chicago, St. Paul, Minneapolis & Omaha Railway, where the deposit, 

which is of considerable extent and 30 feet thick, contains less gravel 

than the average gray drift. After being crushed to 40-mesh, the 

clay was found to have low plasticity but to require 24 per cent of 

water for molding. Its tensile strength was more than 150 pounds 

to the square inch, even when rapidly dried. The air shrinkage was 

4.5 per cent. Burning tests at the Minnesota School of Mines experiment station resulted as follows:

Cono No.

04

03

fl9

i

2

Color.

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

1

1

3

6

8

Absorption.

Pa cent. 

21

20

19

14

10

4

The particles of lime remaining in the burned brick up to the temperature of cone 03 (1,994° F.) cause .its rapid disintegration on 

exposure to the air. The clay became too hard to scratch with a 

knife at this temperature and became viscous at cone 4 (2,210° F.).

Three plants were started to make use of the drift in this neighborhood, but none of them are now at work, though houses built 40 

years ago of brick made here are in fairly good condition. Success 

would depend not only on favorable market conditions but also on 

the adoption of some method of removing limestone pebbles. A partial chemical test of some of the common clay in this county showed 

over 12 per cent calcium carbonate.

At and near Garden City similar gray drift contains more than 

the usual proportion of limestone pebbles.

A deposit several feet thick extends over several acres on the farms 

of Joseph Kern and Frank Pearson, 5 miles southwest of Mankatp. 

Near the surface the lime pebbles of the drift are fewer than in the 

average gray drift. The clay slakes in three minutes and is highly

1 Upham, Warren, Minnesota Geol. and Nat. Hist. Survey Final Rept., vol. 1, 

432-439, 1884.
124 CLAYS AND SHALES OF MINNESOTA.

plastic, requiring 23 per cent of water for molding and showing a 

shrinkage of 5 per cent on drying. Its tensile strength is 100 pounds 

to the square inch but is seriously affected by rapid drying.- A burning test resulted as follows: -^j /;/ .

Cone No.

04

03

01

1

2

5

Color.

.....do......................

.....do..................:...

.....do......................

Shrinkage.

Per cent. 

1

1.5

2

. 5

6

Absorption.

Per cent. 

15

14

13

10

4

The clay becomes steel hard at cone 03 (1,994° F.) and reaches viscosity at about cone 4 (2,210° F.). This deposit overlay one which 

was formerly worked for Cretaceous clay 'of refractory grade but 

which has been exhausted. It should yield a good grade of brick and 

tile, but whether it could be profitably worked depends on the economic conditions.

At Mapleton the whole neighborhood is covered with gray drift 

of the common type, containing the average number of pebbles;

Near Rapidan, along the Chicago, Milwaukee & St. Paul Railway, 

close to a bridge across Le Sueur River, an area of many acres is covered with gray drift whose upper part has been leached and furnishes somewhat better clay than the main body. The clay slakes in 

two minutes, is highly plastic, requires 22 per cent of water for 

molding, and shrinks less than 5 per cent on drying. Its tensile 

strength is nearly 200 pounds to the square inch, even when rapidly 

dried. As burned at the Minnesota School of Mines experiment station it gave the following results:

Cone No.

05

01

2

4

Color.

..:.. do. .....................

.....do......................

Shrinkage.

Per cent. 

1

4

7

8

Absorption.

Per cent. 

22

18

8

2

The clay becomes steel hard at cone 06 (1,886° F.) and viscous at 

cone 3 (2,174° F.). Although the lime pebbles are a serious defect 

it might be used without so extensive a treatment as is undertaken 

at Hutchinson. The market conditions are favorable, though fuel 

would have to be shipped in, and throughout the southern part of the 

State there is competition from the plants in Iowa.

Recent alluvium is found at many points along Minnesota River 

and some of its tributaries, such as the Le Sueur. A-brickyard 2£ 

miles south of Mankato is in" operation on 6 to 12 feet of workable
BLUE EARTH COUNTY. 125

alluvium which extends along Minnesota River in a flood plain of 

very great extent. It is typical of the material at many points between Chaska and New Ulm. An analysis is given in the report on 

Le Sueur County (pp. 187-191). The clay slakes at once and its plasticity is very low. It requires 22 per cent of water for molding and 

shrinks 4 per cent on drying. Its tensile strength is 175 pounds to the 

square inch, whether slowly or rapidly dried. It is rather sandy, and 

some care has to be used to exclude even the coarse gravel which occurs 

in irregular layers. As burned at the Minnesota School of Mines experiment station it gave the f ollowing results:

Cone No.

05

02

1

.3

' 5

Color.

.....do.......................

.....do......................

.....do......................

Shrinkage.

Per cent. 

0

1

7

Absorption.

Per cent.

94

22

10

6

3

The clay burns hard at cone 02 (2,030° F.) and is near viscosity at 

cone 5 (2,246° F.). The plant is making 4,000,000 common red brick 

of excellent quality each season by a soft-mud process.

Other favorable places for the development of this alluvium near 

Mankato are opposite Judson, about a mile up the river, and about 

40 rods north of the city limits of Mankato, along the Chicago, St. 

Paul, Minneapolis & Omaha Railway, where the river basin has a 

width of 3 or 4 miles and the clay lies in a terrace at a somewhat 

higher level than at the present brickyard.

About 3 miles from St. Clair, on the south bank of Le Sueur River, 

a swamp of 40 acres or more has been drained by a ditch that exposes 

a clay deposit about 15 feet in thickness, the upper part of which is 

yellow and the lower part blue-gray. Peat of uneven thickness overlies the clay in part of the swamp. The clay is free from visible impurities. It slakes in six minutes and is very highly plastic, requiring 30 per cent of water for molding. Its tensile strength is about 

80 pounds to the square inch and its air shrinkage 8 per cent. In 

burning it becomes hard and is salmon-colored at cone 06 (1,886° F.), 

at which its absorption is 16 per cent. It contains enough organic 

matter to cause it to swell and crack and develop black cores if rapidly heated, but if slowly heated and thoroughly oxidized it will yield 

good red brick and will not reach viscosity below cone 2 (2,138° F.). 

All conditions seem to be favorable for the manufacture of brick and 

tile, except that the deposit is about a mile from the railroad.

About half a mile south of Good Thunder station a swamp deposit covering many acres was worked for years up to 1904. The 

clay is almost free from limestone pebbles, and the brick made from 

it have stood the test of service for nearly 30 years in some of the
126 CLAYS AND SHALES OF MINNESOTA.

buildings in the town. The "folio wing analysis was made by F. F. 

Grout for J. T. Schlesselman some years ago:

Analysis of surface clay of Dine Earth County. .. ..

Silica ____________ - 70.29 

Iron and aluminum oxides ___ 18. 71 

Magnesia __ - _ 1. 35 

Lime _____________________ _____________ 2.02

Soda_________________ _ . 56 

Potash ________________________________ 1.87

Moisture ____________ 2.15 

Ignition __^________________ __ ______ 3. 60

The clay is probably fairly characteristic of the bog deposits 

throughout much of Minnesota. It may contain some wind-blown 

loess, but it is mad.e up largely of the wash from the neighboring 

hillsides. The humic waters of the bog have leached out the soluble 

lime and iron in some deposits but have left enough iron in most of 

them to make the clay burn red.

BROWN COUNTY.

Recent: Alluvium. 

Pleistocene: Gray drift.

Clay-bearing formations . Cretaceous:

Shales. 

Basal clays. 

Archean; Residual clay.

The only working plants in Brown County are at Springfield and 

New Ulm. The Springfield plant is supplied from an extensive bed 

of laminated Cretaceous shale and the New Ulm plant uses the extensive brown and.yellow alluvial clays along Minnesota River. 

Most of the gray drift in this county contains many pebbles, chiefly 

of limestone, and as clays of much better quality exist in the counly 

the plants which have used the drift have been abandoned and no 

further development of it is to be recommended.

New Vim. The abundance of Cretaceous outcrops in the immediate vicinity of New Ulm has led to several investigations. The best 

clays now available in quantity are a few miles up Cottonwood River, 

out of convenient reach of shipping facilities. However, some of the 

shales near the town have not been thoroughly explored. The Cretaceous beds are subject to change within short distances, and good 

clays may lie in many places between outcrops that are sandy or that 

contain thin limestones.

Red, yellow, and blue clay is exposed in a road cut in park property on the north side of North German Park, close to the New Ulm 

Farmers' Elevator, Most of the clay probably lies under the park,
BROWN COUNTY. 127

though it might also be traced both east and west along the hill. A' 

boring said to have been made some years ago found 26 feet of blue 

clay below that now exposed. (See fig. 15.) No impurities are visible. The sample slakes at once. With 28 per cent of water, the clay 

is highly plastic. It shrinks 8 per cent on drying and has some tendency to crack, but if care is used it develops a strength of nearly 100 

pounds to the square inch. A burning test resulted as follows:

Cone No.

06

04

02

1

2

Color.

.....do......................

Buff........................

Shrinkage.

Per cent. 

0

1

o

4

Absorption.

Per cent. 

21

19

17

11

The clay is hard after burning to cone 06 (1,886° F.) and reaches 

viscosity at cone 2 (2,138° F.). Its decrease in porosity seems to be

FIGURE 15. Section of Cretaceous shale at Farmers' Elevator, New Ulm.

gradual, and it should make well-vitrified brick. It compares favorably with the clay now used at Springfield.

In the southeastern part of New Ulm a pottery that was established 

about 30 years ago obtained its material from a bed 4 to 8 feet thick 

whose extent is uncertain but which is said to underlie the central 

part of the town beneath not more than 10 to 12 feet of overburden. 

The clay slakes in two minutes, is highly plastic, and requires 20 per 

cent of water for molding. It has a tensile strength of 200 pounds to 

the square inch and can safely be dried with artificial heat. Its air 

shrinkage is less than 4 per cent. As burned by the Minnesota 

School of Mines experiment station, it gave the following results:
128 CLAYS AND SHALES OF MINNESOTA.

Cone No.

05

03

1

5

12

Color.

BuJCf...................:........

.....do.........................

.....do..........................

Shrinkage.

Per cent. 

0.7

1.0

1.4

2.5

Absorption.

Per cent. 

14

13

12

11

10

The clay becomes hard at cone 03 (1,994° F.) and, though well vitrified, does not seem to be near viscosity at cone 12* The extent of this 

deposit should be carefully studied.

A much less favorably situated outcrop occurs near the plant of the 

A. Schell Brewing Co. Thin layers of limestone, which occur in the 

outcrop and can not easily be separated from the clay, ruin the products burned from this clay at any temperature.

Near the south side of New Ulm, at the Chicago & Northwestern 

Railway crossing over Cottonwood River, shales are exposed to a 

depth of 40 feet. The extent of the formation is unknown but is 

probably very great. Its lower main part is a rather soft gray clay, 

very favorably situated for development. It slakes very slowly and 

is highly plastic, requiring 29 per cent of water for molding. Its 

tensile strength is 200 pounds to the square inch but is considerably 

injured by rapid drying. Its air shrinkage is 10 per cent. As 

burned by the Minnesota School of Mines experiment station it gave 

the following results:

Cone No.

05

02

01

2

Color.

.....do..........................

Brown .........................

.....do..........................

Shrinkage.

Per cent. 

2

4

5

Absorption.

Per cent 

12

7

3

2

The clay becomes hard at cone 05 (1,922° F.) and viscous above 

cone 2 (2,138° F.). The porosity-decreases gradually. Most of the 

clay is gray, and clay of similar appearance can be traced through 

the neighboring hills. Borings and wells reveal the fact that it extends over considerable territory beneath later deposits.

The upper portion of the deposit is red, sandy, and evidently calcareous and possibly contains some gray drift and Cretaceous limestone. It is certainly much less valuable clay than the lower part, 

but it is thin, and there is 40 feet of the gray clay below.

The extent of plastic Cretaceous clay is shown by a similar deposit 

of even better quality that crops out along Cottonwood River in 

sec. 31, T. 110 N., R. 30 W., 2 miles west of New Ulm. The drift 

cover is heavy, and the outcrop shows less than 10 feet of clay in a 

vertical bank, but the deposit is known by wells and other excava-
BROWN COUNTY. 129

tions to be 16 to 20 feet thick and to underlie probably 300 acres. In 

the high bluffs and hills the clay has a heavy overburden of drift and 

in some places an additional overburden of sandy Cretaceous deposits ; but along the river flat these have been mostly eroded away 

and only 4 to 16 feet of river wash remains above the clay. (See fig. 

16.) Samples from the deposit on the farm of .William Alwin and

=i==:'Cretaceous shale ^=- ' ^=^-="=^=-=

FIGURE 16. Section of Cretaceous shale on Cottonwood River, Brown County.

from the outcrop in the river bank show the same physical character. The shale slakes in three minutes and with 30 per cent of 

water is highly plastic, working well in an auger machine. Its air 

shrinkage is 10 per cent, and if carefully dried it has a tensile 

strength of over 200 pounds to the square inch. Care is needed to 

prevent checking during the drying process. Several burning tests 

resulted as follows:

Cone No.

010

07

04

1

2

5

Color.

.....do..........................

Bed. ...........................

.....do..........................

.....do..........................

.....do.........................

.....do..........................

Shrinkage.

Per cent. 

1

2

4

5

5

5

Absorption.

Per cent. 

14

19

10

7

7

11

The clay becomes hard after burning to cone 010 (1,742° F.) and 

reaches viscosity at about cone 4 (2,210° F.), having thus a range of. 

vitrification of 478° F. as good as that of several clays now used. 

The porosity decreases slowly and, though never low, is entirely satisfactory for vitrified products. The presence of some organic matter and of the iron which makes the clay burn red necessitates a little 

care in oxidation during firing but with slow burning causes no 

trouble. All the conditions are favorable except that the material is

64310° 19 9
130 CLAYS A2TD SHALES OF MINNESOTA.

riot easily shipped. A 2-mile spur up the river would be the most 

convenient method of obtaining connection with the railroads.

A sample of gray shale from the south bank of Cottonwood Elver 

in this immediate neighborhood, in sec. 31, T. 110 N., E. 30 W., was 

sent by John Lind many years ago to the United States Geological 

Survey and was analyzed by T. M. Chatard, with the following results :*

Analysis of gray Cretaceous shale from Cottonwood River.

Silica_________________________________ 61.32 

Alumina _________ __ ________________ 12.27 

Ferric oxide_<___________-__"__________ __ 3. 62 

Ferrous oxide____________________________ 4.18 

Magnesia _______________________________ 1.76

Lime___________________________________ . 99 

Soda____________________________:_______ . 42 

Potash ________________________________ 3. 59 

Ignition_______________________________ 10.73 

Titanium oxide______ __________._________ . 66

Barium oxide___ _ .05 

Phosphorus oxide ___ ______________ .27 

Sulphur trioxide____ _ _ ___ ____ . 19

Manganous oxide___:_ ____:_----- 27

' 100.32'

Within a mile west of these deposits, in sec. 36, T. 110 N., E. 31 

 W., are other Cretaceous outcrops of slightly different character. TJie

 .' ^'.: :-.'--Cretaceous ' ' 

~. .-^-shale'and.sand50. 

FIGUBE 17. Geologic section on Cottonwood River, Brown County, showing Cretaceous

deposits and drift.

relations, as seen on J. Seifert's farm, are shown in figure IT. 1 '''Mitting would be difficult on account of the soft sandy overburden. Tile

!U. S. Geol. Survey Bull. 60, p. 151, 1800.
BROWN COUNTY. 131

clay at water level is somewhat variable in color and texture. The 

plastic masses are mostly red and white and will all pass a 60-mesh 

sieve. A little farther up the river the creamy-white clays are 

gritty and only about 50 per cent will pass a 60-mesh sieve. Samples 

from the largest exposure were tested by the Bureau of Standards. 

The clay slakes in three minutes and requires only 19 per cent of 

water for molding. Its shrinkage on drying is 5 per cent. Machinemolded bricks are inclined to crack, but that is not true of handmolded bricks. In burning, the colors are light pink to buff, with a 

tendency to flash at higher temperatures. At cone 06 (1,886° F.) 

the clays burn too hard to be scratched with a knife, have a very 

small shrinkage, and an absorption of 15 per cent. They are highly 

refractory, maintaining their shape to cone 31£ (3,200° F.), with 

only a small shrinkage and a gradual decrease in absorption. Mr. 

Aufderheide has used this clay in the brickyard at New Ulm and has 

made some fire brick, which stand furnace temperatures very well 

but which do not show satisfactory strength after being repeatedly 

heated and cooled. No other attempts have been made to use these 

clays. It should be possible, by washing, to remove the grit and 

some ferruginous grains and produce a kaolin of good color.

At some of the outcrops in sec. 36 the gritty nature of the clay and 

its massive, nonstratified structure strongly suggest that it is residual 

from the Archean granite gneisses rather than a Cretaceous sediment. The geologic relations are not clearly sjhown, but a study of 

tlie region shows that such residual clays are not improbable.

River clay is known to exist to depths of 8 or 9 feet over several 

acres 1-| miles southeast of the center of New Ulm. The upper part 

of the deposit is dark brown and the loAver part yellow and more 

plastic. The only overburden is the sod, and the impurities are, as 

usual in river clays, scattered patches of sand, a few boulders, and 

some organic matter. The deposit is favorably situated and, since 

1875, has been used in making red brick in a soft-mud machine with 

a capacity of two or three million brick in a season.

Three or four miles south of the Chicago & Northwestern Railway 

at Essig clay crops out along Cottonwood River almost continuously 

for a mile, rising 6 feet above water level and extending to an unknown depth below. It is white to gray and very plastic. The outcrops are not perfectly continuous, and there seems to be a difference 

between the white clay and the gray clay which is associated with it. 

It may be that the white clay exists mostly in pockets. Both the 

white and the gray clay slake in a few minutes and are highly plastic,; requiring 23 per cent of water for molding. Their tensile 

strength is well above 100 pounds to the square inch, even after 

rapid drying. Their air shrinkage is about 7 per cent. As burned by
132 CLAYS AND SHALES OF MINNESOTA.

the Minnesota School of Mines experiment station they have the 

following character: .

White clay.

Cone No.

010

06

01

2

3

5

10

Color.

Buff............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

.....do........:.........,.......

Shrinkage.

Per cent.' 

0

1

4

5

5

6

Absorption.

Per cent. 

15

14

8

6

5

4

4

Gray clay.

Cone No.

010

06

03

2

3

Color.

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

1

3

4

Absorption.

Per cent. 

15

13

8

6

6

At all the specified temperatures the brick made from the white 

clay are hard and undeformed. The absorption changes indicate 

the progress of vitrification through nearly 700° F., and the clay 

will evidently stand a high temperature without becoming viscous.

The gray clay likewise becomes hard but not viscous at the temperatures reported, biit it evidently contains enough organic matter 

to cause danger of the formation of black cores. In a rapid heat 

the brick swelled and cracked at cone 3. Both of the clays, how: - 

ever, show an excellent range of vitrification and should be utilized 

if transportation facilities can be provided. The white clay has 

been tested by the Ked Wing Stoneware Co. with results that are 

said to be favorable, but the material has not been used because it 

is not very easily accessible. The overburden is not a serious handicap, for the clay crops out in a great many places.

/Springfield. Just east of Springfield, about 30 miles up Cottonwood River from New Ulm, the A. C. Ochs Brick & Tile Co. has developed a large patch of Cretaceous clays along the Chicago & Northwestern Railway. The-clay is'20 feet thick above water level and is 

known to extend over 20 acres. It is gray and thin bedded and contains both pyrite and limonite in concretionary masses an inch or two 

thick. Over most of its area it is covered with common gray drift and 

is somewhat variable in sandiness. The clay slakes in two minutes, is 

highly plastic, and requires 29 per cent of water for molding. Its 

tensile strength is 200 pounds to the square inch but is much reduced 

if rapidly dried. Its "shrinkage on drying is about 8 per cent. As 

tested by the Bureau of Standards a sample selected as especially
BKOWN COUNTY. 133

rich plastic shale showed serious auger lamination and much danger 

of cracking on drying. The clay burns buff and pink at low temperatures and chocolate color when vitrified. The range of vitrification is excellent (400° F.). The porosity decreases gradually and 

is less than 1 per cent for over 100° F. without reaching viscosity. 

Burning tests at the University of Minnesota resulted.as follows:

Cono No.

010

07

05

03

1

2

Color.

Buff...................... ......

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

3

4

5

8

9

10

Absorption.

Per cent. 

16

12

10

5

1

The bricklets tested were too hard to be 'scratched with a knife at 

all these temperatures, but they retained their form perfectly. The 

clay is available for vitrified brick and tile and probably for roofing 

tile also, if warping can be prevented in drying. A special die 

might.be successful. For analysis of the clay see page 91.

A. C. Ochs has been operating on this clay for 20 years and has 

manufactured mostly hollow brick and tile, in eight kilns which, 

when full, contain about 4,000,000 brick. It is planned to use a 

steam shovel hereafter in working the bank. Both soft-mud and 

stiff-mud brick are manufactured, and the strength of the product is 

excellent.

, ? The Minneapolis building inspector found that three well-burned 

building tile of 91-inch cross section, with two horizontal holes, has 

an average compressive strength of 965 pounds to the square inch.

The degree of vitrification easily obtained would indicate that 

the material is suitable for paving brick, but no attempts are now 

made to produce pavers. Nearly all the vitrified brick are made 

hollow, to facilitate drying and to make them lighter in weight and 

reduce shipping charges. Such hollow brick show a resistance to 

abrasion which, though not such as a paver requires, is encouraging. 

If the mechanical troubles involved in drying and burning larger 

blocks without holes can be overcome, the brick will probably stand 

a good rattler test.

West of Springfield are other outcrops of Cretaceous shales. A 

shaft sunk here in exploration for coal many years ago passed through 

a thick series of shale beds, a few of which contained enough organic 

inatter to produce dark colors but not enough to interfere with their 

use as clay. The banks of Cottonwood Eiver and its tributary 

gulches have exposed similar shale. Mr. Ochs has recently built a 

tile plant west of Springfield, adding to his work of making brick. 

All the samples taken required a little more heat for vitrification than
134 CLAYS AND SHALES OF MINNESOTA.

the clay east of Springfield, and all showed a good range of vitrification, which may be taken as favorable indications. All the clays slake 

in a few minutes and become highly plastic with about 31 per cent 

of water. Their tensile strength is 200 pounds to the square inch, 

and they can be dried much more rapidly than the clay at the brickyard east of Springfield. The shrinkage 011 drying is 8 per cent. 

Burning tests resulted as follows:

Cone No.

06

03

01

1

3

6

Color.

Buff... .........................

Salmon. ........................

.....do..........................

Red............................

.....do.................:...:.....

.....do......................\...

Shrinkage.

Per cent. 

1

5

7

8

9

Absorption.

Per cent.

9fi

12

8

6

4

19

The clay is hard after heating to cone 04 (1,958° F.) 3 and reaches 

viscosity at about cone 5 (2,246° F.), with a low porosity over a considerable range. The temperature of viscosity is rather low for sewerpipe clay, but the range of vitrification is excellent. On passing the 

point of fusion the clay swells and becomes blebby. Analyses of the 

clay by F. F. Grout are as follows:

Analyses of Cretaceous shales from deposits west of Springfield.

Chemical analysis.

Silica_______________ 63. 65

Alumina ______________ 17. 27

Iron oxides __________:_ 4. 75

Magnesia _____________ 1. 21

Lime _______________ . 06

Bocla_______________ . 91

Potash________'______ 2.47

Ignition______________ 7.36

Moisture _____________ 2. 03

Titanium oxide __________ . 62

100. 33

Mechanical analysis.

Fine clay _____________ 25.5,

Coarse clay ____:___;_:__ 14V6

Silt ___________ '___i__ 58. 6

Pine sand___ ____^____ 1. 4

Coarse sand__________^ . 5

100.0

The Cretaceous clays of Brown County vary in properties, but 

some of them are very promising, and well records indicate that they 

are present throughout most of the southern part of the county and 

in some places are 200 feet in thickness.

Clay-bearing formations

CARLTON COUNTY.

Recent: Alluvium. 

Pleistocene:

Gray laminated clay.

Red clay of Lake Duluth;

Red drift. 

Huronian: Slates.
CARLTOF COUNTY. 135

A very extensive brick industry has been developed at Wrenshal], 

in Carlton County, where gray laminated clays occur in immense' 

quantities. The existing brick plants are within a short distance of 

the station, but similar clay lies along the railroad half a mile farther 

north and for some distance farther east. Other clays in the county 

have not been much developed, though an attempt was made to use 

the slate at Thomson, which is capable of yielding fancy products.

Along St. Louis River from Cloquet to Carlton Huronian slates 

crop out in especially favorable position in glaciated knobs, projecting above the general level of the drift. These slates are not now 

used, and attempts to use them in the past do not appear to have been 

very successful, though details are not available. The slate is metamorphosed and has developed good secondary cleavage (see PL XIII, 

B] , though it is not very satisfactory as roofing material. The variation from a graywacke to a slate is irregular, and the folding and 

crumpling of the formation make it difficult to predict exactly where 

good slates are available; but during a hurried trip over the district 

many convenient places were seen where the thickness is very great 

and there is no overburden. The hardness of the material would increase the difficulty of quarrying, but" all other conditions seem to be 

favorable. The slate is of course nonplastic and has very little tensile 

strength and no air shrinkage. The crushed material requires only 

9 per cent of water for molding. At cone 5 (2,246° F.) it is thoroughly vitrified and dark red. The superintendent of the St. Louis 

River Slate Brick Co., organized in 1892, had a patent or secret process 

which he tried out with considerable thoroughness, but nothing has 

been done for the last 20 years. The product was red pressed brick 

of excellent quality. They were used in several Duluth buildings 

that are still standing. One disadvantage of the brick was their 

high specific gravity, which increased the freight rate per thousand 

brick.

Fancy brick could readily be made from this slate by the addition 

of some of the more easily fusible drift clays of the neighborhood. 

Laboratory tests indicate that the clay of Wrenshall, which occurs 

in so great quantity a few miles east, or, even better ^ the red bouldery 

clay that is widely distributed in the region around the west end of 

Lake Superior, would be excellent for bonding clay. With 5 per cent 

of red clay the mixture becomes so hard at cone 06 (1,900° F.) that 

it can not be scratched with a knife, and at cone 5 (2,250° F.) it is 

still undeformed. The color ranges from light to dark red between 

these temperatures, and the appearance changes from that of common 

red brick to that of a thoroughly vitrified klinker brick. Brick-made 

from a mixture of these clays with slate crushed to lumps a quarter of 

an inch or less in diameter closely imitated the popular rough ap-
136 CLAYS AND SHALES OF MINNESOTA.

pearance of klinker brick. Fancy brick of this type would be in 

great demand in the cities at the head of the lake. By using the 

proper proportion of the fusible red clay the rough lumpy brick may 

be given a glazed appearance, and the excellent quality of the resulting product seems to promise well for this deposit.

Deposits around the west end of Lake Superior make it certain 

that during the retreat of the ice front the Lake Superior basin was 

dammed, so that water was raised 500 to 700 feet above the present 

lake. In this lake, known as Lake Duluth, which extended far out 

into Carlton County, the melting ice dropped red-drift clays and 

gravel, and into it glacial rivers brought various sediments. Water 

sorting formed laminated clays, to which floating ice contributed some 

boulders. Streams from the gray-drift areas to the west produced 

gray clays. The ice itself brought red bouldery clays.

The red bouldery clays have thus far been little used in Minnesota 

but are worthy of more attention both as fusible slips and as plastic 

binders for lean clays near by. In Carlton County they are at least 

60 feet in-thickness and many miles in extent. The southernmost of 

the accessible outcrops is 4 miles east of Moose Lake, on the Minneapolis, St. Paul & Sault Ste. Marie Railway. Occurrences at Hoiyoke are especially favorable, and there is an interesting deposit 

within 2 miles of Wrenshall, where the gray laminated <;lays are also 

well represented. The deposit is no doubt continuous between all 

these localities. Characteristically the clay lacks the pronounced 

lamination and sandy layers of most red glacial lake and river clays. 

The chief distinction between it and common pebbly red deposits of 

the northeastern drift is its greater content of clay and'its faint 

stratification. It is found on all sides of the western part of Lake 

Superior basin, where a deposit having a glacio-lacustrine origin 

would be expected. As stated above (p. 97) Mr. Leverett regards this 

clay not as a strictly lacustrine deposit-but as composing a glacial 

moraine deposited in a lake.

The clay slakes in two minutes and shows a very high plasticity, 

requiring 27 per cent of water for molding. Its tensile strength is 

nearly 100 pounds to the square inch, but it cracks rather seriously if 

rapidly dried. Its air shrinkage is 9 per cent. -A sample taken near 

Holyoke gave the following results in a burning test:

Cone No.

010

06

02

2

Color.

Red..........:.................

.....do............. .............

.....do..........................

Shrinkage.

Per cent. 

1

3

8

9

Absorption.

Per cent. 

16

10

2

1
CAELTON COUNTY. 137

The clay is hard after burning to any of the specified temperatures 

and reaches viscosity at about cone 1 (2,102° F.). Rapid heating 

causes black cores and consequent swelling. Oxidation is a little slow 

on account of the fineness and 'density of the clay. These points can 

easily be cared for in burning: The low fusing temperature of the 

clay and its fineness make it desirable as a slip glaze for brown semirefractory ware. This clay mixed with the Huronian slate, as mentioned above, could be used for making fancy brick.

On account of its very high plasticity and shrinkage the clay was 

tested after being mixed with sand, which is abundant in the neigh- 

-borhood. For common or vitrified brick the addition of sand improved the clay both in working and shrinkage. With 50 to .75 per 

cent of added sanol the range of vitrification is still high enough to be 

satisfactory and the temperature of viscosity is somewhat raised to 

about cone 4 (2,210° F.).

The following analysis of clay of this type from Carlton County 

was made by A. W. Gauger. (See also Cook County, pp. 145-146.)

Analysis of red clay of Lake Dulutn.

Silica-_______________________________ 50. 51

Alumina ______________________________ 15. 89

Iron oxides : ______ ____ 8.21

Magnesia________________________________ 5.14

Lime_________________________________ 7.10

Soda_________________________________ 1. 66

Potash.1 _______________________________ 1.87

Moisture________________________________ 2. 44

Loss on ignition_______________________ _ 7. 35

Titanium oxide________________________ _ . 26

100. 43

The gray laminated clays washed into Lake Duluth from the west 

contain few boulders. They are most abundant in the vicinity of 

Wrenshall, where five large, successful plants have been in operation, 

each utilizing essentially the same type of clay, which has been developed to a depth of about 50 feet and explored to a depth of 80 feet. 

In the uppermost few feet the clay is more or less disturbed and 

mingled with pebbles, but this condition gradually disappears with 

increasing depth and the stratification0 becomes very regular. Gentle 

undulations such as are seen in the laminated clay north of Minneapolis (see p. 114) occur here also. (See PL I, p. 20.) The blue and 

gray parts of the clay burn cream-colored; but the top part of the 

deposit, which has not only been disturbed physically but has 

apparently been chemically altered by leaching, is red and burns red. 

In the upper 10 to 15 feet the disseminated lime has apparently been
138 CLAYS AND SHALES OF MINNESOTA.

segregated into concretions, which, however, are in few places abundant enough to be a serious handicap. The clay extends generally 

under the flat region and is seen along the sides of many deeply cut 

ravines draining into St. Louis River. It extends up the slope about 

300 feet above the flat on which Superior and West Duluth are built. 

The detailed structure of the clay is similar to that of clays along 

Minnesota and Mississippi rivers, but its occurrence in a lake basin 

in a place where no river could have flowed, as well as its wide extent, 

indicate that .it is a lake deposit rather than river silt.

The clay slakes in three minutes and shows fairly high plasticity, 

requiring 23 per cent of water for molding. Its air shrinkage is 4 

per cent and its tensile strength 175 pounds to the square inch, even 

when rapidly dried.

Tests by the Bureau of Standards show that it burns buff at low 

temperatures but becomes greenish yellow when well vitrified. It 

has a short range of vitrification, the porosity dropping from 42 

per cent to nearly zero in about 100°. It is not safe to try to vitrify 

this type of clay, but it makes excellent common brick. An analysis 

by A.'W. Gauger is as follows:

Analysis of clay from WrensJiaH.

Silica ____________________.___________ 48.79

Alumina ___________________-____________ 32.08

Iron oxides_________________.___________ 4. 60

Magnesia ______ __ ___.____________ 5. 54

Lime ____________________.___________ 12.10

Soda __________ ____.____._____________ . 2.. 22

Potash ___________________.___________'_' 2. 05

Loss on ignition______________.____________ 12. 02

Moisture __________________.__________ 1. 26

Titanium oxide _____________.___________ .29

100. 95

The plants have capacities of 40,000 to 140,000 brick a day. Some 

of them find the soft-mud process more favorable, but most of them 

use stiff-mud machines. Very little hollow ware is produced. Red 

brick are obtained only when the upper layers of clay are used 

separately. If clay from the whole deposit is used in proportion as 

it is exposed, the one-fourth o°f red-burning clay is not sufficient to 

affect the color of the three-fourths of cream-burning clay. The 

quality of the products as tested by the experimental engineering 

department of the University of Minnesota is as follows:
CARLTON COUNTY. 

Results of tests of Wren-shall l>ricJc.

139

Nature of brick.

Stifi-mud, red. .................................................

Crushing strength 

(pounds per 

square inch).

Wet.

2,809 

2,834 

4,474 

3,354 

3,770

Dry.

2,166 

4,762 

5,888 

3,233 

5,247

Modulus 

of 

rupture.

982 

926 

1,409 

679 

1,189

Absorption 

(par 

cent).

29.4 

21.7

18.5 

14.3 

13.3

Keel drift of the common pebbly character just north of Barnum 

was used some years ago for red brick. The whole region around 

Barnum seems to consist of pebbly clay, and the pebbles must be 

crushed before the clays will make satisfactory products. The clay 

slakes in five minutes* and has fairly high plasticity, requiring 21 

per cent of water for molding. Its air shrinkage is over 6 per cent 

and its tensile strength about 75 pounds to the square inch. Burning 

tests at the Minnesota School of Mines experiment station resulted 

as follows:

Cone No.

05

02

5

Color.

Ued............... .............

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

2

7

Absorption.

Per cent. 

11

6

The clay becomes hard at cone 04 (1,958° F.) and seems to contain 

enough organic matter to develop black cores and to swell greatly 

if rapidly heated; but if thoroughly oxidized it will stand a temperature of about cone 2' (2,138° F.). Clay of this type is widespread 

throughout the eastern part of the State.

Alluvium has been deposited along St. Louis River in the few 

places at which there are flood plains. At the place where Cloquet 

stood before the fire of 1918 the river flows through an extensive flat. 

Before the lumber yards extended over most of the flat a small brickyard produced some red soft-mud brick of fair quality, which were 

used in buildings at Cloquet. The silt from the northeast side of the 

river was sampled to determine its quality. It slakes at once and 

has low plasticity, requiring 21 per cent of water for molding. Its 

air shrinkage is 3£ per cent, and its tensile strength is over 100 

pounds to the square inch, even when rapidly dried. On being burned 

it gave the following results:
140 CLAYS AND SHALES-OF MINNESOTA.

Cone No.

04

02

1

3

5

Color.

.....do..........................

Red.............................

.....do..........................

Shrinkage.

Per cent. 

1

2

5

7

Absorption.

Per cent. 

19

13

11

7

The clay becomes hard at cone 02 (2,030° F.) and reaches viscosity 

a little above cone 4 (2,210° F.). It should burn to an excellent hard 

red brick.

CARVER COUNTY.

Clay-bearing formations

["Recent: Alluvium.

I Pleistocene:

j Gray laminated clays.

I Gray drift.

The only place in Carver County where brick is being manufactured is at Chaska, on Minnesota River. Gray laminated river clays 

of the glacial River Warren, which was the outlet of Lake Agassiz, 

are used; and the gray drift and alluvium are not exploited in competition with this larger and better deposit.

The section at the clay pit consists of 20 to 40 feet of partly stratified sand and gravel, underlain by 100 to 200 feet of dark-gray clay. 

These beds extend under the river valley for hundreds of acres. 

The laminated character of the clay shows that it was deposited when 

the river was greatly swollen by the melting of glacial ice. When 

the stream was rapid, sand was irregularly mixed with the clay 

and is now found as pockets, "wells," and streaks. These, however, 

are so scattered that by mixing material from different parts of the 

bank a uniform quality of brick can be produced. The clay slakes in 

one minute and shows a fairly high plasticity, requiring 28 per cent 

of water for molding. Its tensile strength is somewhat variable, one 

briquet showing 200 pounds to the square inch and even the sandy 

layers yielding some strong briquets. Two pieces of clay when 

pressed together had almost no adhesion, showing, if the test is reliable, that defective auger structure may be developed. The average clay shows a shrinkage of 7.5 per cent on drying, but admixture 

of some of the particularly sandy layers reduced this to 4.5 per cent, 

apparently without injuring the product. The clay burns buff up 

to the temperature of viscosity and can be burned hard with very 

little shrinkage. Its absorption is over 20 per cent, even in wellburned brick as found on the market, but laboratory tests show that 

this may be reduced before reaching the melting point. The clay 

became hard at cone 02 (2,030° F.) and viscous at cone 4 (2,210° F.); 

and a half-and-half mixture with material from the particularly
CHIPPEWA COUNTY. 141

sandy layers gave very similar results. Four plants using this clay 

are in successful operation, employing over 300 men. All are under 

one management and use essentially the same method, having permanent oblong updraft kilns. Their aggregate capacity varies from 

45,000 to 140,000 brick a day; in a recent year they produced 50,- 

000,000 brick. Coal is the only fuel available. A large proportion of 

the product is solid cream-colored brick, some of which are made in 

the soft-mud machine. Three of the plants have facilities for making hollow ware, and three are provided with steam shovels for digging the clay. Of some products from Chaska tested by the Minneapolis building inspector two sewer brick showed a crushing 

strength of 4,250 pounds to the square inch; four miscellaneous brick 

in one set gave an average strength of 1,600 pounds; a set of 14 

bricks, probably selected with some care (though this was not stated), 

had an average crushing strength of 2,635 pounds; two hollow 

bricks had a strength of 236 pounds; and one hollow tile with three 

horizontal openings had a strength of 158 pounds to the square inch. 

The experimental engineering department of the University of 

Minnesota found that jive soft-mud well-burned Chaska brick, tested 

dry, had an average crushing strength of 2,081 pounds to the square 

,inch, a modulus of rupture of 658 pounds to the square inch, and 

. an absorption of 22.2 per cent. Hollow building blocks had an average strength of 505 pounds to the square inch, a modulus of rupture 

of 600 pounds, and an absorption of 10 per cent. The wet brick had 

M abqut the same strength as the dry.

'' ' '\ CASS COUNTY.

{

Recent: Lake clays. 

Pleistocene: 

Gray drift. 

Red drift.

Cass County is covered with gray drift and outwash, except in its 

tAvo southeastern corners, where red drift is exposed. Lake clays of 

value may be discovered near White City. The clays of the gray 

drift would require cleaning before use.

CHIPPEWA COUNTY.

Clay-bearing formations.

Recent: Alluvium. 

Pleistocene:

Gray laminated clay.

Gray drift. 

Archean: Residual clay.

Throughout Chippewa County the gray drift is abundant and is 

rarely free from pebbles. At Montevideo it was abandoned for river
142 CLAYS AND SHALES OF MINNESOTA.

clays, which were in turn abandoned. Considerable clay is visible 

in the flat near the mouth of Chippewa River. Opposite Minnesota 

Falls and also at Tunsberg 1 are small outcrops of granitic residual 

clays that are not likely to be of much value. Meinzer 2 reports well 

records showing 70 feet of white Cretaceous and Archean clays at 

Montevideo at a depth of several hundred feet.

A railroad cut opposite Granite Falls was deep enough to expose 

unweathered gray drift below the yellow. Both the yellow and gray 

drift contain, numerous limestone and other pebbles and about the 

same proportion of sand as the gray drift used at Hutchinson to 

make draintile. The clays slake in 2 minutes and are highly plastic, requiring 17 per cent of water for molding. Their tensile 

strength is about 150 pounds to the square inch, and their shrinkage 

on drying is less than 4 per cent. These clays require a temperature 

for vitrification somewhat above the average. .The yellow and gray 

clays are essentially similar.

About 5 miles northeast of Appleton and a mile east of the Great 

Northern Railway a well reveals a plastic blue clay which is apparently of the laminated type. It slakes at once and shows a 

high plasticity, requiring 34 per cent of water for molding; its air 

shrinkage is 4 per cent; and its tensile strength is more than 150 

pounds to the square inch but is greatly reduced by rapid drying. 

When tested at the University of Minnesota this clay proved to be of 

very poor quality. The brick burn salmon-colored and show very 

little shrinkage up to the temperature of cone 02 (2,030°" F.), where" 

they had an absorption of 28 per cent. By raising the temperature 

40° the shrinkage increased to 16 per cent, the absorption decreased' 

to 2 per cent, and the clay became viscous. It is certainly not safe to 

burn this clay hard.

CHISAGO COUNTY.

Clay-bearing formations

Pleistocene:

Red laminated clay.

Gray drift

Red drift. 

Cambrian.

At Rush City red brick were made from till for several years. A 

particularly good clay, apparently glacial outwash, was developed 1^ 

miles south of the town. It may have been derived from the ice 

sheet that brought the gray drift, but it contains enough ferruginous 

material from the northeast to make it burn red, and it is here classed 

with the red drift. The Avorkable clay is more than 8 feet thick./ -.It.

1 Winchell, N. H., Geology of Minnesota: Minnesota Geol. and Nat. Hist. Survey Final 

Rept., vol. 2, p. 211, 1888.

2 Meinzer, 0. E., U. S. Geol. Survey Water-Supply Taper 250, p. 153, 1911.
CHISAGO COUNTY. 143

slakes at once and is highly plastic, requiring 27 per cent of water 

for molding. Its tensile strength is between 50 and 75 pounds to the 

square inch, and its air shrinkage between 5 and 6 per cent. Burning: tests resulted as follows:

Cone No.

06

05

01

3

4

Color.

.....do..........................

Red............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

0

5

7

9

Absorption.

Per cent. 

20

IS

10

0

2

The clay becomes too hard to be scratched with a knife at cone 

05 (1,922° F.) and begins to be viscous at cone 5 (2,246° F.). It 

has thus a range of vitrification of over 300° and should burn to a 

very hard, excellent product. Brick were made here for several 

years and were shipped over a spur track to the Northern Pacific 

Eailway, half a, mile away. It is said that the work was abandoned 

on account of the difficulty in getting labor, but if the clay is as 

excellent as it appears it should warrant exploitation under favorable conditions.

Hills of gray drift cover much of Chisago County. A sample of 

clay taken at Center City from an exposure 40 feet thick slakes in 

two minutes and is highly plastic, requiring 19 per cent of water for 

molding; its air shrinkage is less than 4 per cent; and its tensile 

strength is over 150 pounds to the square inch. This clay has 33 

per cent sancl and 7 per cent lime, as against 30 per cent sand and 9 

per cent lime in the material profitably used at Hutchinson. The 

difference should not be important, as the range of vitrification of 

the two clays is essentially the same. The clay burns salmon-colored 

and becomes buff at higher temperatures.

A small brickyard was started many years ago in sees. 14 and 15, 

T. 35 N., R. 22 W., just west of North Branch, on some patches of 

red drift that come to the surface through the prevalent gray drift.

At Taylors Falls red laminated clay is exposed on the Wisconsin 

side but is covered with gray drift in Minnesota. Similar red laminated clay, exposed near Sunrise, was used in 1856. These clays 

crop out along St. Croix Eiver in Chisago County and near by and 

are of the type so extensively used at Menomonie, Wis.

Siliceous shale of Cambrian age crops out in a layer not more 

than 10 feet thick in the bluffs below The Dalles at Taylors Falls, 

about 30 feet below the railway track. Though of fair quality it is 

probably too thin and inaccessible to use. It softens in water but 

does not slake. After grinding, it can be molded with 20 per cent 

of water and develops a strength of over 50 pounds to the square
r

144 CLAYS AND SHALES OF MINNESOTA.

inch. Its air shrinkage is 3.5 per cent. As burned at the Minnesota 

School of Mines experiment station, it gave the following results:

Cone No.

05

03

01

1

3

Color.

.....do..........................

.....do..........................

Red.............................

.....do..........................

Shrinkage.

Per cent. 

0

0

1

. 5

6

Absorption.

Per cent. 

17

16

15

7

2

The clay becomes too hard to scratch with a knife at cone 03 (1,994° 

F.) and becomes viscous at cone 3 (2,174° F.), a range of 180° F. If 

abundant it could be used for hard-burned products.

CLAY COUNTY.

Clay-bearing formations

Pleistocene:

Silts of the Red Eiver valley.

Gray drift 

Cretaceous: Shale.

Dark-blue Cretaceous shales were found at Fargo, N. Dak., across 

the river from Clay County, at a depth of 220 feet and are known to 

be more than 40 feet thick. They no doubt extend into Clay County.

At Moorhead several plants have been built to use the thin upper 

leached and oxidized portion of the silts of the Red Eiver valley. 

Only 16 inches of the clay is of good quality, and an admixture of 

the underlying clay causes too much trouble in drying. To work 

so thin a clay a large area is necessary, and most plants strip the few 

inches of soil from the workable clay and spread it over the shallow 

pit from which the clay has already been removed. This allows the 

continuous use of the soil for farming, except over the few acres that 

are being actively worked. The clay slakes in one minute, and its 

plasticity is low, as it requires 22 per cent of water for molding. Its 

tensile strength is well above 100 pounds to the square inch, even 

when rapidly dried, and its air shrinkage is 5 per cent. As burned at 

the University of Minnesota it gave the following results:

Cone No.

04

01

2

4

5

Color.

Buff............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

0

. 1

3

7

Absorption.

Per cent. 

33

33

29

25

15

The clay becomes hard at cone 3, although satisfactory brick can be 

made at somewhat lower temperatures. Its fusion temperature was
COOK COUNTY. 145

rather higher than that of most of the clays that contain so much 

lime, and its range of vitrification was nearly 200°. The plants that 

have been operated in this neighborhood made soft-mud bricks on a 

rather small scale. They are no longer operated.

At Barnesville samples were taken at two points, one a mile east 

of the town and one about the same distance north, at an old brickyard. Each sample included several feet of the blue clay as well as 

the very thin layer of leached material on top. One of them contained a little gypsum in scattered crystals. The clays slake in two 

minutes and are highly plastic, requiring 29 per cent of water for 

molding. When very carefully dried their strength is more than 100 

pounds to the square inch, but they crack to pieces unless care is 

used. Furthermore, a test of the adhesive quality of pieces of wet 

clay pressed together shows that the use of an auger machine might 

result in very defective structure. The shrinkage on drying is 7 per 

cent. A burning test resulted as follows:

Cone No.

02 04 '

1

2

Color.

Buff............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

2

7

13

Absorption.

Per cent. 

27

20

13

4

The clay is too hard to be scratched with a knife after burning to 

cone 02 (2,030° F.) and reaches viscosity about cone 3 (2,174° F.). 

The clay from sec. 29, T. 137 N., R, 45 W., about a mile east of 

Barnesville, behaves slightly better in the fire than that north of the 

town.

CLEARWATER COUNTY.

Pleistocene gray drift is the only clay reported in Clearwater 

County, and it needs the usual cleaning before it can be used successfully. Lakes are notably less abundant than in neighboring counties.

COOK COUNTY.

Red clays are reported to occur in considerable abundance in Cook 

County and are apparently like the so-called " water-laid moraine " 

so common around the west end of Lake Superior. A sample sent to 

the University of Minnesota in 1897 by Chester McKusick was analyzed by C. P. Berkey, with the following result:

Analysis of red clay from Cook County.

Silica ________________________________ 53. 390

Alumina ___________________.________ 14. 259

Iron oxide_______________________________ 13. 706

643108 19 10
146 CLAYS AND SHALES CXF MINNESOTA.

Lime ___ ____________________________ 3. 033

Magnesia___________-_________-_________ 1. 740 

Alkalies____________________________ Not reported. 

Combined water _________________________ 9. 995 

Carbon dioxide_______________:___________ 4.278

100. 401

 Clay-bearing

COTTONWOOD COUNTY.

[Recent: Lake clay, 

formations ! Pleistocene: Gray drift. 

[Cretaceous: Shale.

About half a mile from Windom station a deposit of gray drift has 

been explored to a depth of 8 feet over a great many acres, and in 

parts of the neighborhood is undoubtedly thicker. It is covered with 

sandy drift to a depth of 1 to 8 feet but is near the surface over many 

acres. The clay slakes in two minutes and is fairly plastic, requiring 

24 per cent of water for molding. Its tensile strength is about 150 

pounds to the square inch and its air shrinkage is 6 per cent. As 

burned by the Minnesota School of Mines experiment station it gave 

the following results:

Cone No.

03

01

1

3

Color.

Brown. ........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

4

7

8

Absorption.

Per cent. 

20

17

5

1

The clay burns hard at cone 03 (1,994° F.) and is viscous at about 

cone 3 (2,174° F.). An attempt was made to use this clay in the 

Windom Brick & Tile Factory, and it is said that the buff or yellow 

brick produced have stood satisfactorily in buildings in the neighborhood.

A lake clay from the northeast side of Bingham Lake, which has 

been used by the Bingham Lake Brick & Tile Co. since 1904, extends 

for only a few acres to a depth of about 9 feet. A few small limestone pebbles have been washed into the upper layers of the clay, 

but the main part of the deposit is entirely free from them. The 

clay slakes in one minute and is highly plastic, requiring 32 per 

cent of water for molding. The tensile strength is more than 125 

pounds to the square inch, but this is decreased somewhat by rapid 

drying. The air shrinkage is 7 per cent. As burned by the Minnesota School of Mines experiment station this clay gave the following 

results:
CROW WING COUNTY. 147

Cone No.

04

03

02

01

2

Color.

Rod. ...........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

2

3

9

Absorption.

Per cent. 

22

20

19

0

The clay becomes too hard to be scratched with a knife at about cone 

03 (1,994° F.) and reaches viscosity at cone 2 (2,138° F.): The company specializes in the manufacture of tile rather than brick, producing about 650,000 tile a year.

Cretaceous shale has been reported in the records of some wells 

drilled in this county. It lies below about 300 feet of drift and sand.

CHOW WING- COUNTY.

Clay-bearing xormations

Pleistocene:

Gray la rn i nated clay. 

Red drift.

About a mile northeast of Brainerd a yard was started in 1876 

to produce creair-colored 'brick from laminated clays exposed in the 

Mississippi River bluff near the dam. The clay is overlain by about 

20 feet of sand, and where protected by the sand from weathering is 

uniformly gray in color and conspicuously laminated. The work 

has been abandoned, as most of the easily accessible clay has been 

used up, and the removal of 20 feet of sand to 'obtain 30 feet of clay 

did not appear to be profitable. The clay is of excellent quality, and 

either this or some neighboring deposit may yet be used, though exposures are not numerous and none are reported closer to the town.. 

The clay slakes at once and shows fairly high plasticity, requiring 

24 per cent of water for molding. Its air shrinkage is 4 per cent and 

its tensile stength well above 100 pounds to the square inch, evenwhen rapidly dried. Burning tests by the Minnesota School of Mines 

experiment station gave the following results:

Cone No.

02

1

2

4

Color.

Buff...........................

.....do.........................

.....do... ......................

.....do.........................

Shrinkage.

Per cent. . 

1

2

2

7

Absorption.

Per cent. 

25

22

22

11

The clay becomes too hard to be scratched with a knife at cone 01 

(2,066° F.) and reaches viscosity at cone 4 (2,210° F.).

In 1886, at about the time the clay along the river was abandoned, 

an outcrop of similar laminated material was found a few hundred 

yards to the east, where a tributary stream had eroded the overlying 

sand. A brickyard is now in operation on this deposit, and the mate-
148 CLAYS AND SHALES- OF MINNESOTA.

rial found is essentially similar in character to that described above, 

although its upper part has been leached and oxidized yellow. It 

seems somewhat more sandy and burns to a red brick. The bottom 

clay, not used at present, will burn buff. The clay is probably available without too much overburden under about 200 acres of land. 

It slakes in 4 minutes, is highly plastic, and requires 24 per cent of 

water for molding. Its tensile strength is only about 50 pounds to 

the square inch, and its air shrinkage is 8 per cent. Burning tests 

resulted as follows:

Cone No.

05

03

1

Color.

Salmon ........................

'.....do.........................

Red............................

Shrinkage.

Per cent. 

1

3

C

Absorption.

Per cent. 

10

12

3

The clay becomes hard after burning at cone 05 (1,922° F.) or less 

and viscous at cone 1 (2,100° F.). This is a better range of vitrification than that of the average gray laminated clay. The plant has a 

capacity of 20,000 brick a day, but works only half-day shifts. It 

produces sand-mold common brick. Wood is used for fuel. The 

clay would probably yield hollow brick and fireproofing if properly 

treated.

An effort was made to find clay suitable for common brick near 

the new towns springing up on the Cuyuna iron range. Two types 

of clay are available the red drift and its worked-over material in 

numerous swamps and along lake shores. A sample of red drift 

from the boat landing near the edge of the town of- Deerwood gives 

good red brick. The clay slakes readily, is very plastic, and has 

a tensile strength of about 100 pounds to the square inch. It 

becomes hard at a low temperature, with moderate to high shrinkage, but does not become viscous if burned slowly and well oxidized. 

Its range of vitrification is from cone 010 (1,742° F.) to cone 01 

(2,066° F.). If an attempt is made to utilize large bodies of the 

clay it will probably be found necessary to use rolls to remove pebbles, 

but these pebbles are not limestone and in the sample taken they did 

not prove injurious.

The nature of the swamp clays along the Cuyuna range is probably well shown by a test made on clay from the south side of the 

lake at Deerwood station. The spur track to the Adams mine passes 

through a cut mostly in a clay bank about 100 paces long. The deposit is roughly stratified and sandy, but the more argillaceous parts 

probably represent the types of clay formed by wash from, the red 

drift of the neighborhood. The clay slakes at once, and the sandy 

portions have a tensile strength of only about 60 pounds to the square
DAKOTA COUNTY. 149

inch. The brick are salmon-colored at low temperatures and become 

red and hard below cone 02 (2.030° F.). They reach viscosity only 

when heated above cone 3 (2,174° F.). The shrinkage in drying and 

burning is small, but the brick are rather,porous. They should be 

wholly satisfactory if burned to cone 02 (2,030° F.).

Samples of several similar clays have been sent in from a swamp 

deposit overlying manganese iron ore at the Northland mine in sec. 

20, T. 47 N., R. 28* W. This deposit must be moved in preparing 

for mining operations. One sample contained a few limestone 

pebbles, but two others made excellent brick. They were hard at 

1,850° F. and reached viscosity at 2,050° F. Some of these available 

swamp clays should be used.

DAKOTA COUNTY.

Clay-bearing formations

Recent: Alluvium. 

Pleistocene:

Loess.

Red and gray drift. 

Ordovician: Decorah shale.

The Pleistocene and Recent clays are not important in Dakota 

County. A small brickyard at West St. Paul, about half a mile from 

the large plant of the Twin City Brick Co., uses leached sandy drift 

which possibly originated as glacial outwash. It is of variable 

thickness but covers many acres. It slakes at once and has rather 

low plasticity, though it requires 28 per cent of water for molding. 

Its tensile strength is over 100 pounds to the square inch, and its 

air shrinkage is less than 4 per cent. Burning tests resulted as 

follows:

Cone No.

04

01

1

3

5

Color.

Red............................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

2

5

7

7

Absorption.

Per cent. 

18

16

10

8

The clay becomes hard at cone 01 (2,066° F.) and just reaches viscosity at cone 5 (2,246° F.). It should therefore be readily burned to 

a very excellent hard product. The plant that has been working this 

deposit was relatively small and has been practically abandoned because of unfavorable shipping conditions and proximity to large 

brick plants.

The principal clay-bearing formation in Dakota County is the 

Decorah shale, which is best developed along the Mississippi River 

bluffs at West St. Paul. Only a small patch is exposed in West St.
150 CLAYS AND SHALES OF MINNESOTA.

Paul (see PI. X), but this patch is remarkably well situated economically and has the maximum thickness attained by the formation. In West St. Paul and Mendota the generalized geologic section is as follows:

Section of Decorah shale at West St. Paul.

Feet 

Drift _________________________________ 65

Decorah shale:

Shale and limestone (many layers of limestone) 40 

Limestone, hard __________ _ 3 

Shale (1-inch lenses of limestone)_ _____ 40 

Limestone _ _ 11 

Shale_____________________________ 3

Platteville limestone ___ 12

The lower part of the large body of shale seems to differ slightly 

in character from the higher shale beds which alternate with the 

limestone. v(See fig. 18.)

Drift 20-50 ft

Green shale with many thin layer? 

and lenses of limestone 40 ft

Limestone 3 ft

Green shale with limestone 

Increasing toward the top 40 ft

Gray shale 2 in. 

c-Limestone 18 ia 

Green shale 2 ft 

Platteville limestone 12 ft

St Peter sandstone 

FIGOEE 18. Geologic section at shale quarry, West St. Paul.

The lower shale is smooth and green in color, slakes in two minutes to scales and small lumps, and is very highly plastic. It requires 28 per cent of water for molding, has a tensile strength of 

nearly 200 pounds to the square 'inch, and is unaffected by rapid 

drying. Its tensile strength is remarkable in that two pieces which 

have been cut apart, as by the auger machine, readily adhere with 

about as much strength as before, without application of very great 

pressure. This eliminates most of the common defects of bricks 

made in Minnesota. The air shrinkage of this clay is less than 6 per 

cent. If rapidly burned it tends to form black cores, with the conse-
DAKOTA COUNTY. 151

quent swelling and destruction of the brick, but if carefully oxidized 

in the early part of the process the results are as follows:

Cone No.

010

06

04

05

Color.

.....do..........................

Red............................

Shrinkage.

Per cent. 

4

6

Absorption.

Per cent. 

12

9

The clay burns too hard to be scratched with a knife at cone 010 

(1,742° F.) and is not yet viscous at cone 02 (2,039° F.) if burned 

very slowly to avoid black cores. In the laboratory tests an efflorescence appeared on the brick taken from the furnace which might indicate a tendency to the production of " kiln white.*'

The upper shale is picked over by hand at the plant, to separate 

most of the limestone layers and lenses, before it is sent to the 

crushing machine. It gives a product of essentially the same sort as 

that from the lower shale, except that the colors are lighter, probably 

owing to the presence of some lime that is not completely separated, 

and possibly also to a difference in the amount of iron present. The 

clay slakes irregularly, owing to variations in the amount of calcareous cement, and needs to be ground before tempering. With 23 

per cent of water it is very highly plastic. Its shrinkage and strength 

are similar to that of the lower shale, 

follows:

A burning test resulted as

Cone No.

010

05

1

3

Color.

Red............................

Shrinkage.

Per cent. 

0

1

1

2

Absorption.

Per cent. 

19

21

13

11

At all temperatures tested (1,688° to 2,200° F.) the clay burns 

to hard fine brick. With rapid heat black cores develop. The porosity 

is never low, but with careful oxidation the brick can be heated above 

cone 3 and thoroughly vitrified without danger of loss. By changing 

the atmosphere in the kiln toward the end of the burn a variety of 

colors can be produced. The range of vitrification for both clays is 

very great and is surprising in a clay of such low fusion temperature.

The following analyses of Decorah shale have been made by F. F. 

Grout:
152 CLAYS AND SHALES OF MINNESOTA. 

Analyses of sliale from West St. Paul.

Chemical analyses.

Soda..........................

Potash........................

1

56.35 

18.63 

6.19 

.65 

.96 

2.97 

.25 

7.37 

2.41 

4.81

100. 59

2

54.66 

24.04 

'6.53 

.66 

.45 

1.08 

.47 

5.37 

2.35 

5.15

100. 76

3

50.81 

20.25 

5.18 

.50 

4.05 

2.13 

.28 

5.69 

2.16 

8.92

99.97

Mechanical analysis of lower shale.

Fine clay. . ...................

Silt...........................

37.8- 

13.2 

46.8 

1.5 

.7

100.0

1. Lower shale, sampled at the base of the brick company's quarry.

2. Lower shale, sampled by another company.

3. Upper shale, sampled by another company.

The plant of the Twin City Brick Co., one of the largest in the 

State, is at the boundary between West St. Paul and Mendota. The 

quarry is very extensive, and the kilns have a capacity of nearly 

100,000 brick a day. The company produces brick and hollow ware. 

Brick are" burned to about 2,100° F., the temperature varying considerably according to the type of product desired. The types produced 

vary according to the proportion of upper and lower shale used, to the 

temperature used in burning, and to the supply of fuel and air- at 

the different stages of burning, resulting in oxidation and reduction. Work was begun in this neighborhood more than 20 years ago 

and has progressed with many changes in method and organization, 

and the final consolidation and success have been due largely to the 

present careful management. Market conditions are of course excellent. Details of manipulation have been patented; and ingenious 

devices, especially methods of quarrying and a chain conveyor, 

have been developed that are worthy of careful study by anyone planning to use the Decorah shale. Although the shale burns red 

under normal and laboratory conditions the color can be altered by 

controlling the fuel supply and by shutting off the air supply. Fancy 

brick, front brick, and klinker brick are produced in so great quantities and bring prices so high that the production of common brick 

has practically ceased at this plant. One of the many interesting 

special products is an interlocking tile for building block.

Prof. Talbot, of the University of Illinois, who has tested the 

products made in West St. Paul, reports a crushing strength of 1,100 

pounds to the square inch for hollow block about 4 by 4 by 13 inches 

with horizontal opening and a strength of 3,500 pounds to the square 

inch for hollow block about 4 by 4 by 4 inches with vertical opening. 

The city building inspector of Minneapolis found a crushing strength 

of 900 pounds to the square inch as an average of 10 tests on hollow
DODGE COUNTY. 153

blocks 4£ by 4£ by 12£ inches, and of 3,300 pounds to the square inch 

(minimum 1,775 and maximum 6,250) as an average of 10 tests on 

solid bricks.

DODGE COUNTY.

{

Pleistocene: 

Gray laminated clay. 

Gray drift. 

Ordovician: Decorah shale. '

Gray drift, such as is being worked at West Concord for the manufacture of draintile, covers most of Dodge County but contains 

numerous pebbles. In the eastern part of the county, along the 

headwaters of the branches of Zumbro Elver, the Decorah shale 

and the Galena limestone crop out. The Decorah shale probably 

underlies most of the county and is the most promising formation for 

the manufacture of clay products. It can best be developed in the 

vicinity of Mantorville and Kasson, where it is available within a 

mile or two of the railroad and has only a moderate overburden.

In the brickyard at West Concord a pit has been opened in 8 feet 

of gray drift, which extends over many acres. Some of the land is 

swampy. The pebbles are not so numerous as in the average gray 

drift but they nevertheless caused the failure of an attempt to use 

the clay. The geologic relations, as well as the scarcity of the pebbles, indicate that the gray drift belongs to the older (Kansan) ice 

invasion. After fine grinding, the clay shows low plasticity and requires 22 per.cent of water for molding. Its air shrinkage is 6 per 

cent. As burned by the Minnesota School of Mines experiment station, it gave the following results:

Cono No.

05

01

1

3

5

Color.

Red............................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

I

3

5

6

6

Absorption.

Per cent. 

15

14

8

7

7

The clay becomes too hard to be scratched with a knife at cone 02 

(2,030° F.) and is still undeformed at cone 6 (2,282° F.). The plant 

has a capacity of about 8,000 tile a day. Fine grinding and burning 

to a fairly high temperature would probably make it possible to 

use this clay with satisfactory results. Similar deposits in other 

abandoned. Samples of better clays have been sent in from the West 

Concord Clay Products Co., indicating new discoveries.

Gray laminated clays occur about 2 miles southwest of Hayfield, 

on the Chicago Great Western Railroad, in a deposit that covers
154 CLAYS AND SHALES OF MINNESOTA.

many acres to a depth of 30 feet. This deposit has been exposed 

along the banks of the creek and is mostly blue and sandy, though 

weathered yellow near the top. The clay has almost no overburden 

along the creek but is covered by 15 feet of soil and drift a short 

distance away. A few small pebbles were observed, but they do not 

seem to be a serious defect. The clay slakes in four minutes, shows 

fairly high plasticity, and requires 19 per cent of water for molding. 

Its shrinkage on drying is 4 per cent and its tensile strength about 

150 pounds to the square inch, even when rapidly dried. Burning 

tests resulted as follows:

Cone No.

05

02

01

2

4

Color.

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

2

2

fi

Absorption.

Per cent. 

16

13

11

5

The clay becomes hard after burning to cone 02 (2,030° F.) and 

reaches viscosity at cone 4 (2,210° F.). If market conditions are 

favorable this material should be used.

DOUGLAS COUNTY.

[Recent: Lake clays. 

Clay-bearing formations [Plelstocene . Gray drift

Attempts have been made at many points in Douglas County to 

work the gray drift for common brick, and where the limestone pebbles are less abundant than usual these attempts have met with some 

success. At Alexandria gray drift is found close to the railroads. A 

sample taken at the intersection of the Great Northern and Minneapolis, St. Paul & Sault Ste. Marie lines was very much like the material used at Hutchinson, having almost the same proportion of sand 

and clay and about 7 instead of 9 per cent of lime. Similar drift 

is exposed on Abbotts Point, on the north side of Lake Miltona; at 

Effington; and elsewhere. This drift has been tested and would require cleaning to remove the pebbles.

Near Alexandria two small brickyards are using a few feet of the 

leached upper part of a mass of gray drift from which the limestone 

pebbles are almost entirely gone. This leaching apparently extends 

over several acres, and there should be enough clay to keep a small 

plant in operation for several years. The air shrinkage of the clay 

alone is 11 per cent, but in practice it is greatly reduced by adding 

35 to 40 per cent sand. Most of the available sand, however, contains
DOUGLAS COUNTY. 155

a good deal of lime, and too great additions are decidedly injurious. 

A burning test resulted as follows:

Cone No.

04

01

2

Color.

Red............................

Sh linkage.

Per cent.. 

0

G

8

Absorption.

Per cent. 

18

G

1

If care is used in oxidation this clay can be burned to good hard 

brick. The addition of sand might assist in the oxidation. Viscosity 

is reached at cone 3 (2,174° F.).

At the northeast edge of Alexandria the McKay Brick Co. for 

several years made brick froni a bog deposit extending over 10 

acres and more than 5 feet deep, though so wet that only 5 feet of it 

was used. Very few pebbles have been washed into this deposit. 

The clay is so rich that 10 to 15 per cent of sand is usually added. 

The sand is obtained conveniently at several points in the neighborhood. On the high ground it overlies the clay. The clay slakes in 

two minutes and is highly plastic, requiring 22 per cent of water 

for molding. The tensile strength is 175 pounds to the square inch 

and is well above 100 pounds even if carelessly dried. The air 

shrinkage is 4 per cent. As burned at the Minnesota School of Mines 

experiment station the clay gave the following results:

Cone No.

05

02

1

3

5

6

Color.

.....do... .......................

Red............................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

2

3

5

G

7

7

Absorption.

Per cent. 

15

12

8

6

0

The clay burns too hard to be scratched with a knife at cone 03 

(1,994° F.) and reaches viscosity at cone 6 (2,282° F.). It should 

yield an excellent hard vitrified product, though apparently it 

has been used only for a good grade of common brick. The deposit 

is situated conveniently to the railroad, but a disagreement among 

the owners caused the abandonment of the plant.

In the northwest corner of the county laminated clays occur along 

the shores of Pelican Lake and on the islands in the lake. These 

clays may be partly of glacial origin and partly more recent. The 

outlet of the lake is being eroded and the lake level is being lowered, 

exposing even the recent deposits. The clay, which is overlain by 

3 or 4 feet of sandy soil, contains some ferruginous concretions. It
156 CLAYS AND SHALES OF MINNESOTA.

slakes in three minutes and is very highly plastic, requiring 31 per 

cent of water for molding. Its tensile strength is 180 pounds to the 

square inch but is considerably reduced by rapid drying. Its shrinkage on drying is 7 per cent. Burning tests resulted as follows:

Cone No.

04

02

2

3

4

Color.

Buff...........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

2

13

14

14

Absorpticn.

Per cent. 

27

25

12

1

1

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at cone 4: (2,210° F.). It should be exploited if there is a 

demand for buff brick in the neighborhood.

FABIBAULT COUNTY.

Clay-bearing formations.

Pleistocene:

Gray laminated clay. 

Gray drift.

Gray drift covers almost all of Faribault County but is too pebbly at most places to be of much economic importance. Laminated 

clay has been used at Blue Earth for brick and tile. The only clay 

plant in operation in the county is one at Winnebago that uses drift. 

Blue Earth ships gray laminated clay for use at the Fairmont plant 

in Martin County.

The Blue Earth deposit is known to be 20 feet deep over 10 acres 

and probably has much greater dimensions both vertically and 

areally. It is covered by only 2 or 3 feet of soil and near the top 

includes a layer that contains many lime pebbles. The clay slakes in 

two minutes and is highly plastic, requiring 33 per cent of water for 

molding. Its tensile strength is 200 pounds to the square inch, but if 

rapidly dried the brick check badly. Its air shrinkage is 8 per cent. 

Burning tests resulted as follows:

Cone No.

05

03

01

2

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent.. 

3

6

7

10

Absorption.

Per cent. 

21

12

10

1

The clay burns hard at cone 04 (1,958° F.) and reaches viscosity at 

cone 2 (2,138° F.). It must be well oxidized in burning to avoid the 

formation of black cores.
FARIBAULT COUNTY. 157

This clay was used at Fairmont, in Martin County, by the 

Fairmont Drain Tile & Brick Co., in a plant whose capacity is 

25,000 tile a day. The plant was erected at a cost of $150,000 to use 

a local clay, but this was found to be so full of limestone pebbles as 

to be quite useless. The whole surrounding country was prospected 

for a suitable clay, but only two or three available deposits were 

found. The Blue Earth material is the only Minnesota clay now 

used, but small amounts are imported from Mason City, Iowa. Hollow brick and tile were produced.

Along the Chicago, Milwaukee & St. Paul 'Railway tracks west of 

Winnebago a 30-foot deposit of clay covered by only 2 or 3 feet of 

soil extends over about 70 acres. It contains some limestone pebbles, 

especially near the top, and care has to be used also to avoid auger 

lamination. However, the Winnebago Hollow Block & Tile Co., 

which uses the clay, is said to counteract the effects of the lime very 

satisfactorily by treating the clay with salt. The salt seems to react 

with the lime pebbles, forming around the burned pebble a vitrified 

shell that prevents it from slaking and breaking the product when 

exposed to the weather. The salt also improves the behavior in 

drying. One short scoopful of crude salt is added to 1£ yafds of clay

that has been disintegrated in a hammer crusher. This is followed ° < 

by thorough tempering in pitg mill, feeder, and auger machine. 

Too much salt makes the product " off color " a lighter salmon tint 

than good tile usually are and too little salt does not correct the 

natural defects due to the limestone. The capacity of the plant is 

about six carloads of tile a day.

At Wells, about half a mile north of the station, leaching has 

made the limestone pebbles less numerous than in the average gray 

drift. The clay was sampled in a 10-foot boring. It slakes in two 

minutes and with 27 per cent of water shows medium plasticity. Its 

shrinkage on drying is 6 per cent. Burning tests resulted as follows:

Cone No.

06

03

1

3

Color.

.....do..........................

Red............................

.....do..........................

Shrinkage.

Per cent. 

1

1

7

8

Absorption.

Per cent,. 

24

22

10

3

The clay is hard after burning at cone 03 (1,994° F.) and reaches 

viscosity about cone 4 (2,210° F.). This behavior seems to be desirable, but the presence of a few limestone pebbles would be a serious 

defect, and the amount of clay available without a superabundance 

of pebbles should be determined before a plant is built.
158 CLAYS AND" SHALES OF MINNESOTA.

Clay-bearing formations

FILLMOBE COUNTY.

Pleistocene: Loess. 

Cretaceous: Clay. 

Devonian: Shales (unimportant). 

Ordovician:

Maquoketa shale: Shales (unimportant).

Galena limestone : Shales (unimportant).

Decorah shale: Shale.

Cambrian: St. Lawrence formation: Shales 

(unimportant).

The loess deposits are the only clays notably exploited in Fillmore 

County, but attention should be paid to the widespread Decorah shale, 1

 i

FIGURE 19. Map of Fillmore County. Dotted area is underlain by Decorah shale.

and careful prospecting is recommended for the clays thought to be 

Cretaceous.

The Decorah shale lies at altitudes of 1,070 to 1,130 feet and has an 

average thickness in Fillmore County of only about 20 feet. It is 

exposed principally in terraces and benches along the banks of Root 

River and its branches, and it constitutes a persistent spring horizon. 

(See map, fig. 19.) 'Preston, the county seat, has an abundance of 

these green shales, some of which are favorably situated for development. Chatfield is also well supplied. A sample from Elmira Township proved to work and burn essentially like the shales at West St. 

Paul, though there were some indications that rapid drying might be 

harmful. The range of vitrification is more than 400° F. (cone 010 

to cone 2). The fire shrinkage is about 4 per cent, and the burned
FILLMORE COUNTY. 159

brick have a low porosity. This shale is not used in the county but 

is recommended as the most valuable material available. '

Although clays thought to be of Cretaceous age occur in Fillmore 

County, they have not been developed. Half a mile north of Hamilton, along the road between Fillmore and Mower counties, is a 

clay which seems to be Cretaceous but may possibly have been 

reworked by glacial action. It is nearly 20 feet thick, and is estimated to extend over 30 acres. It is red near the surface but gray 

and carbonaceous below. It is slightly gritty and has a few ferruginous concretions. The clay slakes at once, and is very highly 

plastic, requiring 45 per cent of water for molding. Its air shrinkage 

is 11 per cent. It burns red and becomes hard at a low temperature, 

not over 1,650° F. If rapidly heated, the organic matter causes 

swelling and black cores, but if fully oxidized it can be heated 

above cone 2 (2,138° F.) without deformation, a range of 500° F. 

It should therefore yield good vitrified ware. The absorption is 

easily reduced to less than 4 per cent, but the fire shrinkage is high.

In the eastern two-thirds of Fillmore County the loess forms a 

mantle 2 to 20 feet thick over the Paleozoic formations. Its greatest 

thickness is seen at the bases of the slopes along the valley. On the 

high prairie land it is not so thick but is much more evenly distributed. Many yards now abandoned have used it in the past, as 

at Kushford, Peterson, Whalen, Lanesboro, Fountain, Spring Valley, Carimona, Forestville, Harmony, and Mabel. Material for red 

brick is available at all these places to-day. (See fig. 9, p. 99.)

One of the thickest loess deposits is at Preston, where the following 

section is exposed (see fig. 20) :

Section of loess at Preston.

Ft. In.

Loess loam___ __ _____ 6 

Yellow loess__________________________ 10 0 

Bluish-gray loess (depth unknown)_______._____ 5+

The yellow loess is used; the blue-gray material is reported as 

more plastic and not so well adapted for use in a sand-mold brick 

plant. The deposit is very extensive and will furnish material for 

good common brick for many years. The plant, which is about a 

mile north of Preston, has a capacity of 30,000 brick a day and 

is usually active. The yellow clay slakes in one minute and shows 

a rather low plasticity, requiring 23 per cent of water for molding. Its air shrinkage is about 3 per cent and its tensile strength 

about 150 pounds to the square inch. Burning tests .resulted as 

follows:
160 CLAYS AND SHALES OF MINNESOTA.

Cone No.

04

03

01

1

3

5

Color.

Red............................

.....do.........................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

2

2

4

 7

8

9

Absorption.

Per cent.

18

18

15

8

2

2

The clay becomes hard at cone 04 (1,958° F.) and reaches viscosity 

at cone 4 (2,210° F.).

A sample of the underlying blue clay showed essentially the same 

properties, and there was no reason to think from the tests made

 L'.'' '.' Ly ' ', i- -T.'' ' Yellow loess I0'.' '._ _ ; i- "' _:' "j"* 1:>,':izzulT':''-^r^T.'_; /"- ^'."'^ r -^: ' '' >: ' r' ; '' 

..^li^jj^^l.il-'rii:;^^^

-'_'-;JJ.-.V ',-:? V 1 - 

' f

FIGURE 20. Section of tlie loess at Preston.

that it would not work equally well in the brick machine or in 

burning. It was a little more porous as burned to the low temperature and required a slightly higher temperature to make it steel hard. 

The following analyses, by F. F. Grout, show the siliceous nature 

of the loess exposed at the brickyard:

Analyses of loess from Preston.

Chemical analysis.

Silica_________ 71. 53

Alumina_____ _ - 8. 07

Iron oxide_________ 5. 63

Magnesia___________ 1. 74

Lime_________:______ 2. 36

Soda_______________ .1. 85

Potash ______________ 1. 97

Ignition______________ 4. 50

Water_______________ 2. 30

Titanium oxide ________ .31

100. 26

Mechanical analysis.

Fine clay_ 

Coarse claySilt _____. 

Fine sand _ 

Coarse sand

6.2

8.5

84.. 3

.0

.1

100.0

The other formations in Fillmore County show very little promise 

of containing available shale. The area mapped as Maquoketa shale 

by the Winchell survey is surrounded by Devonian beds, to which
FILLMOEE COUNTY. 161

the so-called Maquoketa is so similar in physical character that it is 

questionable whether this also is not Devonian. It was sampled at 

the .Etna mill. The Devonian material was sampled at the place 

where Bear Creek crosses the line between Mower and Fillmore 

counties. The samples are very much alike and do not differ widely 

from samples of shales from the St. Lawrence and Galena formations in this county. All the beds are thin, with alternating sandy 

and dolomitic layers.

The Devonian shale slakes "to shaly lumps in a few minutes and 

is highly plastic with 20 per cent of water. The tensile strength is 

about 100 pounds per square inch, and the shrinkage on drying is 3 

per cent. Burning tests resulted as follows:

Cone No.

06

02

1

3.

5

6

Color.

Buff.:.........................

.....do.........................

.....do.........................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Percent. 

0

0

0

0

0

Absorption.

Per cent. 

26

26

26

30

20

The clays are burned hard at cone 1 (2,102° F.) and reach viscosity 

at cone 6 (2,282° F.).

The shale from the Galena limestone, sampled on the State road 

in the SE. £ sec. 1, T. 104 N., E. 11 W., southeast of Chatfield, is

Jordan sandstone 3tt <t

FIGURE 21. Section at quarry west of Rushford.

green, and lies in layers not more than 20 inches thick. Its physical 

behavior is almost like that of the Devonian shale, except that it 

requires a higher temperature (cone 4) to produce a hard brick.

The shale of the St. Lawrence formation is exposed in the city 

quarry, half a mile west of Rushford, where it alternates with the 

quarry rock. (See,fig: 21.) The quarry refuse, including the shale, 

64310° 19 11
162 CLAYS AND SHALES OF MINNESOTA.

is used as road material. The sample taken proved to be very sandy 

and showed no shrinkage on drying. A burning test resulted as 

follows: . .

Cono No.

05

01

1

4

6

Color.

.....do.........................

.....do......................'...

.....do.........................

Shrinkage.

Per cent. 

0

0

1

2

Absorption.

PC r cent. 

29

29

28

24

The clay becomes kard after burning to cone 0.2 (2,030° F.) and 

reaches viscosity about cone 5 (2,246° F.).

FBEEBORN COUNTY.

(Recent: Swarnp clay.

 , . f >.. I Pleistocene: Clay-bearing formations < _. , . , ,

I Gray laminated clay.

I Gray drift

The glacial drift in Freeborn County is too pebbly to be of much 

value. The only two clay plants being worked are at Albert Lea and 

Glenville, but ruins of an abandoned plant remain at Conger. Bluegray or yellow laminated clays are used, and new deposits of this 

nature may be discovered at several places in this region.

Within a mile north of Glenville the Acorn Brick & Tile Co. has 

developed a deposit of laminated clay more than 10 feet thick, which 

extends over at least 10 acres. Where exposed the color is oxidized 

to a yellowish brown. The overburden is 2 to 3 feet thick. A few 

limestone pebbles or concretions occur but are not so abundant as to 

.be a serious drawback. The clay slakes at once, shows fairly high 

plasticity, and requires 30 per cent of water for molding. Its air 

shrinkage is nearly 8 per cent, and its tensile strength very low. 

The briquets show flaws that have developed in drying, and careful work would probably be required to avoid auger structure. A 

burning test resulted as follows:

Cone No.

05

04

02

2

3

Color. x

.....do.........................

Red............................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

1

6

10

Absorption.

Per cent. 

25

24

12

2

The brick are hard after burning to cone 04 (1,958° F.) and reach 

viscosity at cone 3 (2,174° F.) The plant that worked this clay pro-
FEEEBOEN COUNTY. 1G3

duces a few brick and a large number of draintile, but it was not 

operating at the time of the writer's visit.

About 2$ miles southeast of Conger is a 30-foot deposit of laminated clay that extends over nearly 100 acres. The section includes 

3 feet of black soil, underlain by 8 or 10 feet of yellowish clay, below 

which is the blue or gray clay, and at the base a' gravelly streak. In 

1904 a company was organized to work this deposit, but shipping 

facilities were unsatisfactory, and the work ceased after about four 

years. Both the gray and the blue clay were used as dug from the 

pit with the addition of some sand, which had to be hauled from a 

distant point. No tests were made to determine whether the blue 

and gray clays were similar.

At Albert Lea the Albert Lea Brick & Tile Co. has a plant just 

north of the city limits, at a hill of perhaps 25 acres. The section 

comprises an overburden of 2 or 3 feet of soil, 16 feet of yellow clay, 

and 26 feet of blue clay. The clay is laminated and shows the usual 

irregularity of clays of this type. The blue clay is more plastic than 

the yellow and slakes rather more promptly, but both are excellent 

in these respects. The blue clay shows a rather low tensile strength, 

about 60 pounds to the square inch, which is greatly lowered on 

rapid drying, as the manufacturers have discovered at considerable 

cost. The yellow clay is much more satisfactory, having a tensile 

strength of over 100 pounds to the square inch, even when rapidly 

dried. The adhesion of two wet pieces of clay after being pressed 

together and dried was not very great, indicating that auger lamination may be serious. This also has been the experience of the company, which has sought to overcome the trouble by adding to the 

clay about 25 per cent of nonplastic material such as cinders, burnt 

clay, or sand. The drying shrinkage of the blue clay is 6 per cent 

and of the yellow 3 per cent, though the experience of the company 

has been that the blue clay dried more safely than the yellow. As 

burned at the Minnesota School of Mines experiment station, the 

clays gave the following results:

Blue clay.

Cone No.

06

02

2

Color.

.....do.........................

Shrinkage.

Per cent. 

2

4

Absorption.

Per cent. 

30

26

Yellow clay.

05

03

1

2

Buff...........................

.....do.........................

1

1

1

37

36

36
164 CLAYS AND SHALES OF MINNESOTA.

The clay burns to a fairly satisfactory product at these lower temperatures but does not become very hard until near the temperature 

of viscosity. The range of vitrification is approximately from cone 1 

to cone 2. A mixture of the blue and yellow clays stood the burning 

tests very much as the clays did separately. The plant has for some 

time produced 10,000 tile a day, using circular downdraft kilns.

Although preheating effects a remarkable improvement in molding 

and drying this clay, it can not make vitrification, possible. Bleininger 1 says:

An extremely fine grained clay from Albert Lea, Minn., of considerable plasticity but troublesome to dry. The specific gravity of the powdered dry clay is 

2.58. Linear shrinkage in per cent of the wet length is 9.79. Mechanical 

analysis by elutriation gave:

Coarser than 120 mesh_______________________ 0. 24 

Average 0.577 millimeter in diameter______________ . 21 

Average 0.0354 millimeter in diameter_____________ 1.04 

Average 0.0167 millimeter in diameter_____________ . 96 

Average 0.005 millimeter in diameter and less________ 97.31

The viscosity of the clay suspension was determined (water = 1) to range 

from 1.1 when containing 7.5 per cent by weight of clay to 2.21 when containing 

43 per cent by weight of clay, but the curve was not very straight.

.When the clay was heated to a temperature of 200° to 400° C. and cooled and 

worked up to the plastic state it required less water to bring it to good molding 

consistency. The change was greatest (43 to 36) between 200 and 250. After 

a treatment of this sort the volume shrinkage is much less than before, and 

rapid drying causes no injury. The improvement is remarkable in this clay at 

350°. 95 per cent of the brick were cracked before; 0 per cent after. A proposed test for plasticity using the absorption of a colored dye indicates a much 

greater plasticity than in the other clays tested in this same study.

- The following analysis of this clay was made by G. W. Walker, of 

the University of Minnesota, for Mr. Rusfeldt, of the Albert Lea 

Brick & Tile Co.:

Analysis of laminated clay from Albert Lea.

Silica _____________!_________-___________ 54. 90

Alumina ____________________^_________ 13. 94

Iron oxide ____________________ __________ 5.15

 Lime_____________________________ J____ 7. 36

Magnesia __:___________________________ 3. 28 

Potash.____________________________'_____ 1. 88

Soda_________________________________ 2.13 

Titanium oxide____________________ _____ .84. 

Loss on ignition ____________________________ 12. 54

A deposit of extremely fine grained silty clay, possibly of the 

nature of fuller's earth, occurs in a swamp on the. east side of Rice 

Lake, in sees. 11, 12, 13, and 14, T. 103 N., R. 20 W. The material

1 Bleioinger, A. V., Effect of preliminary beat treatment upon drying of clays: Bur. 

Standards Bull. 7, No. 2, 1911.
GOODHUE COUNTY. 165

could probably be used for common brick or draintile. The following analyses are available, the first two made by A/D. Meeds and the 

next two by G. B. Frankforter, both of Minneapolis:

Partial analyses of swampy clay from Albert Lea.

1

55.52

13.55

3.99

8.00

3.16

2

57.60

14.19

2.89

7.00

3.51

3

59.37

11. 82

6.27

6.17

2.09

4

57.62

14.36

2.50

8.11

2.98

NOTE. The remaining 15 per cent is largely water and carbon dioxide, with traces of phosphoric acid, 

chlorine, and the alkali metals. Water constitutes nearly 13 per cent.

GOODHUE COUNTY.

Clay-bearing formations.

Recent: Alluvium. 

Pleistocene:

Loess.

Gray drift.

Cretaceous: Clay, sewer pipe, and stoneware. 

Ordovician: Decorah shale.

Goodhue County is remarkable for having more workable highgrade clays than any other county in Minnesota. The most valuable 

are those of Cretaceous age.

DECORAH SHALE.

The Decorah shale in this county (see PL X and fig. 22) is almost 

identical in section and in detailed behavior of the clay with that at 

West St. Paul, Dakota County,, where it is extensively used. The 

shale is being used at Zumbrota and Wanamingo (see fig. 23), and 

a company is being organized to develop it at Cannon Falls, where 

it has been explored over hundreds of acres. At the plant of the 

Zumbrota Clay Manufacturing Co., in Minneola Township, the shale 

is equally extensive. (See fig. 24.)

Clay from the Wanamingo plant slakes somewhat irregularly but 

becomes highly plastic with about 30 per cent of water. The air 

shrinkage is 8 per cent. Burning tests resulted as follows: ^

Cone No.

06

04

02

2

5

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

3

3

7

8

Absorption.

Per cent. 

15

14

3

1

If the clay is too rapidly heated black cores and blebby structure 

develop, but with careful oxidation the bricks become too hard to 

scratch with a knife after burning to cone 06 (1,886° F.) and reach
166 CLAYS AND SHALES OF MINNESOTA.

viscosity at cone 3 (2.,174° F.). It is clear that the slow, steady decrease in porosity indicated by the absorption is favorable for the 

production of vitrified ware. The plant has a capacity of 120,000 

brick a day but is now producing hollow ware of several sorts in 

preference to brick. It was planned to use electric power from 

Cannon Falls. The property has changed hands several times and 

now appears to be operating at a profit.

In Minneola Township the Zumbrota Clay Manufacturing Co.'s 

plant used a rather massive bed of the shale 15 feet thick. Tests 

by the Bureau of Standards gave uniform vitrification, with increase

T.IIZN.

109

R.I8W.

10 MILES

FIGURE 22. Map of Goodhue County. Dotted area is underlain by Decorah shale.

of temperature, to a very low porosity. The best temperature of 

burning (as is characteristic of the Decorah shale) is rather lower 

than for most other good clays. In all physical tests this clay resembles the average Decorah shale. The plant has a capacity of 

about 50,000 brick a day but makes draintile and hollow brick in 

addition to common brick. Six hollow building blocks with two 

holes lengthwise tested on the side and on the edge by the Minneapolis building inspector gave an average strength of 330 pounds 

to the square inch, and one block tested on the end showed 5,100 

pounds to the square inch.
GOODHUE COUNTY. 167

Around Cannon Falls the overburden of-the Decorah shale is nowhere more unfavorable than % at West St. Paul, where the ihale is 

now used. Samples were taken on the land of. F. E. Tate, 3 miles 

south of Cannon Falls, and on property of the Goodhue County Clay

Surface loam- and loess 4 ft

Green shale 4 ft

Limestone I ft.

Limy green shale 3 ft

Limestofte 12 ft..

Limy hard shale 2 ft

Shale 4 ft.

St. Peter sandstone

FIGURE 23. Geologic section at Wanamingo.

Co., 1£ miles southeast of Cannon Falls. These exposures and others 

in the region are essentially alike. The shale slakes only to lumps 

but is very .highly plastic with 30 per cent of water. The tensile 

strength is 130 pounds to the square inch and is not greatly reduced 

by rapid drying. The clay works well in an auger machine. The 

shrinkage on drying is 8 per cent. Burning tests resulted as follows:

Cone No.

010

06

03

01

2

Color.

Red..................'..........

.....do..........................

.....do..........................

Shrinkage.

Per cent.

4

6

7

Absorption.

Per cent. 

15

8

6

3

The clay must be well oxidized to prevent the formation of black 

cores, but this can be done with no great difficulty. The brick are 

hard after burning to cone 010 (1,742° F.) and reach viscosity very 

gradually at about cone 1 (2,102° F.). The shale seems to be similar 

to that at St. Paul. A company has been organized and is building 

a plant at Cannon Falls to use the shale.
168 CLAYS AND SHALES OF MINNESOTA.

CRETACEOUS CLAYS.

The stoneware and sewer-pipe factories at Red Wing, which are 

famous for their high-grade products, derive their excellent clays 

from tw.o similar deposits, of which the better known is at Clay Bank, 

about 13 miles south of Red Wing. A careful study of the deposit at 

Clay Bank long ago led Sardeson i to conclude that it represents a remarkable example of the transportation of a large mass of bedrock 

formations by glacial ice. The clay as opened in the pits is underlain by gravelly, drift and the stratification is considerably disturbed, 

crumpled, and irregular. (See PL XIV.) The usable clays are separated by layers of sand and sandy clays and must be carefully sorted 

out. For a long time several grades were shipped from the pit, some 

of which were used for sewer pipe and the rest for stoneware, but as

Drift and loam 8 ft 

Thin iron-stained layer

-S^Sr£PH3 Soft shale, red, blue, green; 

and yellow, 10 ft.

Hard green shale 2 ft 

;£R^ Hard blue gritty shale 2/2 ft

Hard blue fossiliferous shale 2 ft

 - | Platteville limestone 12 ft

St. Peter sandstone

FIGUIIE 24. Geologic section at Minneola.

the material has been found to cover only about 160 acres a plant for 

washing the lower-grade darker clay has been installed to make .it 

available for the higher-priced stoneware. The deposits where locally 

exposed are complex. (See fig. 25.) The clay ranges in thickness 

from 10 to 45 feet.

The Red Wing Union Stoneware-Co. has produced stoneware since 

1872 and now uses 75 tons of clay a day. The clay is mined by hand 

digging in benches and vertical-sided rectangular pits and is loaded 

directly on the cars for shipment to Red Wing, where it is stored. 

Several grades are recognized, some of which are so pure as to require 

no preliminary treatment. In general, the darker clays are the more 

impure.

1 Sardeson, P. W., The so-called Cretaceous deposits in southeastern Minnesota : Jour. 

Geology,'Vol. 6, p. 679, 1898.
U. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE XIV

DISTURBED CRETACEOUS CLAYS AT CLAY BANK, NEAR RED WING.
IT. S. GEOLOGICAL SURVEY 

MOLDED STONEWARE AT RED WING.
GOODHUE COUNTY. 169

 v'dnft

3 clay

i'sand 

I ' 'clay 

i-'sand

6'clay

I- sand 

i'clay

2'sand

The bulk of the clay for the manufacture of stoneware is washed 

to remove sand and other impurities. It is reduced to a slush in 

blunger mills, passed through rotary sieves or lawns (SO-mesh), and 

run into large settling vats or cisterns. Live steam is used in the 

blunger mills and throughout the washing process, and the slush 

is kept almost at the boiling point to facilitate the washing and 

pressing. The coarser sand and impurities are removed in rotary 

sieves or sifters. The slush is then pumped into 

large* filter presses, where the water is squeezed 

out and the clay is pressed into cakes weighing 

about 40 pounds each, which are sent to the mill 

room and tempered in pug mills. The clay is 

then loaded on small trucks and distributed to 

the molders. The molded pieces go to tunnel 

dryers, where they are kept for 36 hours and the 

moisture removed. When the ware comes from 

the dryer it is finished and glazed and is ready 

for the kilns. (See PI. XV.) Slip glazes are 

imported from Albany, N. Y., and from Michigan, but some Minnesota clays have very similar 

properties. The ware is burned at a temperature 

of about 2,200° F., and the heat is maintained 

from 45 to 60 hours, the time depending upon 

the product desired. About nine days is required 

to convert the raw clay into the finished product.

The average clay slakes in three minutes, has 

a fairly high plasticity, and requires 34 per cent 

of water for molding. It has a tensile strength 

of about 100 pounds to the square inch, whether 

dried rapidly or slowly. The shrinkage on drying is about 7 per cent. The best selected clay 

has a range of vitrification from cone 04 (1,958° 

F.) to cone 20 (2,786° F.). At all temperatures 

in this-range the products are very hard, the 

absorption decreasing from about 15 to 3 per 

cent and the porosity from 28 to 6 per cent. 

The colors are cream and buff, changing to gray. Fire shrinkage increases very gradually to 7 per cent. Some grades of the material 

are less refractory for instance, a dark-blue layer that occurs in 

small amounts and is used for sewer pipe or is mixed in small proportions with the stoneware clay for large jars.

The stoneware clay is most abundant at Clay Bank, but as mined 

it contains some impurity and most of it is now washed at Red Wing. 

The following analyses, as well as the appearance of the coarse sand

i'sand 

i'clay

10+sand

FIGURE 25.- 

section 

Bank.
170 CLAYS AND SHALES OF MINNESOTA.

from me mechanical analysis, indicate that washing eliminates a 

number of ferruginous concretions and some sand and scales of-mica. \ 

Several other analyses are reported on page 90.

Analyses of materials from Red Wing. 

[F. F. Grout, analyst.]

Chemical analyses.

Silica..........................

Iron oxide. . ...................

1

69.92 

17.39 

1.68 

1.11 

.60 

.07 

2.25 

5.45 

1.10 

.63

100.20

2

.69.26 

18.57 

1.93 

.62 

.45 

.06 

2.41 

5.58 

1.10 

.77

100.75

3

64.98 

11.38 

12.03 

2.51 

.68 

.00 

1.93 

5.28 

1.08 

.71

100.58

Mechanical analysis (sample 1)

Silt...........................

20.7 

16.0 

49.8 

6.5 

1.0

100.0

1. Clay as shipped to the stoneware plant, ready for washing. 

3!

2. Washed-clay; sampled at the plant.

3. Refuse of washing; sampled at the plant.

The Red Wing Sewer Pipe Co., which has plants at Red Wing 

and Hopkins (see PI. XVI, A), uses Cretaceous clays from a deposit half a mile east of Belle Chester, Goodhue County, as well as 

the darker clays from Clay Bank. The deposit at Belle Chester ( 

(PI. XVI, .Z?)-has been discovered much more recently than that at 

Clay Bank, and its successful development may be taken as an indication that still other deposits of similar excellent clay may yet be 

brought to light. It was discovered by careful prospecting and observation of fragments in the drift, followed by careful drilling 

before any excavation Avas undertaken. It ranges from 1 to 30 feet| 

in thickness (average 10 feet) over 40 acres. Its appearance is so 

similar to that of the deposit at Clay Bank that its origin is assumed' 

to be the same. The deposit is capped by 3 to 6 inches of ferruginous 

sandstone.and is underlain by a similar sand rock that is apparently, 

of Cretaceous age, though its crumpled condition would seem to 

indicate transportation by glacial ice. (See PL XVI, J., and fig. 26.)

Some of the clay at Belle Chester, though a smaller proportion 

than at Clay Bank, is suitable for use in stoneware or can be washed 

to make it suitable. It has exactly the same behavior as to stoneware clay described above. The sewer-pipe clay, which is .more 

abundant, is also similar, as shown by the results given below. It 

slakes in three minutes, has good plasticity with 27 per cent of water, 

shrinks 8 per cent on drying, and has a tensile strength of over 100 

pounds to the square inch.
U. S. GEOLOGICAL SURVEY BULLETIN 678 PLATE XVI

A. SEWER-PIPE PLANT AT MINNEAPOLIS.

B. CLAY PIT AT BELLE CHESTER.
GOODHUE COUNTY. 171

Cone No.

010

06

02

3

0

10

Color.

.....do.......................... Bun.:..........................

.....do..........................

Shrinkage.

Per cent. 

1

2

3

4

6

7

Absorption.

Per cent. 

15

12

9

7

4

.The clay is hard after burning to any of the temperatures specified 

and reaches viscosity at about cone 10 (2,426° F.), or a little higher 

in some samples. Though the point of viscosity is usually lower 

than that of the stoneware clay the range of fusion is very great and 

the product is excellent. A greenish efflorescence noted on one Belle 

Chester sample would probably not injure sewer pipe, which, is salt 

glazed.

The company manufactures, in addition to sewer pipe, a few vitrir 

fied draintile and other specialties. Its capacity is 35,000 carloads a 

year. The quality of such products as are made at Red Wing and. 

such clay as is obtained there is best judged 

by the excellent reputation of the ware.

Although the deposits at Clay Bank and 

Belle Chester are the only ones of their quality 

now known in Minnesota, traces of such clay 

are numerous in -the form of fragments, 

streaks, pockets, and thin lenses in the drift. 

Many " ironstone " fragments similar to the 

ferruginous shale layers associated with the 

clays at Clay Bank and Belle Chester are also 

found in the drift. These indications seem to 

be most numerous northwest of the deposits 

now being worked; and there are strong possibilities that systematic prospecting with 

drills or augers will result in the discovery of 

other isolated areas of Cretaceous clay in the 

eastern part of the county.

OTHER BRICK MATERIALS.

10'drift

i* limonita 

3'clay

I * red sand 

s'clay

i red sand 

3'clay

I limonite

Coarse sand

FIGUUE 26. Geologic section at Belle Chester. -

A deposit of gray drift has been explored 

by the Red Wing Sewer Pipe Co., near Goodhue, in sec. 10, T. Ill N., R, 15 W., in the hope that it will 

be available as a plastic bond for mixing with the less plastic 

Cretaceous sewer-pipe clay. The deposit is 20 feet thick and covers 

80 acres. It is dark broAvn to yellowish and is covered by 4 feet 

of sand and soil. Although it is to be classified as glacial drift 

it is remarkably free from pebbles and may be composed mainly of
172 CLAYS AND SHALES OF MINNESOTA.

debris from Cretaceous deposits over -which the ice passed. The clay 

slakes in one minute, is very highly plastic, and requires 26 per cent 

of water for molding. The tensile strength is well above 50 pounds 

to the square inch but is considerably lessened by rapid drying. 

This clay would have a good effect in increasing the strength of a 

less plastic sewer-pipe clay. Its air shrinkage is 9 per cent. Burning 

tests by the Minnesota School of Mines experiment station resulted 

as follows:

Cone No.

07

05

1

2

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

3

4

7

8

8

Absorption.

Per cent. 

13

10

4

3

2

The clay burns hard at cone 07 (1,850° F.) and becomes viscous at 

about cone 8 (2,354° F.). Having thus a range of vitrification of 

500° it would seem available for making vitrified ware, such as sewer 

pipe, but some preliminary experiments by the Bed Wing Sewer Pipe 

Co. have resulted rather unfavorably. Its cracking and shrinkage 

on drying are probably serious defects. The United States Bureau of 

Standards reports very favorably on a mixture of two-thirds Cretaceous sandy clay and one-third gray drift, stating that the mixture be-. 

haves better both in working and in burning than either clay alone.

At the town of Pine Island the loess is exposed over ,a very large 

territory to a depth of 5 or 10 feet. The deposit was worked up to 

about 1909 and produced a fair quality of red brick. The local demand is not great. (See also fig. 9, p. 99.)

Ten miles from Vasa, along Belle Creek, a sandy alluvial clay is 

rather favorably exposed but is apparently too sandy to make good 

brick. Some brick were made here about 50 years ago and seem to have 

stood the test of service, but the sample taken was so sandy and weak 

that it could hardly have been possible to pile the brick into a kiln.

At Frontenac John Bartrom owns a deposit of alluvium along 

Wells Creek. It is not known to be over 4 feet thick and is a considerable distance from the railroad. An analysis made for Mr. 

Bartrom by F. F. Groiit is as follows:

Analysis of alluvial clay from Frontenac.

Silica ____________________.___________ 63.32

Alumina ___________________.____________ 12.68

Iron oxides__________________.____________ 2. 66

Lime __* __._________-,______...___________ 5.08

Magnesia ___________________.. ______L ______ 3. 94

Moisture _________-________.____________ 1. 83

Loss on ignition_______________...___________ 8. 47

Alkalies, etc., by difference_______...___________ 2.02
HOUSTON COUNTY. 173

. Sand-lime brick are manufactured at Red Wing. The lime is 

shipped from Iowa and the sand is taken from a hill of modified 

glacial drift near the factory.

GRANT COUNTY.

_, . [Recent: Lake clays. Clay-bearing formations,' 17 [Pleistocene: Gray drift.

Gray drift covers most of Grant County. An attempt made to 

use it at Elbow Lake was not very successful on account of the common trouble with limestone pebbles. Some laminated clays along 

the shores of Pelican Lake may be worthy of development.

HENNEPIN COUNTY.

Clay-bearing formations,

rRecent: Alluvium. 

Pleistocene:

Gray laminated clays.

Red and gray drift. 

Ordovician: Decorah shale.

On the north side of Minneapolis the glacial river clays have been 

utilized in making cream-colored brick, pottery, and fireproofing. 

An abundant supply still remains, but the value of city property 

tends to crowd brick works northward into Anoka County. '(See 

pp. 113-115 for a description of the days.) Similar clay occurs on 

the southeast side of Minneapolis but is deeply covered with drift. 

The pebbly gray drift of Hennepin County and recent alluvium 

along Mississippi River can not well compete with this deposit, nor 

can the red drift, which is in some places deeply eroded. Swamp 

clay was used at Hanover, and gray drift was once used at Rogers, 

but not successfully. The Decorah shale is mostly eroded, is partly 

buried, and occurs on property more valuable for building than for 

the manufacture of clay products.

Attention should be called to the sand-lime brick factories at Minneapolis.

HOUSTON COUNTY.

{

Pleistocene: Loess. 

Ordovician: Decorah shale. 

Cambrian: Shale of St. Lawrence formation.

The shales of the St. Lawrence formation crop out in man}^ bluffs 

in Houston County but have no value at present.

The Decorah shale occurs in the extreme southwest corner of the 

county. It can be best developed in the vicinity of Spring Grove, 

where it is well exposed but is not very thick. A mantle of loess 

covers most of the county.

No brickyards are now in operation in Houston County, but in 

former years there were plants at Money Creek, Spring Grove, La
CLAYS AND SHALES OF MINNESOTA.

Crescent, Houston, and most other towns in the county. Common red 

brick can be made from the loess nearly anywhere. (See fig. 9.)

Clay-bearinj

HUBBABD COUNTY.

[Recent: Lake clays, formations-' . , _ n ... [Pleistocene: Gray drift.

About 1-| miles from the Great Northern Railway near Akeley a 

plant has been operating on a lake deposit which is known to extend 

over 80 acres to a depth of 40 feet and which may be at least partly 

of glacial age. The upper half of the deposit is yellow and the 

lower half blue-gray. Both portions,' except a few inches at the top 

from which the lime has been leached, burn to cream-colored brick. 

At the plant the production is about 200,000 stiff-mud cream-colored 

brick a year.

Gray drift was once used for brick a few miles from Park Rapids, 

but the plant has not been active since 1894. The clay is said to be 

fairly free from limestone, and work was stopped because the market 

was small and the funds were not sufficient to tide the company over 

bad times.

ISANTI COUNTY.

) Pleistocene: 

Gray laminated clays. 

Gray drift.

At Cambridge and elsewhere along Rum River gray laminated clay 

was used for many years, beginning in 1881. The clay is exposed for 

20 feet but is overlaid in the bluff by about 25 feet of sand. It could 

be profitably worked in only a small area, in which the overlying 

sand has been at least partly eroded. The clay slakes at once and 

shows fairly high plasticity, requiring 29 per cent of water for 

molding and shrinking 7 per cent on drying. Burning tests resulted 

as follows:

Cone No.

05

03

01

2

3

Color.

.....do..........................

.....do..........................

.....do......................

Shrinkage.

Per cent. 

0

2

3

5

Absorption.

Per cent. 

24

22

13

5

The brick were too hard to be scratched with a knife after burning to 

cone 04 (1,958P F.), and they reached viscosity at cone 3 (2,174° F.) 

The addition of 50 per cent of sand to the clay increases the range of 

vitrification and seems to improve the general character as brick material. The brick produced were equally good. A small plant made 

salmon-colored brick from this clay by using a high proportion of 

the overlying sand, but work has been abandoned.
ITASCA COUNTYi 175

Clay-bearing formations

. One or two attempts to use the gray drift without removing the 

limestone, pebbles met with the usual difficulty.

ITASCA COUNTY.

Recent: Lake clays. 

Pleistocene:

Gray laminated clay.

Gray drift.

Red drift 

Htironiaii: Paint rock, etc.

No clays were worked in Itasca County up to 1900, but since that 

year the development of the iron ranges has led to several attempts 

at brick-making. Brickyards were started to utilize gray laminated 

clays at Grand Rapids and Verna. A sand-lime brick plant at Peiigilly is a competitor of the clay-brick industry.

The Verna Brick Co. is developing the deposit at Verna, near 

Wacba station on the Great Northern Railway. The portion of the 

deposit that is considered available is about 10 feet thick and extends 

over about 10 acres. It is yellowish gray in color and has apparently 

been leached. Underlying it and extending over a great many acresof the surrounding country is a blue laminated clay containing a few 

limestone concretions. The gray clay burns cream-colored and the 

blue clay is said to burn red and to show a much greater shrinkage. 

Any attempt to mix the blue and gray-clays encounters the difficulty 

common to all attempts at mixing a stiff, plastic clay with .a lean, 

sandier clay. The plastic,lumps remain suspended in the more fluid, 

mass and require very thorough pugging or some other form of mixing to get a satisfactory structure and avoid auger laminations. The 

yellowish-gray clay, which is being used, slakes at once and shows 

very low plasticity, requiring 23 per cent of water for molding. The 

air shrinkage is 3 per cent, and the tensile strength is well above 100 

pounds to the square inch, even after rapid drying. As burned at ths 

Minnesota School of Mines experiment station it gave the following 

results:

Cone No.

03

01

2

3

Color.

Buff.................... ........

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

4

12

Absorption.

Per cent. 

3J

23

The clay becomes hard at cone 02 (2,030° F.) and reaches viscosity 

at cone 3 (2,174° F.). The plant has a capacity of 35,000 brick a 

day and makes a common brick of cream color, using wood as a fuel. 

At Grand Rapids bricks were burned from a lean, very sandy 

laminated clay that lies along the banks of a small creek at the 

northeast edge of town. The clay is yellow and seems to be very
176 CLAYS AND SHALES OF MINNESOTA.

sandy when dry. It slakes in one minute and has very low plasticity, requiring 21 per cent of water for molding. Its shrinkage is 

3 per cent on drying. Its tensile strength is over 130 pounds to the 

square inch, but the adhesion test indicates that it would not work 

well in an auger machine. As burned at the Minnesota School of 

Mines experiment station it gave the following results:

Gone No.

03

1

3

Color.

Red............................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

Absorption.

Per cent. 

21

13

10

The clay burns too hard to be scratched by a knife ai> cone 02 

(2,030° F.) and becomes viscous at cone 5 (2,246° F.). Two attempts 

at brickmaking were made by soft-mud -methods and one by a stiffmud machine. None were particularly successful, and work has 

ceased. Shipping facilities are not very favorable. 

 Cretaceous shales were, reported by Grant 1 to occur on Deer River 

near its mouth. River erosion had removed the overlying glacial 

drift and left the shales with a smooth, polished surface that resisted erosion much more successfully than the drift. Limy concretions have generally been considered rare in the Cretaceous deposits, but a trip through the Deer River neighborhood revealed no 

outcrops that did not contain a rather large number of lime concretions or pebbles. The claj^s are probably of Pleistocene age.

On Bigfork River, 2 miles below the mouth of Deer River, blue clay 

crops out near water level. It is sticky and tough but is so inaccessible and so covered with water as to be unprofitable. A similar 

outcrop occurs on Bigf ork River, 2 miles above the mouth of Deer 

River.

On Deer River, half a mile above the mouth, 4 to 6 feet of apparently good clay crops out for 50 feet along the bank and is 

probably continuous with another outcrop close to the mouth of the 

river. The clay is laminated with alternate light and dark blue 

layers. It is covered by about 10 feet of glacial drift and contains 

a few rounded pebbles. The deposit is somewhat more .accessible 

than those on Bigfork River mentioned above and is perhaps the 

most promising clay discovered in this region. The clay slakes in 

two minutes and shows medium plasticity with 33 per cent of water. 

Its tensile strength is 100 pounds to the square inch and it shrinks 9 

per cent on drying. A burning test by the Minnesota School of 

Mines experiment station resulted as follows:

 1 Grant, U. S., Geology of Minnesota: Minnesota Geol. and Nat. Hist. Survey Final 

Rept, vol. 4, p. 183, 1899.
ITASCA COUNTY. 177

Cone No.

010

04

02

2

Color.

Salmon.. . ......................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

4

11

13

Absorption.

Per cent. 

16

12

1

0

This clay has to be heated slowly and oxidized or it will develop 

black cores and fail at very low temperatures.

The mantle of gray drift over the county is largely modified by 

the action of water and is sandy, but its surface is irregular and 

contains many lakes. Clays have accumulated in these lake basins, 

probably beginning in glacial time but continuing to the present. 

At Lilly Lake, south of Grand Rapids, numerous test pits and borings have revealed deposits of clay and irregularly interbedded sand, 

which seem to be of excellent quality for common brick. The clay

Hwonfan

FIG DUE 27. Geologic section at Coleraiue.

slakes in three minutes and shows fairly high plasticity, requiring 

28 per cent of water for molding. Its air shrinkage is 7 per cent, 

and it checks considerably unless carefully dried, so that its tensile 

strength ranges from 50 to 150 pounds to the square inch. Burning 

tests gave the following results:

Cone No.

05

04

01

1

2

Color.

.....do..........................

Red............................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

3

4

8

9

9

Absorption.

Per cent. 

17

15

3

3

2

The clay becomes hard at cone 05 (1,922° F.) arid reaches viscosity 

at cone 2 (2,138° F.).

At Coleraine the "paint rock" of the iron-ore formation is over 

20 feet thick and.is especially troublesome in the mines. (See fig. 

27.) It is all moved in getting the ore, and if a little care were used

64310° 19 12
178 CLAYS AND SHALES OF MINNESOTA.

to keep it free from ore and the sandier layers of taeonite it could 

be used for red brick, though it could not be safely vitrified. It 

slakes promptly and is plastic with 27 per cent of water. Its ailshrinkage is small. Brick made from it do not become thoroughly 

hard below a temperature of cone 4 (2,210° F.). An analysis is 

given in the report on St. Louis Comity (pp. 225-230).

At Pengilly, where a particularly sandy phase of modified drift 

extends over a large area, a sand-lime brick plant has recently been 

erected. It has every chance of success if the product is kept up 

to the high grade possible.

JACKSON COUNTY.

Clay-bearing formations

Recent:

Lake clay.

Alluvium. 

Pleistocene:

Gray drift.

Brick and tile are manufactured from gray drift at Jackson, where 

15 feet of yellow clay, with very little limestone or other impurities, 

extends over an area of 14 acres. The deposit is close to the Chicago, 

Milwaukee & St. Paul Rail way ? and conditions seem to be favorable 

for the development of a considerable industry. This plant has used 

the dry process of separating limestone from the clay. The pit is 

kept dry and the clay is plowed over a considerable surface and 

gathered up only after the wind and sun have dried it thoroughly. 

It is then transferred to sheds for further drying with protection 

from rain. The crushing is done in a modified dry pan, from which 

an elevator carries the clay to a screen. When pebbles accumulate in 

the dry pan it is stopped and cleaned out. Lack of shed room 

limits the capacity and output of the plant.

At Okabena similar gray drift has been used in two small plants 

to make hand-molded brick.

The nature of the gray drift of Jackson County is indicated by 

the following tests. The clay slakes in two minutes and is highly 

plastic, with 29 per cent of water. It shrinks 6 per cent on drying 

and develops a tensile strength of 125 pounds to the square inch. 

Burning tests gave the results set forth below:

Cone No.

04

02

01

1

2

Color.

Buff.............

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

2

3

5

8

10

Absorption.

Per cent. 

25

22

14

6

1

The clay is too hard to scratch with a knife after burning to cone 

02 (2,030° F.) and reaches viscosity at cone 2 (2,138° F.). If the
. JACKSON COUNTY. 179

limestone pebbles are not removed most of the burned products 

slake after exposure; if they are removed good brick are produced.

River alluvium, known to be 5 feet thick, occurs at Jackson over 

about 20 acres along the flood plain and is said to pverlie blue clay. 

It was developed about six years ago. The product, consisting of 

red brick, was used in several buildings in Jackson. The clay seems 

to work and burn well, but it contains a few, limestone pebbles, which 

have caused difficulties. ,

A gentle slope of about 100 acres on the shore of Heron Lake is 

underlain by 12 feet of yellow laminated clay, probably in part of 

glacial origin and in part recent. The laminae are of variable thickness, and many of the vertical joints are stained with iron. The 

deposit is surrounded on-'all sides by pebbly gray drift, except along 

the lake. Bleininger 1 says:

A glacial calcareous clay from Heron Lake, Minn., possessing good plasticity 

and working properties, though somewhat too fine grained for drying when 

made into larger pieces.

Specific gravity, powdered dry clay = 2.654.

Linear shrinkage, in per cent of wet length = 7.72.

After a heat treatment of from 250° to 400° C. the plasticity is found to be 

lower and the air shrinkage is'greatly decreased. The decrease is greater the 

higher the temperature of preheating.

This sample was evidently not suited to yield such data as were hoped by 

experiments in preheating, as the raw clay showed no more cracking than the 

preheated clay and was as good as the others after preheating. The effect of 

preheating on fineness of grain explains some of the variation found in plasticity and shrinkage.

The tensile strength of the clay is 150 pounds to the square inch, 

and the shrinkage.on drying is 5 per cent. Burning tests resulted 

as follows:

Cone No.

04

02

01

2

Color.

Buff............................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

2

5

. 7

13

Absorption.

Per cent. 

30

23

19

1

The clay is hard after burning to cone 04 (1,958° F.) and reaches 

viscosity at cone 2 (2,138° F.). The following analysis is available:

Mechanical analysis of clay from Heron Lake. 

Fine clay__"______________________________ 9.3 

Coarse clny_______________________________ 16. 8 

Silt ____________________________________ 69. 4 

Fine sand _______________________________ 4.1 

Coarse sand __ _____________________ .4

100.0

a Bleininger, A. V., Effect of heat treatment upon drying of clays: Bur. Standards Bull. 

7, No. 2, 1911.
180 CLAYS AND 'SHALES OF MINNESOTA.

A company at Heron Lake has been at work since 1890 producing 

hollow brick and title in a number of downdraft kilns with a capacity of about 80,000 a day. The product is cream-colored if burned 

hard and salmon-colored at lower temperatures. The clay is more 

suitable for hollow brick and tile than for any other products. The 

fusion is so sudden that the products are seldom vitrified.

KANABEC COUNTY.

Clay-bearing formations{

Pleistocene: 

Gray laminated clay. 

Red drift. 

A.lgonkian(?) : Red clastic series.

At Mora an attempt was made years ago to use the shales of the 

red clastic series for terra cotta. These shales are hard and red and 

occur at several horizons in the sandstone formation. Wells show 

that the clay has considerable areal extent below the drift and that 

its thickness is as a rule not over 10 fe'et. In sec. 1, T. 39 N., R. 24 

W., near Mora, a 3-foot bed is visible along the river for about 100 

yards. An attempt was made also to use the ferruginous shaly sandstone near by, but as now exposed it contains very little clay and 

has no strength at all. The clay slakes in two minutes and is very 

plastic, requiring 22 per cent of water for molding. Its air shrinkage is 5 per cent. Burning tests resulted as follows:

Cone No.

06

03

2

5

12

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

1

2

3

Absorption.

Per cent. 

17

16

14

12

Melted.

The clay becomes hard at cone 06 (1,886° F.) and reaches viscosity 

at about cone 8 (2,354° F.). The range of vitrification is over 400° 

F., and if a large body, is discovered it should make excellent 

products.

Yellow laminated clays crop out in the bank of the river at the 

northwest side of Mora. The deposit apparently extends over many 

acres and was sampled to a depth of 6 feet without reaching the 

bottom. It appears to contain rather numerous limy concretions, 

and its quality was not good. Its shrinkage on drying, for example, 

was over 19 per cent, and on burning it checked, formed black cores, 

and showed still further shrinkage. Its successful use would require 

extreme care. It can hardly be recommended for any purpose.

At several other' points in Kanabec County attempts have been 

made to manufacture brick from glacial clays. At one point at
KITTSON COUNTY. 181

least just east of Rice Creek on the road from. Brunswick to Grasston laminated lake clays, including some sandy layers 6 inches 

thick, were used. The clay slaked at once, was fairly plastic, and 

had an air shrinkage of 8 per cent. Burning tests resulted as follows:

Cone No.

05

03

01

1

2

Color.

.....do.........................

.....do..........................

.....do..........................

Shrinkage.

 Per cent. 

1

3

7

g

Absorption.

Per cent,, 

n

20

5

The clay is hard after burning to cone 05 (1,922° F.) and reaches 

viscosity at cone 2 (2,138° F.). Favorable shipping facilities are 

lacking, but if the local market were good this clay deposit might 

again be used.

A similar deposit is reported near the station at Grasston, but 

only gray drift is now exposed.

KANDIYOHI COUNTY.

Clay-bearing formations

Pleistocene:

Gray laminated clay. 

Gray drift.

The laminated clays are the chief clay resources of Kandiyohi 

County, though graj^ drift is abundant. A little over a mile west of 

Willmar, along the Great Northern Railway, is a deposit of laminated clay known to extend over about 25 acres. It consists of 15 

feet of yellow oxidized material underlain by at least as much blue 

clay. The yellow clay contains a few limestone pebbles or concretions. The blue clay is, as usual, more plastic than the yellow and 

shows greater shrinkage when used alone. Both the yellow and 

the blue clay burn cream-colored at high temperatures but salmoncolored if underburned. The Willmar Brick Co. has been at work 

here for 20 years, making about 2,000,000 stiff-mud cream-colored 

brick and some draintile each season. Another plant on the northwest side of Nest Lake used similar clay for some time.

Kandiyohi County contains many lakes and marshes, some of 

which may be underlain by alluvial clays.

KITTSON COUNTY.

' Kittson County is no doubt supplied with clay like that used at 

Grand Forks and Winnipeg the silts of the Red River valley. Well 

records report clay to a depth of 136 feet, and it is no doubt usable 

to as great a depth as at Grand Forks.
182 CLAYS AND SHALES OF MINNESOTA. 

KOOCHICHING COUNTY.

'Recent: Alluvium. 

Pleistocene:

^, , . . ,. Gray laminated clay. Clay-bearing formations , .,/ , ^ - ,- . % Silt of the Red River valley.

Gray and red drift. 

Cretaceous (?): Shales (?).

The erosive action of the waves of Lake Agassiz and of streams 

and the deposition of eroded material in the lake have left Ivoochiching Count}7 flat and largely swampy. Clays occur in some of the 

swamps, but in few places are they of good quality. Where streams 

have cut through this surface material other types of clay are ex-, 

posed, of which the Cretaceous shales are of doubtful identity and 

the red drift is not prominent because buried under later gray drift 

and laminated clay and still later modified by Lake Agassiz. The 

laminated clays are the most valuable for clay products.

The surface material is apparently very uniform. Its quality is 

shown by samples taken near International Falls, where it is found 

to be a sticky clay to a depth of 40 feet. Its upper part is leached 

and to a depth of 6 feet is relatively pure, but below that limestone 

pebbles and concretions are numerous. Clay, of this type is easily 

accessible eastward from the town, toward the "French settlement," 

and probably elsewhere. The clay slakes in two minutes and shows 

a very high plasticity, requiring 29 per cent of water for molding. 

Its air shrinkage is 9 per cent, and it probably shows considerable 

tendency to crack on drying. If drying is done slowly and with care 

the tensile strength is nearly 200 pounds to the square inch, but with 

rapid drying the strength is below 50 pounds to the square inch. A 

burning test resulted very much like that on the gray drift full of 

limestone pebbles (see pp. 55-56), indicating that this coarser limy 

gravel must be removed before the clay can be safely used. The proportion of such gravel, however, is very much less than in the common gray drift so successfully used at Hutchinson, and it is doubtful 

if the process used at that place will apply with equal success to the 

clay near International Falls. The success of the Hutchinson process 

depends not only on the removal of limestone, but on the quality and 

the mixing of the materials left. The percentage of lime in this clay 

is much the same as in the drift (7.5 per cent as compared with 9 

per cent), and the essential clay substance shows the same behavior 

in the fire. But the gray drift contains approximately 30 per cent of 

sand that would be caught in the 100-mesh sieve, and the clay in the 

Lake Agassiz basin contains only about 3 per cent of sand. Sand is 

not abundant anywhere in the neighborhood, and it is suggested that 

those who wish to use the clay should grind rather than wash it.
COUNTY. 183

The details'of the vitrification of-one sample of the leached upper 

clay are as follows:

Conol o.

00

03

02

3

Color.

:... .do.. ........................

Rod............................

.....do..........................

Shrinkage.

Per csnt.

3

9

9

10

Absorption.

Per cent. 

19

15

3

2

1

The clay is hard after heating to cone 03 (1,994° F.) and reaches 

viscosity at cone 3 (2,174° F.). It requires slow, careful oxidation to 

avoid black cores.

A small creek at the west edge of Big Falls has cut into irregular 

layers of sand and clay, which overlie the usual pebbly drift of the 

region and which may be partly leached drift and partly alluvium. 

If the deposit is as extensive along the creek as it seems to be it 

might furnish a local brick supply. The clay slakes in one minute, 

is highly plastic, and requires 20 per cent of water for molding. 

Its tensile strength is well above 200 pounds to the square inch, 

even when rapidly dried. Its air shrinkage is 4| per cent. As 

burned at the Minnesota School of Mines experiment station, it gave 

the following results:

Cone No.

02

01

2

3

4

Color.

.... .do. ..........................

.....do..........................

Shrinkage.

Per cent. 

I

1

4

5

0

Absorption.

Per cent. 

18

17

11

7

2

The clay becomes hard at cone 02 (2,030° F.) and viscous at cone 4 

(2,210° F.). The range of vitrification is therefore over 150°, and 

it can safely be burned hard.

The best clays in Koochiching County have not been found at 

easily accessible points. Several steep clay banks along Bigfork and 

Littlefork rivers have exposed laminated clays or shales of a type not 

exactly duplicated anywhere else in Minnesota. From their location it is supposed that they correspond to the patches formerly 

mapped as Cretaceous. However, some of them rest on glaciated 

rock surfaces and hence are now classed as postglacial or interglacial. 

Though they differ from the glacial clays of the neighborhood in 

containing no limestone pebbles, they are very much like the laminated glacial clays farther south at Wrenshall. In their behavior 

in firing arid in their chemical composition they also resemble glacial 

clays much more closely than Cretaceous shales.
184 CLAYS AND SHALES OF MINNESOTA.

At Big Falls, southwest of International Falls, Bigfork River' 

has cut a rather extensive gorge below the falls from which the 

town is named. The bluffs in most of the gorge reveal a blue 

clay weathered to yellow near the surface and containing numerous 

limestone pebbles; but a little below the mouth of Sturgeon River,'' 

on the farm of Ben Lind, there is an outcrop showing a clay of 

different type. The section is as follows:

Section 011* Bit/fork River beloio Sturgeon River.

Soil.

Feet. 

1

Common pebbly clay of the Luke Agassiz Basin_________ 10

Plastic yellowish-gray clay________:____________ 10

Very fine sandy clay^_______________________ 30

The clay crops out for several hundred yards along the bluff and 

represents a -large deposit, though somewhat inaccessible in the 

present state of development of the country. The plastic yellowishgray clay of the section slakes at once, shows medium plasticity, 

and requires 28 per cent of water for molding. Its tensile strength 

is over 150 pounds to the square inch, even when rapidly dried, and 

its air shrinkage is 3 per cent. Burning tests resulted as follows:

Cone No.

03

02

1

3

Color.

Buff... .........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

9

Absorption.

Per cent-. Q1

26

14

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at cone 3 (2,174° F.). The working and burning qualities 

of the clay are not injured by the addition of a large proportion of 

the surface silt, but if all layers are mixed the proportion-of sandy 

clay is too great. The overburden ol clay, 10 feet thick, is no more 

valuable than the clay found nearly everywhere through the county.

Still more difficult of access in the banks of Littlefork River, several miles east of Big Falls, are some exposures of a nearly white, 

smooth clay, which crops out at intervals for miles. The clay is 

slightly laminated with alternating white and light blue-gray layers 

about 1 inch thick and has no visible impurities.

Clays of somewhat darker gray crop out in places farther up 

Littlefork River and probably for some distance up Bigfork River. 

The outcrop in this county closest to transportation lines is on 

Littlefork River at the boundary between St. Louis and Koochiching 

counties. A few similar outcrops still farther east in St. Louis 

County are close to the station at Cook and are more accessible.
KOOCHICHING COUNTY. 185

Samples taken at the head of Net Lake Rapids and for a few miles 

down the river, in sees. 36 and 26, T. 64 N., R. 23 W., in sec. 1, 

T. 64 N., R. 24 W., and in sec. 15, T. 65 N., R. 24 W., are fairly uniform in general character. Only the sample from the most northern 

locality burned red, and this was taken at water level and was probably leached.

All these laminated clays slake in a few minutes and develop fairly 

high plasticity. The shrinkage on drjdng is 5 to 8 per cent, and the 

tensile strength is 150 to 200 pounds to the square inch. The following results of burning tests are representative of the blue-gray 

laminated clay below Net Lake Rapids:

Cone No.

03

04

02

2

3

Color.

.....do..........................

Buff... ........ .................

.....do..........................

.....do...........................

Shrinkage.

Per cent. 

0

1

7

9

10

Absorption.

Per cent, 

n

22

10

4

1

The clay is hard after burning to cone 05 (1,922° F.) and reaches 

viscosity at cone 3 (2,174° F.), having thus a range of 250° F. This 

clay was analyzed by A. W. Gauger, with the following result: .,.

Analysis of laminated clay from Koochichiny County.

Silica__________________1___________.____ 47.70

Alumina_________________________________ 13. 58

Iron oxides__________________________ ._____ 6. 51

Magnesia______________________________ 3.13

Lime____________________________1_.___ 11.70

Soda_____________________________.___ 1. 05

Potash___________________________.___ 2. 34

Loss on ignition_______________________.____ 13. 23

Moisture____________ _ _ ___________ 1. 79

Titanium oxide_________ ________.__ . 31

101. 34

A similar clay from the head of Net Lake Rapids gave the following results of burning tests:

Cono No.

04

03

02

2

Color.

Buff.... ........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

 4

8

9

Absorption.

Per cent. 

23

13

G

5

,The clay-is hard after burning to cone 03 (.1,994° F.) and reaches 

viscosity at cone 4 (2,210° F.). At the bottom of the exposure the 

beds are more sandy, but a mixture of the whole bank gave results 

almost identical with those just reported. This clay was exceptional
186 CLAYS AND SHALES OF MINNESOTA.

in containing a number of calcareous concretions. (See PL II, Z), 

p. 36.) It is of interest and may be a matter of some importance that 

pottery is found along Littlefork Eiver in such situations as to1 indicate that the Indians made use of these laminated clays.

The outcrop in sec. 1, T. 64 N., E. 24 W.,. is exposed by a series of 

landslides along the steep banks of the river. The unusually lightcolored clay is very smooth and plastic. Outcrops are most numerous between two small creeks that enter the river from the south. 

Burning tests of this clay resulted as follows:

Cone No.

06

02

01

2

5

Color.

Buff............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

1

2

4

8

Absorption.

Per cent. 

23

20

20

13

1

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at cone 5 (2,246° F.).

The only red-burning laminated clay was the weathered sample 

from sec. 15, T. 65 N., R. 24 W., which gave the following results:

Cone No.

06

03

01

2

3

5

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

2

4

5

5

6

Absorption.

Per cent. 

17

13

10

5

2

The clay is hard after burning to cone 06 (1,886° F.) and reaches 

viscosity a little above cone 3 (2,174° F.), with a fairly slow decrease 

in porosity.

LAC QUI PAULB COUNTY.

{

Pleistocene: Gray drift. 

Cretaceous: Shales. 

Archean: Residual clay.

Gray drift, somewhat modified by leaching near the surface, covers 

Lac qui Parle County, and the Cretaceous shales and Archean clay 

are found only in wells. At and southwest of Dawson white clay 

having the appearance of the Archean is found at a depth of 160 

feet.

LAKE COUNTY.

Lake County contains red drift and associated lake clays, but they 

have not been used. Possibly swamp deposits occur. The Keweenawan shows thin shale lenses of no value.
LE SUEUR COUNTY. 187

The red clay resembles the red clay of Lake Duluth. (See Carlton 

County, pp. 134-140.) No samples are available except one sent in 

from Beaver Falls, "which shows the extremely high shrinkage characteristic of the type. The clay slakes in three minutes, and when the 

extreme amount of 55 per cent of water is added it remains stiff and 

of good molding consistency. It has an air shrinkage of 13 per cent 

and is likely to crack. It develops a.tensile strength of over 100 

pounds to the square inch if carefully dried. Burning tests show 

that a further high shrinkage occurs. The volume of well-vitrified 

bricks is less than 35 per cent of the volume as molded wet. The 

results of the tests were as follows:

Cono No.

010

06

04

02

01

Color.

.....do..........................

Red............................

.....do..........................

.....do.....:....................

Shrinkage.

Per cent. 

5

6

10

19

Absorption.

Per cent. 

25

23

15

2

The clay is hard after being burned to cone 010 (1,742° F.) and 

reaches viscosity at cone 01 (2,066° F.). The great fire shrinkage 

results in a tendency to crack, but the range of vitrification is good 

(300° F.) and the clay may be valuable as a plastic bond or a slip 

clay.

The following analysis, made by J. A. Dodge, represents a shaly 

sand rock half a mile below the first falls of Baptism Eiver, which is 

thought to be of Keweenawan age: l ,

Analysis of slialy sand rock from Lake County.

Silica _________________________________ 66.72 

Alumina _ ______:______________________ 7. 41 

Ferric oxide ____________________________ 10.13 

Ferrous oxide____________________________ . 69 

Magnesia ______________________________ 4. 06 

Lime ___________________________________ 3.10 

Soda__________________________________ . 86 

Potash_____________________________-___ .42 

Loss on ignition_______________________^_____ 5. 32

3.71

LE SUEUR COUNTY.

Clay-bearing formations 

Recent: Alluvium and swamp clay. 

Pleistocene: Gray drift. 

Cretaceous: Shale.

In Le Sueur County interest centers in a refractory clay near Ottawa, though clays of other types have been used at several places

1 Minnesota Geol. and Nat. Hist. Survey Thirteenth Ann. Rept., p. 100, 1885.
188 CLAYS AND SHALES. OF MINNESOTA.

for common brick. The most promising occurrence near Ottawa is 

.a shale deposit that was developed a little over half a mile up Cherry 

.Creek and half a mile from the Chicago & Northwestern Railway. 

Mr. Randall, on whose farm the clay occurs,. reports that it was 

tested to a depth of 27 feet without reaching the bottom. It underlies an unknown area of the high, prairie east of Ottawa. The 

geologic section is as follows:. . 

Geologic section near Ottawa.

Feet

Yellow and gray drift_^_ 100 

White clay__ _ _ __ _ 4 

Blue clay___________________ ____________ 8 

White clay _________ __ _ _ 4 

Fine white sandy clay.

This clay crops out in the bed of Cherry Creek, and there might be 

some difficulty in draining and mining it. It slakes in one minute 

and is very plastic, requiring 26 per cent of water for molding. It 

shrinks 4 per cent on drying. Burning tests by the Minnesota School 

of Mines experiment station resulted as follows:

Cone No.

05

02

2

4

6

13

Color.

Cream...:......................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

4

5

8

8

10

. 12

Absorption.

Per cent. 

20

20

14

14

11

6

The clay has a hardness of 6 at cone 05 (1,922° F.), is fully steel 

hard at a slightly higher temperature, and apparently does not even 

approach viscosity at cone 13. The Bureau of Standards reported 

that it behaved like a refractory clay. Although it may prove to 

be highly refractory it appears to burn dense at moderate temperatures. The analyses available average as follows (see also p. 90):

Average composition of clay near Ottawa.

Silica________________________________ 56. 70

Alumina _______________________________ 28. 50 

Iron oxides _ _____ - _ ___ _ .18 

Magnesia _________________ ____ _________ . 23 

Lime__________________________________ . 69

The St. Paul Fire Brick Co., organized to exploit this deposit, 

built a rather extensive plant with dry-pan, wet-pan, and re-press machines, having a capacity of several million brick a year.. No 

products have been turned out for several years. The deposit should 

be considered for further work.
LE SUEUR COUNTY. 189

Another clay near Ottawa lies half a mile below the railroad 

.bridge over Cherry Creek, between the Jordan sandstone and the 

Shakopee dolomite. It is only 2 or 3 feet thick where exposed, and 

there is considerable evidence that it is not conformable with the 

Jordan and the Shakopee but has been washed in during Cretaceous 

or pre-Cretaceous time. It seems to belong to a type which is 

widely distributed throughout the Minnesota Valley from Shakopee 

to New Ulm. (See Blue Earth County, pp. 121-126.) The clays are 

variegated red, yellow, and white and in many places lie like stratified 

sediments unconformably over either the Jordan or the Shakopee. 

Another common occurrence is in large waterworn cavities and 

fissures.

Before the deposition of these Cretaceous clays the rocks of the 

Minnesota Valley had been eroded by rivers and other agents into 

irregular basins, potholes, and hollows 5 to 25 feet in depth, many 

of them with overhanging walls. These pocket-like cavities are 

smoothly waterworn. Winchell 1 has described an instructive section of the Shakopee dolomite and its associated deposits of this 

clay in a cut near the railroad bridge that crosses Blue Earth River 

about a mile above its mouth.

This cut is perhaps 70 feet above the river, the bank of which is composed 

entirely of rock, the lower portion of which is the Jordan sandstone and the 

upper the Shakopee limestone, the latter composing about 20 feet. In general, 

this railroad cut shows a mixture of Cretaceous clay with the Cambrian, the 

top of the whole being thinly and irregularly covered over and chinked up 

with coarse drift. The Cambrian is more or less broken and tilted; at least, 

the bedding seems to have been cut into huge blocks by divisional planes, 

which, either by weathering or water wearing, were widened, the blocks themselves being subsequently thrown to some extent from their horizontally, 

tipping in all directions. The opened cracks and seams were then filled with 

the Cretaceous clay, which is deposited between these loosened masses, and 

sometimes even to the depth of 20 feet below the general surface of the top 

of the rock. The clay sometimes occupied nooks and rounded angles, sometimes sheltered below heavy masses of the Cambrian beds. The clay is uniformly bedded, about horizontally, with some slope in accordance with the 

surface on which the sedimentation took place. But the most interestirig and 

important feature is the condition of these old Cambrian surfaces. They are 

rounded by the action of the water, evidently waves. The cavities and porous 

spots are more deeply eroded, making little pits on the face of the rock; or, 

along the lines of section of the sedimentation planes with the eroded surface, there are furrows due to the greater effect of water. The rounded surface of these huge masses of limestone is coated with a thickness of about a 

half inch, or an inch and a half, of iron ore, which scales off easily and is 

easily broken by the hammer. While this scale of iron ore is thicker near 

the top and on the upper surface of the blocks, yet it runs down between the 

Cretaceous clay and the body of the rock.

1 Winchell, N. H., Minnesota Geol. and Nat. Hist. Survey Second Ann. Rept., p. 178, 

1874.
190 CLAYS AND SHALES OF'MINNESOTA'.

The sample collected at Ottawa slakes in two minutes, is very 

highly plastic, and requires 31 per cent of water for molding. Its 

tensile strength is over 100 pounds to the square inch, even when 

rapidly dried. Its shrinkage on drying is 8 per cent. As burned 

at the Minnesota School of Mines experiment station it gave the 

following results:

Cone No.

010

06

04

03

1

6

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

. 4

7

9

10

10

Absorption.

Per cent. 

18

14

11

7

4

3

The clay becomes hard below cone 010 (1,742° F.) and viscous at 

cone 10 (2,426° F.). Its qualities are thus shown to be so excellent 

that it may be quite worth while to search out more deposits of this 

character arid see if some of them may not be of a size and accessibility to warrant further development.

Half a mile from the Chicago, St. Paul, Minneapolis & Omaha 

Railway station at Ottawa the river bluffs for a considerable distance expose 50 to 100 feet of gray drift. A few feet of coarse gravelly drift overlies the boulder clay, which was sampled. The clay 

slakes in three minutes and has low plasticity, requiring 19 per cent 

of water for molding. Its air shrinkage is 3 per cent, and its tensile 

strength is nearly 200 pounds to the square inch, though it checks 

slightly if rapidly dried. The abundant particles of limestone 

cause disruption of ware burned up to the temperature of cone 2 

(2,138° F.), and melting occurs at a temperature a few degrees higher. 

Before using this material it would be absolutely necessary to remove 

the limestone pebbles; but it seems worth while to call attention to it, 

because mixtures of it with the high-grade Cretaceous clays that 

occur in the same neighborhood would increase the variety of products without greatly increasing the expense or difficulty of manufacture.

The gray drift in other parts of Le Sueur County is not so good as 

the other available clays. An attempt was made to use it for brick 

at Waterville, but some swamp clays that are more promising are 

available.

At Le Sueur the alluvium of Minnesota River is favorably exposed 

beside the Chicago, St. Paul, Minneapolis & Omaha Railway and 

is typical of the deposits of the neighborhood. The river flood plain 

is not exactly level, and the clay is a little richer on the low ground 

and more sandy on the high ground. It slakes at once, has fairly
McLEOD COUNTY. 191

high plasticity, and requires 28 per cent of water for molding. Its 

air shrinkage is 6 per cent, and its tensile strength about 50 pounds to 

the square inch. Burning tests at the Minnesota School of Mines 

experiment station gave the following results:

Cone No.

03

01

1

2

3

Color.

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

3

4

7

Absorption.

Per cent. 

26

20

18

11

2

The clay becomes hard at cone 02 (2,030° Fi) and reaches viscosity at cone 3 (2,174° F.) An analysis of this clay is given on 

page 103, in the discussion of Eecent alluvium. The plant here can 

produce about 10,000 soft-mud red brick a day. These brick have 

stood the test of service since 1882 in some of the buildings in 

Le Sueur. The kiln is not down on the flood plain and so escapes the 

high water which even yet occasionally covers the deposit.

LINCOLN COUNTY.

Gray drift covers the whole of Lincoln County, and is probably 

not well situated for development, though attempts to use it have 

been made in a small way in the past. Cretaceous shales are known 

by well records only.

LYON COUNTY.

(

Pleistocene: Gray drift. 

Cretaceous: Shales. 

Archean: Residuals.

Gray drift covers Lyon County, but attempts to use it without 

removing its limestone pebbles and concretions have failed. At 

Marshall, where shipping facilities are good, it might be possible to 

clean the clay, but the business would meet competition in a wellestablished concrete block and tile factory.

Cretaceous clays are known from many well records to lie within 

50 feet of the surface, but their quality is unknown. Clay shown 

in a record as " white earth " probably has the character of the basal 

Cretaceous.

In this county the Archean probably lies too deep for consideration.

McLEOD COUNTY.

The only clays known in McLeod County are in the gray drift, but 

some recent lake clays may yet be found. .
192 CLAYS AND SHALES OF MINNESOTA.

The only brickyard in the county is at Hutchinson, where brick 

and draintile of excellent quality are manufactured from the ordinary gray drift. The glacial drift here is the same as that found 

over large sections of the State and is full of lime and quartz pebbles, 

sand, gravel, and even large boulders. The plant has been successful 

in the use of this material, with which many others have failed, 

because of the special washing process devised by M. C. Madsen, 

whereby the pebbles are completely separated from the clay. This 

process is of especial importance to all who may be interested in the 

ceramic industry, because it opens up a field for the utilization of a 

vast amount of material which has heretofore proved almost valueless. A description of this plant and the methods used is given on 

pages 55-56.

The gray drift exposed at Hutchinson consists of 16 feet of 

oxidized yellow clay, underlain by a considerable thickness of clay, 

blue in color but otherwise similar to the yellow clay. The extent 

of the deposit is to be measured in scores of square miles. As overburden there is a few inches of soil.

The clay, as used at the plant, slakes in five minutes, is fairly 

plastic, and requires 24 per cent of water for molding. Its tensile 

strength is nearly 100 pounds to the square inch and more than 75 

pounds to the square inch when rapidly dried. Its shrinkage on 

drying is 6 per cent. Burning tests resulted as.follows:

Cone No.

06

05

03

1

3

Color.

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. ' 1

1

2

7

8

Absorption.

Per cent. 

24

24

23

9

8

The clay burns too hard to be scratched with a knife at cone 06 

(1,886° F.) and becomes viscous at cone 3 (2,174° F), thus having'a 

range of about.300°. It can safely be burned to a hard but somewhat 

porous product.

A special study has been made as to the exact effects of washing on 

the nature of the clay. Samples were taken of the clay as dug from 

the bank, of the washed clay as settled in different parts of the pond, 

and of the mixture made up from the different settlings for molding 

into tile. In composition this mixture varies slightly. Analyses of 

its component clays are given in columns 2, 3, 4, and 5 of the table 

below. Column 1 gives, for comparison, an analysis of the average 

drift before washing.
MAKSHALL COUNTY. 193

Analyses of clay and washed clay at Hutchinson. 

F. F. Grout, analyst.

Silica. ...............................................

Soda.................................................

Combined water. ....................................

Titanium oxide. .....................................

1

58.85

7.25

4 97

Q At*

9.42

1.37

1.76

} 2.10

11.20

.36

100.73

2

70.21

6.27

3.16

1 V\

7.28

2.11

1.53

1 .60

\ 1.38

6.00

.19

100.28

3

62.60

6.96

3.75

3.59

7.78

1.94

1.82

1.80

2.90

7.10

.33

100.57

4

50.65

9.01

<; 9fi

3.60

10.20

1.32

1.83

3.40

6.10

8.20

.53

100. 10

5

50.55

g 41

6 19-

3.62

10.20

1.22

1.85

3.10

6.05

8.00

.60

100.79

1. Average gray drift.

2-5. Washed gray drift: 2, Coarse sand; 3, fine sand; 4, coarse clay; 5, fine clay.

Samples 2 to 5 were taken at successively greater distances from 

the inlet of the pond. It is noteworthy that though silica is high 

in sample 2, indicating a good deal of quartz sand, a notable amount 

of calcium carbonate is also present. Samples 4 and 5, though, 

taken at different distances from the inlet, are much alike in composition and apparently also in size of grain. The alumina and 

combined water are higher in this fine clay, indicating more kaolinite, but so also are the iron oxides and calcium carbonate. It" appears to the writer that the washing process has been of benefit in 

the matter of texture rather than in that of composition. The great 

and essential change is the elimination of the limestone pebbles. .

MAHNOMEN COUNTY.

Pleistocene gray drift, with a little more lime and less sand than 

is usually found in the gray drift, covers Mahnomen County except 

where recent swamp deposits occur. The swamp deposits may prove 

to be worth investigation, but such clays are not so abundant as in. 

counties near by.

MARSHALL COUNTY.

The silts of the Red River valley overlie the gray drift in much 

of Marshall County. North of Warren the clay along the river has 

been used for many years. It is known to extend over 100 acres. 

The following is an average section:

General section north of Warren.

Feet.

Black soil_______________-____ - * 

Yellow to brown alluvial clay___________ 4 

Pebbly brown alluvial clay_ -, 6-10 

Yellow-gray stratified sand and gravel . 10 

Hard blue smooth, plastic clay. 

64310° 19 13
194 CLAYS AND SHALES OF MINNESOTA.

The upper 4 feet are almost free from pebbles and are used occasionally for making soft-mud cream-colored brick. The underlying 

blue clay was tested at the plant and reported useless for common 

brick.

MARTIN COUNTY.

Companies with capital invested have sought for good clay in 

Martin County, and have offered prizes for its discovery without 

Buccess. A fine silty clay of doubtful origin, suitable only for hand 

molding, occurs at Granada. Surface loam was used for brick on 

the south side of Buffalo Lake, but the product was not of high 

quality. The rest of the county is covered with gray drift, which is 

usable only if the limestone pebbles can be economically removed.

A plant at Fairmont formerly used clay from Blue Earth, Faribault County. (See p. 156.)

MEEKER COUNTY.

(

Pleistocene: 

Gray laminated clay. 

Gray drift.

Near Litchfield and Kingston brickyards were operated for years 

on some laminated clays that were apparently formed in basins in the 

ice. Limy concretions occur in layers. The gray drift.north and 

west of Litchfield consists largely of clay but is somewhat pebbly. 

South of Watkins the gray drift crops out at many places, but would 

require the usual cleaning treatment before successful use could be 

made of it. An attempt which did not include the removal of limestone pebbles was a complete failure.

MILLE LACS COUNTY.

 

Recent: Lake and swamp clay.

~, , . ,. ,. Pleistocene: Clay-bearing formations < _ . , , .

1 Gray laminated clay;

Red drift.

At Brickton, north of Princeton, two or more brick factories are at 

work upon a deposit of laminated clay, apparently of the common 

yellow-gray type, which extends across Mille Lacs County in a belt 

apparently controlled by the position of the glacial ice. Under the 

soil lies a superficial layer of clay, rarely over 4 feet thick, which 

has lost its- laminated structure and which has apparently been so 

leached of lime that it burns red. Below this is 10 feet of yellow 

clay, underlain by 10 feet of gray clay. All these clays are usually 

worked together, mixed in the same proportion in which they are 

found. Below the gray clay is a considerable thickness of joint 

clay, which is reported as being greasy but which cracks too readily
MILLE LACS COUNTY. 195

on drying to be satisfactorily used. Wells drilled through this joint 

clay find a water supply in gravel and sand just below it. (See 

fig. 28.) A few layers of the clays used contain ferruginous and 

calcareous concretions, but these do not cause much difficulty. As is 

usual in such deposits, 

sand occurs throughout 

in pockets or irregular 

streaks. The clay in 

some pits is more suitable for soft-mud than 

for stiff-mud processes, 

but the main product is 

manufactured with stiffm u d m a c h i n e s. A 

smaller proportion is 

made light, for fireproofing, by a central 

opening. Auger laminations cause considerable difficulty unless the 

clay is well mixed.

The clay slakes at once and develops only medium or low plasticity requiring 25 per cent of water. The shrinkage on drying is 7 

per cent, and the tensile strength is over 150 pounds to the square 

inch, even when rapidly dried. Burning tests resulted as follows:

28. Geologic section at Brickton.

 9110 No.

05

03

01

2

3

Color.

Buff. ......................./...

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

1

2

8

10

Absorption.

Per cent. 

28

27

24

14

8

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity about cone 4 (2,210° F.).

The combined capacity of the plants operating at Brickton is 

about 15,000,000 brick in a season. The average brick produced 

were found by the experimental engineering department of the 

University of Minnesota to have a crushing strength of 2,000 pounds 

to the square inch.

The surface clay at Brickton, where weathered and leached, is 

reported as shrinking 8 per cent on drying,-but it fuses about as 

suddenly as the main mass of clay. It has a good red color when 

.burned.

Nearly all the rest of Mille Lacs County is covered with gravelly 

red drift. Only one attempt has been made to manufacture brick
196 CLAYS AND SHALES OF MINNESOTA.

from it at Wahkon, on the Minneapolis, St. Paul & Sault Ste. 

Marie Kail way. Here the drift contains fully the average amount 

of sand and gravel and was used with no attempt at cleaning or 

even at fine crushing. The product made in the one kiln that was 

burned was naturally of rather- low quality. The clay, after being 

crushed to pass a 40-mesh sieve, has a fairly high plasticity, requiring 20 per cent of water for molding. The air shrinkage is about 

5 per cent and the tensile strength about 100 pounds to the square 

inch. Burning tests gave the following results:

Cone No.

05

03

1

2

3

Color.

Eed...... ...................... .....do....................:....

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

3

6

6

Absorption.

Per cent. 

14

10

4

5

The clay becomes hard at cone 0-1 (1,958° F.) and reaches viscosity at 

cone 3 (2,174° F.). Such clay, or even better red drift, may very 

likely be discovered nearer to favorable markets or shipping facilities. There is probably some near Milaca, but it is not well explored.

In the midst of large areas of red drift there are numerous 

swamps, some of which cover 40 acres, and in the few places where 

the clay is exposed in the bottoms of the swamps it is of va-rying 

thickness, dependent on the depth of water in the original.lake. A 

few feet of gray and brown clays have been exposed in ^several places 

by drainage ditches. A sample taken west of Wahkon, near the 

middle of sec. 24, T. 42 N., R. 26 W., slakes at once and shows high 

plasticity, requiring 20 per cent of water for molding. Its tensile 

strength is about 100 pounds to the square inch, even when rapidly 

dried, and its air shrinkage is 5 per cent. Burning tests resulted as 

follows:

Cone No.

05

04

02

1

Color.

Red............................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

1

4

6

Absorption.

Per cent. 

15

14

1

The clay,becomes hard at cone 05 (1,922° F.) and reaches viscosity 

at cone 1 (2,102° F.). It is evidently typical of the lake and swamp 

clays of the red-drift region. Most of them would be capable, of 

making a thoroughly hard, satisfactory brick.
CLAYS AND SHALES OF MINNESOTA. 197

MORBISON COUNTY.

Clay-bearing formations.

Pleistocene:

Gray laminated, clay.

Gray drift.

Red drift.

Cretaceous: Shale and conglomerate. 

Huronian: Residual clay.

Bed drift has been deposited over most of Morrison County, 

though in some places the abundance of limestone pebbles makes it 

more like the northwestern gray type. Gray laminated clays were 

brought in by streams from the gray-drift area and are the clays 

now used. Cretaceous deposits fare of interest but are not yet 

developed.

Two or three miles west of Little Falls, Pike Creek has eroded 

a channel through a deposit of laminated clay which has been utilized 

for cream-colored brick at two yards. The upper 6 feet is yellow 

and is underlain by an unknown depth of a much more plastic gray 

clay, here called joint clay. Thin layers of the joint clay alternate 

with the yellow in the lower part of the bank now worked, and 

about 2 feet of the thoroughly fresh joint clay can be mixed with' 

the (3 feet of yellow clay without causing too much danger from 

checking. The average clay slakes in three minutes, is highly plastic, and requires 24 per cent of water for molding. The air shrinkage is 5 per cent, and the tensile strength is about 150 pounds to 

«the square inch, even when rapidly dried. As burned at the Minne- 

*sota School of Mines experiment station it gave the following results:

Cone No.

01

2

3

5

Color.

Yellow.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

91

f

Absorption.

Per cent. 

30

25

25

The clay becomes too hard to be scratched with a knife at cone 01 

(2,066° F.) and reaches viscosity at cone 4 (2,210° F.). It has been 

used for nearly 30 years, mostly for soft-mud cream-colored brick, 

though stiff-mud machinery has been used in recent years. Each 

plant has a capacity of about 40,000 brick a day.

Two River has cut a channel at Bowlus into a deposit of laminated clay which is many acres in extent and appears to be almost 

identical with that at Little Falls. The tensile strength of this clay; 

 however, is somewhat lowered by rapid drying, and the temperartur6 of vitrification is slightly lower. The Bowlus Brick & Tile Co. 

was organized several years ago to work this deposit and can manufacture 40,000 soft-mud brick a day.
198 CLAYS AND SHALES OF MINNESOTA.

Along Mississippi River, from Little Falls southward, there are extensive outcrops of the staurolitic 

biotite schist and its decomposition products that 

are of interest in this connection. (See fig. 29.) As 

noted by Winchell,1 a dike of basic dolerite about 10 

feet wide crosses the schists diagonally just below 

Little Falls. Preglacial decomposition of the slates 

(or schists) produced a clay which has locally been 

protected by a more resistant dike from both water 

and ice erosion. A few miles south of Little Falls, 

at the Minneapolis, St. Paul & Sault Ste. Marie 

Eailway bridge, there is to be seen a similar layer 

of decomposed mica schist which apparently had no 

harder rock to protect it. The decomposition therefore seems to have been general, and the resulting 

clay is of wide extent under the drift. It could be 

followed 100 yards and was seen on both sides of 

the river. With an auger it was shown to be over 6 

feet thick and to become only slightly harder at 

that depth. It is probably many feet to solid rock. 

The clay still contains a large amount of partly decomposed mica but is so much decomposed that it is 

waxy and plastic and can be easily molded. It is 

interesting to note that in some places the schist is 

Staurolitic, and that the staurolite remains as loose 

crystals in the clay. Still farther south, near, the 

mouth of Little Two Eiver, material of the same 

sort is exposed at the wagon-road bridge. ; This material, on account of the silvery mica scales, formerly caused great agitation and considerable prospecting for silver. The further extent of material 

of this sort is indicated in a report by Upham.2 At 

the mouth of Two Eiver a well was dug 25 feet and 

bored 4 feet farther into decomposed schist. All the 

rock thrown out weathered to powder within a few 

weeks. As a clay, this material slakes at once and 

requires 33 per cent of water for molding. It 

shrinks 5 per cent on drying. It burns red but remains soft up to cone 6 .(2,282° F.) and is past viscosity at cone 12 (2,498° F.). It can hardly be considered safe for vitrification but is a peculiar tjp& 

that is more refractory than the common drift and 

recent clays. An analysis by A. .W. Ganger resulted as follows:

1 Winchell, N. H., Minnesota Geol. and Nat. Hist. Survey Final Kept., vol. 2, p. 596, 

1888.

2 Upham, Warren, idem, p. 599.

v'o t

a>

T
MORRIS01T COUNTY.

Analysis of clay from decomposed biotite schist on Two River.

Silica___________________________________ 57.20 

Alumina _________________________________ 18. 23 

Iron oxides ____________________________ 11.04 

Magnesia ___________^__________________ 1. 02 

Lime __________________________ __________ . 72 

Soda-_____ ________________________ . 61 

Potash________________________________ . 98 

Loss'on ignition ____________.______________ 5.96 

Moisture ________________________________ 2. 48 

Titanium oxide______,______________________ 1. 52

199

99. 76

Cretaceous clay and shale apparently overlie the clays just described. They dip slightly to the south' and are best exposed in the 

banks of Mississippi and Two rivers, 2 miles east of Bowlus. An 

instructive outcrop occurs at the bridge on the road from Bowlus to 

Royalton. (See fig. 29.) A few hundred yards north of the outcrop, 

near the mouth of Little Two River, where one might expect the 

same clay to occur higher in the bank, it has evidentty been eroded 

and the Huronian residual material is exposed. The Cretaceous 

clays were obviously derived by erosion of the weathered Huronian 

below. In the outcrop near the bridge the material ranges from 

massive white clay to a highly concretionary, very ferruginous red 

clay. The two extremes were separately sampled but were found to 

behave very similarly. They do not slake when placed in water nor 

develop much plasticity even after grinding. They remain soft up 

to a temperature of cone 13, although the more ferruginous sample 

becomes harder than the other. They stand the temperature of cone 

13 (2,534° F.) without the slightest deformation and are evidently 

somewhat refractory. Analysis No. I,1 in the following table, was 

apparently made on the hard light-gray clay of concretionary type, 

and both the analysis and the texture indicate the mineral bauxite. 

The presence of bauxite in the more ferruginous material has been 

confirmed by Oliver Bowles.

Analyses of bauxitic clay near Little Two River.

Silica ...............................................................................

1

19.81

52.43

1.32

23.23

1.64

98.87

2

22.42

.43

.59

18.45

98.75

1, Analysis by Prof. Bodge; 2, analysis by Oliver Bowles.

1 Winchell, N. H., Minnesota Geol. and Nat. Hist, Survey Final Rept., vol. 2, p. V G02, 

1888.
200 CLAYS AND SHALES OF MINNESOTA.

Mr. Bowles further tested the material to ascertain the amount 

extracted with sulphuric acid and gives the following estimate of the' 

mineral composition:

Mineral composition of bauxitic clay near Little Two River.

Bauxite_____________________.___________ 22.24 

Kaolin_^___________'.______________.___________ 48.21

Limonite_____________________.___________ 24.98

The bauxite could not.be concentrated by simple crushing or grind-"1, 

ing and screening. This deposit has probably as high a proportion' 

of bauxite as any other in Minnesota. (See also Redwood County,' 

pp. 216-220.)

A little farther south a shale containing Cretaceous fossils and a' 

thin layer of lignite was sampled near the road bridge over Missis- \ 

sippi River, a few rods up Two Eiver from its mouth. It is exposed 

for a thickness of 10 feet and can be traced for more than 200 yards 

along the banks. It is gray and waxy and apparently contains 

numerous small mica scales. Where exposed it had very little over-' 

burden, but if followed any distance it would undoubtedly be found 

covered with glacial drift. It dips a few degrees toward the soutK 

and is underlain by the white basal Cretaceous clay already described.' 

The clay slakes in two minutes and is not very plastic. It requires. 

26 per cent of water for molding and shrinks less than 4 per cent on 

drying. At cone 4 (2,210f F.) it is salmon-colored and has just 

become hard. It reaches viscosity at about cone 10 (2,426° F.). It 

is hoped that some of the more plastic layers will serve ks a plastic 

bond for the nonplastic refractory clay which occurs in the vicinity.

MOWER COUNTY.

Clay-bearing formations

Pleistocene:

Loess.

Gray drift. 

Cretaceous: Shale. 

Devonian: Shaly limestone.

At Austin clays that appear to be Cretaceous overlie the eroded 

edges of the Devonian rocks. A quarter of a mile northwest of the 

Chicago, Milwaukee & St. Paul Railway station the Austin Brick & 

Tile Co. has opened a deposit 1 to 20 feet thick that underlies perhaps 

93 acres. Although the clay is described as Cretaceous, it is somewhat 

modified and is disturbed apparently by glacial action, and its Cretaceous age is questioned by Sardeson.1 The clay is variegated in 

color and contains a few pebbles and rocks, especially where "most' 

disturbed near the surface. Glacial drift overlies it but is only a few 

feet thick. The irregular surface on which it rests is composed of

1 Sardeson, F. W., The so-called Cretaceous deposits in southern Minnesota: Jour. Geology, vol. 6, p. 679, 1898.
MOWER COUNTY. 201

sandstone and dolomite with a thin upper layer of blue clay rarely 

over 6 inches thick. (See fig. 30.) The clay slakes in three minutes 

and has a very high plasticity, requiring 31 per cent of water for 

molding. It shrinks 7 per cent on drying and has a tensile strength

5ft

^=^sg=^g Ferruginous shale and flint 1 ft

Mixed and sllckenslded clay, red,

yellow, brown, and blue.

10-20 ft

%S^ a/X^IX ResWual ClaV °n

^~~^-^/ I ^ eroded surface 6 ia

1 - Devonian sandy dolomite FT

i

FIOCRE 30. Geologic section at Austin.

of about 100 pounds to the square inch, even when rapidly dried. 

1 As burned at the Bureau of Standards it gave the following results:

Cone No.

013 

010

< . 08 ' 

06

03

Color.

Salmon ........................ 

.....do.........................

.....do......................... 

Bed............................

.....do.........................

Shrinkage.

Per cent. 

High......

...do...... 

...do...;..

...do......

Absorption.

Per cent. 

25 

20

9 

1

1

There was a little trouble from checking, but it was not serious. The 

porosity was low over a good range of temperature. The clay is 

hard -but not melted at all the specified temperatures.

The factory has a capacity of 60,000 brick a day. Experiments 

with the different materials available for making high-grade products have yielded excellent results. The clay commonly burns red, 

but when mixed with the underlying Devonian rock it yields buff 

and cream-colored ware of equally high grade. The Devonian rock 

alone burns to a lime rather than to a clay product. To obtain the 

light colors, a fairly high proportion of the rock must be used. 1 

The lime may lower the melting point so much that the mixture 

is undesirable for making vitrified brick, but it is good for com-' 

mon brick. The 6-inch layer of blue clay between the bedrock and 

the''Cretaceous has also been burned, but the deposit is too small to] 

be of much value. It does not differ greatly from the main body of.
-202 CLAYS AND SHALES OF MINNESOTA.

the clay. Both contain a little organic matter and need thorough 

oxidation in burning.

At the northwest corner of the property, about a quarter of a mile 

from, the present pit, an excellent clay that is at least 20 feet thick 

and covers several acres has been developed by drilling. It is somewhat stratified and very highly plastic, though it contains some fine 

grit. Only 2 or 3 feet of soil lies above it, and no impurities were 

discovered except a 6-inch layer of sand. The clay slakes in five 

minutes and is highly plastic but requires only 15 per cent of water 

for molding. It has a tensile strength of over 100 pounds to the 

square inch, and its air shrinkage is less than 4 per cent. As burned 

by the Minnesota School of Mines experiment station, it gave the 

following results:

Cone No.

05

1

3

5

13

Color.

Buff..........................

.....do:.......................

.....do........................

.....do..!....:................

Shrinkage.

Per cent. 

0.3

1.0

1.0

2.0

Absorption.

Per cent. 

10

9

9

8

4

The clay becomes too hard to be scratched with a knife at cone 05 

(1,922° F.) and is undeformed and perfect at cone 13 (2,534° F.). 

It may prove to be highly refractory, but as it burns dense at moderate temperatures it is more suitable for stoneware or retorts than 

for fire brick. Probably such Cretaceous deposits may be found elsewhere in the neighborhood by detailed prospecting with augers and 

drills. An outcrop near Frankford seems toloe Cretaceous.

A clay from the vicinity of Brownsdale was analyzed by C. F. 

Sidener. 1 Its origin is not stated, but it is probably similar to that 

near Austin.

Analysis of clay from the vicinity of Broionsdale. 

Silica___________!_____________________ C3. 64 

Alumina_____:__________________________ 24. 95 

Iron oxides_____________________________ 4.90 

Magnesia____________________'___________ . 20 

Lime____________________________________ 1. 02 

Soda______.___________________________ . 66 

Potash____;_______i_______________j»__ . 31 

Loss on ignition________,.__________________ 4. 32

100.00

The gray drift covers nearly all of Mower County, except the bottoms of the stream valleys. At many places, where free from gravel 

and other coarse impurities, it may be utilized for common red brick;

1 Minnesota Geol. and Nat. Hist. Survey Nineteenth Ann. Kept., p. 122, 1891.
NICOLLET COUNTY. 2oa

The loess of this county is unimportant. Abandoned brickyards were 

note.d near Frankford, High Forest, and Leroy, where common brick 

were made from the glacial drift and the loess.

Limy shale and shaly limestone of Devonian age occur at several 

localities in Mower County, notably near Frankford along Deer 

Creek, and near Leroy along upper Iowa River, in the eastern part 

of the county. The Devonian clays at Austin contain 15 per cent 

of magnesia and 20 per cent of lime. Probably none are of value for 

brick or other clay products, for they are all nonplastic, sandy, and 

impure.

MURBAY COUNTY.

Murray County has only gray drift of the usual pebbly type, which 

has been tested and found identical in behavior to that used at 

Hutchinson.

NICOLLET COUNTY.

Clay-bearing formations

Recent: Alluvium. 

Pleistocene: Gray drift. 

Cretaceous: Shale.

In Nicollet County, opposite Mankato, -brick are manufactured 

from river clay, which seems to be essentially similar to that on the 

Mankato side in Blue Earth County. The clay is not continuous over 

"the whole of the river flat but occurs in patches surrounded by more 

sand}r or gravelly deposits. The plant has a capacity of over 

2,000,000 brick a season. Similar clay is found at Judson, several 

miles up the river on the Nicollet County side.

At St. Peter, where the Chicago & Northwestern Railway crosses 

Minnesota River, a considerable area is occupied by alluvial clay, 

which has the usual appearance and is apparently of the same 

quality as that found all along the river. It was used 20 years ago 

for brick to build the asjdum at St. Peter, and a similar deposit was 

developed just across the river at Kasota. Both plants are now 

closed. The clay slakes at once and has low plasticity. Its tensile 

strength is 150 pounds to the square inch and its shrinkage 4 per 

cent. In burning it gave the following results:

Cone No.

02

01

1

3

4

Color.

.....do........................

.....do........................

Shrinkage.

Per cent. 

1

2

6

10

Absorption.

Per cent. 

25

20

15

7

The" c\&y becomes hard at cone 01 (2,066° F.) and reaches viscosity 

at cone 4 (2,210° F.).
204 CLAYS AND SHALES OF MINNESOTA.

Clay and limestone 3 ft.

Several outcrops of Cretaceous shale are shown on geologic maps 

of the county. These are very close to New Ulm and are apparently similar to those in Brown County. A shale 10 feet thick in

sec. 34, T. 110 N., R. 30 W., 

that outcrops at John Heinmanri's limekiln, can be traced 

by poorer exposures for several hundred yards along a 

small creek and by scattered 

outcrops for miles. The shale, 

which is easily accessible at 

the limekiln, underlies glacial 

drift and contains some small 

layers of limestone. Its color 

is variegated, and its quality 

seems to differ within short 

distances. (See fig. 31.) The 

clay slakes only to lumps in 

10 minutes. It is highly 

plastic and requires 23 per 

cent of water for molding. Its air shrinkage is 7 per cent, and its 

tensile strength is over 100 pounds to the square inch, though somewhat less if rapidly dried. As burned by the Minnesota School of 

Mines experiment station it gave the following results: |

_~I_T"-T~_lr_ir"_n~jr_rjI~_7_3small amount of limestone

(4 ft. observed)

31. Geologic section opposite New Ulm.

Cone No.

05

03

2

Color.

.....do........................

Red..........................

Shrinkage.

Per cent. 

0

1

3

Absorptioi.

Per cent. 

14

13

9

The clay becomes hard at cone 05 (1,922° F.) and is still undeformed 

at cone 3 (2,174° F.) if not heated too rapidly. Organic matter is 

likely to cause the formation of black cores with great swelling and 

deformation, unless time is allowed for thorough oxidation. Similar clays can be traced by scattered outcrops for several miles along 

the Nicollet County side of the river.

NOBLES COUNTY.

The clay in Nobles County is the common gray drift, most of 

which is somewhat pebbly and not very satisfactory, though brick 

and tile were made at Worthington from a bank less pebbly than the 

average. If market conditions favored it a plant of the type working at Hutchinson or Jackson might succeed.
OLMSTED COUNTY. 205

NORMAN COUNTY.

Half a mile from Ada is a deposit of the laminated clay of the 

Bed River valley that has been proved over 5 acres and apparently 

covers the whole region. Borings 15 feet deep did not reach its bottom. There is no overburden but the soil. The clay is weathered 

yellow for about 10 feet below the surface and includes one 6-inch 

sandy layer. Brick made from this clay have been used in nearly 

all the brick buildings in Ada and have stood the test of service 

very well. The plant has not been operated since 1906. The usual 

differences are observed between the blue and yellow clays.. The 

blue clay is exceptionally plastic and requires 52 per cent of water 

for molding. It shows a shrinkage of 17 per cent on drying. It is 

almost impossible to prevent serious cracking during drying, but 

if care is used the tensile strength is over 250 pounds to the square 

inch. This clay has the further defect of containing so much 

organic matter as to form black cores and to swell considerably, 

even if heated with great care. The yellow upper part of the deposit apparently gives best results without addition of much of the 

lower blue clay. A burning test on the yellow clay resulted as 

follows:

Cone No.

' 04

02

2

3

5

Color.

Buff..........................

.....do........................

.....do........................

.....do........................

Shrinkage.

Per cent. 

1

2

4

6

Absorption.

Per cent. 

19

16

11

6

The clay is hard after burning to cone 03 (1,994° F.) and reaches 

viscosity at cone 4 (2,210° F.).

The blue clay below this yellow clay, though so fine grained and 

so full of organic matter that it is difficult to burn, becomes hard 

at cone 012 (1,634° F.), a much lower temperature.

Clay-bearing formations

OLMSTED COUNTY.

Recent :

Marsh and lake clays.

Alluvium. 

Pleistocene:

Loess.

Gray drift. 

Ordovician:

Shale in. Galena limestone.

Decorah shale.

Red brick have been made from the glacial and recent clays at a 

number of localities in Olmsted County. There is hardly a town
206 CLAYS AND SHALES OF

of any size in the county that has not a deposit of gray drift, loess, 

or alluvium from which common brick of fair quality could be made. 

Such brick have been made in years past at Byron, Simpson, Oronoco, 

Eyota, and Pleasant Grove. The most valuable clay formation in 

the county, the Decorah shale, has never been utilized, though it 

should receive attention rather than the inferior glacial drift and 

alluvium, which in many places are mixed with loess.

The distribution of the Decorah shale in Olmsted County is shown 

on the accompanying map (fig. 32). Its elevation above sea level is 

1,125 to 1,200 feet. The most favorable localities for its use in the 

manufacture of ceramic products are in the vicinity of Eochester and 

Byron. In the southern part of the county the shale crops out on

FIGUHE 32. Map of Olmsted County. Dotted area underlain by Decorab shale.

both sides of the north branch of Root Eiver, but it is of small thickness and is inaccessible at present. The relation of the shale to the 

topography is shown in figure 33. Shale also crops out on the 

South Branch of Zumbro River. Where the overlying limestones 

are missing and where the shale is covered by nothing but the glacial 

.drift its presence is not easily detected, but where the neighboring 

outcrops give no sign of its removal it has been mapped as if present. 

Around Rochester, where a thin layer of the Decorah shale caps 

many of the hills, it is covered only by a few feet of drift and soil. 

Its use is recommended.

About 2£ miles north of Byron, on the Patterson farm, the Decorah is about 50 feet thick and covers many acres. Although the 

economic conditions are not especially favorable here the shale is
OLMSTED COUNTY; 207

certainly indicative of what could be found in other parts of the 

county. Its plasticity is very high. It requires 35 per cent of water 

for molding and has a shrinkage of 11 per cent on drying. In burning it has the usual tendency to form a black core and destroy the 

brick if the heating is too rapid. The brick are red and are hard 

after heating to cone 012 (1,634° F.) and a temperature of cone 02 

(2,030° F.) can be reached in a slow furnace without the loss of the 

product. The range of vitrification, is as great as the Decorah shows 

elsewhere, and well-vitrified products can be made.

At Eochester there is a considerable deposit of alluvium along 

Zumbro Eiver, covering an area of 40 acres to a depth of 5 feet or 

more. Its clay content at least in part is thought to be derived from 

the neighboring Decorah shale. It occurs in patches alternating 

with sandy and even gravelly material, as in most alluvial deposits. 

A sample taken on Charles Kruessel's land slakes in one minute, is

FIGCKE 33. Profile showing topographic features of Decorah shale outcrop in Olmsted

County.

highly plastic, requires 32 per cent of water for molding, and shrinks 

6 per cent on drying. Burning tests gave the following results:

Cone No.

00

05

1

3

5

6

Color.

Salmon. ......................

Red..........................

.....do........................

.....do........................

.....do........................

.....do........................

Shrinkage.

Per cent.

2

5

6

6

6

Absorption.

Percent.

13

9

8

6

5

The clay becomes hard at cone 05 (1,922° F.) and has not reached 

viscosity at cone 5 (2,246° F.). It has thus a range of vitrification 

of considerably over 300° and should be capable of burning to 

thorough vitrification without loss. Its extent and quality recommend it for further investigation.

A mile south of Byron, at a bridge on the county road, there is 

an exposure of 5 or 6 feet of the Galena shale interbedded with
208 CLAYS AND SHALES OF MINNESOTA.

limestone. This shale is not of as good quality as the sample from 

Fillmore County (pp. 158-162). It contains a larger proportion of 

lime and requires a higher temperature for thorough burning, its plasticity is not so good, and the abundance of lime has a very strong 

tendency to destroy the bri-ck, even after burning to as high a temperature as cone 4 (2,210° F.).

For 25 years a plant was at work near Byron station, on the 

Chicago & Northwestern Railway, on a deposit of yellowish sandy 

loess, which is 4 feet thick and extends over many acres. Over a 

million brick a year were produced, but the plant was burned in 

1910 and has apparently been abandoned. (See fig. 9, p_. 99.)

OTTER TAIL COUNTY.

{

Pleistocene: 

Gray laminated clay. 

Gray drift.

* In Otter Tail County the gray drift is abundant, but the widespread laminated clays are much more valuable.

In Fergus Falls a deposit of laminated clay was used 20 years ago 

in making a rather soft and poor grade of yellow brick. The poor 

grade was possibly due in part to the method of burning, but probably also to the sandy nature of the clay. The clay is covered by 

only a thin layer of soil and contains no pebbles. Its working qualities seem to be satisfactory, though its plasticity is low. It shrinks 

4 per cent on drying and develops a tensile strength of 100 poundsto the square inch. It burns buff and has an absorption of 35 per 

cent up to cone 2. Viscosity is reached at cone 5. If market conditions are favorable it is worthy of further investigation. The hills 

south of Fergus Falls may contain similar clay.

Two miles west of Perham station is a deposit of laminated clay 

that covers at least 20 acres and is at least 15 feet thick. Yellow and 

blue-gray clays alternate in this deposit, and the oxidation that produced the yellowish color apparently affected the beds that allowed 

more rapid circulation. A very few limestone pebbles and a great 

many cylindrical ferruginous concretions were observed. The clay 

lies under an overburden of thin soil. Its working qualities are fair, 

though it is likely to crack in drying. A burning test resulted as 

follows:

Cone No.

03

01

2

3

Color.

Buff............................

.....do.........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

5

6

7

9

Absorption.

Per cent. 

24

20

15

3
OTTEK TAIL COUNTY. 209

The clay is hard after burning to cone 03 (1,994° F.) and reaches 

viscosity at cone 3 (2,174° F.) but has a strong tendency to warp 

and check and cause loss. The Northwest Brick Co. has been producing common yellow brick from it for nearly 40 years. Economic 

conditions, except in the matter of railroad shipping facilities, are 

excellent.

The Deer Creek Brick Co. has opened a pit 4 miles northwest 

of Deer Creek, in- which are exposed 15 feet of yellow clay and 15 

feet of blue-gray clay, all laminated in horizontal layers. The clay 

underlies 3 to 6 feet of bouldery drift. Its working qualities seem 

to be excellent. It burns hard and buff-colored at cone 2 and reaches 

viscosity at cone 6. The company, which was organized several 

years ago, has been producing about 10,000 brick a day on half-day 

shifts.

At two points near Battle Lake laminated clays of the same type 

are known. A. C. Hatch's brickyard used a clay which occurs on the 

opposite side of Battle Lake, is mined by blasting when frozen, and 

is hauled across the lake on the ice. A reasonable success was made 

of a small plant, but the clay is nearly exhausted. Two miles southeast of Battle Lake, on the banks of Clitherall Lake, deposits of 

similar clay more than 12 feet thick cover many acres.

At Pelican Rapids the following section was observed in sec. 22, 

T. 136 N., R, 43 W.:

Section of drift at Pelican Rapids.

Feet.

Gray drift______________________________ 1-15 

Yellow laminated clay______________________ 12-14 

Blue laminated clay________________________ 4- 6 

White sand.

The clay, both yellow and blue, was worked until about 1905, when 

a part of the deposit was reached in which the overburden was so 

great that operations were no longer profitable. Each clay slakes 

promptly and shows a fair degree of plasticity with 30 per cent of 

water. The top of the yellow clay is in some places more sandy 

than the clay below. The tensile strength is about 150 pounds to 

the square inch, and the air shrinkage is 6 per cent. Burning tests 

were more favorable for the blue clay, which gave the following 

results:

Cono No.

ni

02

01

2

5

Color.

.....do..........................

Buff...........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

2

9

Absorption.

Per cent. 

27

26

25

16

64310 c -14
210 CLAYS AND SHALES. OF. MINNESOTA.

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at cone 4 (2,210° F.). The yellow clay has a similar but 

slightly more rapid vitrification.

A mile north of Pelican Kapids is a very extensive accumulation 

of clay more than 10 feet thick, which has about the average character of the gray drift. It can hardly compete with the laminated 

clays near by.

PENNINGTON COUNTY.

At Thief River Falls a considerable deposit of clay 4 or 5 feet 

thick, probably worked over by Lake Agassiz, was used many years 

ago. The deposit is nearly worked out so far as satisfactory material is concerned. The fact that excellent brick were riiade here 

indicates that if other alluvial clays are found they may be.profitably 

developed.

PINE COUNTY. .

Clay-bearing formations

Recent: Swamp clay. 

Pleistocene:

Red laminated clay.

Red drift.

The red drift of most of Pine County was deposited by a glacier 

that traversed the Lake Superior basin, but older red drift from the 

north lies below, and the gray drift extends into the southern part 

of the county. Recent swamp clays are most promising and occur at 

many accessible points. In a few years, if railroads are extended to 

points along St. Croix River, it may be possible to develop red 

laminated clay at Sunshine and many places near Grantsburg. These 

clays are almost identical in occurrence and behavior with the laminated clays now extensively used at Menomonie and Grantsburg, 

Wis. For analysis of this red clay see page 97.

A plant was in operation for many years just south of Pine City 

along the railroad, using a deposit of glacial outwash. The clay 

slakes at once and is too sandy to show much plasticity. It shrinks 

only 2 per cent on drying and has a tensile strength of over 

100 pounds to the square inch. Burning tests resulted as follows:

Cone No.

04

02

1

3

Color.

Rod.............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

0

1

o

Absorption.

Per cent. 

10

14

11

10

The clay is hard after heating to cone 02 (2,030° F.) and reaches 

viscosity at about cone 4 (2,210° F.).
POLK COUNTY. 211

PIPESTONE COUNTY.

A large territory around and east of Pipestone is covered with 

gray drift over 10 feet thick. As compared with that at Hutchinson, 

which is successfully used, this material contains 22 per cent of sand 

instead of 30 per cent, and 6 per cent of lime instead of 9 per cent, 

but as the clay vitrifies with about the same range and temperature 

the slight differences are of no consequence. The shipping facilities 

at Pipestone are favorable, four railroads branching in different 

directions. Competition is almost entirely from the south, partly 

from Sioux City, Iowa, and partly from Luverne, in Rock County, 

Minn. It seems certain that products of the excellent quality now 

produced at Hutchinson can be made here, -and this locality is recommended for careful consideration. (See fig. 10, p. 100.)

POLK COUNTY.

(

Recent: Lake clays. 

Pleistocene * 

Silts of'the Red River valley. 

Gray drift.

The silts of the Red River valley are worked at Fertile, East 

Grand Forks, and Crookston. They are of several types, because 

clays accumulated in the Lake Agassiz basin by several different 

methods. Lake clay has been tried out at Langby. The pebbly drift 

is not used.

At Fertile the deposit resembles a river delta, occupies about 40 

acres to a depth of 40 feet, and is distinctly bedded, the beds dipping' 

toward the present river channel. The clay is yellow and calcareous 

and has very little overburden. Many sandy layers are included 

and are in proper proportion to improve the working quality if 

the whole section from top to bottom of the bank is used. The 

clay slakes in five minutes and becomes highly plastic. The air 

shrinkage is 6 per. cent, and the tensile strength is about 130 pounds 

to the square inch. Burning tests resulted as follows:

Cone No.

03

1

3

4

5

Color.

Bud...................... .....

.....dn..... ............. .......

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

0

5

10

Absorption.

Per cent . 

25

24

18

9

The clay is hard after burning to cone 1 (2,102° F.) and reaches 

viscosity at cone 6 (2,282° F.). The plant is producing cream-colored 

and white brick by the stiff-mud process. The capacity is about 

3,000,000 brick a season, but the brickmaking is interrupted to make 

some hollow blocks and draintile. The brick have been tested by
212 CLAYS AND'SHALES OF'"MINNESOTA.

E. Brydone-Jack, of Winnipeg, and have a crushing strength of 2,000 

to 3,500 pounds to the square inch. The hollow brick have a strength 

of over TOO pounds to the square inch.

Two companies are operating on laminated clays at Crooks'ton. 

The Boukind Carlson Brick Co. has a deposit within the city limits 

which can be traced along the river and is known to a depth of at 

least 12 feet. It is covered only with soil and is underlain by brown 

and blue clay of unknown thickness. It contains a "few limestone 

pebbles and limy concretions. The laminae are paper-thin in the 

upper part of the bank but thicken to 3 or 4 inches in the lower part. 

The clay can not be rapidly dried without" checking, and it shrinks 

10 per cent in the process; but it is plastic and has a tensile strength 

of 160 pounds to the square inch. Burning tests resulted as follows:

Cone No.

03

2

4

6

Color.

Buff.............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

1

2

7

Absorption.

Per cent. 

24

20

8

The clay is hard after burning to cone 2 (2,138° F.) and reaches 

viscosity at cone 6 (2,282° F.). The plant produces about 4,000,000 

common brick a season by a soft-mud process. The fuel has been 

wood, but recently oil fuel has been tried. The Crookston Brick & 

Tile Co. exploits the same deposit close to the sawmill. The clay 

here, as exposed in the pit, is a little more sandy but otherwise is of 

the same character as that just described. The capacity of the plant 

is about the same. The city building inspector of Minneapolis, in 

testing a set of six brick from this deposit at Crookston, found a 

range from 1,950 to 3,350 pounds to the square inch, with an average 

of 2,500 pounds. The blue clay of the lower levels shows the usual 

checks in drying and is so full of organic matter that it is very -difficult to prevent black cores. It burns hard, however, at cone 010 

(1,742° F.), a very low temperature.

At East Grand Forks the silts are 100 feet deep and extend for 

miles up and down the Red River valley. The upper 5 feet is 

leached and weathered yellow, and this portion has been'used for a 

long time in making cream-colored brick. On the east side of the 

river work has been in progress over 20 years, and at Grand Forks, 

on the North Dakota side, for an even longer time. The same company controls the yards in both North Dakota and Minnesota. 

Steam shovels and more modern machinery have been installed on 

the North Dakota side, so that if the market demand is not at its 

greatest, the Minnesota plant is closed; but the character of the clay 

is said to be essentially the same at both plants. The clay slakes at 

once and has a very low plasticity. It requires 26 per cent of water
POLK COUNTY. 213

for molding and shrinks less than 4-. per cent on drying. Its tensile 

strength is well above 100 pounds to the square inch. As burned 

at the Minnesota School of Mines experiment station it gave the following results:

Cono No.

03

1

4

6

Color.

Bufl. ........ ..................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

2

3

Absorption.

Per cent. 

36

30

28

The clay becomes hard at cone 01 (2,066° F.) and reaches viscosity 

at cone 5 (2,246° F.). It is capable of being burned to hard, porous 

brick. The plant on the Minnesota side of the river has a capacity 

of about 50,000 brick a day.

The North Dakota Geological Survey 1 obtained the following 

results on clay from Grand Forks:

Cone No.

010

05

03

01

Color.

Pink...........................

Shrinkage.

Per cent. 

0.5

1.0

.1

2.0

Absorption.

Per cent. 

31

33

22

18

The bricklets, except the one burned to cone 01, were not very strong. 

The clay was incipiently fused at cone 1, became rapidly vitrified 

at cone 3, and viscous at cone 4.

Several analyses of this clay from Red River are available, as 

follows:

Analyses of the leached silts of the Red River valley.

Silica. .........................................................

Potash. ........................................................

1

48.30

8.16

2.84

4.93

16.34

Undet.

Undet.

18.00

98.57

2

51.27

9.33

3.52

2.31

11.15

2.08

.50

3

29.45

14.04

4.51

.54

26.30

+21.80

96.64

4

w I1)

8 87

4.71

6.62

9.21

6.60

2.26

6.07

1.94

.37

no 07

1. Analysis furnished by the Red River Valley Brick Corporation.

2. Leonard, A. G., North Dakota Geol. Survey Fourth Bienn. Kept., pp. 184-186,1906.

3. Dodge, J. A., Minnesota Geol. and Nat. Hist. Survey Ninth Ann. Kept., p. 447,1881.

4. Clay from yard at East Grand Forks. A. W. Gauger, analyst.

The underlying gray clay on the Minnesota side was more plastic 

and showed a greater shrinkage than the clay that was being worked.

1 Leonard, A. G., Economic geology of North Dakota clays: North Dakota Geol. Survey 

Fourth Bienn. Kept., pp. 184-186, 1906.
2.14 CLAYS AND SHALES OF MINNESOTA.

A burning test resulted in a brown instead of a buff.brick and the 

temperature of fusion was-a few degrees lower.

In the neighborhood of Lengby there are several lakes in which 

clay deposits overlie common clay drift. There is hardly enough 

of the lake clay to be used alone, and the gray drift is, as usual, full 

of pebbles. If the lakes were drained, as seems quite possible, clay 

deposits of considerable thickness would be exposed, judging from 

current reports. The good quality of the lake clays for common 

brick is pretty well determined by some brick that were burned eight 

years ago for the village school.

POPE COUNTY.

At Glenwood a small plant was at work many years ago on a 

superficial leached deposit of gray drift, from which most of the 

limestone had apparently been removed. As the town has grown 

this particular deposit has been leveled off and subdivided into city 

lots, and no similar deposit has been developed in the neighborhood. Although its plasticity, shrinkage, and strength are fair, it 

does not burn hard until within a few degrees of the temperature 

of fusion. It is therefore unsafe for hard-burned brick. Gray drift 

of the usual quality is abundant, however, along all the hills in the 

neighborhood, and, if cleaned, is available-for brick and tile.

BAMSEY COUNTY.

Clay-bearing formations

Pleistocene:

Red laminated clay.

Gray laminated clay.

Red and gray drift. 

Ordovician: Decorah shale.

The Decorah shale, which is used so extensively at West St. Paul, 

in Dakota County, occurs also in Ramsey County, but only in localities where property is too valuable for excavation. The only Pleistocene materials used recently for brick were also on the Dakota 

County side.

The general section of the drift in Ramsey County is as follows: *

Section of the drift in Ramsey County.

Feet.

Loam ____________________________________ 3-10

Gray drift:

(d) Sand, gravel, and boulders_______________ 0-10 

(c) Laminated brick clay__________________ 0-16 

(6) Sand, gravel, and boulders_______________ 20 

(a) Till (seen) ________________________ 0- 2

Red drift:

(6) Laminated brick clay__________________ 0-10 

(a) Till ____________________________ 10-20

iWlnchell, N. H., Minn. Geol. and Nat. Hist. Survey Final Kept, vol. 2, p. 371, 1888.
RAMSEY COUNTY. 215

Leached gray drift has been used in the northern part of the city 

of St. Paul for red brick, but it has the common defect of containing too much limestone.

The red laminated clay is somewhat sandy, like that at Stillwater. 

It was once used on Daytons Bluff. Just south of Como Park laminated clays 10 feet thick are visible beneath 5 to 20 feet of gray 

drift at the crossing of Lexington Avenue under the Northern 

Pacific Eailway. A sample taken here indicates the quality of these 

clays in the neighborhood of the Twin Cities. In St. Paul, especially 

between Sibley and Wacouta streets, red'laminated clays were once 

exposed in quantities. In both these places the value of the land is 

undoubtedly so great that ceramic industries will not make use of 

the clay, but the samples indicate the quality of material of this 

type. Tests by the Bureau of Standards show that the clay contains too much fine sand to work well in an auger machine. The 

water needed for molding is 20 per cent and the shrinkage on drying is 4 per cent. The clay burns red and is so sandy that it retains 

 a high porosity over 35 per cent up to the point of vitrification. 

It reaches viscosity at about cone 2 (2,138° F.). Soft-mud brick 

could be made from such a clay as this, as has been demonstrated successfully at Menomonie, Wis., where two plants make use of clay 

of this type and have developed the work to such an extent that their 

brick are shipped across Minnesota and even farther west. Analyses 

of the laminated red clay, by F. F. Grout, are given below. In the 

mechanical analysis the small lumps of shale were not easily broken 

up by shaking, or even rubbing with a rubber pestle, so that the percentage of fine clay reported is probably smaller than it should be!

Analyses of red laminated clay.

Chemical analysis.

Silica _______________ 57. 79

Alumina ______________ 12. 63

Iron oxides ___________ 8. 88

Magnesia_______ . ___ 4.11

Lime ____________'. ______ 3. 33

Soda ____________i__ l. J5

Potash ______________ 2. 71

Loss on ignition_________ 6.10

Moisture _____________ 2. 50

Titanium oxide _________ . 82

100. 62

Mechanical analysis.

Fine clay _____________ 28. 0 

Coarse clay ____________ 29. 7 

Silt _________________ 42. 0 

Fine sand _____________ . 3 

Coarse sand ___________ Trace.

100. 00

A large part of the county is underlain by red drift of a common 

pebbly type, though in many places gray drift overlies this deposit. 

In St. Anthony Park, near the city limits, between Minneapolis and 

St. Paul; the drift seems to be coarsely and irregularly stratified. It
216 CLAYS AND SHALES OF MINNESOTA,

consists of a pebbly clay which slakes in two minutes and shows 

low plasticity with 21 per cent of water. It shrinks 4 per cent on 

drying and has a tensile strength of 100 pounds to the square inch. 

Burning tests resulted as follows:

Cone No.

06

02

01

2

3

Color.

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

1

3

5

5

Absorption.

. Per cent. 

18

14

12

4

4

The clay is hard after heating to cone 02 (2,030° F.) and reaches 

viscosity at about cone 4 (2,210° F.). .

BED LAKE COUNTY.

Half a mile from the station of Red Lake Falls is a deposit of 

gray drift, modified by Lake Agassiz, which was used for brickmaking many years ago, but the enterprise has been abandoned, 

probably because of the difficulty with the pebbles. If a clean- 

.ing process of either the Hutchinson or the Jackson type could be 

successfully applied a plant might pay, for the situation seems to 

be favorable both as to market in a part of the State which is being 

rapidly settled and as to shipping facilities near the Great Northern and Northern Pacific railways.

REDWOOD COUNTY.

Clay-bearing formations,

Recent: Alluvhini. 

Pleistocene: Gray drift. 

Cretaceous:

Shale.

Basal white clay. 

Archean: Residual clay.

Most of the gray drift of Eedwood County is not so good as the 

alluvium of Minnesota River that is used near Morton for good 

brick and tile. Thin layers of Cretaceous shale have not proved of 

value, but the underlying concretionary white clay and the associated 

Archean residual clay warrant more careful prospecting.

A sample of Archean residual clay was taken from the gorge 

below Redwood Falls, where the banks of the river form a bluff and 

the lower 50 feet consists of weathered granite gneiss. (See fig. 34.) 

This clay in some places underlies the basal Cretaceous clay. The 

outcrops extend for nearly a mile along the river. The clay is well 

situated with respect to railroads, but the property at the exact 

point of the outcrop is a State park, and the scenic features prohibit
REDWOOD COUNTY. 217

the development of ceramic industries on the ground. Probably 

other deposits of the same type lie near by under the drift.

As tested in the laboratory, the clay slakes in one minute. Its 

plasticity is low, and it requires 33 per cent of water. Its tensile 

strength is about 50 pounds to the square inch. It burned salmoncolored and steel-hard at once 1 (2,102° F.) and became brown at 

cone 13 but was still undeformed. It gave every indication of being 

a refractory clay of good grade. Where, the original rock is highly 

ferruginous the residual clay may not be as white and refractory as 

the average. At one point in this gorge the red stain of iron oxide

FIGURE 34. Sectiqn across the gorge of Redwood River below Redwood Falls. The bluff 

for about 50 feet is largely kaoJin derived from the weathering of granite gneiss. Under 

the drift the weathering to kaolin may have been relatively shallow. 

t

is so great that a " red paint mine" was opened, and a few tons of 

paint rock was shipped.

Between Redwood Falls and Morion, on the south bank of Minnesota River, a test pit has been dug by the Morton Brick & Tile 

Co. into a bank of residual decomposed gneiss, which has retained 

its granitoid texture. The ferromagnesian minerals have altered to 

chlorite and the feldspar to clay. The clay burns gray, becomes hard 

at cone 2 (2,138° F.), and is thoroughly vitrified, but not melted, at 

cone 13 (2,534° F.). Analyses by F. F. Grout follow:

Analyses of decomposed gneiss from locality soutli of Morion.

Chemical analysis. Mechanical analysis.

Silica _______________ 60. 61

Alumina______________ 18.12

Iron oxides___________ 7. 51

Magnesia___________*._ 1.14

Lime________________ . 03

Soda _______________ . 54

Potash _______________ 3. 56

Loss on ignition_________ 7. 20

Moisture _____________ . 28

Titanium oxide ________ 1.30

100. 29

Fine clay_____________ 5. 6

Coarse clay____________ 8. 9

Silt _________________ 25. 4

Fine sand _____________ 21. 4

Coarse sand____________' 38. 7

100.0

Near Morton, but south of the river, on the road to Redwood 

Falls, the river bluff shows'one of the most instructive outcrops
218 CLAYS AND SHALES OF MINNESOTA.

of the Cretaceous beds in Minnesota. (See fig. 35.) The basal 

Cretaceous is very thick and shows a definite conglomerate at the 

contact with the Archean and enough of the overlying Cretaceous 

shale to determine the relations, definitely. Both/the concretionary 

or pebbly clay (see PL XI, B, p. 88) and the smooth white clay, 

whether free from grit or not, burn white and soft and undeformed at cone 33 (3,254° F.) and are therefore extremely refractory 

fire clays.

The deposit here is not large enough to make it worth while to 

attempt the production of vitrified ware by the use of mixed clays 

owith a high percentage of the fire clay, but it is not at all impossible that larger deposits might be found. Outcrops in Renville 

County are somewhat thicker than here, and 'a similar stratum may 

be traced up and down the Redwood gorge wherever the Archean

"^ ~ i*-'*'

FIGURE 35. Section on road from Morton to Redwood Falls.

clays form the main part of the bluff. Other exposures are easily 

found. These scattered outcrops strongly indicate the existence 

of a large body of high-grade clay. Relatively small amounts of 

the fire clay unmixed with other clays have been worked up into 

fire brick, but these, like the fire brick made at New Ulm, lack 

strength after repeated heating and cooling. Their refractoriness 

is, however, all that could be desired. Tests of these clays by the 

Bureau of Standards showed low plasticity even after grinding. 

For molding 29 per cent of water is required, and the drying shrinkage is 4 per cent. The burned color is not quite so clear a white 

as that of commercial kaolin. The softening point is above cone 

32 (3,218° F.). There is a rather serious tendency to check in burning. It is likely that the burned color of the clay could be made 

as good as that of commercial kaolins by a washing process. Analyses by the Bureau of Standards are given on page 219. (For other 

analyses see p. 79.)
REDWOOD COUNTY.

Analyses of Cretaceous clays from deposits near Morton.

219

Silica. ..............................................................................

Iron oxides. .. .......................................................................

Soda. . ..............................................................................

Potash. .............................................................................

Smooth 

white 

clay.

45.14

'}? Qd

1.01

1.09

.46

.08

.36

09

14.10

Concretionary 

clay.

44.12

sa 10

1.06

1.17

.28

.11

.30

.17

14.70

In view of the concretionary texture of some of these beds, especially in connection with the concretionary texture of bauxitic beds 

of Morrison County, a careful test of these clays for bauxite was 

made by Oliver Bowles. The portion soluble in sulphuric acid indicated only 3 to 4 per cent of bauxite.

The Minneapolis Fire Brick Co., of Minneapolis, has acquired a 

property near these exposures and by the use of some Missouri clay 

for a binder makes excellent fire brick. This company finds the 

Cretaceous white clay over 30 feet thick.

In Redwood County, near Morton, Eenville County, the alluvium 

of Minnesota River occupies a great many acres of the river flat 

to a depth of 10 feet. The section consists of sod, 5 feet of black 

sandy clay, and 5 feet of yellow-sandy clay, underlain by river 

gravel. The clay slakes at once, is highly plastic, and requires 27 

per cent of water for molding. Its tensile strength is nearly 100 

pounds to the square inch, though it may be somewhat less if 

carelessly dried. The air shrinkage is 7 per cent. As burned at 

the Minnesota School of Mines experiment station, the results are as 

follows:

Cone No.

05

02

1

2

Color.

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

1

5

6

Absorption.

Per cent. 

22

22

12

9

The clay becomes too hard to be scratched with a knife at cone 05 

(1,922° F.) and reaches viscosity a little above cone 2 (2,138° F.). 

The Morton Brick & Tile Co. for many years manufactured red brick 

and draintile in a very excellent plant of medium capacity. It uses 

an auger machine and sometimes a re-press and has six round downdraft kilns. The company has made a series of experiments to ascertain the possibilities of making paving brick or some high-grade 

product by the addition of small amounts of the high-grade residual
CLAYS AND SHALES OF MINNESOTA.

and Cretaceous clay of the neighborhood to this alluvium but with 

little success.

EENVILLE COUNTY.

fRecent: Lake clays.

Clay-bearing formations Pleistocene: Gray drift 

I Cretaceous: Clay. 

[Archean: Residual clay.

Lake clays of unknown quality are reported at Boon Lake, in the 

northeast corner of Renville County. The gray drift is of the common type, and the older formations resemble those in Redwood 

County. Large deposits of Archean. residual clay and basal Cretaceous clays occur from Beaver Falls eastward along Minnesota 

River. On Birch Cooley Creek, three-quarters of a mile up the creek 

from the river bluffs, the concretionary bauxitic clay reaches a thickness of 18 feet the maximum recorded in Minnesota. Well records 

show that it is at many places beneath 100 to 300 feet of drift. This 

drift overburden is the chief drawback to its extensive development.

On the north bank of Minnesota River, opposite the test pit of the 

Morton Brick & Tile Co., in Redwood County, several ravines have 

cut through the drift and into a decomposed granite, exposing a yellowish mass that differs somewhat from the green-mottled clay of 

Redwood County but that burns with essentially the same qualities. 

Samples of these clays have been used as refractory material at the 

plant of the Morton Brick & Tile Co. The depth of such material 

over other parts of the county back from the river may be indicated 

by a well record at Seaforth, which shows white clay at depths of 50 

to 85 feet. A clay of this type, found by drilling, was analyzed by 

Prof. L. B. Pease, of the Minnesota School of Mines experiment station, who found that it contained 62.04 per cent of silica, 25.54 per 

cent of alumina, and 1.24 per cent of iron oxide. This is probably 

a good average for the material seen. However, a somewhat different 

composition is shown in the following analysis by A. D. Meeds: a

Analysis of decomposed gneiss from Birch Cooley.

Silica______________________.__________ 41.71

Alumina_________________________________ 34. 61

Ferric oxide__________________.__________ 4. 58

Ferrous oxide_________________.__________ 6. 88

Magnesia_______________"_____.__________ . 22

Lime______________________.__________ 1.16

Soda __ ____________.__________ . 11

Potash________________________________ Trace.

Loss on ignition_______________.._________ 12.69

101. 96

1 Hall, C. W., The gneisses and associated rocks of southwestern Minnesota: U. S. Geol. 

Survey Bull. 157, p. 76, 1899.
RENTILLE COUNTY. 221

About 3 miles west of Fort Creek a bed of grayish-white clay 

7 feet thick crops out with level stratification in an excavation on 

the upper side of the river road, in sec. 34. This deposit may be 

related to the white concretionary or conglomeratic clays in Redwood 

County (pp. 216-220) and in Birch Cooley, in Eenville County. 

. Winchell * gives the following notes:.

At a point 2 miles below the lower Sioux Agency, sec. 10, T. 112, R. 34 

[in Birch Cooley], on the north side of the Minnesota, a smaller creek joins 

the river. Up this creek, about three-quarters of a mile from the river bluffs, 

the Cretaceous appears in its banks. A concretionary marl, or apparently 

limy earth, of a white color, crumbles out under the projecting1 turf. It 

appears in fragments of an inch or two or sometimes larger, with angular 

outline. The surfaces of .these pieces show a great number of round or oval 

spots or rings, which seem to be formed by the sections of concretions inclosed 

in the mass. It is rather hard when dry and nearly white. It is associated 

with a blue clay, the relations of which can not here be made out.

At a point a little farther up this creek appears a heavy deposit of concretionary, rusty marl * * * in heavy beds that fall off in large fragments 

like rock. The first impression is that the bluff is composed of ferruginous 

conglomerate, but there is not a foreign pebble in it. Every little round mass 

has a thin shell which is easily broken, revealing either a cavity or a loose, 

dry earth. These concretions are generally not more than one-fourth or onehalf inch in diameter; seen 18 feet. Under this is the light concretionary 

clay or marl already described.

This description evidently refers to a bauxitic clay. The thickness (18 feet) is the greatest reported in the State.

The gray drift was sampled in a few places near Olivia, as it 

would be desirable to develop brick material there. On several areas 

of low ground the lime pebbles are less abundant than the average. 

However, no good-sized body of clay has been found sufficiently free 

from them to be satisfactory, except by the application of a cleaning 

process such as that used at Hutchinson. The best samples were 

found a few rods north of the railroad, half a mile east of the 

station. These clays slake in five minutes and are highly plastic 

with 33 per cent of water. They shrink 8 per cent on drying and 

have a strength of over 300 pounds to the square inch. Burning 

tests resulted as follows:

Cone No.

06

04

02

1

3

Color.

Salmon ........................

Red............................

.....do..........................

Shrinkage.

Per cent. 

1

2

4

7

9

Absorption.

Per cent. 

20

20

12

4

2

The clay is hard after burning to cone 03 (1,994° F.) and reaches 

viscosity at cone 3 (2,174° F.).

1 Winchell, N. I-L, Minnesota Geol. and Nat. Hist. Survey Second Ann. Kept, p. 187, 

1874; also in Final Eept, vol. 2, p. 197, 1888.
222 CLAYS AND SHALES OF MINNESOTA.

Clay-bearing formations

 f*'=^a.-±i gt=-.:o

ZZST-.O*-*. f^TTT.O;'-

 ^ ~

=~==~=EF=

 =^

=-- ==

 : : : zz.

 __

=:::r~ - ~=== |

 - r-=j

=rr=:::-:~~~

ill I

( i iii

1 III

1 III

 : , =

III 1

1 1 1 1

I I ] 

1 III

III 1

II II

1 1 1 1

III 1

1 1 1

II II

1 1 1 1

=====

11.11

.' Ill

, -I' 1 1 1

I.I II

ill i

.11 1

1 III

1 1 1 1

i i . i

v;i i 'ix

Drift

aV'shale

10 limestone

i'z"shale

6 shale

5" limestone)

/ " LI

7"shaly limes 

7 "shale.

II "shale

5" shale

Z" limestone. 

'iVshale-

> Platteville

30. Geologic section of the 

Decorah shale south of Faribault.

BICE COUNTY.

'Recent: Lake and swamp clay. 

Pleistocene:

Aftonian (?) soil (no value; see p. 92).

Gray drift. 

Ordovician: Decorah shale.

Common red bricks are made from 

leached gray drift at Faribault. In 

former years brickyards were operated on gray drift at Northfield, 

Morristown, and several other localities in Rice County. The Decorah 

shale crops out for many miles along 

both sides of Straight River, and 

also far along the east side of Cannon River, from Faribault northward almost to Dundas. It also 

fringes the hills in Cannon City, 

(Wheeling, Northfield, and Bridgewater townships.

A very promising outcrop of the 

Decorah shale occurs L| miles south 

of Faribault and a quarter of a mile 

above the Chicago, Rock Island & 

Pacific Railway bridge over Straight 

River. At this point 10 feet of shale, 

with, interbedded limy .layers, lies 

just above the Platteville limestone 

and underlies (with an intervening 

thin bed of limestone) several feet 

more of shale below the drift overburden. (See fig. 36.) The shale 

as sampled is considerably weathered. 

This is one of the points where the 

Decorah shale should be used, the 

tensile strength of these clays being 

considerably greater than that of the 

clays in the same formation farther 

north. The water required for molding is 31 per cent and the air shrinkage 7 per cent. A burning test on 

the main shale bed, conducted by 

the Minnesota School of Mines experiment station, resulted as follows :
BOOK COUNTY. 223

Cone No.

06

04

01

2

5

Color.

.....do..........................

.....do..........................

Buff...........................

Shrinkage.

Per cent. 

0

1

2

5

10

Absorption.

Per cent. 

19

20

23

The clay becomes too hard to be scratched with a knife at cone 02 

(2,030° F.) and is not yet viscous at cone 6 (2,282° F.). It showed 

some tendency to develop an efflorescence (kiln white), but this would 

not persist to vitrification.

The upper shale at this outcrop is more fusible and has a much 

greater tendency to form black cores and develop bleb structure. A 

"combustible shale" from this county, probably from the Decorah 

shale, was analyzed years ago by S. F. Peckham,1 and found to 

contain 22.87 per cent of organic or combustible matter. The upper 

shale near Faribault is probably not so carbonaceous. It burns 

salmon-colored at moderate temperatures. The clay is hard after 

being heated to a temperature as low as cone 010 (1,742° F.), and 

the absorption is small, as is usual with the Decorah shale. Vitrification is gradual, and the heat may be carried to cone 02 (2,030° F.).

There are many extensive swamps in the .county, and a sample was 

taken from one with an area of about 60 acres, 6 miles northwest of 

Faribault. In this swamp the clay is overlain by about 2 feet of 

loam and peat. The clay, which seems to be free from sand and 

gravel, slakes in four minutes and develops a high plasticity with 

about 30 per cent of water. It shrinks about 8 per cent on drying 

and cracks so badly that its tensile strength can hardly be measured. 

If sand were available in the neighborhood and market conditions 

were favorable, it might be used for common red brick. Burning 

tests, unless conducted with slow heat and long oxidation, entirely 

ruin the brick. The following results were obtained:

Cone No.

04

02

01

2

4

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

3

3

4

5

6

Absorption.

Per cent. 

14

13

12

4

3

The clay is hard after burning to cone 03 (1,994° F.) and reaches 

viscosity if slowly burned at about cone 4 (2,210° F.).

BOCK COUNTY.

At Luverne a brick and tile plant has been active at times for the 

last 20 years, producing excellent brick and tile from the gray drift, 

which covers a large part of Rock County and is worked here to a

1 Minnesota Geol. and Nat. Hist. Survey Eighth Ann. Kept, p. 152, 1880.
224 CLAYS AND SHALES OF MINNESOTA.

depth of 10 feet. The limy pebbles that occur in the drift are said to 

have a less serious effect than usual, and though they may somewhat 

injure the product the loss by crumbling is very small. The larger 

pebbles are removed from the clay, and many of the smaller ones are 

crushed by conical rolls. Four round downdraft kilns are available, 

and the cooling kilns supply heat for the driers. The plant has a 

capacity of about 50,000 brick a day. A company making sand-lime 

brick at Luverne recently bought up the clay-brick and tile plant but 

did not make a success of either. The tile company plans to resume 

operations soon. On the south side of the road where the railroad 

crosses Beaver Creek the gray drift is rather more sandy than the 

average gray drift and contains much gravel, a large part of which 

is limestone. (See fig. 10, p. 100.)

BOSEAU COUNTY.

A quarter of a mile from the station at Badger the gray drift has 

been worked over to some extent by the waters of Lake Agassiz and 

is rich enough in clay to make brick but contains a rather high proportion of limestone pebbles. The plant is of small capacity and its 

product is not of high grade.

At Koseau similar modified drift, at least 10 feet thick, covers 

several acres. It is highly calcareous but contains no limestone 

pebbles. In working and burning it shows very much better quality 

than that at Badger. It is hard after burning to cone 2 (2,138° F.) 

and has an absorption of 32 per cent. A few yellow brick were made 

from it several years ago.

The recent growth of the town of Roosevelt has led to a search for 

brick clay in that neighborhood. Two samples sent in one by 

Mr. Richard Olson and one by Mr. H. Robberstad, showed high 

plasticity and strength, with about 7 per cent shrinkage on drying. 

Mr. Olson's sample gave the following results:

Cone No.

03

2

4

Color.

Buff...........................

.....do.. ...... ....................

.....do..........................

Shrinkage.

Per cent. 

0

3

4

Absorption.

Per cent. 

29

23

19

The clay becomes hard below cone 2, but even at cone 4 the lime 

pebbles cause the disruption of the brick. 

Mr. Robberstad's sample gave the following results:

Cone No.

010

06

.03

2

Color.

.....do..........................

Red............................

.....do..........................

Shrinkage.

Per cent. 

0

0

1

6

Absorption.

Per cent. 

19

19

16

3
ST. LOUIS COUNTY. 225

The clay is hard at cone 06 (1,886° F.) and reaches viscosity at about 

cone 3 (2,174° F.). Vitrification is abrupt and should not be attempted, but if the limestone pebbles are no more abundant than 

appears from the sample good common brick might be made from, 

this clay.

ST. LOUIS COUNTY.

Recent: Swamp and lake beds. 

Pleistocene:

Gray laminated clay.

Red clay of Lake Duluth.

Red laminated clay.

Red drift.

Gray drift.

Algonkian(?) : Red clastic series. 

Huronian: Paint rock and slate.

Clay-bearing formations

The swamp clays and the red clay of Lake-Duluth have been used 

in a small way in St. Louis County, but other clays occur and may 

prove to be of value. The red and gray drift do not seem to be of 

value for clay products. A few houses in West Duluth are built of 

brick made many years ago from the sticky red clay so common in 

the neighborhood. At New Duluth, near the steel plant, such clay is 

covered with a sandy bed, and the combination will make good 

common brick.

Swamps are numerous in this county, and many of them have deposits of smooth plastic clay. Just south of Tower is a swamp which 

covers several hundred acres and in which borings have shown 40 feet 

of clay near the center. The clay is overlain by several feet of peat 

and contains very few limy pebbles. The North American mine, 

close to this deposit, is likely to drain off most of the water in the 

swamp but has not yet done so. The clay slakes at once, shows a 

high plasticity, and requires 39 per cent of water for molding. The 

air shrinkage is 13 per cent. The clay can hardly be prevented from 

cracking, and its tensile strength is consequently small. Burning 

tests resulted as follows:

Cone No.

010

06

04

02

Color.

.....do..........................

Red............................

.....do..........................

Shrinkage.

Per cent. 

0

0

2

6

Absorption.

Per cent. i A

20

11

2

The burning must be conducted slowly to avoid cracking. The clay 

is hard after heating to cone 010 (1,742° F.) and gradually becomes 

viscous at about cone 01 (2,066° F.), thus having a fair range but 

not such as would be required for making sewer pipe or stoneware.

64310° 19 15
226 CLAYS AND SHALES OF MINNESOTA.

An analysis by F. F.- Grout is probably typical of St. Louis County

swamp clays. . 

Analysis of swamp clay fro-n Tower.

Silica___j_____________________.______ 52.92 

Alumina_____________ . 15.05

Iron oxides_______________ - . 6. 66 

Magnesia_____________ _________.___ __ 3. 78 

Lime__________________________.______ 5. 95 

Soda_________________________________ . 97 

Potash_______________..________________ 2. 32 

Loss on . ignition___________________________ 8. 85

Moisture___________________________:_____ 3.33 

Titanium oxide______________:_____.______ .52

100.35 .

A plant was started to manufacure brick and tile from this material, but it experienced difficulty in drying the ware. On account 

of the good range of vitrification, this clay might be valuable for the 

manufacture of sewer pipe, if it could be safely dried and if the 

burned ware was strong. However, the low temperature of fusion, 

as compared with that of most good sewer-pipe clay, indicates a 

comparatively weak product. If less plastic material could be found 

in the neighborhood and mixed with this clay its properties might be 

more satisfactory.

Another swamp clay was sampled at Buhl, where the Grant openpit mine has removed, in stripping, an extensive body of swamp clay 

10 feet thick, together with the underlying gray drift. As this material must be moved anyhow, it might be possible with a little care 

to separate the clay from the drift. It could be burned to common 

brick, though it has much the same quality and defects as that at 

Tower. It is hard after burning to cone 05 (1,922° F.) and viscous 

at cone 2 (2,138° F.). Enough organic matter is present to require 

considerable time in burning to avoid black cores.

The gray laminated clays vary slightly in character in different 

parts of the county. They crop out extensively enough along Littlefork River near Koochiching County to be of some interest. The 

type has already been described under Itasca and Koochiching 

counties (pp. 175-178, 182-186). In St. Louis County the deposits 

are closer to the railroad but are still too far away for economical 

shipping.

The most accessible of the laminated clays on Littlefork River 

is on the farm of Gilbert Haugan, 3 miles from Cook, where an 

extensive deposit is covered only by thin soil. It is somewhat 

weathered and contains small limy concretions, but no limestone 

pebbles. The clay slakes in ten minutes and is of medium plasticity, 

requiring over 40 per cent of water for molding. The air shrinkage
ST. LOUIS COUNTY. 227

is about 15 per cent and the tensile strength 200 pounds to the 

square inch. Burning tests resulted as follows:

Cono No.

010

06

03

01

Color.

.....do..........................

Red............................

.....do..........................

Shrinkage.

Per cent. 

2

3

6

Absorption.

Per cent. 

18

17

14

The clay is hard after burning to cone 010 (1,742° F.) and reaches 

viscosity gradually at about cone 02 (2,030° F.). The red color of 

the brick and the tendency to develop black cores indicate that the 

sample was weathered and contained organic matter and was not 

entirely representative of the gray laminated type.

A series of samples taken along the river to the county line all 

resulted in red brick, with only slight variations in physical properties. An instructive outcrop occurs near Ableman's, on the county 

line at Wigwam Rapids, where the river has removed the laminated 

clay from the underlying greenstone bedrock surface and exposed the 

glacial striae. The clay there contains concretions of a type not observed at many other points (see PL II, Z>, p. 36), but these would 

not cause much trouble. The clay slakes in three minutes and is 

highly plastic with 36 per cent of water. It shrinks 10 per cent'on 

drying and has a tensile strength of 175 pounds to the square inch. 

Burning- tests resulted as follows:

Cone No.

06

04

02

1

2

Color.

Red............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

3

5

11

11

12

Absorption.

Per cent.

 18

12

2

1

0

The clay is hard after heating to cone 05 (1,922° F.) and reaches viscosity at cone 2 (2,138° F.). Fragments of Indian pottery have been 

found in great abundance across the river and in the neighborhood, 

and may still be found in the garden back of Mr. Ableman's house. 

Two samples of clay, probably similar to that described above, sent 

by Mr. F. D. Lapping, of International Falls, to the Minnesota 

School of Mines experiment station from sec. 8, T. 70 N., E. 21 W., 

were partly analyzed, with the following results:

Analyses of clays from sec. 8, T. 70 N., R. 21 W.

Silica...........................................................................

Gray clay.

54.43

18.15

4.20

3.98

Red clay.

49.60

15.82

1.70
228 CLAYS AND SHALES OF MINNESOTA.

At Floodwood the gray laminated clays on the west give place to 

the red laminated clays on the east. About a mile northwest of the 

town a well on the land of Mr. McCormick passed through 12. feet of 

yellow clay and 6 feet of'gray clay without finding its bottom. The 

deposit can be traced over several acres and may extend much 

farther. It is covered only by a thin soil. The clay slakes at once 

and has a rather low plasticity, requiring 24 per cent of water for 

molding. Its tensile strength is well above 100 pounds to the square 

inch, and it shrinks 2^ per cent in drying. Burning tests of the 

yellow clay by the Minnesota School of Mines experiment station 

resulted as follows:

Cone No.

05

1

3

5

Color.

Buff............................

.....do..........................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

I

4

8

10

Absorption.

Per cent. 

35

30

21

13

The clay becomes hard at about cone 1 (2,102° F.) and reaches viscosity at cone 5 (2,246° F.).

A similar test on the blue clay showed a slightly greater tendency 

to shrink and warp during the process. It can be burned to hard 

but somewhat porous buff brick. Other clays of the same neighborhood, described below, yield very different products.

In Floodwood the red laminated clays were discovered in digging 

a sewer and are exposed along Savanaugh River near its mouth, at 

the southeast edge of the town. The exposure is 10 feet thick, and 

the bottom is not seen. Laminated clay of the same type, with a 

slightly darker, purplish-red color but showing the same behavior in 

firing, was found in several excavations about 2 miles east of Floodwood. The clay slakes in two minutes, shows fairly high plasticity, 

and requires 25 per cent of water for molding. A test by the Bureau 

of Standards shows that it needs lubrication to work in the auger 

machine. Its tensile strength is nearly 100 pounds to the square inch, 

and its air shrinkage 6 per cent. As burned by the Minnesota School 

of Mines experiment station, it gave the following results:

Cone No.

05

04

01

1

 Color.

Red............................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

3

8

11

Absorption.

Per cent. 

20

15

6

2

The clay becomes too hard to be scratched with a knife at conc 05 

and reaches viscosity at cone 1. Clays of several other types were 

easily accessible, and a number of mixtures were burned, but none
ST. LOUIS COUNTY. 229

seem to show a greater range of viscosity or other especially desirable 

properties. At lower porosities this clay shows a well-vitrified structure. It resembles very closely the clays developed so successfully 

at Menomonie, Wis., and it almost certainly will make brick of the 

same grade as those now shipped in large quantities from Wisconsin into and across the State.

On the railroad above Fond du Lac is an outcrop of soft finegrained red shale associated with the red sandstone of the west end 

of Lake Superior. The shale includes a few small gray circular 

areas, which, except in color, do not appear to differ from the rest 

of the rock. A chemical analysis of this rock gave the following 

result: 1 .........

Analysis of shale from Fond du Lac.

Silica________________________________ 48.92 

Alumina _______________________________ 18. 45 

Ferric oxide_______________________________ 16.88 

Ferrous oxide____________________________ . 57 

Lime _________________________________ . 70 

Magnesia ______________________________ 3. 68 

Soda _________________________________ .48 

Potash________________________________ 1. 32 

Water __,____________________________ 7.14

98.14

The clay does not slake and is nonplastic. When crushed it can be 

molded, and burning tests at temperatures between cone 02 and cone 

5 yielded an excellent vitrified but somewhat rough red brick. If 

the clay occurred in larger quantities it would be worthy of further 

exploration.

On the Mesabi range, notably at Coleraine and Hibbing, the openpit mines have found, interbedded with the iron ore, bodies of clay 

that contain iron, though not enough to constitute ore. The clay 

is highly colored and is commonly known as " paint rock." The layer 

is variable in thickness, in relation to the associated ore, and in 

texture. In places the clay is sandy but more generally is smooth 

and plastic. Where the ore occurs both above and below the paint 

rock it becomes necessary to remove the paint rock, and if a use 

could be found for this material it could easily be separated with 

a steam shovel. At Coleraine 20 feet of paint rock is being removed. The paint rock slakes very quickly and is highly plastic, 

requiring 27 per cent of water. Its tensile strength is a little over 

50 pounds to the square inch, and its air shrinkage is 4.5 per cent. 

In spite of its high content of iron it does not burn hard below

1 Geology of Minnesota: Minnesota Geol. and Nat. Hist. Survey Final Kept, vol. 5, p. 

G05, 1900.
230 CLAYS AND SHALES OF MINNESOTA.

2,200° F. but is viscous at 2,500° F. Another material of a claylike 

sort from the iron formation has been analyzed by C. F. Sidener,1 

with the following results: -

Analysis of banded " silica kaolin " from sec. 6, T. 58 N., R. 17 W.

Silica_______________ .________________ 77.89

Alumina______________"________________'. 13. 55

Iron oxide_____________________________ 1. 83

Magnesia____________________ j._________ . 36

Lime_______________________________^ Trace.

Soda________________________________ . 58

Potash______________________________ . 84

Water______________________________. 4.45 -:

99.50

Immediately above the iron ore lies the Virginia slate. The chief 

outcrops are at the east end of the Mesabi range for a few miles. Tho 

slate is highly ferruginous and could hardly be expected to become 

plastic. It has a very low tensile strength and does not burn hard 

at a temperature of 2,300° F.

SCOTT COUNTY.

Clay-bearing formations'

Recent: Alluvium. 

Pleistocene:

Gray laminated clay.

Gray drift. 

Cretaceous: Clay.

Alluvium occurs along the entire length of Minnesota River in 

Scott County, and gray laminated glacial clays appear in the bluffs 

at many points. A sample of gray drift from a deposit 3 miles 

south of Shakopee has too many limestone pebbles to be of value. 

At La Huiller Mound, between Jordan and Shakopee, a white clay 

resembling the Cretaceous farther southwest was sampled by N. H. 

Winchell.

At Shakopee the river alluvium is known to extend over 20 acres 

to the unusual depth of 30 feet. A dark clay some distance from 

the river is more plastic than that closer by, and the two are mixed 

to produce material proper for soft-mud red bricks. Some repressed brick are made at the same plant. The clay slakes in three 

minutes and has a rather low plasticity. It requires 23 per cent 

of water for molding and shrinks 4 per cent on .drying. Its tensile 

strength is about 150 pounds to the square inch and is not much 

reduced if the clay is rapidly dried. Burning tests resulted as 

follows:

1 Minnesota Geol. and Nat. Hist. Survey. Bull. 10, p.- 81, 1894.
SCOTT COUNTY. 231

Cone No.

02

2

3

5

Color.

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

3

. 5

Absorption.

Per cent. 

22

15

13

The clay becomes hard at cone 01 (2,066° F.) and reaches viscosity at 

cone 4 (2,210° F.) The plant has a capacity of about 3,000,000 brick 

a season. Burning is conducted in a patent 30-arch kiln by what is 

known as the John G. Boss system.

At Blakeley a deposit used in the manufacture of cream-colored 

brick consists of laminated clay about 30 feet thick, whose upper 

half shows the characteristic weathered yellow color. The extent of 

the deposit is somewhat obscured by talus from the overlying hill 

of drift, but it can be traced for some distance along the Minnesota 

River bluff. There is the usual difference between the upper and 

lower clays. The tensile strength of both is high about 150 pounds 

to the square inch. The upper clay shows an air shrinkage of 1.5 per

FIGURE 37. Geologic section south of Belle Plaine.

cent, but the lower shows over 5 per cent. A sample of a mixture 

such as is used at the plant gave the following results:

Cone No.

1

3

4

Color.

Buff...........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

5

7

Absorption.

Per cent. 

30

20

2

, The clay becomes hard at about cone 1 (2,102° F.) and is near viscosity at cone 4 (2,210° F.). A plant at Blakeley has been operated 

pretty steadily since about 1890, at first on common brick but recently 

in large part on hollow ware, produced with a stiff-mud machine 

that has a capacity of about 35,000 a day.

A plant was operated about a mile south of Belle Plaine on a bank 

whose structure is shown in figure 37. The different parts of the
232 CLAYS AND SHALES OF MINNESOTA.

bank are not regular in their stratification, but the bedded clay 

exposed forms a sort of arch about 100 yards across. Each part 

of the section grades into the overlying and underlying parts. The 

yellow silt can be used as sand in tempering the lower clay. The 

clay slakes at once, requires only 21 per cent of water for. molding, 

and is never very plastic. Soft-mud brick are to be made from it. 

The shrinkage on drying is 2 per cent, and the tensile strength less 

than 100 pounds to the square inch. Burning tests resulted as 

follows:

Cone No.

(19

011

4

6

Color.

Buff...........................

.....do.........................

.....do..........;..............

.....do.........................

Shrinkage.

Per cent. 

0

0

1

2

3

Absorption.

Per cent. 

35

33

33

28

The clay is hard after burning to cone 01 (2,066° F.) and reaches 

yiscosity at cone 6 (2,282° F.). The plant can produce about 30,000 

soft-mud cream-colored brick a day.

SHERBTTRNE COUNTY.

Clay-bearing formations 

Pleistocene:

Gray laminated clays. 

Red drift. 

Gray drift.

In several areas near the town of Elk Eiver the red drift lacks 

the overlying mantle of gray drift found in much of Sherburne 

County. The most accessible bank seen is a mile east of Elk Kiver. 

The samples taken here slake in four minutes and show a low plasticity and a shrinkage of 1 per cent on drying. The tensile strength 

is about 120 pounds to the square inch. Burning tests gave the 

following results: -

Cone No.

06

04

02

1

3

5

Color.

Red............................

.....do.........................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

1

2

3

3

5

Absorption.

Per cent.

 16

15

13

10

9

4

The clay becomes hard at cone 02 (2,030° F.) and reaches viscosity 

at cone 6 (2,282° F.). Where.this drift is available there is little 

need of using the gray drift. Two miles south of East St. Cloud, 

just across Mississippi River from some brickyards in Stearns
STEARNS COUNTY. 233

County, a brickyard at one time produced cream-colored brick from 

yellowish laminated clay.

SIBLEY COUNTY.

c

Gray drift covers nearly all of Sibley County, except along Minnesota River, where alluvium is found. The alluvium makes fair red 

brick. At Henderson 50 per cent of sand from the bed of the river 

is added to the richer clay for making sand-mold brick. The clay 

without the additional sand shows medium plasticity with 23 per 

cent of water and shrinks 7 per cent on drying. The tensile strength 

is 100 pounds to the square inch. Burning tests resulted as follows:

Cone No.

04

02

01

1

Color.

.....do.........................

Rod............................

Shrinkage.

Per cent. 

3

5

9

Absorption.

Per cent. 

24

16

3

The clay is hard after heating to cone 03 (1,994° F.) and reaches 

viscosity at cone 2 (2,138° F.). The plant can produce about 10,000 

red brick a day.

STEARNS COUNTY.

Recent: Lake clay. 

Pleistocene:

Gray lake and river clays.

Red drift.

Gray drift. 

Cretaceous:

Upper shale.

Basal clay. 

Arcliean: Residual.

Clay-bearing formations

In Stearns County good common brick are made from the laminated glacial clays south of St. Cloud and from the recent lake 

clays of Eden Lake. The drift is less satisfactory. Attempts were 

made to use it near St. Cloud, Collegeville, and Richmond. Older 

formations which have not been much developed are worthy of 

investigation.

Just west of Richmond, at the west end of a wagon bridge over 

Sank River, is an exposure of the Cretaceous beds that has been 

explored by shafts and tunnels in search of coal. Gray shales crop 

out above water level. A shaft about 100 feet deep, after passing 

through a large mass of "basal Cretaceous conglomeratic formation 

and below an underlying white gritty clay retaining some traces of 

granitoid texture, reached granite. The geologic section resembles
234 CLAYS AND SHALES OF'MINNESOTA.

that exposed in Redwood County. The clay is probably decayed 

granite of Archean age. It is plastic and has an air shrinkage of 

4 per cent. At cone 04 (1,958° F.) it is buff and is too hard to be 

scratched with a knife. At cone 13 (2,534° F.) it is purple, but is 

still undeformed and very porous. °

The bottom of the basal conglomeratic clay is below water level in 

the river, and the overlying Cretaceous shale is exposed for many feet 

above. The hard white clay just at water level was tested by an 

auger and found to be at least 13 feet thick, half of it above water 

level. The exact line between the Cretaceous clay and the underlying Archean can not be determined, but both of them are of similar 

refractory character. The concretionary phase was tested by Oliver 

Bowles, with the following result, indicating the presence of some 

highly aluminous mineral, such as bauxite:

Partial analysis of concretionary clay from Richmond.

Silica ___________________________________ 40.61 

Alumina_________________ _____________ 40. 88

Iron oxide_____________________________ . 82 

Loss on ignition____________- _ 15. 91

The dark-gray shale contains some small lignite layers. Some 

shafts in the hill west of the river passed through a 6-inch layer

Gritty kaolin 10 

Shales reported below

FIGURE 38. Geologic section west of Richmond.

of lignite inclosed in blue clay that extended to a depth of 50 feet. 

(See fig. 38.)

Shale of the same general appearance was observed 2 miles north 

of Richmond in a ravine. It slakes in three minutes and is fairly 

plastic though somewhat waxy in feeling, apparently on account of 

included mica scales. It requires 16 per cent of water for molding 

and has a tensile strength of over 200 pounds to the square inch.
STEARNS COUNTY. 235

Burning tests by the Minnesota School of Mines experiment station 

resulted as follows:

Cono No.

OH

07

05

02

1

Color.

.....do.........................

.....do.........................

.....do.........................

Ked..... ........ ....... I.......

Shrinkage.

Per cent. 

0

1

1

3

Absorption.

Per cent. 

15

14

13

7

The clay becomes too hard to be scratched with a knife before reaching cone Oil (1,688° F.), and if carefully burned can be heated to 

cone 1 (2,102° F.) without deformation. Organic matter, however, 

causes black cores, with great swelling and cracking, if the clay is not 

thoroughly oxidized. ' The range of vitrification is sufficient to make 

it quite safe to burn this clay to a dense product, but its low fusion 

temperature makes it less desirable as a binder for the nonplastic 

kaolins which underlie it.

About 3 miles south of St. Cloud, along the west bank of the 

Mississippi, laminated clays occur over many acres to a depth of 

over 30 feet, though in much of the adjacent territory they are deeply 

buried under more recent deposits of sand. At this particular point 

a .tributary stream, Threemile Creek, has washed the sand off and 

made enough of the clay accessible to supply a couple of brickyards. 

As usual, the .clay has irregular pockets and layers of sand, the finer 

parts of which are called quicksand, and the operations have to be 

carefully watched or the brick will be altogether too weak. If proper 

attention is paid to the mixing of the plastic and sandy parts of the 

deposits, excellent cream-colored brick can be produced. If an 

auger machine is used, it may often be necessary to provide lubrication probably with water to prevent "ragging" the co.rners. 

The clay is fairly plastic with 29 per cent of water and shrinks X 

per cent on drying. Its tensile strength is 100 pounds to the square 

inch. Burning tests resulted as follows:

Cone No.

05 .

03

2

3

Color.

Buff...........................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

1

6

6

Absorption.

Per cent. 

27

30

21

19

The clay is hard after burning to cone 03 (1,994° F.) and reaches 

viscosity at cone 4 (2,210° F.). Each plant has a capacity of over 

20,000 brick a day. At one plant both tile and brick are made and 

some downdraft kilns have been installed, so that the burning of the 

tile can be more accurately controlled.
236 CLAYS AND SHALES OF MINNESOTA.

A little farther south an exactly similar deposit at St. Augusta 

was worked from 1890 to 1911.

At Collegeville brick were burned for local use in the St. John's 

College buildings from a small deposit of yellowish laminated clay, 

which is apparently surrounded by coarse gravelly drift. It may 

be a fragment of some larger deposit, which was caught up by the 

last ice sheet and deposited in the midst of a gravelly moraine. 

The exposure sampled contains a number of limy concretions, but 

the brick that have been made do not seem to be damaged by them. 

Though too small and inaccessible to be of much interest, the clay 

was tested. It shows fair plasticity with 19 per cent of water. The 

shrinkage on drying is 3 per cent, and the tensile strength is 110 

pounds to the square inch. Burning tests resulted as follows:

Cone No.

05

02

01

2

Color.

Bed............................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

2

4

6

7

Absorption.

Per cent. 

20

1611

g

2

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at about cone 3 (2,174° F.).

Brick have been made from clay obtained at the southwest side of 

Albany in the banks of a stream. The clay near water level is said 

to be entirely free from lime pebbles and burns red, probably much 

like that at Collegeville. At the top of the bank the gray drift is full 

of limestone and unsuitable for brick manufacture without cleaning.

The gray drift hag been somewhat leached of its lime contents over several acres north of Miers Grove. Thorough leaching 

extend.s to a depth of only 3 or 4 feet, and apparently the original 

deposit contained a great many pebbles besides those of limestone. 

The clay slakes in three minutes and is fairly plastic, requiring 29 per 

cent of water for molding. Its pebbly character keeps its tensile 

strength rather low 100 pounds to the square inch. Its air shrinkage, however, is nearly 7 per cent. Burning tests resulted as follows:

Cone No.

04

02

1

3

Color.

Red............................

.....do..........................

.....do..........................

Shrinkage.

Per cent. 

0

5

7

.7

Absorption.

Per cent. 

18

14

12

11

The clay is hard after burning to cone 04 (1,958° F.) and reaches 

viscosity at cone 3 (2,174° F.). The plant that has been working 

this clay has a capacity of 20,000 brick a day. The product is a 

very weak red brick.
STEELE COUNTY. 237

Near Paynesville a brick plant has started work on a delta deposit 

on the shore of Eden Lake, near the mouth of the incoming creek. 

The deposit has been excavated to a .depth of 16 feet without finding 

bottom and is known to extend over 8 acres, with a much larger area 

under the water of the lake. Water had to be pumped from the 

pit, which extended below the level of the lake, but the seepage 

through the clay was relatively slow. The clay slaked at once, was 

highly plastic, and required 21 per cent of water for molding. It 

shrinks 3 per cent on drying and has a tensile strength of about 

150 pounds to the square inch, even when rapidly dried. Burning 

tests resulted as follows:

Cone No.

04

01

3

5

Color.

.....do..........................

Shrinkage.

Per cent. 

1

2

8

9

Absorption.

Per cent. 

22

19

4

3

The clay is hard after burning to cone 01 (2,066° F.) and reaches 

viscosity at cone 6 (2,282° F.). The plant makes stiff-mud brick 

and has a capacity of 30,000 a day.

A plant is said to have been opened recently to use the drift clay 

at Melrose.

STEELE COUNTY.

Deep-well sections in Steele County show the Decorah and overlying shale, probably Galena, at several localities, beneath the drift, 

notably . at Owatonna. Fire clay was reported a mile east of 

Owatonna, but the report could not be verified.

Half a mile west of Meriden station, on the Chicago & Northwestern Bailway, and extending into Waseca County, is a deposit of 

clay several feet thick that extends over at least 60 acres. It resembles loess, but as it lies in a swamp and is not all exposed it may also 

contain some glacial and recent sediments. The clay slakes at ojice 

and shows a rather low plasticity with 27 per cent of water. It 

shrinks 4 per cent on drying and has a tensile strength of 150 pounds 

to the square inch. Burning tests resulted as follows:

Cone No.

05

02

1

o

Color.

.....do..........................

Shrinkage.

Per cent. 

1

1

13

Absorption.

Per cent. 

29

30

6

The vitrification is sudden, between cone 02 and cone 2. The clay 

does not seem to be as promising as other loess and swamp clays. An
238 CLAYS AND SHALES OF;'MINNESOTA.

analysis by E. P. Harding, of the University of Minnesota, is given

below: . Analysis of clay from Meriden,

Silica______________________________ 60.00 

Alumina ___________ _ _ _______ 11. 45 

Iron oxides________ - ___ _______ 3.90 

Magnesia__________ __ ___________ _ 4. 05 

Lime______________________-___________ 6. 48 

Potash_________________________________ 4. 09 

Soda__________________________________ 2. 84 

Moisture __________________:_______________ 2. 32

STEVENS COUNTY.

Stevens County has a cover of gray drift which, where modified or 

worked over as outwash, can be made into fairly good brick. This 

was done at Morris. At other points the drift must be cleaned. Kecent lakes may contain some good clay.

SWIFT COUNTY.

Clay-bearing formations .

Recent: Alluvium. 

Pleistocene: Gray drift.

Archean: Residual clay.

Gray drift and associated outwash deposits are the chief source 

of clay in Swift County, and neither is promising for anything except 

common brick. Alluvium is of small extent in this county. Decomposed granite was encountered at a depth of 400 feet in drilling a 

well at Benson and penetrated for 300 feet. At Appleton and elsewhere decomposed granite is closer to the surface. At Benson some 

sandy surface clays in the nature of outwash and surface wash were 

used for red brick but were found too full of limestone to make good 

products.

TODD COUNTY.

Recent: Lake clay. 

Pleistocene:

n, i .* ,. Gray laminated clay. Clay-bearing formations , ~ . Outwash clay.

Red drift. 

Gray drift.

Most of Todd County is covered with gray drift, and many attempts to use it have failed from common defects. The best clays 

are probably those of the glacial lakes and recent lakes and swamps.

 The most valuable deposit of the laminated clays seems to be one 

on Sauk Lake, most easily reached from Sauk Center, in Stearns 

County, 3 or 4 miles to the south. The clay bank rises steeply from 

the shore of the la,ke to a height of 15 or 20 feet and extends several 

rods back under the level surface. The clay directly underlies the 

soil, although in some places its upper beds are sandy. Pits have
.TODD COUNTY. 239

been, opened at numerous points along the shore, exposing sections 

that vary considerably. Limy concretions occur in a few places. 

The best clay which is reported to lie at water level is gray in color, 

and the main part of the bank above water level is yellowish white. 

Upham * concluded that this clay accumulated in a channel^ in the 

melting ice sheet while a large mass of ice still occupied the basin of 

Sauk Lake. Products made from the different parts of the bank 

include both red and cream-colored brick, hollow brick, terra cotta, 

and flower pots. Samples of the yellow and gray clays show the 

usual differences. The average air shrinkage is 3.5 per cent, but that 

of the blue clay is 5.5 per cent. An average mixture of the material 

in the bank was burned at the Minnesota School of Mines experiment 

station, with the following results:

Gone No.

05

02

2

3

Color.

.....do..........................

Buff...........................

.....do..........................

Shrinkage.

Per cent. 

0

1

Absorption.

Per cent. 

21

22

14

The : clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at cone 3 (2,174° F.), having thus about the same range 

as the average gray laminated clay in other parts of Minnesota. 

Selected samples from different parts of the deposit differed in plasticity but were almost identical in their behavior in the fire. Mr. 

David Pangburn, who has taken the lead in developing the deposits 

and in experimenting with them, has retired, and active work on 

the deposit has been dropped; but plans are in progress for a reorganization, and it is thought that, in view of the amount of good 

clay available, shipping facilities will be provided and excellent 

products will be turned out.

A similar deposit on the banks of Fardens Lake, 3 miles from 

Little Sauk, beside Battleham Church, was opened for a kiln of 

brick, but there was some difficulty in drying, and the location was 

not favorable for continuous operation. The clay slakes in one 

minute and is highly plastic with 30 per cent of water. It shrinks 

6 per cent on drying and has a tensile strength of 200 pounds to the 

square inch if carefully dried. Burning tests resulted as follows:

Cono No.

06

03

01

1

3

Color.

.....do..........................

Bull..-.. .......................

.....do..........................

.....do..................;.......

Shrinkage.

Per cent. 

0

1

7

7

10

Absorption.

Percent. ' 

27

26

13

12

3

1 Upham, Warren, Minn. Geol. and Nat. Hist Survey Final Kept., vol. 2, p. 578, 1888.
240 CLAYS AND SHALES OF MINNESOTA.

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at cone 4 (2,210° F.).

Many years ago a brick plant made use of some laminated clay 

found along the north shore of Birch Lake, about a mile east of the 

town of Birch Lake, near the railroad. The deposit may be in part 

a relatively recent formation but is probably also in part of glacial 

origin. The clay is similar to those at Sank Lake and other lakes, 

but its extent is much less certain.

Just southwest of Burtrum two brick plants have been built to use 

outwash from the red drift. The beds are sandy and irregular but 

can be traced over many acres and are exposed in some places to a 

depth of 16 feet. The clay slakes at once and has a rather low 

plasticity. It requires 21 per cent of water for molding, and shrinks 

5 per cent on drying. Its tensile strength is nearly 200 pounds to 

the square inch, though somewhat less if rapidly dried. The clay 

burns salmon-colored at low temperatures but buff to green at higher 

temperatures, indicating the presence of considerable lime, probably 

derived from wash from the gray drift, which extends nearly up to 

this point. It burns hard at cone 01 (2,066° F.) and reaches viscosity 

at cone 4 (2,210° F.). Neither of the plants is now in operation, 

but their suspension is thought not to be the fault of the clay, which 

is fairly good for common brick.

At Clarissa Spur, near Clarissa, a plant uses a sandy laminated 

clay that is known to be 12 feet thick and extends over several acres, 

with an overburden of only 2 or 3 feet. It slakes in four minutes 

and has a rather low plasticity and an air shrinkage of less than 

3 per cent. The tensile strength is nearly 150 pounds to the square 

inch. The range of vitrification is from cone 1 (2,102° F.) to cone 5 

(2,246° F.) or more. The plant has a capacity of 10,000 soft-mud 

brick a day. Drainage causes difficulty if the whole thickness of 

clay is worked.

A mile or two east of Staples along the Northern Pacific Railway 

is a deposit of laminated clay several acres in extent that has been 

worked at two brick plants to a depth of 6 feet, below which it is 

said to contain too many limestone concretions to be of value. 

The plants have a combined capacity of about 40,000 common red 

brick a day. The clay slakes in two minutes and is highly plastic, 

requiring 28 per cent of water for molding. Its tensile strength is 

over 100 pounds to the square inch, but there is danger of cracking 

if the ware is rapidly dried. The air shrinkage is nearly 6 per cent. 

Burning tests gave the following results:
TRAVERSE COUNTY. 241

Cone No.

05

03

01-

1

Color.

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

2

2

Absorption.

Per cent. 

25

23

23

The clay becomes hard at cone 03 (1,994° F.) and reaches viscosity at 

conel (2,102° F.).

In the morainic belts there are a great many swampy kettle holes 

where the wash from the gray drift has accumulated. Two miles 

west of Long Prairie a brickyard has used some small deposits of 

this sort for common red brick, but the deposits are nearly worked 

out and no others so easily accessible are known. Another such deposit about half a mile east of Beaver Bend was used for a kiln of 

brick several years ago, but it contains too many -limestone pebbles 

and is too small to be of much promise.

TRAVERSE COUNTY.

rPleistocene: Gray drift. Clay-bearing formations {Cretaceous . Clay>

Gray drift, somewhat modified by Lake Agassiz, is* the chief available clay in Traverse County. A very large part of the county is 

underlain by Cretaceous clay, most of which, however, is covered 

with glacial drift and is inaccessible. Just across the river in South 

Dakota are some exposures, reported by Mr. A. Parker, of Browns 

Valley, in which the clay is at least 40 feet thick and extends for 

miles along the valley. The clay is stratified with blue and yellow 

layers, and, where sampled, underlies about 20' feet of glacial drift. 

It is favorably situated for excavation but is a mile from any railroad. The clay slakes in four minutes and is highly plastic, requiring 34 per cent of water for molding. Its tensile strength is over 

100 pounds to the square inch, even when it is rapidly dried. It develops considerable adhesive strength after being slightly compressed, even if it has been separated into parts as in the auger machine, being one of .the few clays tested that showed this desirable 

quality. Its air shrinkage is 11 per cent. Burning tests at the Minnesota School of Mines experiment station resulted as follows:

Gone No.

010

06

02

2

Color.

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

4

7

7

Absorption.

Per cent.

' 15

9

3

3

64310° 19 -16
242 CLAYS AND SHALES OF MINNESOTA.

The clay becomes too hard to be scratched with a knife somewhat 

below cone 010 (1,742° F.) and is still undeformed at cone 3 

(2,174° F.), giving a range of vitrification of about 400°. If rapidly 

heated the organic matter causes swelling and the formation of black 

cores, but this can be easily avoided by thorough oxidation. The 

analysis of the clay is given on page 91.

WABASHA COUNTY.

Clay-bearing formations

Recent: Alluvium. 

Pleistocene:

Loess.

Gray drift. 

Cretaceous: Clay (?),

At Wabasha a plant was in operation for about 20 years on loess 

loam, which covers at least 40 acres to a depth of 4 or 5 feet on a 

terrace of Mississippi River. Although the material is rather sandy, 

it produced a good red brick. The plant has averaged about 500,000 

brick a year, but work was stopped several years ago on account of 

poor market conditions.

Half a mile from Elgin station loess loam, locally 12 feet thick, 

overlies a deposit of stratified sand in an area of 25 or 30 acres. 

A small hand-mold brick plant has been in operation here for over 

30 years, producing about 250,000 brick a season. A similar deposit 

occurs near the station at Plainview, and the material was used for 

a time in a similar plant. (See also fig. 9, p. 99.)

The alluvial clays along the Mississippi have never been worked 

and are not likely to be of much value. Gray drift occurs in most 

of Wabasha County but is inferior to the loess and alluvium.

Cretaceous clays probably exist in this county, but no such clay 

has been seen in place. Small pieces of clay similar to the Cretaceous clays of Belle Chester and Clay Bank were observed in the 

glacial drift at numerous localities. It is not unlikely that careful 

prospecting would result in the discovery of local deposits of Cretaceous clay in 'the northern part of the county, particularly in the 

region near Oak Center.

WADENA COUNTY.

Several attempts have been made to use* the common gray drift 

in Wadena County, but the limestone pebbles caused the usual difficulty, and no one has used the process necessary for removing them.

WASECA COUNTY.

Small yards at several localities in Waseca County formerly manufactured common brick from the gray drift. It may be possible to 

find glacial or recent clays worth developing. The Decor ah shale is 

buried deeply under the drift.
WASHINGTON" COUNTY. 243

. The loesslike clay west of Meriden has been described under 

Steele County (pp. 237-238).

A deposit of the gray drift in the northern part of Waseca County, 

34 miles south of Waterville (Le Sueur County), along the Chicago 

Great Western Railroad, contains very few pebbles and may have 

been formed as a sort of outwash. The clay, with some sand added, 

was successfully used for brick about 25 years ago. It slakes in two 

minutes and is fairly plastic with 30 per cent of water. It shrinks 

5 per cent on drying and has a tensile strength of 150 pounds to 

the square inch. Burning tests resulted as follows:

Cone No.

04

01

1

Color.

Salmon. .......................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

I

5

11

Absorption.

Per cent. 

25

18

2

The clay is not very hard until heated to a temperature of cone 02 

(2,030° F.) and becomes viscous at about cone 2 (2,138° F.).

WASHINGTON COUNTY.

Clay-bearing formations

Recent: Lake clay. 

Pleistocene:

Reel laminated clay.

Red and gray drift.

All the clays of Washington County have been used, but few deposits are favorably situated for development.

The Forest Lake Brick & Tile Co. had a pit just south of Forest 

Lake along the Northern Pacific Eailway in an extensive deposit 

of gray drift, which is a little less pebbly than usual. At the plant 

the clay was ground but not cleaned from the lime. The capacity is 

about 10,000 red brick a day. The clay slakes very promptly and 

shows a fairly high plasticity. Its air shrinkage is 4 per cent and 

its tensile strength about 125 pounds to the square inch. Burning 

tests by the Minnesota School of Mines experiment station resulted 

as follows:

Cone No.

04

02

01

2

Color.

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

1

1

Absorption.

Per cent. 

10

14

12

The clay becomes hard at cone 03 (1,994° F.) and shows no sign 

of becoming viscous at cone 3 (2,174° F.). Lime particles shattered 

the brick at all these temperatures. Although this clay might be
244 CLAYS AND SHALES OF MINNESOTA.

improved by the removal of limestone pebbles, it appears to be furnishing a satisfactory product by simple grinding. It must, however, be burned to a fairly high temperature or the lime particles 

will greatly weaken the'product. Two round downdraft kilns are 

in use at the plant.

The plant at first used red drift from the other side of the lake, 

several miles away. This material had to be loaded on cars, hauled 

a quarter of a mile, and reloaded on a barge for transportation 

across the lake. Owing to the great expense of getting the material 

in this way the red drift was abandoned in favor of the- more accessible gray drift. A sample, however, indicates the excellent quality 

of the red drift of the region. It slakes at once and, after the gravel 

has been crushed to 40-mesh, has a fairly high plasticity. The tensile strength is considerably over 100 pounds to' the square inch, 

even after rapid drying. The water required for molding is 20 per 

cent, and the air shrinkage is 4.5 per cent. Burning tests resulted as 

follows:

Cone No.

07

05

1

3

Color.

Red............................

.....do.........................

.....do.........................

.....do.......................:.

Shrinkage.

Per cent. 

1

2

7

8

Absorption.

Per cent. 

15

14

5

4

The clay becomes hard at cone OG (1,880° F.) and is approaching 

viscosity at cone 3 (2,174° F.).

A sample of the red drift 2 or 3 miles south of Afton, obtained by 

Mr. Frank Squ}^ers, seemed to be much less pebbly than usual and 

showed the usual satisfactory range of vitrification. The material 

may have been reworked by recent river action. It is not especially 

accessible to any of the large markets but is of good quality.

At Stillwater deposits of red laminated clay occur along Browns 

Creek just above its mouth. These were described by Winchell as 

tripoli (for analyses and reference see p. 97), because they were 

rather more gritty than most of the laminated deposits discovered. 

Winchell, however, notes the probability of their having an origin 

similar to that of the laminated clays at St. Paul. The extent of 

the deposits has not been accurately determined, but many similar 

deposits are exposed farther north along St. Croix River. The clay 

slakes in one minute, is not very plastic, and requires only 20 per cent 

of water for molding. The tensile strength is a little less than 100 

pounds to the square inch, but the clay can be rapidly dried without 

injury and shows considerable strength even after having been cut 

in two if again pressed together in the plastic state. .This would 

seem to indicate successful working with the auger machine, but the
WATONWAlsr COUNTY. 245

plasticity is hardly sufficient. The air shrinkage is only 2 per cent. 

Burning tests at the Minnesota School of Mines experiment station 

resulted as follows:

Cone No.

05

03

01

1

2

Color.

.....do.........................

Red............................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

2

5

6

8

Absorption.

Per cent. 

20

17

10

3

2

The clay becomes hard at cone 02 (2,030° F.) and reaches viscosity 

at cone 2 (2,138° F.). This is the type of cl,ay used at Menomonie, 

Wis., for excellent building brick. These Minnesota clays might 

make as good brick as those now brought from other States.

Just south, of Stillwater, on the shores of Lily Lake, are deposits 

of lake clays of a quality suitable for hard common red brick. They 

are known to be 10 feet thick over several acres. They are not convenient to any market, as no railroad comes near and a steep hill lies 

between them and Stillwater. The clay is, however, of excellent 

quality. It slakes in two minutes and is very highly plastic, requiring 19 per cent of water for molding. It shrinks a little over 3 per 

cent on drying and has a tensile strength of nearly 100 pounds to the 

square inch. Burning tests at the Minnesota School of Mines experiment station resulted as follows:

Cone No.

06

02

1

3

5

Color.

Red............................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

I

2

4

5

6

Absorption.

Per cent. 

14

12

9

6

0

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at cone 5 (2,246° F.).

WATONWAN COUNTY.

Clay-bearing formations [Recent: Lake and swamp clays. 

1 Pleistocene: Gray drift.

In Watonwan County most of the surface material under the soil, 

is the common gray drift, but the kettle holes and swampy depressions .contain clay washed from the gray-drift hills. The drift in 

sec. 13, T. 106 N., R, 32 W., near St. James, would have to be cleaned 

of the limestone pebbles to be used successfully for brick or tile. It, 

is almost identical with that used at Hutchinson.
246 CLAYS AND SHALES OF MINNESOTA.

There are -several deposits <of swamp -clay in the midst of the 

drift .area, and some of them seem to be -of 'excellent quality. A 

deposit at Low Lake, 2 -miles northeast of Madelia, was utilized in a 

brickyard operated about 1900. Sand was mixed with the clay, and 

the product was a light-red brick. At Odin a similar deposit 16 feet 

thick and many -acres in extent has been thoroughly prospected but 

has not yet been developed. Both these clays slake promptly and are 

fairly plastic with 24 per cent of water. Their air shrinkage is 5 

per cent and their tensile strength over 100 pounds to the square inch. 

Burning tests .at the Minnesota School of Mines experiment station 

resulted as follows:

Clay near Madelia.

'Gone No.

0503 

1

3

5

OoloT.

Salmon ......................... .....'

.....do.........................

.....do.........................

Shrinkage.

Percent.0 '

1 ':

2 .

3 ;

Absorption:

 Percent. , 

26

!24 '

'21

14 :

Clay from Odin.

06

03

01

2

3

Red............................

....-do.. ....................... .....:

.....do.............................

.....d-o........... ................

.....do.........................

0

1 '

3

4 .

5

15

14

11

7

3

Both clays show a fair range of vitrification; that from Odin is 

hard after burning to cone 05 (1,922° F.) and reaches viscosity 

about cone 3 (2,174° F,).

WILKIN COUNTY.

Wilkin County has only the -common gray drift, modified north of 

Breckenridge by Lake Agassiz and Eed Elver.

About a mile north of Breckenridge a brickyard has been operated at-times since 1880 on clay that crops out in the east bank of 

the river in places with a thickness of 30 feet. Where exposed and 

weathered the clay is highly plastic and requires 23 per cent of water 

for molding. The air shrinkage is 14 per :cent, and the clay has 

so strong a tendency to crack in drying that its tensile strength is 

Bkely to be small. It burns hard at an unusually low temperature, 

below 1,700° F.., and on being burned to higher temperatures tends 

still more to crack. With careful drying and slow oxidation it 'has 

a good range of vitrification and might be burned to a vitrified 

product.
CLAYS AND SHALES OF MINNESOTA. 247

Clay-bearing formations 

WINONA COUNTY.

Recent: Alluvial clays. 

Pleistocene:

Loess clays.

Gray laminated clays. 

Ordovician: Decorah shale. 

Cambrian: Shale of St. Lawrence formation.

There is very little drift in Winona County. The chief formation of value for brick and tile is the loess loam, which forms a 

mantle covering the entire county, except along the bottoms of the 

stream valleys, where it has either been washed away or modified 

by stream action. Even in these valleys, especially near Mississippi 

River, the loess thickly covers many terraces and lower valley 

slopes. The best deposit observed is at Dresbach, where it was 

worked for about 30 years in the manufacture of common red brick 

and where at one time four large brickyards were using it. No work 

has been done at this locality for several years. Other workable 

deposits are at Winona, Dakota, Homer, Lewiston, Utica, and St. 

Charles. (See fig. 9, p. 99.)

At Homer, in sees. 32 and 33, T. 107 N., E; 6 W., an undeveloped 

deposit of loess on a terrace on the side of a ravine is 4 or 5 feet 

thick over at least 6 acres and is probably much more extensive. 

The clay slakes in one minute and shows a fairly high plasticity. 

It requires 24 per cent of water for molding and shrinks 5 per cent 

on drying. Burning tests at the Minnesota School of Mines experiment station resulted as follows:

Cone No.

05

02

01

2

5

Color.

.....do.........................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent.

1

2

4

5

8

Absorption.

Per cent. 

20

17

14

13

5

The clay becomes too hard to be scratched with a knife at cone 02 

(2,030° F.) and reaches viscosity at about cone 6 (2,282° F.). It 

is not known whether the clay is abundant enough to warrant a large 

plant, but its quality seems to insure very excellent hard-burned or 

even vitrified red brick.

About 4 miles northwest of Winona loess loam covering more than 

100 acres is exposed to depths of 8 to 20 feet. The clay is irregularly sandy and contains some streaks of gravel. A plant of medium 

grade is turning out red brick of good quality at the rate of about 

35,000 a day.
248 CLAYS AND SHALES OF MINNESOTA.

Three miles southwest of Winona a deposit at a brickyard shows 

the following section:

Section 3 miles souiliivcst of Winona.

Soil

Ft. in. 

6

Sandy yellow loess________________________ 2 0

Very plastic red clay__________________________ 1 2

Plastic yellow massive clay___________:_______ 3 6

Stratified yellow sandy clay__________________._ 4 0

A sample taken to include all of the section except the soil slakes 

in a very few minutes and develops a fairly high plasticity. The 

mixture requires 36 per cent of water for molding and has an air 

shrinkage of 10 per cent, resulting in a strong tendency to crack on 

drying. When properly burned it forms red brick which becomes 

hard at cone 010 (1,742° F.). If the clay is rapidly burned, the 

organic matter will develop black cores and destroy the brick, but 

if slowly burned it does not become viscous at a temperature of cone 

2 (2,138° F.). It has thus a range of vitrification of about 400° F. 

and can be safely burned to a fairly good hard product.

Near the deposit just described alluvium has accumulated along 

Burns Creek to a depth of 12 to 14 feet over more than 40 acres. 

The .clay is blue-black and very plastic and in many places is quite 

free from pebbles. It is used for mixing with other clays in the 

neighborhood. The plant has the disadvantage of being distant 

from the railroad. The clay slakes in four minutes and requires 23 

per cent of water for molding. Its air shrinkage is 2 'per cent and 

its tensile strength 200 pounds to the square inch. Burning tests 

resulted as follows:

Cone No.

02

01

2

4

5

Color.

Salmon. .......................

.....do.........................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

0

0

2

7

8

Absorption.

Per cent. 

279 1;

20

n

The clay is hard after burning to cone 01 (2,066° F.) and reaches 

viscosity at cone 5 (2,246° F.). Brick are produced at the rate of 

3,000,000 _ a season.

The Decorah shale occurs in a small area in the southwest corner 

of the county, near St. Charles, where it is 40 feet thick under 30 

feet of drift and might be developed. It has the plasticity, strength, 

and generally good working behavior characteristic of the Decorah 

shale. Burning tests resulted as follows:
WEIGHT COUNTY. 249

Cono No.

01006'

04

02

Color.

Salmon ........................

Rod............................

.....do.........................

do

Shrinkage.

Per cent . 

7

11

Absorption.

Per cent. 

10

3

Clay-bearing formations .

The clay is hard after burning to cone 010 (1,742° F.), above which! 

it tends to develop black cores and bleb structure. However, by 

oxidizing very thoroughly the vitrification might be carried along to 

a-very low porosity.

The shales of the St. Lawrence formation crop out at Dresbach 

but are too thin to be of value. A sample taken does not slake or 

develop much plasticity or tensile strength. In burning it retains a 

porosity of 20 per cent up to cone 4, when it becomes gray and hard.

WRIGHT COUNTY.

Recent:

Alluvium.

Lake and swamp beds. 

Pleistocene:

Gray laminated clay.

Gray drift.

Gray drift covers most of "Wright County. At Otsegb an attempt 

to use it failed because of the limestone it contained. Two or three 

attempts have been made to use the deposits around Buffalo, some 

of which are of a peculiar type, described below. Brick have been 

made from the upper leached portion of the drift in places where 

it is relatively free from limestone pebbles. Laminated clays are 

more promising and have been used at Dayton, Hasty, and Annandale.

At Dayton, near the mouth of Crow River, laminated clays of the 

usual character have accumulated in great quantity. Prosper Vassar's brickyard has been operating on these clays since 1880 but has 

thus far used only the upper leached yellow portion of the deposit, 

which contains a few limy concretions but has yielded excellent common brick for local use. The plant has a stiff-mud machine and 

makes 30,000 brick a day. The yellow clay is fairly plastic with 24 

per cent of water. It shrinks 4 per cent on drying and has a tensile 

strength of 125 pounds to the square inch. It was burned at the 

Minnesota School of Mines experiment station, with the following 

results:

Cone No.

04

1

3

4

5

6

Color.

Bud...........................

.....do.........................

.....do.........................

.....do.........................

.....do.........................

Yellow

Shrinkage.

Per cent:, 

0

2

6

12

15

Absorption.

Percent. 

34

30

22

10

4
250 CLAYS AND SHALES Or MINNESOTA.

The clay becomes hard at cone 1 (2,102° F.) and shows signs of 

viscosity at cone 6 (2,282° F.).

The underlying blue clay is more plastic, requires more water for 

molding, shrinks about three times as much, and has a lower temperature of vitrification, apparently reaching viscosity before the yellow 

clay becomes hard. It has a strong tendency to form black cores, 

being so fine grained that oxidation is very slow.

Up the river from this deposit there is good laminated clay at St. 

Cloud, but between the good clays at Dayton and St. Cloud, a mile 

or more from Hasty, is a deposit of laminated clay which appears 

to be similar but caused trouble at the plant by checking. The 

sample taken slakes in three minutes and is very highly plastic, 

requiring 36 per cent of water for molding. It shows an air shrinkage of 10 per cent, and even when carefully dried shows a tensile 

strength of not over 10 pounds to the square inch, indicating that 

the shrinkage caused cracks that weakened it. Burning tests gave 

the following results:

Cone No.

06

05

03

1

2

Color.

*.... do....... ..................

.....do.........................

Buff...........................

.....do.........................

Shrinkage.

Percent. 

2

2

3

9

10

Absorption.

Per cent. 

22

24

21

' 5

3

The clay becomes hard at cone 06 (1,886° F.) and reaches viscosity 

at cone 2 (2,138'° F.). Apparently its only serious drawback is its 

tendency to crack on drying, though there may be some serious 

trouble from the laminated structure produced by the auger machine. These difficulties could be easily remedied if a more sandy 

layer could be found for mixing with the clay now used. The plasticity is high enough, and sand would improve the clay in several 

ways.

The Annandale Brick & Tile Co. has built a plant a mile east of 

Annandale on the Minneapolis, St. Paul & Sault Ste. Marie Railway, 

to make use of a deposit of laminated clay known to> extend over 

several acres to a depth of at least 15 feet. The clay is covered with 

only a .thin soil and has very few limy or ferruginous concretions. 

When traced for 200 yards eastward along the railway it is found to 

be very much sandier and not so good. The clay used was sandy 

enough, so that this very sandy part of the deposit remained untouched. The working and burning qualities of the clay seem to be 

excellent, but some difficulty has been encountered at the plant in 

getting the clay to dry without cracking and thus losing its strength. 

The water of plasticity is 31 per cent, and the shrinkage on drying 

is 4 per cent. Burning tests resulted, as follows:
YELLOW MEDICINE COUNTY. 251

Cone No.

04

02

01

2

Color.

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

5

6

Absorption.

Per cent. 

28

25

18

The clay is hard after burning to cone 02 (2,030° F.) and reaches 

viscosity at about cone 2 (2,138° F.).

In sec. 27, T. 120 N., R. 25 W., about 2£ miles'from Buffalo and' 

1£ miles from the railroad, a rather extensive swamp has been' 

drained by a State ditch, the material thrown out from which contains fragments of shale in great abundance and is relatively free 

from limestone pebbles. Its pebbly texture shows that it is not a 

lake or swamp deposit, but it nevertheless differs noticeably from the 

average gray drift. Such material has not been noted in any other! 

part of Minnesota except near Alexandria. It slakes at once and is 

highly plastic, requiring 25 per cent of water for molding. Its air 

shrinkage is 5 per cent, and its tensile strength is 150 pounds to the' 

square inch, though it checks rather badly on drying. Burning tests 

by the Minnesota School of Mines experiment station resulted as 

follows:

Cone No.

04

09

i

3

4

5

Color.

Red............................

.....do.........................

.. ...do.................... ......

....do-.. .....................

.....do.........................

.....do.........................

Shrinkage.

Per cent. 

1

1

2

4

5

5

Absorption.

Per cent. 

17

16

14

11

10

9

The clay becomes hard at cone 02 (2,030° F.) and shows no sign of 

becoming viscous at cone 5 (2,246° F.), having thus a range of over 

200° during vitrification. The cross fracture of a well-burned brick 

gives every indication that it is good material for paving brick, and 

simple laboratory estimates show that it is both hard and tough. 

The deposit is recommended for further exploration and testing.

A lake deposit occurs along the shores of Lake Mary, 6 miles from 

the station of Howard Lake. The clay was mixed with coarse sand, 

which is available in the same neighborhood, and was manufactured 

into red brick.by a soft-mud process. The plant had a capacity of 

250,000 brick a year but is now abandoned.

'At Monticello brick Avere made some years ago from a very sandy 

and probably alluvial clay in the banks of Mississippi River. The 

deposit seems to contain less than 20 per cent of clay substance, and 

the brick produced were common red brick of very poor quality.

YELLOW MEDICINE COUNTY.

Yellow Medicine County is covered with gray drift, 

once made near the town of Yellow Medicine.

Brick were

INDEX.

Page.

Acknowledgments for aid 13-14 

Acorn Brick & Tile Co., operations

of ___________ 162-163 

Ada, clay near__.. 205 

Adhesion test .for clay, description

of ________ 46 

Adobe clay, nature of 1 45 

Afton, clay near-..__ ___ 244 

Aftonian ( ?) soil, composition of 92 

Age of clay, indications derived

from ___________ 42-43 

Aitkin County, clays of __ 111-113 

Akeley, clay near _____ 174 

Albany, clay at_____________'_ 236 

Albert Lea, clays at________ 163-165 

Albert Lea Brick & Tile Co., operations of________ 163-164 

Alexandria, clay at 155 

Algonkian period, events of_____ 72-73 

slates of_______________ 79-81 

Alkalies, effects of, in clay products. 27 

Alluvial clays, origin of_ _____ 20 

Alteration of clay___________ 18-19 

Alumina, content and effects of, in

clay ____________ 22 

American Clay Working Machinery

Co., acknowledgment to_ 14

Analyses of clays- 24, 79, 90, 91, 92, 95-96,

97, 98, 103, 114, 120, 126,

130, 134, 137, 138, 145, 152,

160, 164, 170, 185, 187, 188,

199, 202, 215, 217, 219, 220,

226, 227, 229, 230, 234, 238

rational, object of__ ___ 28

Analyses of fresh and weathered

rocks ..______ 17 

Annandale Brick & Tile Co., operations of____ __ 250-251 

Anoka County, clays of 113-118 

Appleton, clays at and near_ 142, 238 

Archean period, events of_____ 72 

Archean rocks, clays .residual

from .._ _______ 78-79, 

106-107 

Auger machine, use of, in molding

clay products_ 58-59, 60-61 

Austin, clays at__.. 200-202,203

B.

Badger, clay at_ ._ 224 

Banldnd Carlson Brick Co., operations of____ _ 212 

Barncsville, clays at ._ 145 

Battle Lake, clay near____ 209

Beaver Bend, clay near______ 241 

Beaver Falls, Lake County, clay at- 187

Renville County, clay at __ 220 

Becker County, clays of ____ 118-119 

Belle Chester, clay at______ 170-172

clay pit at, plate showing _ 170 

Belle Plaine, clays near_____ 231-232 

Beltrami County, clays of __:__ 119-120 

Bemidji Lake, clay on_______ 120 

Benson, clay at____________ 238 

Benton County, clays of ____ 120-121 

Berkey, Dr. C. P., acknowledgment

to ___ ___ 14 

Bibliography _______ _____ 14 

Big Falls, clay at___ __ 183 

Big Stone County, clays of 121 

Bigfork River, clay on___ 176, 183-184 

Billingsley, J. J. W., .cited_____ 69-70 

Bingham Lake, clay at__ ___ 146-147 

Binns, C. F., and Coates, M. A.,

cited _________ 56 

Birch Cooley Creek, clay on_ 220 

Birch Lake, clay on_ _____ 240 

Blakely, clays at____ ______ 231 

Bleininger, A. V., cited _____ 164,179 

Blue Earth, clay at__________ .156-157 

Blue Earth County, clays of_____ 121-6 

Bonding power of clay, definition of_ 39 

Boon Lake, clay on___________ 220' 

Bowles, Oliver, work of________ 13 

Bowlus Brick & Tile Co., operations

of_____________ 197' 

Brainerd, clays near_______ 147-148- 

Breckenridge, clay near _______ 246. 

Brick, auger structure in, plate showing__ _'_ 60.

clays required for^_ _ __ 43-44.

dry-press, making of- _____ 61-62..

drying of, on cars in tunnels,

plate showing __ 62.

bellow, molding of________ 62.

klinker, burning of _ 36 

imitation of__, _____ 61, 67- 

plate showing . _ 30 

production of _ 85,

lamination in, correction of __, 61.

lumps of clay in, effects of___ 59>

molding of______-______ 59-62,

paving, use and advantages of_ 67-68.

re-pressing of___________ 61.

roughened, from West St. Paul,

plate showing __ 36;

saturation of lime in 56-57

Sheds for drying, plate showing- 60.

slop, making of_ __ 59,

253
254 INDEX.

Page. 

Brick, smooth., from West St. Paul,

plates showing____ 30 

soft-mud, machine for making,

plate showing_____ 55 

making of ____M _ _ 59 00 

stiff-mud, making of________ 60-61 

temperatures for firing ____ 36-39 

wire-cut, plate showing___ _ 60 

Brick kiln, down draft, plate showing___________ 63 

scove, plate showing __ __ 63 

Brick machine, four-mold dry-press,

plate showing 61 

Bricklets burned in laboratory tests,

plate showing____ 36 

Brickton, clays at_________ 194-195 

Brown County, clays of 126-134 

Brownsdale, clay near ___ _ 202 

Buffalo, clay near__________ 249,251 

Buhl, clay at_______:_______ 226 

Bureau of Standards, acknowledgment to_ 14 

Burning of clay products, care required in ____ ___ 66-67 

Burns Creek, clay on ___ _ 248 

P.urtrum, clay near __ 240 

Byron, clays at ________ 206,207-208

C.

Calcium, compounds of, in clay___ 23-25 

Cambrian period, clays of _____ 81-82

events of____-______-__ 73-74 

Cambridge, clay at__ ________ 174 

Cannon Falls, clay at_________ 167 

Carbon compounds, effect of, in clay

products_-______ 2C 

Carlton County, clays "of _____ 131-140

slate of, plate showing: 115 

Carpenter, R. C., cited_________ 69-70 

Carver County, clays of______ 140-141 

Cass County, clays of_ _____ 141 

Cement, estimating of chemical constituents for._____ 29 

Center City, clay at__________ 143

Chaska, brick making at ___ 140-141 

Chatfleld, clay near__________ 161

shales at______________ 158 

Checking, remedy for _________ 33 

Chemical determinations, comparison.

of clays by _______ 29 

Chemical reactions in the burning of

clay____________ 35 

Cherry Creek," clay on_________ 188 

Chinaware, clay required for____ 44 

Chippewa County, clays of_____ 141-142 

Chisago County, clays of_____ 142-144 

Chisholm, Boyd & White Co., acknowledgment to___ 14 

Clarissa, clay near __ 240 

Classifications of clays ______ 40-49 

Clay Bank, clay at__________ 168-170 

Clay County, clays of________ 144-145 

Clearwater County, clay of____ . 145 

Clitherall Lake, clay at________ 209

Page. 

Coates, M. A., Binns, C. P., and,

cited___________ 56 

Coleraine, clay at____ 177-178, 229-230 

Collegeville, clay at__________ 236 

Color of clay products, substances

producing _______ 29, 57 

Comparison of clays, aid of chemical

determinations in _ 29 

Composition, chemical, of clay___ 21 

Concretions, limy, in gray laminated clay, plate showing. 36 

Cones, Seger, after heating, plate

showing 88 

Conger, clays near________ __ 163 

Cook, clay near___________ 226-227 

Cook County, clays of____'. _____ 145-146 

Coon Creek, brick from_______ 116-117 

clay bank at, plate showing__ 115 

tests of clay from________ 48-49 

Copper, effects of, on clay products- 27 

Cottonwood County, clays of 146-147 

Cottonwood River, clay on_____ 128-132 

Cretaceous period, clays of_.____ 87-91 

disturbed clays of, plate showing ____________ 168 

events of _ 75-76 

pebbly clay of, plate showing__ 88 

refractory clays of, distribution

of_____________ 107 

Crookston, clay at______ 212 

Crookston Brick & Tile Co., operations of___t__ _ 212 

Crow Wing County, clays of___ 147-149 

Cuyuna iron range, clays on_ 112-113,

148-149

D.

Dakota County, clays of__ _ 149-153 

Dawson, clay near_______ 186 

Dayton, clay at_________ 249-250 

Daytons Bluff, clay at_______ 215 

Decorahi shale, clay from___ __ 83-85 

Deer Creek Brick Co., operations of_ 209 

Deer River, clay on __ 176-177 

Deerwood, clay at 148 

Definition of clay 15 

Deposition of clay 17-18 

Detroit, clay near ___ 118-119 

Development of clay deposits, economic considerations 

on_________ __ 50-51 

Devonian period, clays of _ 86-87 

sediments of___________- 75 

Differences in origin and utility of

clays ._____________ 20-21

Digging clay, methods of_______ 52-53

Distribution of n on refractory

clays __________ 108-110

refractory clays____ _ 106-107 

semirefractory clays___ 107-108 

Dodge County, clays of___ 153-154 

Dolomite, effects of, in clay produ'cts ________ 25 

Douglas County, clays of _ 154-156 

Drainage of clay pits _ __ 53
INDEX.

Page. 

Drainage of farm lands, advantages

of___..________ 08-69

directions for_..________ G9-70

Dresbach, clay at ..__ 247,249

Drift, gray, clays of-.. 92-94

gray, clays of, commercial value

of_____________ 93-94

red, clays of___!__ 96

nature and utilization of- 139 140

Drying of clay products?, methods of _ 63-64

Duluth, clays near _ 225

E.

East Grand Forks, clay at_____ 212-213 

East St. Cloud, brick making near_ 232-233 

(Economic aspects of clay industries__.-_______ 50-51 

Eden Lake, clay at__.. 237 

Efflorescence, formation of, in the

kiln __.._______ 67,151

on clay products,- prevention of- 64

substances producing 29

Elbow Lake, clay at_ _ 173

Elgin, clay near_____________ 242

Elk River, clay near__________ 232

Elmira Township, clay from___ 158-159

Eutectic, definition of ____ __ 24

Eyota, brickmaking at __ ____ 206

F.

Fairmont, plant at . 194 

Fardeus Lake, clay on_..______ 239-240

Faribault, clays near __... 222-223 

Faribault County, clays of ___ 156-157 

Feldspar, addition of, to clay ___ 27, 28 

Fergus Falls, clay at__..________ 208

Fertile, clay at_____ ______ 211-212

Fillmore County, clays oil______ 158-162 

Fineness of grain in clay, fusion affected by , _____ 39

Flashing, color brightened by ____' 67 

Flint, addition of, for clay products_____________ 28

Floodwood, clays at_________ 228-229 

Fond du Lac, clay near_ __ _ 229 

Forest Lake Brick & Tile Co., operations by______ 243-244 

Fort Creek, clay on__________ 221 

Frankford, clay near____ ___ 203 

Freeborn County, clays of_____ 162-165 

Frontenac, clay at __.._______ 172 

Fuels, choice of, for burning clay

 products _..______ 65 

Fuller's earth, property of ____ 45 

Fusibility of clays, classification

based on . _ _ 41-42

effect of impurities o:n _____ 29

Fusion in clays, features of_____ 35-36

Galena limestone, description of__ 85 

Garden City, clay near _ _ 123 

Geologic section, general, of the

State, plate showing 72

Page.

Geology of clay ___ : ___ 15-21 

Geology of Minnesota 70-105 

Glacial clays, deposition of_____ 20 

Glaze, use of ______________ 63 

Glazed ware, testing of clay for_ 45 

Glenville, clay at___________ 162-163 

Glenwood, clay at___________ 214 

Good Thunder, clay near_____ 125-120 

Goodhue, clay near_________ 171-172 

Goodhue County, clays of_____165-173 

Goodhue County Clay Co., operations

of ___________ 165,167 

Grand Eapids, clay at 175-170 

Granite Falls, clays at________ 142 

Grant County, clays of _______ 173 

Grasston, clays near_________ 181 

Grinding machines for clay_____ 54 

"Grog," uses of 33,45 

Gypsum, effects of, in clay 25

H.

Harrington, G. L., work of_____ 13 

Hamilton, clay at 159 

Handy, F. M., adhesion test developed

by_____________ 46 

work of ____- 13 

Hasty, clay at____________ 249,250 

Hayfleld, clay at 153-154 

Heating, effects of, on clay 34-39 

Henderson, clay at___ __ 233 

Hennepin County, clays of_____ 173 

Heron Lake, clay at________ 179-180 

Hibbing, clay at __________ 229 

History^ geologic, of Minnesota 72-78 

Hollow ware, drying of, plate showing_____________ 62 

Homer, clay at 247 

Houghton, J. G., acknowledgment to_ 14 

Houston County, clays of _ 173-174 

Hoyt, E. S., acknowledgment to _ 14 

Hubbard County, clays of_______ 174 

Huronian series, rocks of______ 79-80 

Hutchinson, clay at________ 192-193 

Hutchinson gray drift, analysis of 24 

Hutchinson process for removing

pebbles, description of_ 55-56

I.

Impurities in clay_________ 21,27-28 

limits of, for manufactures 28 

Increase in output of clay products,

suggestions for 67 

Indian pottery, relics of 227 

International Falls, clays near 182, 227 

Iowa, clay in Minnesota border of 15 

Iron, effects of, in clay_____ 25, 34-35 

Itasca County, clays of 175-178 

Isanti County, clays of 174-175

J.

Jackson, clays at 178,179 

Jackson County, clays of- 178-180 

Johnston, A. W., acknowledgment to_ 14
256 INDEX;

Joint clay, properties of______

Jordan sandstone, features of.

K.

Page. 

42 

82

Kanabec County, clays of _ ISO-181 

Kandiyohi County, clays of 181 

Kaolin, definition of_________ 19

testing of______ __ 48 

Kaolinite, impurities in 21

properties of 15 

Kasota, clay at_____ 203 

Keweeawan series, rocks of 81 

Kiln, continuous, description of 65

down draft, description of 65

up draft, descriptions of 64 

" Kiln white." See Efflorescence. 

Kilns, plates showing 63 

Kingston, clay near_ 194 

Kittson County, clay of _ 181 

Koochiching County, clays of__ 182-;186

L.

Lac qui Parle County, clays of 186 

Lake Agassiz, clays deposited in_ 182-186 

Lake County, clays of 186-187 

Lake Duluth, red clays of 97-98 

Lake Mary, clay on _ 251 

Lakes, laminated clays deposited

in______ 20, 94-96, 96-97 

Recent clays deposited in__ 20, 104 

Laminated clays, nature and distribution of__ 94-96, 96-97 

gray, nature and utilization

of___________ 137-130 

of irregular structure, plates

showing 114 

Le Sueur, clay at_____ 190-191 

Le Sueur County, clays of ___ 187-191 

Lengby, clay at_ _ _ 214 

Leroy, clay near 203 

Leverett, Frank, acknowledgment to_ 14 

Light-burning vitrifying clays, distribution of _____ 107-108 

Lilly Lake, clay at___________ 177 

Lily Lake, clay on_______ 245 

Lime, content and effects of, in

clay_____ 23-25, 29 

Limestone pebbles, grinding and

screening of _ 56 

occurrence of, in the gray

drift _________ 92,93 

removal of, from clay_ 55-56 

saturation of, in brick ____ 56-57 

Lincoln County, clays of 191 

Litchfleld, clay near 194 

Little Falls, clays near__ 197, 198 

Little Sauk, clay near____ __ 239-240 

Little Two River, clay on_____ 199-200 

Littlefork River, clay on 183, 184-186 

Loess, nature and distribution of 98-101 

Long Prairie, clay near 241 

Luverne, clay at___:___ 223-224 

Lyon County, clays of_ _ 191

M.

Page.

McLeod County, clays of_____ 191-193 

Madelia, clay near__________ 246 

Madsen, M. C., acknowledgment to_ 14 

Magnesium, compounds of, in clay 25-26 

Mahnomen County, clays of____ 193 

Manganese, effects of, on clay products __________ 27 

Mankato, brickyard opposite_____ 203. 

clays near._____ 121-122, 123-125 

Mapleton, clay at__________,,_ 124' 

Maquoketa shale, description of__ S3 

Marine clays, origin of________ 19-20 

Marshall, clay at_________j.__ 191 

Marshall County, clays of_____ IDS-194 

Martin County, clays of____:___ 194, 

Meeker County, clays of_______ 194 

Meriden, clay near_________ 237-238 

Middleton, Jefferson, acknowledgment to_________ 14. 

Miers Grove, clay near______ 236 237 

Mille Lacs County, clays of____ 194-196 

Miltona, clay at___________ 154-155. 

Minerals, occurrence of, in clay__ 21-28 

Minerals from which clay is derived- 15-16 

Minneapolis, clays near________ 173 

sand-lime brick making at___ 173; 

. sewer-pipe plant at, plate show- 

; ing __________ 170

Minneapolis Brick & Tile Co., operations of _ ___ 115 

Minneapolis Sewer Pipe Co., operations of________ 170-173 

Minneola Township, clay iia____ 166 

Minnesota, general geologic section

of, plate showing___ 72 

map of, showing large clay deposits.^ ' __ 83 

Minnesota, University of, acknowledgment of_______ 14 

Minnesota Farmers' Brick & Tile Co.,

operations of____ 200-202 

Minnesota Fire Brick & Terra Cotta

Co., operations of__ 219. 

Minnesota Paving Brick Co., operations of_____ 115,116-117 

Minnesota School of Mines, acknowledgment to_ 14. 

Mixing of clays, benefits of_____ 57' 

Montevideo, clays at_______ 141-142 

Monticello, clay at ___ 251 

Moorhead, clay at_____ : 144-145 

Mora, clays at__________ _ ISO 

Morris, clay at_______ _ 238 

Morrison County, clays of 197-200 

Morristown, clay at____ 222- 

Morton, clays near_____ 217-220 

Morton Brick & Tile Co., operations of ________ 219, 220- 

Mower County, clays of______ 200-203 

Murray County, clay of 203

N.

Net Lake Rapids, clays near 185-18$ 

New Duluth, clay at__ 225(
INDEX. 257.

Page.

New TJlm, clays near. 126-128 

Nicollet County, clays of_____ 203-204 

Nobles County, clay of 204 

Norman County, clays of _ 205 

North Dakota, clay in Minnesota

border of________ 15 

North Dakota Geological Survey

cited___________ 102 

Northfleld, clay at___ _ 222 

Northland mine, clays at__ 149 

Northwest Brick Co., operations of 209 

NorthwesternFireprooflng Co., operations of _ 115

O.

Odin, clay at 246

Okabena, clay at ._ 178 

Olivia, clay at 221 

Olinsted County, clays of____ 205-208 

Oneota dolomite, description of 82 

Ordovician period, clays of _ 82-86

events of-..__________ 74-75 

Organic matter, effects of, in. clay

products 26

oxidation of______ 66 

Origin of clay.._________ - 15-19

classification from 41

relation of, to uses _ 43 

Oronoco, brick making at_ 206 

Orthoclase, effects of, in clay products 27 

Otsego, clay at-_ 249 

Ottawa, clays n<2ar____ 187-190 

Otter Tail County, clays of 208-210 

Outline of the report 11 

Outwash clays, quality of 98 

Owatonna, clay at _ _ 237 

Oxidation of cl£.y, care required in 66-67

P.

" Paint rock," occurrence of _ 177-

178, 229-230 

Pan, double 8-foot wet, for clay,

plate showing _ 54 

dry, for clay, plate showing 54 

Paper clay, properties required in 45 

Park Rapids, clay near _ _ 174 

Paving brick, rattler test of 117 

Payncsville, clay near- _ 237 

Pebbles, limestone, removal of, from

clay______ ____ 55-56 

Pelican Lake, clays on__ 155-156,173 

Pelican Eapids, clay at _______ 209-210

Pengllly, sand-lime brick making at- 178 

Pennington County, clays of 210 

Perham, clay near __________ 208-209 

Phosphorus, effects of, in clay products _ 27 

Physical properties of clays _ __ 29-40 

Physiography of the State 70-72 

Pine City, clay at________ _ 210

Pine County, clays of 210 

Pine Island, clay at __ 172

64310°~19 17

 Page.

Pipestone County, clay of __ 211 

Plainview, clay near__________ 242 

Plant for working clay, location of 51 

Plasticity of clay, cause of _ _ 31

definition of__________ 30 

Platteville limestone, description of_ 83 

Pleasant Grove, brickmaking at_ 206 

Pleistocene epoch, clays of_____ 91-102

events of____________ 76-78 

Polk County, clays of______J. 211-214 

Pope County, clay of __________ 214

Porcelain, clay required for______ 44

Pottery, clay required for __ 44

making of _________ 62-63 

Preheating of clays, benefits of___ 34, 57 

Preparation of clay for molding - 53-59 

Preston, loess at-________ 159-160

shales at ______________ 158 

Products from clay, output of _ 106 

Properties of clay, minor physical 39-40 

Prospecting for clay, stratigraphlc 50

usual method of _______ 49-50 

Pug mill, tempering of clay ia___ 58-59 

Pyrite, effect of heat on_'.______ 25

Q.

Quaternary period, clays of_ _ 91-104 

events of ____________ 76-78

R.

Ramsay County, clays of 214-216 

Ra-pidan, clay near____ _ ' 124 

Recent deposits, clays of 102-104 

Recent epoch, events of_ 78 

Red bouldery clays, nature and availability of_______ 136-137 

Red clastic series, features of 81 

Red Lake County, clay of ___ 216 

Red River silt, analysis of 24 

Red River valley, claysi of 101-102 

Red Wing, disturbed Cretaceous 

clays, near, plates 

showing ______ 168 

saad-lime brick making at 173 

tests of clay from 48-49 

Red Wing Sewer Pipe Co., operations of _-__-__ 170-173 

Red Wing Union Stoneware Co., operations of 168-170 

Redwood County, clays of- __ 216-220 

Redwood Falls, clays near _ 216-218 

Refractory products, clays required

for ____ _ > 45 

Renville County, clays of _ 220-221 

Residual clays, origin of 19 

Rice County, clays of______ 222-223 

Rice Lake, clay on ___ 164-165 

Rich, J. H., acknowledgment to 14 

Richmond, clays near___ 233-235 

Ring pit, tempering of clay ln__ 58 

Rivers, clay deposited by_ _ 20 

laminated clays deposited by 94-96,

96-97
258 INDEX.

Page.

Elvers, Recent days deposited by_ 102-103 

Rochester, clay at__________ 206, 207 

Rock County, clays of_______ 223-224 

" Rock flour," definition of ____ 17 

" Rock rot," definition of ____ 17 

Roosevelt, clay near________ 224-225 

Roseau, clay at__ _ _ 224 

Roseau County, clays of_______224-225 

Rush City, clays at__________142-143 

Rushford, clay near________ 161-162

St. Augusta, clay near___ _ 236 

St. Charles, clay near_______ 248-249 

St. Clair, clays near_________ 125 

St. Cloud, clay near________ 235, 250 

St. James, clay near_ _ 245 

St. Lawrence formation, rocks of__ 82 

St. Louis County, clays of____ 225-230 

St. Louis River, Huronian slate

on __________ 135-136 

St Paul, clays in_>__________ 214-216 

St. Paul Fire Brick Co., operations

of ____________ 188 

St. Peter, clay at___________ 203 

St. Peter sandstone, description of- 83 

Salt, slaking of lime prevented by_ 55 

Salts, soluble, in clay, indication of_ 29 

Samples of clay, method of taking_ 45 

Sand-lime brick, making of__ 173, 178, 224 

Sardeson, P. W., acknowledgment

to ____________ 14

Sauk Lake, clay on_________ 238-239 

Scope of.the report-_______ 11,13

Scott County, clays of________230^-232 

Screening of clay_ ____ 55

Sea, clay deposited in_________ 19-20 

Seger cones after heating, plate

showing _______ 88

temperatures measured by___ 38 39 

Sewer pipe, clay required for 44 

molding of _____________ 62 

plant for making, plate showing ______________ 170

press for making, plate showing 61 

Shakopee, clays near_:_____ 230-231 

Shakopce dolomite, description of 83 

Shale, definition of___________ 42 

Sherburne County, clays of____ 232-233 

Shrinkage of clay, causes of 32-33 

Shrinkage in clay products, causes of- 29 

Sibley County, clays of ______ 233 

Siderite, effect of beat on_______ 25

Silica, proportion and effects of, in

clay _____ 21-22

" Silica kaolin," analysis of____- 230 

Simpson, brickmaking at 206 

Sizes of grains, classification of clays

by____________- 48 

Slaking, definition of__________ 39 

Slate of Carlton County, showing 

cleavage, plate showing_____:______ 115

Page. 

Slates, origin of__________ __ 20

Slip clay, properties required in _ 45 

" Slumming," removal of pebbles by_ 93 

Soak pit, tempering of clay in __ 58 

Soper, B. K., work of- _ _ 13 

South Bemidji, clay at_______ 119-120 

South Dakota, clay in Minnesota

border of J5 

Spring Grove, clay at 173 

Springfield, clays near______ 132-134 

Staples, clay near _ _ 240-241 

Stearns County, clays of__ __ 233-237 

Steele County, clays of -237-238 

Stevens County, clays of-___ - 238 

Stillwater, clays near________ 244-245 

Stoneware, molded, plate showing 169 

Strickler, Dr. 0. C., acknowledgment

to____________ 14 

Suddenly melting clays, occurrence

of___________ 108-110 

Suggestions, commercial 67 

Sulphur, effects of, in clay products- 546 

Summary of tests of clays 104-105 

Sunshine, clay at^.-_- 210 

Swift County, clays of 238

T.

Taylors Falls, clay at 143-144 

Technology of clay_ 49-67 

Tempering of clay, methods of _ 57-59

water required for _ _ 30-31 

Tensile strength of clay________ 33-34 

Terra cotta, clay required for_ 44

molding of _____________ 62 

Tertiary system, doubtful representation of- 91 

Tests of clays 45-49

summary of _ _ 104-105 

Thief River Falls, clay at ______ 210 

Tile, clays required for 44

drain, resistance to frost by_ 93, 94 

Tile, drain, use of_ 69-70

hollow, molding of 62

interlocking, making of 152 

Titanium, effects of, on clay products- 27 

Todd County, clays of 238-241 

Toughness, testing of clay for 45 

Tower, clay near___ 225-226 

Transportation of clay 53 

Traverse County, clays of _ _ 241-242 

Twin City Brick Co., operations

of ___________ 152-153 

Two River, clay on 198-199, 200

U.

Use of clay products, precautions for. 67-70 

Uses of clays, classification of _ 40-41

V.

Vasa, clay near __: 172 

Verna Brick Co., operations of 175
INDEX. 259

Page. 

Vitrification of clay, effect of lime

on __ 29

features of 36 

temperatures required for 36-39 

Vitrifying nonrefractory clays, distribution of____- 108-110 

semirefractory clays, distribution of_______,_ 107-108 

Volatile matter, expulsion of, .from

clay products 34-35

W.

Wabasha, brick making at 242 

Wabasha County, clays of 242 

Wadena County, clay of 242 

Wahkon, clays near ___ . 196 

Wanamingo, clay at ___ 165-166 

Warba, clay near ___ 175 

Warren, clay near____ 193-194 

Waseca County, clays of 242-243 

Washing of clay, effects of __-. 192-193

method of 54,160 

Washington County, clays of 243-245 

Water, combined, in clay 22

included, in clay__ __ 22-23 

Waterville, clay at and near 190, 243 

Watkins, clay near 194 

Watonwan County, clays of 245^-246 

Weathering of rocks, process and results of__ __ 16-17

Page.

Wedging, tempering of clay by 59 

Wells, clay at 157 

West Concord, clay at 153 

West D«luth, clay at__-___ 225 

West St. Paul, clays at______ 149-153 

clays at, tests of 48-49 

Wet pan, tempering of clay in __ 58 

Wigwam Rapids, clay at _ 227 

Wilkin County, clay of 246 

Willmar Brick Co., operations of__ 181 

Winchell, N. H., cited_______ 189, 221 

Windom, clay near 146 

Winnebago, clay at 157 

Winona, clays near __ 247-248 

Winona County, clays of 247-249 

Wisconsin, clay in Minnesota border

of____________ 15 

Wrenshall, brick plants at 135

section in clay pit at, plate

Bhowing___ _ __ 20

tests of clay from 48-49 

Wright County, clays of____ 249-251

T.

Yellow Medicine County, clays of 

Z.

251

Zumbrota Clay Manufacturing Co.,

operations of _ __ 166

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