DEPARTMENT OF THE INTERIOR

UNITKD STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIRECTOR

359

MAGNETITE DEPOSITS OF THE 

CORNWALL TYPE

IN

PENNSYLVANIA

BY

ARTHUR C. SPENCER

WASHINGTON

G O V E R N M K NT PRINTING OFFICE

1908

CONTENTS.

Page;

Introduction _ ___________________________ _ 7

Geology of eastern Pennsylvania.._______________________ 7

General statement__________________________ 7

Sedimentary rocks___________________________ 8

Igneous rocks._________________________________ 9

General description of ore deposits_____________________ 10

Composition of the ores__________________________ 11

Distribution of the ores___________________________ 12

Geologic relations of the ores______________ 12

Origin of the ores_________________________________ 13

Replacements _________________ ____________ 13

Source of the iron___________________________ 13

Differential metarnorphism_______________________ 16

Practical conclusions.___________________________ 16

Cornwall and vicinity_______________________^________ 17

Cornwall deposits___'._____________________________ 17

Distribution and surface relations__________________ 17

Diabase intrusions.____________._______________ 19

Structure of the beds___________________^_____ 20

Extent of the deposits________________________ 21

General statement_______________________ 21

The Cornwall ore body._________.___________ 22

Near-by deposits________________1______ 23

Mines west of Cornwall____________________________ 28

Carper deposit_______________:______________ 28

Hummelstown deposits.______________________ 29

Berks County deposits________________________________ 29

Wheatfleld group________1_______________________ 29

General description___________________________ 29

Diabase intrusion________________________ 30

Character of the ores___________________________ 31

Structure of the rocks_________________________ 31

Practical conclusions._________________________ 34

Raudenbusch mine.________________ ________ 36

Fritz Island and vicinity_________________________- 38

Island mine _______________________________ 38

East bank of Schuylkill River______________________ 40

West bank of Schuylkill River___________________ 41

Esterly mine__________-________________ ___ _ 41

Boyertown deposits________________________________ 43

General description_________________________ 43

Geology of the district______________ _____ 44

The workings._______________________.________ 47

Descriptions by Willis_______________________ 47

3
4 CONTENTS.

Berks County deposits Continued. Page. 

Boyertown deposits Continued. 

The workings Continued.

Descriptions by D'lnvilliers____________________ 49

'Phoenix upper and middle slopes_____________ ' 49

Phoenix lower slope, or California mine_______._ 50

Warwick mine.______________________ 51

Gabel mine._______________________ 53

Later developments________________________ 55

Practical conclusions_________________________ 57

Deposits southwest of Boyertown_____________________ 61

Deposits north of Boyertown__________________________ 63

Jones mine___*_______________________ j_________ 65>

Warwick mine______________________._______._ 69

York County deposits_______________________________ 71

General statement--__________ _______________ 71

Dillsburg mines _____________ __ _____ 74

Introduction ________________ _ 74

Description of mines_______________________?__ 75

Logan mine._______-___-__ _ __ __ __ 75

Cox mine.____________ ___ __________ 76

Price miue____________ _________ ____________ 77

Grove mine._____________ ____________________ 77

Prospects near Price fannhouse_____________________ 77

Bell mine_________________________.._____ 78

King and Jauss mines.________-__-___-_-___________-____ 79

Altland mine_______________________________ __ 81

Smyser mine_________________..___________ ___ 82

Underwood workings..---_______________ ___ S3

Longuecker mine.-___________________ __ 86

McCormick mines____________________________ * 88

Diabase intrusions west of the mines___ __ ____.__._____ 92

Practical conclusions_____________ _____ ______ __ 93

Grantharn mines._________________ _____ 96

Mines southwest of Wellsville__________________ 98

Bender mine._________^__.___ ___ __ _ _ 100

Index ________________ _- _ ______ _____ 101
ILLUSTRATIONS.

Page.

PLATE I. Map of the Mesozoic belt In Pennsylvania____________ 8 

II. Geologic sketch map, vicinity of Cornwall______ ________ 18

. III. Structure sections, vicinity of Cornwall_______________ 20

IV. Geologic map, Cornwall mines __________________ 20

V. Geologic sketch map, district south of Reading__________ 80

VI. Geologic sketch map, vicinity of WheatHeld mines___,___ 82

VII. Map of Fritz Island mines_____________________ 88 

VIII. Surface map of Boyertown mines, showing position of ore

bodies at 400 feet depth_____________________ 44

IX. Geologic sketch map, vicinity of Boyertown________ 44

X. General plan of workings, Boyertown mines - 46

XI. Cross section at Boyertown mines (along line A-B, PI. X)____ 46

XII. Gross section at Boyertown mines (along line C-D, PI. X) 48

XIII. Cross section at Boyertown mines (along line J3-F, PI. X)____ 50

XIV. Cross section at Boyertown mines (along line (r-ff, PI. X)__ 52

XV. Cross section at Boyertown mines (along line E-fi, PI. X)____ 54

XVI. Plan showing position of fault, California and Warwick mines,

Boyertown ._____ _ _ _ ___ ________i 56

XVII. Geologic sketch map, vicinity of Jones and Warwick mines 66

XVIII. Topographic map of vicinity of Jones and Kinney mines___ 68

XIX. Geologic sketch map of Mesozoic area near Dillsburg 72 

XX. Geologic and topographic map of Dillsburg iron-ore fields___ 74 

Fio. 1. North-south structure section 400 feet east of Ruth mine, WheatHeld group. _ _____ ____ 81

2. North-south structure section near slope No. 1, Wheatfield group. 82

3. East-west structure section, Wheatn'eld group.____ ___ 33

4. Sketch section at north end of Fritz Island _______ 89

5. Sketch section along river bank east of Fritx Island mines___ 89

6. Plan of upper level of Warwick mine, Boyertown _ .. 48

7. Sketch, showing possible structure between Hagy and Eastern

veins_________ _ _ _ _____________ 50

8. Sketch section illustrating relations of Black vein and diabase

slll____________ _____^________________ 00

9. Geologic sketch map of vicinity of Boyertown__________ 61

10. Geologic sketch map of region northeast of Boyertown_______ 63

11. East-west structure section, Jones mine 66

12. North-south structure section, Jones and Kiuney mines___-_. 6T

13. East-west structure section, Kinney mine___ ______ ______ 68

14. Structure section, Warwick mine- _ _ _____________ 00

15. Plan and sections of Beil mine _ ___ __ - __ T8

16. Surface plan showing probable structure at Bell mine______ TO

17. Survey of workings, Jauss mlna _ 79

18. General structure section, Jauss mine_____________ . 80

19. Map of Underwood and lLongnecker mines, showing probable

trend of ore bed _ J___ ___ 85

20. Plan and section of Longnecker mine___:______._.______ 87

21. Sketch map showing situation of pits and test holes on McCormick tract____-__ _________________ UO

MAGNETITE DEPOSITS OF THE CORNWALL TYPE 

IN PENNSYLVANIA.

By ARTHUR C. SPENCER.

INTRODUCTION.

The deposits of»iron ore which form the subject of the present report occur near the edges of the belt of Mesozoic rocks which enters 

Pennsylvania along Delaware River above Trenton, N. J., and extends across the State in a general southwesterly direction to the 

Maryland line. Though the deposits have been described by several 

geologists the present study was undertaken in the belief that an investigation of somewhat broader scope than any of those previously 

attempted might lead to an understanding of the manner in which 

the ores were formed, and that a knowledge of their genesis might 

warrant practical suggestions looking to the discovery of ore bodies 

as yet unknown. The work has been somewhat disappointing, because the observed facts do not establish a complete theory regarding 

the origin of the ores, but from a practical standpoint the results 

are thought to be of value.

The older descriptions deal mainly with those relations of the ore 

bodies exhibited in the mines or pits from which ore was being extracted, but the deposits are here considered in the light of their 

geologic setting. The writer has used much of the information recorded by earlier geologists and has quoted some of their statements, 

to which many of his own observations are merely supplementary. 

The field work was done during the autumn of 1906 and the summer 

of 1907.

GEOLOGY OF EASTERN PENNSYLVANIA. 

GENERAL STATEMENT.

The rocks of Pennsylvania, as recognized by the first-State geologist, H. D. Rogers, fall naturally into three main divisions the 

pre-Cambrian gneisses, schists, and volcanic rocks; the Paleozoic 

stratified formations; and the Mesozoic stratified formations with

7
8 MAGNETITE DEPOSITS IN PENNSYLVANIA.

associated igneous rocks. All these divisions are represented in the 

southeastern portion of the State, in the region covered by Franklin, 

Adams, York, Chester, Lancaster, Dauphin, Lebanon, Berks, Montgomery, Delaware, Philadelphia, Bucks, and Lehigh counties, though 

the pre-Cambrian and Mesozoic rocks are confined to the region which 

lies southeast of the Allegheny Mountain front and to the limestone 

valley which trends from southwest to northeast through Cumberland, Dauphin, Lebanon, Berks, and Lehigh counties.

By folding and faulting the original surface between the ancient 

crystalline rocks and the lowest Paleozoic beds has been complexly 

contorted and broken, so that great masses of the Paleozoic formations are downset into the basement rocks. In four districts deep 

erosion of relatively upthrown blocks has revealed the pre-Cambrian 

formation. In Franklin and Adams counties the pre-Cambrian 

rocks of South Mountain are largely of volcanic origin. They are 

here intricately infolded with Paleozoic quartzites and limestone. 

In the vicinity of Philadelphia and southwestward from that city the 

pre-Cambrian rocks include schists and massive igneous 'intrusions. 

In northern Chester County and in Berks and Lehigh counties they 

are mainly granular gneisses.

SEDIMENTARY ROCKS.

Of the many lormations which are comprised in the whole of the 

Pennsylvania Paleozoic section only the Cambrian quartzites, the 

Cambro-Ordovician limestones, and the Ordovician shales occur in 

the region here under discussion. In the following pages these divisions of the Paleozoic sequence are designated as " No. I " sandstone, 

" No. II" limestone, and " No. Ill" shale, in accordance with the 

usage of the Second Geological Survey of Pennsylvania. Taken

together, formations " I " to " III " extend over a belt of country from 

10 to 20 miles wide, lying southeast of the Allegheny Front. The 

limestone, being relatively much thicker than the sandstone, is- the 

more prominent of the two, while, as the uppermost of the three members, the shale has been more extensively removed by erosion than the 

limestone and sandstone. . .

The Mesozoic strata, made up principally of coarse-grained red 

sandstone and red shale, are distributed in a belt from 8 to 12 miles 

wide, extending from Delaware Kiver in a southwesterly direction 

to the Schuylkill, thence westward to the Susquehanna, and from 

the Susquehanna again southwestward to the boundary between 

Pennsylvania and Maryland. Locally, heavy beds of limestone conglomerate are present.

Though these red formations are now commonly designated the 

Newark group, they are here called simply Mesozoic, the term being
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. I

MAP OF THE MESOZOIC BELT IN PENNSYLVANIA, SHOWING PRINCIPAL INTRUSIONS OF DIABASE. 

Data in part from Second Geological Survey of Pennsylvania.
GEOLOGY OF EASTERN PENNSYLVANIA. 9

consistent with Paleozoic, which it has been found convenient to 

employ in the descriptions that follow. Considered in reference to 

other stratified Mesozoic formations which overlap the Newark rocks 

in eastern New Jersey, the latter are properly designated as lower 

Mesozoic, but failure thus to particularize their position in the stratigraphic column leads to no confusion in discussing the geolog}r of 

Pennsylvania.

The belt of Mesozoic rocks in eastern Pennsylvania is part of an 

unbroken curving zone about 300 miles in length, extending from the 

west shore of Hudson River across New Jersey, Penns}dvania, and 

Maryland, and into Virginia as far as Culpeper County. Several 

outliers in the continuation of the general course of this belt are 

found in southern Virginia and in North Carolina, while northward 

from Hudson River there is an extensive basin of corresponding 

rocks in the valley of Connecticut River, and another bordering the

southeast side of the Bay of Fundy in Nova Scotia.

In Pennsylvania the Mesozoic strata were deposited upon a previously eroded surface on which were exposed all the older rocks now 

represented in the region. In places along the borders of the Mesozoic belt pre-Cambrian gneisses are present. Elsewhere " No. I " 

sandstone or " No. Ill" shale is overlapped by the Mesozoic strata, 

but on the whole "No. II" limestone forms the usual basement. 

Bowlders entering into the make-up of the limestone conglomerates 

that occur in places along the edge of the belt have evidently been 

derived from the formation last mentioned.

IGNEOUS ROCKS.

The zone comprising the various Mesozoic basins is characterized 

by intrusions of diabase or surface flows of basalt, both of which are 

commonly called trap rock, or simply trap (PI. I). The diabase 

dikes occur in the districts between the several basins, and southward 

along the general trend of the zone they persist across South Carolina 

and well into Alabama. Although the strip of country rh which the 

dikes are present is considerably wider than any of the separate .belts 

of Mesozoic strata, the great bulk of the igneous material is associated 

Avith the Mesozoic rocks. In New England and New Jersey both 

extensive surface flows and invading masses are present, but in Pennsylvania nearly all of the igneous rock is distinctly intrusive. The 

intrusions are mainly sills which follow the bedding of the invaded 

formations more or less closely, but local and even extensive crosscutting may be observed.

As the igneous material could not have originated either within 

the mass of the Mesozoic sediments or Avithin the underlying Paleozoic 

formations, a deep-seated source must be admitted. In order to have
10 MAGNETITE DEPOSITS IN PENNSYLVANIA.

reached the positions which it now occupies the diabase must have 

come up through channels traversing' the lower Mesozoic strata and 

the basement rocks beneath them. Presumably the ordinarily narrow dikes that occur outside of the Mesozoic belt were feeders for 

intrusive sills and for surface flows associated with portions of the 

Mesozoic sediments which have been removed by erosion. If this be 

true the feeders of the sills that still remain are perhaps for the most 

part similar narrow dikes.

The ore deposits described in the following pages are intimately 

associated with intrusive masses of diabase and most of them are 

contained in calcareous strata, either in the limy rocks belonging to 

Paleozoic " No. II " limestone, outcropping near the edge of the Mesozoic belt, or in the beds of limestone conglomerate that locally mark 

the base of the Mesozoic section. Since the deposits are situated in 

each case near the surface of unconformity between the Mesozoic and 

the underlying Paleozoic formations, there is reason to believe that the 

diabase .masses associated with the ores are bodies which cut across 

the Paleozoic basement rocks. These masses are of considerable size. 

Some of them were evidently the feeders of sills which penetrate the 

Mesozoic strata. ' . 

GENERAL DESCRIPTION OF ORE DEPOSITS.

The Cornwall type of iron ore is so called from the important Cornwall mine in Lebanon County, Pa. The ores are essentially magnetite, but they contain pyrite in amounts which make it necessary to 

roast them before they can be used in the blast furnace. Some 

specular hematite occurs in certain of the mines, but the amount of 

this mineral is relatively unimportant.

The Ore OCCUrS in large and small masses of varying form, either 

entirely inclosed by stratified sedimentary rocks or lying in such rocks 

where they come in contact with masses of intrusive diabase. The 

ore minerals appear to have been formed by more or less complete 

chemical substitution in the body of the rock, the portion of 

the rock not replaced constituting the principal gangue of the ore. 

Aside from the deposition of the iron minerals the limy strata associated with the ore bodies show remarkably little metamorphism, and 

though a few characteristic minerals of contact metamorphism occur 

they are so uncommon as to almost escape observation. The Cornwall mines have yielded more than 20,000,000 tons of ore, from what 

is essentially a single great ore body, though it contains extensive 

partings of barren rock. The other deposits are all much smaller, 

though several of them are still of important size.
GENERAL DESCRIPTION. 11

COMPOSITION OF THE ORES.

The iron content of these ores is extremely variable, but as the ore 

is mined probably averages not far from 45 per cent. Rather constant chemical characteristics are low phosphorus, high sulphur, silica, 

lime, and magnesia, and the presence of copper. Small amounts of 

cobalt have been found in ores from Cornwall and Dillsburg. Many 

analyses of ore from the different mines may be found in the reports 

of the Pennsylvania Geological Survey, from which the following 

are extracted:

Partial analyses of Cornwall ore.

[A. S. MeOeath, analyst.]

Metallic iron ..................................................

1.

G4.900

.158

.005

.324

1.010

1.131

.071

.014

3.980

.021

2.

51.450

.072

.559

1.080

2. COO

6.652

2. 459

.010

12. 270

.019

3.

48.800

.057

.599

2. 315

4.330

5.531

1.807

.018

12. 940

0.03C

4.

41.900

.194

.319

4.970

2.810

7.457

.428

.019

20. 910

.045

" Lesley, J. P., and D'lnvilliers, E. V., Cornwall iron ore mines: Ann. Kept. Second 

Geol. Survey Pennsylvania for 1885, 1886, pp. 532, 533.

1. Analysis of 115 pieces of niggerhead ore from Middle Hill.

2. Analysis of fine or soft No. 3 ore from west cut, north side, Middle Hill.

3. Analysis of " No. 1 ore " from east face, Middle Hill.

4. Analysis of "No. 1 light ore" from west cut, south face, Middle Hill. 

All the above were dried at 212 + ° F. before analysis.

Partial analyses of ores from Berks and York counties.a

1.

43.40

11.13

18.90

.01

.01

.43

.09

2.

43.00

14.02

13.86

.59

.53

.02

3.

42.75

22. 10

11.45

.59

.01

4.

39.60

20.20

19.18

.12

.23

1.94

.06

5.

38.05

16.13

19.77

.56

.42

1.14

.04

6.

34.55

21,21

22. 38

.17

.21

1.64

.03

ore,

"Lesley, J. P., arid D'lnvilliers, E. V., op. cit, p. 537.

1. Black 163 pieces, from Warwick mine, Boyertown, Berks County, A. S.

McCreath.

2. Magnetic ore from Island mine, Reading, slope No. 1, Leonard Peckitt, Reading.

3. Dillsburg ore from A. Underwood's mine, A. S. McCreath.

4. Magnetic ore from Wheatfield mine, Berks County.

5. Magnetic ore, 25 pounds, from Island mine, Reading, A. S. McCreath.

6. "Blue ore," 20 pounds, from Phoenix mines, Boyertown, A. S. McCreath.

Workings at the surface formerly furnished soft ore free from sul- 

.phur, but this material gives place to hard sulphurous ore at relatively shallow depths.
12 MAGNETITE DEPOSITS IN PENNSYLVANIA. 

DISTRIBUTION OF THE ORES.

So far as known, ores of the Cornwall type do not occur outside 

of Pennsylvania, : though certain small veins of magnetite occurring 

in masses of intrusive diabase in Nova Scotia may be more > or less 

closely related to them. In Pennsylvania the ores have been mined 

on a considerable scale at five localities in Berks Count}7 , namely: At 

Boyertown; at two places south of Reading; 7 miles southwest of 

Reading, near Fritztown; and near Joanna station, 2£ miles northeast 

of Morg'antown. In Chester County they were formerly mined at 

Warwick, though this deposit is entirely exhausted. The great Cornwall mines are situated in Lebanon Count}7 , and near them are two 

other small deposits. In York County a large number of operations 

have been carried on in the vicinity of Dillsburg. Of all the deposits 

which have been mentioned only the one at Cornwall is now worked 

in a large way, though the several interests which formerly controlled 

the Boyertown properties have recently been consolidated so that these 

mines may be started at an early date. At Dillsburg some ore was 

mined in 1903, and surface mining on a small scale was in progress 

at the Wheatfield group in 1906; the other mines have been abandoned for many years.

GEOLOGIC RELATIONS OF THE ORES.

Though in the past there has been considerable discussion concerning the stratigraphic position of the deposits, it is now agreed that 

in York County the}7 lie in Mesozoic strata and in most of the other 

localities in limestones or limy shales of Paleozoic age.a

The Cornwall deposit is situated at the top of " No. II" limestone 

of the Pennsylvania section, just under the " No. Ill" (" Hudson ") 

shale; the Boyertown. Fritz Island, Raudenbusch, Wheatfield, and 

Jones deposits are in strata which apparently belong near the base of 

" No. II" limestone. The Warwick deposit lies at the base of Mesozoic beds that rest upon pre-Cambrian gneisses.

It has been found that large masses of intrusive diabase are present 

near each of the existing ore bodies and usually in actual contact with 

them. The existence of diabase near the mines is noted in every published description of these magnetite deposits, and the present 

investigation has served to emphasize both the size of these igneous 

masses and the importance of their relation to the ore deposits. It 

is thought, indeed, that the origin of the ores must have been directly 

connected with the intrusion of the igneous rocks.

0 Lesley, J. I*., and D'lnvilliers, E. V., op. cit. Also, D'lnvilliers, E. V., Iron ore mines 

and limestone quarries of the Cumberland-Lebanon Valley: Ann. Kept. Second Geol. 

Survey Pennsylvania for 1886, pt. 4, 1887.
GENERAL DESCRIPTION. 13 

ORIGIN OF THE ORES. 

REPLACEMENTS.

If the various deposits be considered together the theory of origin 

which seems to be required by their geologic relations is that the 

magnetite ore bodies of the Cornwall type have been formed by the 

more or less complete metasomatic replacement of sedimentary rocks 

by iron minerals precipitated from heated solutions set into circulation by the invading diabase. The rocks which have been thus 

replaced are usually limestones, limy, shales, or limestone conglomerates.

Previous writers, including H. D. Kogers, T. Sterry Hunt, Persifor 

Frazer, jr., J. P. Lesley, and E. V. d'lnvilliers, have held that while 

the present magnetic condition of the ores might be due to the metamorphosing effect of the trap rocks (diabase), the deposits had been 

formed before the introduction of these rocks.ft

Material from almost any one of the mines affords abundant evidence that the ore minerals have been deposited by substitution or 

chemical replacement of the limy rocks. Much of the lean ore consists of alternating layers of the iron minerals and unaltered rock, 

showing definitely that certain portions of the rock have been more 

favorable for replacement than others. At Cornwall many examples 

may be seen in which thin layers of ore conforming to the stratification of the limy shales are connected by cross seams, which show 

beyond a doubt that the ore minerals could not have been formed 

contemporaneously with the inclosing rock, but that they must have 

been introduced subsequently. It is the writer's conception that the 

solutions which accomplished the deposition of the ores must have 

been in the condition of vapor when they penetrated the rocks.

SOURCE OF THE IKON.

The source of the solutions concerned in the formation of the ores 

and in the general metamorphism of the rocks in the vicinity of the 

igneous masses and the source of the iron which the deposits contain 

can not be satisfactorily determined. The observed facts lead to no 

definite conclusion on either of these points, though, all things- con0 Rogers, H. D., Geology of Pennsylvania, vol. 2, 1858, pp. 687, 708, 718.

Hunt, T. S., The Cornwall iron mine and some related deposits in Pennsylvania: Trans. 

Am. Inst. Min. Eng., vol. 4, 1875, pp. 508-510.

Frazer, P., jr., Second Geol. Survey Pennsylvania, Rept. CC, 1877, pp. 198-400. Also, 

A study of the specular and magnetic iron ores of the new red sandstone in York 

County, Pa.: Trans. Am. Inst. Min. Eng., vol. 5, 1877, pp. 132-143.

Lesley, J. P., and D'lnvilliers, E. V., Report on the Cornwall iron-ore mines, Lebanon 

County: Ann. Rept. Second Geol. Survey, Pennsylvania, for 1885, 1886, pp. 491-570; 

Final Rept. Second Geol. Survey Pennsylvania, vol. 1, 1892, pp. 351-357.

D'lnvilliers, E. V., The Cornwall iron-ore mines, Lebanon County, Pa.: Trans. Am. 

Inst. Min. Eng., vol. 14, 1886, pp. 473-904.
14 MAGNETITE DEPOSITS IN PENNSYLVANIA.

sidered, if it be admitted that the heat of the intrusive rocks was the 

prime cause of the circulation of the solutions which formed the ore 

it appears more likely that both the waters and the iron were furnished by the igneous rock than that they could have been derived 

from an outside source. Possibilities which naturally present themselves are as follows:

1. The water was of meteoric origin and the iron came from the 

sedimentary rocks.

2. The water was of juvenile origin (that is, it was expelled from 

the igneous rocks) and the iron came from the sedimentary rocks.

3. The water was of juvenile origin and contained the iron in solution \vhen it escaped from the igneous rocks.

The suggestion that ordinary ground waters could have been heated 

by the invading igneous rocks and thus have been enabled to cause' 

extensive induration of the invaded Mesozoic strata, leaching them of 

their contained iron and concentrating it into ore deposits occupying 

the observed situation, is opposed by several considerations. In the 

first place, it appears that waters from any source outside of the 

igneous rock, whatever their natural courses of circulation, if unaffected by the intrusive masses, could never closely approach the 

heated bodies of rock, for the reason that steam.would be generated 

in the vicinity of the contacts and the resulting pressure would tend 

to drive all waters outward from the source of heat. Under such conditions if ore deposits were formed they would not be segregated at 

the igneous contacts, but instead would be some distance away, which 

is contrary to the existing relations. A second argument against the 

suggestion is that the deposits are neither as numerous nor as widely 

distributed as would be expected if the iron had been contributed 

by the invaded formations. The only sedimentary rocks which can 

be considered as at all competent to have furnished sufficient iron for 

the known deposits are the Mesozoic sandstones and shales that occur 

in the vicinity of all the deposits, as the Paleozoic formations are made 

up of rocks containing very small amounts of iron. In so far as they 

have not been altered by the influence of the intrusive diabases the 

Mesozoic rocks are of almost uniform appearance throughout the 

region and from a few recorded analyses it may be judged that they 

carry from 5 to 8 per cent of iron oxide. Everywhere in the neighborhood of the intrusive masses the sandstone and shales have been 

extensively metamorphosed. In places balls of epidote have been, 

formed in the shales; elsewhere small segregations of specular hematite occur in coarse sandstones; and in conglomerates some of the 

pebbles are surrounded by rims of garnet, tremolite, and hornblende. 

Changes of this sort characterize the more intense phases of metamorphism and are observed only near the diabase contacts; more exten-
GENERAL, DESCRIPTION. *' 15

sive alteration of a less striking nature is manifested by a general 

induration of the rock and by a loss of the original red color.

Though the general bleached condition of the Mesozoic strata in the 

neighborhood of the intrusive masses points to these rocks as a possible source of the segregated iron, it is not certain that the whitened 

rocks have actually lost their iron, for the original amount of this 

element may still be present in a different chemical state. No investigation has been made to settle the question thus raised, but it does 

seem that if the iron of the sandstones has been depleted in a few 

places the same thing must have taken place generally, because the 

appearance of the altered rocks is the same in many places. If the 

known deposits of iron ore had been formed from solutions of this 

origin a certain amount of segregation should be found in association with the bleached rocks wherever they occur. The fact that the 

ore deposits are so localized is thus against the idea that the iron 

which thejr contain has been furnished by the sedimentary rocks.

The conclusion that the sedimentary rocks are not likely to have 

furnished the iron applies as well when the active waters are regarded 

as having come from the igneous rocks as it does when a meteoric 

source is assigned to them.

It can hardly be doubted that the general alteration of the shales 

and sandstones near the igneous rocks has resulted from the action 

of heated Avater and steam percolating through the sandstones and 

shales. If the waters which took part in the metamorphism had 

come out of the igneous rocks, either from the masses adjacent to 

the altered sediments or from much deeper masses which have not 

been exposed to view, they could hardly have made an excursion 

through the stratified rocks and later returned to the contact, as they 

must have done to have deposited the ore bodies at Boyertown, at 

Cornwall, at the Jones mine, and at the larger ore beds of the Dillsburg field.

Only one of the several adverse considerations presented above 

stands in the way of the suggestion that both the waters which effected the metamorphism and the iron which was deposited by these 

waters were driven from the igneous rocks; namely, the uncommonness of the deposits. If certain of the intrusive masses furnished 

iron for large deposits, why is it that similar segregations do not 

occur in association with every important mass of diabase? Though 

the question can not be satisfactorily answered, our general knowledge concerning the occurrence of ore deposits at igneous contacts 

points to the conclusion that the nature of the solutions given off by 

different parts of igneous rock masses is subject to wide variation, 

so that it is by no means necessary to believe that identical materials 

must have been introduced everywhere in the vicinity of intrusive
16 MAGNETITE TI DEPOSITS IN PENNSYLVANIA.

masses of the diabase, even though the igneous rock be accepted as 

the source of the iron segregated locally at the contact with the invaded strata.

DIFFERENTIAL METAMORPHISM.

Whatever the actual source of the iron may have been, it can not 

be doubted that different masses of diabase within the same general 

field may have differed greatly in respect to efficiency in producing metamorphism, but, other things being equal, it can be assumed 

that the directness of the paths by which the intrusions came into 

their present positions must have been a very important factor 

influencing the relative amount of alteration and mineralization 

which the various masses of diabase were capable of producing. It 

seems evident that the transfer of heat and the movement of mineralizing waters must have continued for a much longer period in the 

vicinity of strongly crosscutting masses of igneous rock than adjacent 

to others having less direct connection with the deep-seated reservoir 

which' supplied the molten rock material. This is accepted because 

the deep reservoir is conceived to have been the original source of all 

the energy involved in the chemical reactions of metamorphism and 

ore deposition.

PRACTICAL CONCLUSIONS.

The geologic features of the various deposits which have been 

studied are thought to warrant the following general suggestions 

to those who in the future may make 'practical explorations for new 

ore bodies in this field.

1. Ore bodies are to be sought only on or near the walls of masses 

of diabase.

2. Large masses of diabase are more favorable for ore deposits 

than smaller masses.

3. Crosscutting intrusions and highly inclined sills are more favorable than sills of low inclination.

4. Limestones and limy shales are far more likely to be replaced 

by ore than clay shales or sandstones.

5. Particularly favorable locations for ore are found in masses of 

limestone that lie between bodies of diabase and beds that are in a 

marked degree less susceptible than limestone to the metamorphosing 

influence of the igneous rocks.

6. The most promising situations will be found at places where 

the largest number of the above-stated favorable conditions occur in 

combination.

Many or all of the more favorable conditions enumerated existed 

at places where the larger ore deposits of the Cornwall type were 

formed, and as several of these conditions may be fairly inferred
CORNWALL DEPOSITS. ' 17

to exist in a few other localities, usually in the vicinity of the mines 

which have been .operated, still other deposits of iron ore may yet 

be found in the same field. The geologic descriptions which follow 

have been prepared with especial reference to the possibility of indicating situations in which it may prove worth while to look for 

. deposits of iron ore as yet unrecognized.

CORNWALL AND VICINITY.

CORNWALL DEPOSITS. 

DISTRIBUTION AND SURFACE RELATIONS.

The Cornwall ore banks are situated 5 miles from Lebanon, Pa., 

on the south side of the Lebanon Valley, along the edge of which 

Paleozoic limestones and slates give place to intrusive diabase and to 

conglomerates, sandstones, and shales of Mesozoic age (PL II). The 

different formations have a general east-west trend through all this 

region, and for several miles both east and west of Cornwall the older 

(Paleozoic) and newer (Mesozoic) formations are separated by an 

intrusive mass of diabase which has a width in outcrop of 1,400 to 

2,900 feet. The mines lie just south of this diabase in an isolated area 

of limestone, the southern boundai^ of which is formed by overlapping Mesozoic beds. Eastward from the ore hills for a distance of 

somewhat more than a mile a narrow strip of slaty rocks comes between the diabase and the lowermost Mesozoic strata exposed in this 

vicinity. West of the workings a narrower strip of the same rock in 

similar position outcrops for perhaps 1,000 feet. The limestones and 

interlayered limy shales south of the diabase have been more or less 

completely replaced by magnetite, somewhat contaminated by pyrite 

and chalcopyrite, and it is these impregnated strata that constitute the 

great deposit from which more than 21,000,000'tons of iron ore have 

been extracted since 1853.

The position and surface relations of the ore-bearing strata to the 

various rocks which have been -spoken of in the foregoing paragraph 

are clearly exhibited on the maps (Pis. II and IV), and the crosssections (PI. Ill) indicate the supposed relations underground. These 

sections are intended to show the kind of structure that seems to be 

required by the existing surface distribution of the various kinds of 

rocks and'by their strikes and dips, in so far as these can be observed. 

As guides the sections are believed to be of some value, but thicknesses, 

strikes, and dips of buried strata are manifestly not ascertainable 

factors in cases like the present, where masses of intrusive rock, and 

in addition a great unconformity of deposition, are involved in the 

structure to be interpreted.

54370 BnlJ. 359 03 2
18 MAGNETITE DEPOSITS IN PENNSYLVANIA.

On the surface the ore, together with such masses of lean or barren 

rock as accompany it, is bounded on the west, north, and east by diabase, a tongue of which likewise limits the Big Hill mine on the 

south. Between the tongue of diabase that forms the southern side of 

Big Hill and the first exposure of Mesozoic beds in the low ground 

immediately south of Miners village the slope is covered by loose 

debris, so that it is impossible to say what the distribution of the vari- 

' ous rocks actually is. It seems very likely, however, that some of the 

strata which are elsewhere converted into ore occupy at least a portion of this hidden ground. South of the mines scattered outcrops 

serve to indicate rather closely the northerly limit of the Mesozoic 

rocks, the lowest bed of which is a conglomerate composed of angular 

quartz fragments in a cement of bluish clay. This peculiar rock has 

been called porphyry by casual observers, but its clastic nature is 

obvious on close examination. South of the present workings in 

Middle Hill, and for some distance toward the west, loose debris derived from the near-by hill covers the edge of the ore, but the blue 

conglomerate has been revealed in a reservoir excavation near the 

Mount Hope road, and this rock probably constitutes the immediate 

capping of the ore-bearing strata from this place eastward to the 

exposures along the railroad track just below the superintendent's 

office. West of the Mount Hope road the same rock may be followed 

for some distance, but in this direction its outcrop approaches the 

diabase, and the rock is considerably baked and indurated. On the 

little knoll just west of the road a narrow strip of slate is present 

next to the diabase, as previously mentioned.

The blue conglomerate appears to lie at the bottom of a series of 

carbonaceous shales which are partially -exposed along the Mount 

Hope road, and are well exhibited 2 miles farther west in a cutting 

along the Cornwall and Lebanon Railroad. On the geologic maps 

(Pis. II and IV) the conglomerate and carbonaceous shales are 

represented by one pattern.

The area over which the ore-bearing strata were naturally exposed or have been revealed by stripping is roughly 4,000 feet long 

and from 400 to 800 feet wide, and its extent beneath a superficial 

covering of loose gravel and sandstone debris, though as yet not 

fully determined, would seem to be considerably more. From diamond-drill borings south of the present workings it is known that 

ore continues in this direction for at least several hundred feet 

beyond the edge of the Newark strata that cap the deposit, but the 

information afforded by these holes has not been available in the 

present study.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. II

LEGEND

S§«SSSSSSi&«

-i- + + 4- + -f

4- -f + + + + + - + -h H- 

+-+.4- 4- +

iMiiiiti SS8S$S8«

iitfiiiiMtiit

«^X<>^\\^\\\>^£XN:^ 

^^^&fe<

GEOLOGIC SKETCH MAP OF VICINITY OF CORNWALL, LEBANON COUNTY, PA.
COBNWALL DEPOSITS. 19 

DIABASE INTRUSIONS.

The diabase next to the Cornwall deposit is an intrusive mass of 

considerable size and of complex shape. Along the north slope of the 

4 hills that face the Lebanon Valley its outcrop forms a continuous 

east-west band from a third- to a half mile in width and 9 miles 

in length. This body is connected by two southward-trending arms 

with a second band, which lies about 2 miles farther south and 

extends with a west-southwest course across the Susquehanna into 

York County. This southern mass of diabase has the form of a sill 

which follows a group of carbonaceous shales showing generally 

northward dips. Shales of the same group may be traced along the 

edges of the connecting arms both east and west of the Cornwall 

mines, and though local crosscutting may be noted, it is evident from 

the field relations that these surface connections are merely portions 

of the extensive sill that have been uncovered by erosion. On the 

other hand, the diabase of the northern band is a crosscutting 

mass, for it is bounded on the extreme west by massive sandstones 

of the Mesozoic; then by the same rocks on the south and by 

Paleozoic limestones on the north; next", just south of Bismarck, by 

black Mesozoic shales on both sides; farther east by these shales and 

blue conglomerate on the south and by the slates which form Mill 

Ridge on the north; at the mines by the limestones impregnated with 

ore and the slates of Mill Ridge; east of the mines as far as Rexmont 

by these slates on both sides; and thence, to a point beyond the 

Lebanon waterworks main reservoir, by Paleozoic limestones on the 

north and by Mesozoic strata on the south, except where small outcrops of slate and limestone just south of the dike have been revealed by two of the three streams that supply the waterworks. 

(Through an error only two of these streams appear on the sketch 

map, PL II.)

From the conclusions that the southern diabase band is the cropping of a sill and that the northern band is a dike, it is but a natural 

step to regard the latter as having been the feeder of the former; and 

the warrantable belief that this is the actual relation forms the basis 

of the structure represented in the cross sections (PI. III). That 

there is a connection between the dike and sill in the vicinity of the 

mines is indicated by the reported presence of diabase beneath the 

ore-bearing strata in all the diamond-drill holes that have been bored 

south and southwest of the present workings. It is hardly to be 

doubted that the sill forms a continuous sheet beneath the oblong 

area about 6 square miles in extent, which is surrounded by an unbroken outcrop of the diabase.
20 MAGNETITE DEPOSITS IN PENNSYLVANIA. 

STRUCTURE OF THE BEDS.

Within this area, rimmed by diabase, the observed dips are toward 

the north, and the average inclination of the strata has been taken 

by Lesley and D'lnvilliers a to be between 12° and 15°. If, however, 

the diabase mass be accepted as a sill following the group of carbonaceous beds, it is evident from the distribution of these shales that 

in that part of the area lying west of the Cornwall Railroad the 

effective dip toward the north must be much less than 12°, because 

the shales outcrop on the south side at. elevations between 700 and 

800 feet, and just south of the mines their croppings are barely 100 

feet lower. East of the railroad the strata may be somewhat more 

steeply inclined, as higher and higher horizons of the Mesozoic strata 

come into contact either with the diabase dike or with the slates 

which adjoin it for nearly 2 miles eastward from Miners village. 

In this direction it seems that the carbonaceous shales are overlapped 

by higher beds of sandstone arid red-shales, so that their contact with 

the Paleozoic rocks ma}r lie well back from the edge of the diabase 

dike and some distance below the lowest Mesozoic strata locally 

exposed by the stream cuttings.

In Lancaster County (Pis. II and III), beyond the southern edge 

of the sill, lower and lower Mesozoic strata emerge, with east-northeast strikes .and constantly increasing northward dips, until the 

boundary with underlying slates is encountered about 2 miles south 

of Penryn. The basal contact on this side of the Mesozoic belt is a 

nearly straight line, trending slightly south of west, extending from 

Hopeland past Brickerville to the bend of Chickies Creek, just north 

of Whiteoak station, and thence nearly to Mastersonville, where it 

takes a more southerly course, reaching Susquehanna River at Bainbridge. Near this southern boundary the dips of the M.esozoic strata 

are steep and locally are even overturned. Allowing for the observed gradually decreasing inclination toward the north, we have 

an estimated thickness of strata amounting to about 6,500 feet between the bottom of the Mesozoic and the group of carbonaceous 

shales in which the intrusive sill occurs; yet near the Cornwall mines, 

barely H miles north of the point where the shales outcrop, and south 

of Bismarck, about 2 miles distant, the same beds are seen to have 

been deposited directly upon the Paleozoic rocks. This striking relation and its proper interpretation have an evident bearing on the 

correct understanding of the structural features of the Cornwall 

deposit, and consequently on any attempt to determine the possibility 

of the existence of other similar deposits in the neighborhood. The 

explanation suggested is that the Mesozoic beds were laid down 

under such circumstances that successively higher strata were spread

a Cornwall iron-ore mines: Ann. Rept. Geol. Survey Pennsylvania for 1885, 1886.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. Ill

500 

Sea level O

Diabase 

SECTION ALONG LINE A-B, PL.

Diabase

SECTION ALONG LINE C-D, PL. SECTION ALONG LINE E-F, PL. U

500

0 Sea level

Mesozoic 

777/77777777777777777

500

0 Sea level

50O 

 Sea level O

Sandstone once 

/Ore carbonaceous beds

500

0 Sealevel

Diabase S'ate//;

SECTION ALONG LINE G-H, PL. II

Diabase late in 

SECTION ALONG LINE I-J, PL.

Horizontal scale 

 3L 3 5 miles

STRUCTURE SECTIONS IN VICINITY OF CORNWALL, LEBANON COUNTY, PA.
U.S. GEOLOG ICAL SURVEY 

GEORGE OTIS SMITH DIRECTOR BULLETIN NO.359.PL.lv

LEGEND

-MTesozoic

c onglomer ale 9,

sandstones, and.snales

Base from Geological Survey of 

Pennsylvania, Annual Report,1885

GEOLOGIC MAP OF CORNWALL MINES AND VICINITY, LEBANON COUNTY, PENNSYLVANIA

500 o 500 1000 IGOO ___2000 feet

Geology by A.C.Spencer

Contour interval 5 feet

Beckon is mean sea level

1908

conglomerate 

Tied at Taase of 

Mesozoic

Paleozoic 

^Nb.H limestone 

and. limy sKale, 

the latter partly

Paleozoic Bo.HI slate

ll" slate of 

Le siey tmi 

D Invilliers)

dialmse
COKNWALL DEPOSITS. 21

farther and farther toward the north against a continually receding 

shore. In other words, the facts observed indicate that the Mesozoic 

basin was sinking and widening as deposition went on, so that from 

south to north there is a marked overlap of the Mesozoic .strata upon 

the Paleozoic basement. On the assumption that to this overlap is 

due the disappearance of the lower strata toward the north, a structure section from Lebanon to Whiteoak station has been drawn to 

show the general relations of the rocks (PL III). The north end of 

the section as far as Mill Ridge has been copied from the report of 

Lesley and D'lnvilliers.0 It is to be observed that inasmuch as nothing is known concerning the width of the dike below ground or the 

attitude of its Avails in depth the representation of these features on 

the section is entirely conjectural; also that in showing the Paleozoic 

limestone and slate beneath the Mesozoic rocks the intention is 

merely to suggest that they form a basement upon which the younger

strata were deposited, and not to present even a guess concerning the 

structure or distribution of these formations underground.

EXTENT OF THE DEPOSITS.

General statement. Attention may now be directed to the manner 

in which the Cornwall deposits embody all the favorable conditions 

listed on page 16. They occur next to a considerable body of diabase, 

which exhibits crosscutting relations to the stratified rocks adjacent. 

They are confined to limestone strata cut by this diabase, and these 

beds of the limestone are capped both by Paleozoic slates and by 

Mesozoic carbonaceous shales. Metamorphism of the sort which has 

affected the limy strata is almost lacking in both of these cap rocks; 

and though they are baked in the near vicinity of the diabase, the conclusion seems to be justified that they were not permeated by the 

mineralizing waters to the same extent that the limestones were. It 

seems a fair assumption that these rocks were from their nature relatively impervious to the solutions which formed the ore, and that they 

served in a very important degree to prevent the dispersion of these 

waters and to confine their movements and effects to the limestones 

and limy shales beneath them, a great body of which had been caught 

up in the angle between the crosscutting dike on the north and the sill 

extending out toward the south. There is every reason to believe that 

the great magnetite deposit at the Cornwall mines was formerly 

capped entirely over by beds of sandstone and shale, and that the appearance of the ore body at the surface is due to rather modern erosion. If so, two questions which naturally present themselves are: 

(1) What part of this deposit is still buried beneath barren rock?

0 Cornwall iron-ore mines : Ann. Kept. Geol. Survey Pennsylvania for 1885, 188G, p. 526.
22 MAGNETITE DEPOSITS IN PENNSYLVANIA.

(2) Is it not probable that at other localities in the vicinity there are 

like deposits which, though not uncovered by natural processes, may 

be found by exploration?

The Cornwall ore body. Diamond drilling now (1906) in progress 

will, if systematically continued, eventually delimit the Cornwall ore 

body. From a geologic point of view the strata which carry the ore 

may be expected to run out under the Mesozoic cover toward the south 

in the form of a wedge, the thin edge of which will be encountered 

where the sill of diabase, rising toward the south, reaches the unconformable surf ace. between the ore-bearing strata and the overlying 

carbonaceous shales (PL III). That magnetite should continue to 

form so large a proportion of the rock in this direction as it does near 

the crosscutting dike seems improbable from the theory which has 

been stated concerning the origin of the ores.

Just west of the Grassy Hill mine the diabase is seen on the surface to trend directly across the strike of the ore-bearing strata and 

to come into contact with the overlying slate, which is exposed on 

the north slope of the little knoll west of the Mount Hope Avagon 

road. It seems possible that the limy beds which elsewhere carry 

the ores may be present beneath this patch of slate, but farther west, 

where the carbonaceous shales appear in contact with the diabase, 

the sill seems to be entering this group of beds, so that in this vicinity 

there is no place south of the dike for the limestone beds to be present 

except beneath the sill. Starting from a point about 1,000 feet west 

of the Mount Hope Avagon road, AA^here the carbonaceous shale overlaps the slate and comes into contact with the diabase, an irregular 

line drawn to the southern edge of the ore-bearing strata, when the 

position of this edge is determined by the drill, Avill indicate the 

general limit of these strata south and southwest of Grassy Hill.

East of the railroad and south of the diabase hook AA'hich forms 

the south side of Big Hill, the ore-bearing strata should be present 

just beneath the rather thick coA^er of surface debris. Slates appear 

on the hill slopes north of the eastern part of Miners village, and 

as these beds are known to lie stratigraphically above the limy beds, 

the latter are probably in contact A\7 ith the diabase dike at a moderate 

depth beneath the capping of slate.

The slates continue as a narroAV band from Miners village to the 

Rexmont-Overlook road. The presence or absence of the uppermost 

strata of the A^alle}^ limestone immediately beneath the slate, and, 

if present, the thickness of the mass, are dependent on the local existence of a direct connection betAveen the dike and the sill and on 

the depth at AA'hich they join. It is evident that if a connection 

betAA^een the sill and the dike exists just beneath the slate there can 

be no limestone above the sill, and that the deeper the connection the
CORNWALL DEPOSITS. 23

thicker will- be the mass of limestone caught in between the dike 

and the sill. However far the limestone strata may extend along 

the southern wall of the dike, which trends northeastward from 

Miners village, just so far are the structural relationships between 

the different sorts of rock similar to those which have favored the 

deposition of ore at the Cornwall mines. All of this ground, as far 

as the road leading from Eexmont to Overlook, is regarded as likely 

to contain a continuation of the Cornwall ore bed and to warrant 

such expenditure as would be required to prospect it adequately. 

(See Eexmont-Overlook section, PL III.)

To summarize, it seems that exploration should be extended along 

the strike of the deposit for about 1,000 feet toward the west and for 

at least 5,000 feet toward the east.

Near-ly deposits. In regard to the possibility that similar deposits may occur in other localities, it may be said that from the geologic

point of view they may very well exist in several places.

East of the Eexmont-Overlook wagon road the southern edge of 

the Cornwall diabase dike exhibits a crosscutting contact Avith the 

Mesozoic beds as far as the first of the three creeks which afford Leb-. 

anon's water supply. Here outcrops of slate on the AA^estern bank of 

the stream and next to the diabase presumably correspond Avith the 

slate occurring in Mill Eidge and on the opposite or south side of 

the dike in the neighborhood of the Cormvall mines. On the ridge 

above this outcrop Mesozoic rocks are found, and the surface of overlap or unconformity lies somewhere betAveen.

The next ravine to the east has been dammed to form a collecting 

reservoir, along the shores of which flat-lying strata of shale and 

limestone are Avell exposed. During the construction a mass of magnetite, which, though it proved to be a pocket, is said to have furnished 500 tons of ore, Avas encountered in an excavation on the east 

side of the creek below the dam. From what may be seen at present, 

it is evident that this pocket of ore occurred between the Avail of the 

diabase dike and limy strata lying just under the overlapping Mesozoic beds. All the sedimentary rocks are considerably metamorphosed, silicate minerals and small segregation of specular hematite 

being largely developed in the Mesozoic strata for several hundred 

feet to the south.

Several years ago the Lackawanna Iron and Steel Company put 

down three test holes in this vicinity, hoping to develop a AArorkable 

deposit of magnetite. Hole No. 1 Avas situated a short distance north 

of the excavation referred to above, No. la about 125 feet farther 

north, and No. 2 on the ridge about 300 feet east of the excavation 

and about 120 feet above the creek. The folloAving records of these 

holes have been furnished by the company:
24 MAGNETITE DEPOSITS IN PENNSYLVANIA. 

Records of drill holes near collecting reservoir.

HOLE No. 1.

Feet.

Earth_________________ 4*. 

Diabase___________.____ 14H

146 

HOLE No. la.

Earth______1__________ 10*

Diabase_____________ 914

HOLE. No. 2.

Feet.

Earth_________________ 41

Soft sandstone___________ 26*

Diabase_.. ___________ 54"*

White limestone__________ 24

Diabase_______________ 27

102

The configuration of the surface is such that hole No. 2, though 

173 feet deep, penetrated only 51 feet below the level of the stream. 

Two interpretations may be placed on the section determined by hole 

No. 2 that the two bodies of diabase are wedges from the main dike 

extending out into the stratified rocks, or that there is here merely a 

waving contact between the dike and the stratified rocks penetrated 

by it. -A hole situated 100 feet or more farther south might be expected to encounter a greater thickness of Paleozoic limestone, and 

. there is the possibility that certain layers might be impregnated with 

magnetite. On the whole, in spite of the unfavorable result of the 

tests mentioned above, it seems that it may yet be worth while to 

make further explorations along the south side of the Cornwall dike 

from the reservoir westward to the Rexmont-Overlook road, and, 

as already suggested, thence to Miners village. In all probability a 

bore hole situated 100 or 200 feet south of hole No. 2 on the ridge 

above the reservoir would penetrate a considerable thickness of 

Paleozoic limestone beneath the overlapping Mesozoic beds, and there 

is no obvious reason why certain layers of the limestone'may not be 

replaced by magnetite.

Eastward from the reservoir, where the pocket of ore was found, 

the limestone lying beneath the- Mesozoic beds can not extend far 

before being cut by the dike, which within a short distance turns 

southward into the Mesozoic area and changes from a strongly crosscutting dike to a sill following the-bedding of the Mesozoic rocks.

In all probability a bore hole or shaft less than 50 feet deep located above the diabase in the ravine southeast of Rexmont would 

reveal slate or limestone, either one of which if present would warrant deeper exploration, even if no ore were discovered in the uppermost layers of the limestone. A fact which would seem to mark this 

as a promising place for prospecting is the occurrence of ore on the 

opposite side of the diabase dike at the old Doner mine northeast of 

Rexmont.

The southern border of the Cornwall diabase dike westward from 

its junction with the sill southwest of Cold Spring crossing shows a
CORNWALL DEPOSITS. 25

strongly crosscutting contact with massive Mesozoic sandstones. Between this contact and the outcrop of the diabase sill to the south no 

detailed observations have been made, so that little definite information concerning the structure of the area of Mesozoic rocks lying 

north and south from the Cornwall and Lebanon Railroad is at hand. 

However, red sandstone beds exposed near the railroad crossing onehalf mile northeast of Mount Gretna station show a dip of about 

25° N.j and the contour of the west edge of the sill between the mountain known as Governor Dick and the railroad west of Cold Spring 

crossing likewise indicates a strong inclination of the strata in a 

northerly direction. Furthermore, only northerly dips are observed 

south of the railroad along the outcrop of the sill, and it is fairly 

assumable that the whole block between the two bands of diabase is 

rather strongly tilted in this direction. If this is accepted as a fact,

the group of carbonaceous shales would nowhere meet the crosscutting dike less than 100 feet below the contact line as seen on the 

surface, except within a few hundred feet from the point where the 

southern edge of the dike crosses the wagon road west of Cold 

Spring. As the sill is known to lie in the carbonaceous shales for a 

long distance westward from the headwaters of Chickies Creek, and 

also, as it follows these strata both east and west to Cold Spring crossing, it seems most likely that it continues to occupy this position beneath the Mount Gretna block all the way from the southern outcrop 

to its buried junction with the feeding dike. This probability 

points to the failure of explorations which might-be undertaken between the Cornwall-Colebrook road and the diabase dike, with the 

expectation of locating limestone strata in contact with the diabase 

dike, unless the search be extended beneath the sill of diabase.

Along its northern edge the diabase dike is bounded in different 

parts of its course by four distinct sets of strata. On the extreme 

west its northern wall is formed by Mesozoic sandstones for a distance of 1^ miles to a point a short distance west of the wagon road 

leading from the Horseshoe pike to Mount Gretna (PI. II). From this 

place to the next north-south road the bounding rock is evidently 

limestone, though the line of contact is completely obscured by a cover 

of surface debris. The boundary has been represented on the map by 

a random line, the accuracy of which might possibly be improved 

by more detailed examination than has as yet been made in this 

vicinity. On general principles this contact may be included among 

favorable situations for the occurrence of iron ore, though but little 

emphasis is placed on the suggestion in view of the very slight study 

which has been given to the locality. Should the surface Avash prove 

to be as deep as it seems to be at first glance, failure to have discovered float ore in tilling the fields can not be regarded as a strong 

argument against the possibility of ore masses being present in the
26 MAGNETITE DEPOSITS IN PENNSYLVANIA.

limestone near the wall of the intrusive dike. The only one of the 

five features favorable to ore segregation mentioned on page 16 which 

seems lacking in this- vicinity is an impermeable cap rock over the 

strata lying adjacent to the diabase. At the same time the limestones do not include the strata immediately beneath the slates which 

comprise the ore-bearing beds at Cornwall.

Farther east there is an extensive patch of carbonaceous shale between the valley limestone and the diabase. Being identical in appearance with the Mesozoic black shales in the railroad cutting on 

the south side of the dike,, within the narrow angle between the dike 

and the sill, these beds are supposed to belong to the same horizCi.:.. 

They lie nearly horizontal, and are supposed to rest directly upon the 

limestone or possibly in part upon slate, as do similar beds just south 

of the ore banks. Every geologic consideration points to this as good 

prospecting ground. It may be that slates (corresponding to those 

which outcrop in the wagon road one-half mile southwest of Bismarck) lie between the- carbonaceous shale and the limestones in the 

vicinity of the diabase contact, but somewhere at no great depth beds 

of limestone belonging to the same horizons as those which have been 

converted into ore at the Cornwall mines must come into contact with 

the intrusive diabase. Capped as these beds are by strata only 

slightly permeable b}^ circulating waters, the conditions would seem 

to be very similar to those which led to the production of the Cornwall deposit. If the boundary betAveen the shales and the diabase 

can be taken to indicate the general shape of the northern wall of the 

dike, there is here an embayment from the north resembling in a 

way the one from the south, which is occupied b}^ the Cornwall 

deposit.

From the Bismarck-Mount Hope road to Rexmont the Cornwall

diabase dike is bounded on the north by slates, which occupy a band 

300 to 400 feet wide along a line of hills known as Mill Ridge. These 

slates were assigned by Lesley and D'liivilliers to " Formation No. 

Ill " of the Pennsylvania Paleozoic section, and they were regarded as 

resting conformably upon the limestones of " No. II," with a generally 

rather low dip toward the south. t These suggestions seem entirely 

correct, and it is concluded that as far as these slates extend east and 

west along the north side of the diabase dike the uppermost beds of 

the valley limestone, or " Formation No. II," must come into contact 

with the diabase at a very moderate depth and offer a favorable condition for the existence of iron ore. Though this suggestion is made 

entirely on the basis of the principles set down on page 16, it finds 

strong corroboration in the fact that ore occurs just be3^ond the 

eastern outcrops of the slate at the old Doner mine. The strata in 

which the ore occurs at this point are evidently to be included among 

the uppermost layers of the valley limestone, and their contact with
COENWALL DEPOSITS. 27

diabase, though hidden by surface wash, can not be far distant from 

. the mine. It is believed that the geologic features of the Doner mine 

are essentially those which exist beneath the surface for more than 

2 miles westward from Rexrnont, and there is every indication that 

the rocks are identical in stratigraphic position with those which 

contain the great deposit of ore in the Cornwall mines. Separated 

from the mines only by the dike of diabase held to be responsible 

for the segregation of iron in the deposits already known and worked, 

this ground Avould seem worthy of systematic exploration.

From the north-south road leading to Rexmont as far eastward as 

Horst's mill, deep wash derived from the near-by hills completely 

hides the northern edge of the diabase dike, and it is only at the 

Doner mine that rocks near the contact are exposed at all, and even 

here nothing definite can be made out regarding the attitude of the

strata. The mine is said to have furnished 5,000 tons of ore similar 

in every way to the surface ore at the Cornwall banks but occurring 

intermixed with loose sand. The pit from which the ore was mined 

is now completely caved in, but seems to have been 40 or 50 feet Avide 

and perhaps 250 feet long. North of the workings bowlders of hard 

magnetite are found in the soil over an area 700 to 800 feet square. 

This material is supposed to be float from the Doner deposit. Several years ago two or three holes Avere drilled on this property, but 

beyond the report that no attractive ore body Avas encountered records 

of this work have not been procured. From the fact that the old 

workings extended east and west, three possibilities may be considered as to the shape of the ore mass in its original state, before it 

became broken doAvn by surficial Aveathering, and it is believed that 

negative results at this place are not to be considered as finally adverse to the presence of a Avorkable ore body until tests have been 

carried out Avith reference to each of these possibilities: (1) The 

impregnated rock may have been a layer in the limestone capped over 

by a barren stratum. If, then, the beds have a soutliAvard dip the 

edge of the diabase may lie some distance to the south; (2) the ore 

may have formed along the Avail of the dike as a replacement of a 

limited amount of limestone in contact Avith the intrusive rock; in 

this case the diabase Avould be found A^ery near the old Avorkings; 

(3) the ore may have been deposited along the Avails of a fissure 

running parallel Avith the AA7 all of the dike, but at some distance from 

it. The deposit of ore at the old Carper mine, 8 miles Avest of CornAvail, seems to have had this origin.

The contact of diabase Avith the valley limestone eastward from 

the Doner property to the main reservoir of the Lebanon waterAvorks 

is hidden by a heavy apron of sandstone debris, so that the line 

representing the boundary on the sketch map is only an approximation. Though ore may occur along this contact, prospecting Avould
28 MAGNETITE DEPOSITS IN PENNSYLVANIA.

hardly be taken up unless favorable results had been obtained in some, 

of the more accessible localities suggested above.

MINES WEST OF CORNWALL.

Near the edge of the Mesozoic belt between Cornwall and Susquehanna River there are two minor occurrences of magnetic ore one 

at the old Carper mine in Lebanon County, about 1 mile southeast of 

Mount Pleasant, the other in Dauphin County, about 2 miles southeast of Hummelstown.

CARPER DEPOSIT.

The Carper deposit, from which 1,500 tons of ore have been mined, 

appears to lie in a fault break, which may be regarded as a westward 

extension of the fissure which holds the Cornwall diabase dike. North 

of the ore pit the rocks are Paleozoic limestone, while to the south 

are baked shales, followed by diabase. The shales were regarded by 

Lesley and D'lnvilliers as equivalent to the slates of Mill Ridge 

occurring at Cornwall,* but to the writer they seem to belong with the 

Mesozoic strata.

The diabase which outcrops south of the mine is a sill which follows the Mesozoic strata. The sill strikes northeast and southwest, 

and dips toward the northwest. The trend of the diabase is diagonal 

to the course of the fault, and the intrusive rock does not continue 

north of the break. On the geologic map (PL II) it has been represented as ending at the fault, though exposures are not sufficient to 

show that it actually extends as far toward the northeast. Toward 

the southwest the diabase widens in outcrop and is known to constitute a large mass. The sandstones and shales near it are strongly 

baked or indurated, and are also bleached to a considerable extent. 

The occurrence of the ore in the fault fissure, the presence of the igner 

ous rock near by, and the fact that the inclination of the diabase mass 

toward the north and northwest would carry it beneath the place 

Avhere the ore outcrops make it probable that the deposit was formed 

by solutions circulating along the fault break and impelled by the 

heat of the buried diabase. If the true relations of the deposit are 

as here suggested, the ore should persist in depth and should also 

occur at other points along the fault both east and west of the old 

mine. Though the exact position of the fault is hidden by overwashed debris from the adjacent hills, no serious difficulty would be 

experienced in finding it by means of excavations. This fault appears to be the westward extension of the fissure occupied by the 

crosscutting mass of diabase at Cornwall.

Iron ore is reported to occur about 1 mile southwest of Mount 

Pleasant, where some prospecting was done several years ago. This

a Ann. Rept. Geol. Survey Pennsylvania for 1885, 1886, p. 544.
BERKS COUNTY DEPOSITS. 29

locality was not found, and it is not known that the ore is of the 

Cornwall type. In this neighborhood the Paleozoic limestones contain several masses of intrusive diabase, so that it would not be at 

all surprising to find ore like that of the Cornwall mine.

HUMMELSTOWN DEPOSITS.

The deposits 2 miles southeast of Hummelstown are situated well 

within the belt of Mesozoic rocks on the east side of Waltonville 

Brook. The ore, consisting of magnetite and specular hematite somewhat contaminated by pyrite, occurs in pockets, several of which have 

been worked out, but from what may be seen the deposits could hardly 

have been of any great importance. A small amount of garnet occurs 

with the ore minerals. The old workings are in the valley of a small 

stream and extend in a general east-west direction for a distance of 

about 2,500 feet. Except along the wagon road there are few exposures of rock in place in the vicinity. North of the ravine in 

which the ore pits are situated the strata stand in nearly vertical 

position, but south of the ravine the beds of sandstone have a northerly clip of about 20°. From these observations it is evident that the 

deposits occur adjacent to and probably in part along a strong fault 

break. EveryAvhere in the vicinity of the fault .the sandstones are 

greatly bleached and indurated, as similar rocks are elsewhere in the 

neighborhood of diabase masses, and, though no outcrops of the 

igneous rock appear in the immediate' vicinity, it is believed that 

diabase must be present at some unknown depth beneath the- surface 

and that waters heated by this rock, or perhaps derived from it, were 

responsible for the general metamorphism and for the segregation of 

the iron ores.

Though the deposits are of interest to the student of ore genesis, 

it does not seem that they offer sufficient encouragement for more 

extensive exploration.

BERKS COUNTY DEPOSITS.

WHEATFIELD GROUP.

« 

GENERAL DESCRIPTION.

The Wheatfield group of mines, with which the Ruth mine is here 

included, is situated about 7 miles southwest of Reading and a short 

distance southeast of Fritztown station, on the Columbia division 

of the Philadelphia and Reading Railroad. (See PL VI.) In their 

geologic features the deposits of iron ore at this place show certain 

striking resemblances to the Cornwall deposits 20 miles to the west. 

The ores occur as irregular masses, having a general layer-like form,
30 MAGNETITE DEPOSITS IN PENNSYLVANIA.

interbedded with limestone strata, but the ore bodies are numerous 

rather than large, and lack of persistency is a marked characteristic. 

In respect to stratigraphic position, the strata which carry the deposits do not correspond with those of the Cornwall mine, for they 

apparently belong at the base of the Paleozoic limestones (" No. II " 

of the Second Pennsylvania Survey), as at the Raudenbusch and 

Island mines near Reading and at Boyertown. This conclusion regarding the equivalence of these strata is not based on a critical study 

of the question by the present writer, but is deduced from recorded 

descriptions by D'lnvilliers and from the distribution of the Paleozoic 

formations as exhibited on his geologic map of Berks County.®

Like the deposits at Cornwall, Reading, and Boyertown and at the 

Jones mine, the Wheatfield deposits occur very near the overlap of 

Mesozoic beds and adjacent to a large intrusion of diabase.

DIABASE INTRUSION.

The ore-bearing strata, appear at the surface along the east and 

north sides of a roughly rectangular area of sedimentary rocks, forming a northward /embajonent in the principal diabase mass of the 

district. The greater part of this area, which is nearly a mile long 

and three-fourths of a mile wide, is covered by Mesozoic rocks. The 

older strata, in which the ore occurs, are restricted to a band 150 to 

250 yards wide next to the curving edge of the diabase intrusion. 

The south edge of this band is formed by the overlap of the Mesozoic 

beds, south of which there is an outlying, irregularly shaped mass of 

diabase opposite the embayment in the main intrusion. (See Pis. 

V and VI.)

The mass of diabase that curves around the Wheatfield group of 

mines constitutes the western termirication of an intrusion which 

extends 7 miles eastward to Schuylkill River and thence somewhat 

more than 10 miles in a southeasterly direction along the western 

side of the broad Schuylkill Valley (PL V). The outcrop of this 

diabase is from one-third mile to 1 mile wide. Throughout the 

greater part of its course it lies wholly within the Mesozoic area, 

where it has the form of a sill, closely following the stratification of 

the incasing rocks. Near the Schuylkill, however, where its course 

changes from east to southeast, and also near the Wheatfield mines, 

marked crosscutting may be observed, and Paleozoic as well as Mesozoic rocks come into contact with the diabase. It is in these Paleozoic strata near the diabase that the ore deposits occur at the Fritz 

Island and Raudenbusch mines south of Reading, and at the Wheatfield mines 7 miles farther east. (See cross sections, figs. 1, 2, and 3.)

a Geology of the South Mountain belt of Berks County: Second Geol. Survey Pennsylvania, Kept. D3, pt. 1, atlas, 1883.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. V

Mesozoic j^d. sandstones 

and shales

Mesozoic limestone 

conglomerate

Paleozoic limestones 

carrying ore deposits

Diabase Mines and prospects

GEOLOGIC SKETCH MAP OF DISTRICT SOUTH OF READING, BERKS COUNTY, PA.
BERKS COUNTY DEPOSITS. 31 

CHARACTER OF THE ORES.

The Wheatfield mines have not been extensively worked for more 

than twenty years, though small amounts of surface ore have been 

extracted from time to time, the last mining having been done in 

1905 and 1906. The ore to a depth of 30 or 40 feet is reported to be 

invariably soft or earthy, evidently as a result of the ready decompo-' 

sition of the original ore, owing to the presence of considerable 

pyrite. These soft ores have been desired by ironmasters for mixtures, but the unweathered or hard ores seem to have found little 

favor, as they are at once of rather low iron content and so high in 

sulphur as to require roasting before they can be used in a blast furnace. Apparently for this reason, and because the deposits are not 

large or even persistent, these mines have not been more systematically developed.

STRUCTURE OF THE ROCKS.

Most of the old workings of the group are situated near the east 

side of the area of sedimentary rocks which sets back from the south

FIG. 1. North-south structure section 400 feet east of Ruth mine, Wheatfield group 

(along line A-A', PL VI). 1, Mesozoic heels ; 2, Paleozoic slate ; 3, Paleozoic limestone ; 

4, diabase intrusion.

into the diabase dike and south of the east-west public road which 

follows the upper valley of Cacoosing Creek. About a dozen open 

pits have been operated at various times, and in addition many 

slopes and several vertical shafts. Across the creek, on the north 

side of the Avagon road, there is an opening, formerly known as 

slope No. 1, and in 1905 some surface ore was taken out by means of 

a slope located a short distance east of these old workings. The 

Ruth mine is situated about one-half mile west of slope No. 1, about 

200 yards east of the direct road from Fritztown to Adamstown.

In the more southerly Wheatfield workings the strikes of the strata 

run nearly north and south, as shown both by the direction in which 

the pit workings extend and by the beds of limestone exposed in the 

old excavations; but farther and farther north the strata turn more 

and more toward the northwest and finally run nearly east and west 

at slope No. 1. Dips are here invariably toward the concave edge 

of the curving band of ore-bearing rocks and aAvay from the Avail 

of the surrounding diabase. At the Ruth mine, Avhere the strata are
32 MAGNETITE DEPOSITS IN- PENNSYLVANIA.

fairly well exposed in the open cut, the stratification is found to be 

nearly horizontal, though the ore body is reported to dip 30° S., 

indicating that it is not conformable to the bedding of the inclosing 

rocks. Both here and at slope No. 1 the foot wall of the ore is diabase and the immediate hanging wall is limestone or limestone breccia. In both places also the limestone capping above the ore is overlain by slate, and in the hills south of the Ruth mine debris of this 

slate and a few shallow excavations show it to have a thickness of 

about 80 feet. At slope No. 1 its thickness can not be determined and 

the area which it covers can not be defined, owing to lack of exposures. 

No stratum corresponding to the slate mentioned above has been 

encountered in the workings situated south of the public road, but 

the changing strike of the bedding toward the north along the ore 

band toward slope No. 1, together with the fact that the limestone 

layers in the Ruth mine, in slope No. 1, and in several of the southern 

workings are similarly composed of fragments, would make it appear that the strata occurring in the southward-trending leg of the

5000 feet

FIG. 2. North-south structure section near slope No. 1, Wheatfleld group (along line 

B-B', PI. VI). 1, Mesozoic beds; 2, Paleozoic slate; 3, Paleozoic limestone; 4, Paleozoic 

quartzite; 5, diabase intrusion.

strip in which the ore is found lie stratigraphically below the bed of 

slate. In this case, as the beds dip toward the west, it is possible 

that the slate may be present west of the main workings beneath the 

surface capping of the Mesozoic sandstones.

Two beds of limestone, one solid and the other made up of fragments, are exposed, with low southerly dips, in the creek bed between the two main tributaries from the south (PI. VI).' These 

strata are supposed to correspond with those in the main Wheatfield 

workings, and their presence in this place suggests that the slate at 

slope No. 1 can not be connected by continuous outcrop with the slate 

at the mine. The dips at the two places are not in accord, and it may 

very well be that there is a fault between.

In the bed of the more westerly of the two northward-flowing 

brooks (PI. VI), 500 or 600 feet above its junction with the main 

creek, green clays containing disseminated crystals of magnetite are 

found. This material resembles some of the earthy material from 

the mines, and with little doubt it represents the weathered crop of a 

stratum belonging to the set of beds which carries the ore deposits
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. VI

Mesozoic red sandstones 

and shales

Paleozoic slate Paleozoic limestones 

carrying ore deposits

Mines and prospects

GEOLOGIC SKETCH MAP OF VICINITY OF WHEATFIELD MINES, BERKS COUNTY, PA.
BERKS COUNTY DEPOSITS. 33

1-| miles to the east. Appearances also favor the opinion that this 

horizon is nearly the same as that of the ore-bearing beds at slope 

No. 1 and at the Ruth mine. Outcrops of Mesozoic sandstone are 

seen on the east bank of the brook near by, and 1,000 feet or so upstream red shales and sandstones are present, striking N. 10° E. and 

dipping 30° W. In the bed of the eastern brook the strike is the 

same, but the dip is only 10° W.

The attitude of the rocks in the several places mentioned above 

shows that there is a strong unconformity between the Mesozoic 

sandstone and the set.of strata which carries the ores; this is also 

shown by the fact that in some places the younger beds rest directly 

upon the limestones, whereas in others, as on the knoll south of the 

Ruth mine, they were deposited upon the stratigraphically higher 

slate. This relation makes it evident that none of the rocks which 

incase the ore can belong to the Mesozoic, though the contrary was

believed to be the case by Rogers, whose opinion was accepted by 

Willis," and by D'lnvilliers & at the time his report upon the geology 

of Berks County was written.

FIG. 3. East-west structure section 1,000 feet south of public road, Wheatfield group 

(along line C-C', PI. VI). 1, Paleozoic slate; 2, Mesozoic beds; 3, Paleozoic limestone ; 4, diabase intrusion.

The rocks in the neighborhood of the Wheatfield group of mines 

are sufficiently exposed to reveal very, complicated geologic relations 

without being well enough shown to make possible the determination 

of these relations in detail. Information is lacking: which might

o G

suggest the shape of the diabase intrusion underground or which 

might lead to an estimate regarding either the thickness of the calcareous beds which carry the ore deposits or the nature of the strata 

which lie below them. All these points must be known in at least a 

general way before geologic cross sections of any practical value can 

be drawn. The sedimentary rocks of the area which sets back into 

the main dike .of diabase may be partly or entirely underlain by a 

mass of igneous rock forming a connection between the main crosscutting dike and the southerly body of diabase, or it may be that the 

surrounding masses of diabase approach each other only at rather

" Willis, Bailey, Tenth Census, vol. 15, p. 228.

6 Second Geol. Survey Pennsylvania, Kept. D3, 1883.

54370 Bull. 359 08 3
34 MAGNETITE DEPOSITS IN PENNSYLVANIA.

great depth. Whatever the actual relations may be, they can not be 

made out from features observed on the surface, and .their determination must await information furnished by diamond-drill explorations. 

Systematic study of the Paleozoic formations of the district might 

definitely fix the position of the Wheatfield ore-bearing strata with 

reference to the quartzite which occurs"in the ridge just north of the 

diabase intrusion, and furnish a basis for estimating their thickness 

in the vicinity of the mines. These determinations would be, however, of small practical value compared with data which might be 

procured incidentally if a few well-located holes were drilled to test 

the downward extension of the ore-bearing strata and the degree to 

which they are mineralized in depth.

PEACTICAL CONCLUSIONS.

Though so much is indefinite or unknown regarding the geology of 

the Wheatfield deposits, yet the number and distribution of the ore 

beds already worked, the observable structure of the strata in which 

the deposits lie, and the general relations which they bear to the diabase mass and the overlying Mesozoic strata, when considered together, suggest that the expense.of a certain amount of exploration in 

the northern half of the sedimentary embayment would be justified by 

the chances of locating important bodies of ore. As already stated, 

the impression gained from strikes and dips in the band of ore-bearing 

strata, and from the occurrence of the two patches of slate at the Ruth 

mine and slope No. 1, is that the strata which carry the ore beds in 

the southern group of mines lie stratigraphically below the slate. At 

the Ruth mine the slate and limestone beds lie nearly horizontal, and 

it seems that a hole drilled anywhere between this old opening and the 

first northward-flowing creek to the east must penetrate the whole set 

of ore-bearing beds unless part of them are cut out beneath by the 

intrusive diabase. The proximity of the diabase would lead to the 

expectation that beds suitable in composition for impregnation with 

iron minerals would be, in part, at least, converted to ore. Southward 

from the Ruth mine the limy strata are overlain at first by slate and 

finally by sandstone as well, but beneath perhaps 150 feet of this capping they doubtless come into contact with the cross-cutting mass of 

diabase Avhich forms the bold hills west of the wagon road, and the 

vicinity of this contact is again favorable to the presence of ore.

It is probable that under the meadow which extends along the 

creek the set of ore-bearing strata would be encountered immediately 

beneath the valley wash, as indicated by the beds of limestone outcropping between the two northward-flowing tributaries. Furthermore, the southward dip of the diabase wall in slope No. 1 suggests 

that these strata will be found resting upon the inclined floor of the
BEKKS COUNTY DEPOSITS. 35

intrusive rock in a manner reproducing in a way one of the striking 

features of the Cornwall deposit.

From a practical standpoint deep prospecting in the vicinity of the 

main workings of the Wheatfield group would seem to offer somewhat 

better chances for a successful outcome than explorations elsewhere 

in the neighborhood, because the presence of ore in so many places 

reveals the fact that there has been a very important amount of mineralization. With reference to the theory that the ores of the Cornwall type have been produced by replacement of limy strata induced 

by the intrusive diabase, it is more than likely-that the mineralizing 

solutions percolating through the rocks moved away from the hot diabase rather than toward it and at the same time tended mainly upward toward the surface rather than downward toward the source 

of heat.

This line of reasoning leads to the expectation that the ore bodies 

coming to the surface along the eastern leg of the band of Paleozoic 

strata may increase in number as well as in size and persistency as 

the ore-bearing strata are followed downward along their west and 

southwest dips.

The practical question whether hard iron ores of the grade thus 

far found in the unweathered portions of the Wheatfield deposits, if 

discovered in comparatively large amount, would be worth developing 

at the present time lies beyond the scope of the present investigation. 

The writer believes, however, that the fact that the owners have never 

attempted to determine the real possibilities of the property by systematic prospecting can not be taken as evidence that such exploration 

is not fully warranted as an undertaking likely to give adequate 

returns on the required outlay.

As already pointed out, the Wheatfield mines, as well as the Haudenbusch and Island mines, which lie about 7 miles to the east, are next 

to the same mass of intrusive diabase at the only localities where it 

comes into contact with the Paleozoic formations on the surface (Pis. 

V and VI). Throughout the interval the diabase has the form of a 

northward-dipping sill outcropping parallel with and from one-half 

to 1 mile south of the northern edge of the Mesozoic belt. Somewhere 

beneath the surface the sill must reach the Paleozoic rocks beneath 

the cover of Mesozoic shales and sandstones, and it seems very likely 

that here its form changes to that of a dike. If this be the case, conditions favorable for the occurrence of ore may exist along the walls 

of the dike wherever limy Paleozoic strata come into contact with it. 

Probably the most favorable condition would be realized if strata 

which correspond in stratigraphic position with those at the Wheatfield mines could be found next to the dike.

Though the broad suggestion that buried ore bodies may exist in 

the situation indicated seems entirely valid, the chances of locating
36 MAGNETITE DEPOSITS IN PENNSYLVANIA.

deposits of value are "regarded as too remote to be seriously considered 

from a practical standpoint. Prospecting along this strip of country 

north of the diabase sill is therefore not recommended except where 

the intrusion approaches the northern edge of the Mesozoic belt, and 

even here the possibilities can hardly be regarded as very encouraging. 

For 2-| miles east of Fritztown station the diabase is in contact with 

Paleozoic rocks, but beyond the fact that the hills north of the diabase 

are composed of quartzite (in one place dipping 50° S.), nothing 

concerning the local geology can be stated at the present time, because 

the country has not been examined in detail. If limestone beds are 

present above the quartzite, and if the general dip of the formations 

is toward the south, so as to carry them down beneath the diabase, 

the vicinity of the contact would seem to offer favorable conditions 

for the occurrence of ore masses like those which are present immediately opposite, on the south side of the dike.

RAUDENBUSCH MINE.

Describing the Raudenbusch property in 1858, H. D. Rogers says: a

About half a mile'west of the preceding [Island mine] is the Raudenbusc.li 

mine, which, we are informed, yields its proprietors at the Phoenixville furnaces 

5,000 tons of ore per annum. The vein ranges a little north of east. Its foot 

wall is white metamorphic limestone, or marble, and its hanging wall or roof 

a dull sea-green, serpentine-like rock which on exposure soon crumbles down 

like ordinary shale. The vein, dipping 36° S., is followed by a slope 280 feet 

beneath the surface. At the bottom gangways are driven 200 feet west and 

400 feet east to a fault cutting out the vein. A higher level, 160 feet from the 

surface, is driven 300 feet east. The ore is now taken from this level. Like 

all others, this vein is exceedingly variable; while wholly or almost entirely 

absent in some places, in others it has been found 30 feet thick. Its average 

bulk will not exceed 12 feet. The gangue stone of the ore is a light-blue rotten 

limestone, from which the ore is scarcely distinguishable except by its greaterweight and deeper tint. Of the entire ground wrought, about one-half of the 

material is sufficiently rich in iron for the furnace; the remaining rubbish is 

used as stopping in the old workings.

D.'Invilliers states: 6

There are two small shafts on the property, one of them 50 feet deep. On 

the dump are seen gray, greenish, and black limestones very much decomposed, some of which may represent the presence of the brecciated Mesozoic 

" all sorts " [i. e., limestone conglomerate] so characteristic of this part of the 

range, but none such is seen in place on the surface. * * * Most of the 

limestones seem altered, which is accounted for by the proximity of the trap 

dike [diabase] to the south. This trap shows in the 50-foot shaft, as also 

some light-gray to white limestone, the latter showing a slight coating of 

hematite.

n Geology of Pennsylvania, vol. 2, 1859, pp. 716-717.

b Geology of Berks County : Second Geol. Survey of Pennsylvania, Kept. D3, 1883, pp. 

342-343.
BEKKS COUNTY DEPOSITS. 37

To the present writer it seems unlikely that any Mesozoic rocks, 

either limestone conglomerates, shales, or sandstones, are present 

north of the diabase in this vicinity. The only rock now to be seen 

at the surface is white limestone exposed in the farm road that gives 

access from the public road to the fields just north of the old mine. 

South of the wagon road, on the slope of the hill, a shaft not mentioned above was sunk through a green shaly rock, probably the same 

as that referred to by Rogers as forming the hanging wall of the ore. 

This material seems to be of sedimentary origin, a*h-d it evidently lies 

between the ore and associated limestone beds and the mass of diabase 

that forms the adjacent hill. The surface distribution of the diabase 

is shown on the sketch map (PI. V), from which it may be seen that 

it is a northward offshoot from the intrusive sill described in the discussion of the Wheatfield mines. In relation to the Mesozoic strata, 

this northward-reaching arm is evidently crosscutting, .though in. 

respect to the Paleozoic strata it may be locally following the bedding, as is suggested by the southerly inclination of the old mine 

slope.

It seems a reasonable conclusion from what is known concerning 

the distribution of quartzite, slate, and limestone along the south 

edge of the Paleozoic area that the Raudenbusch deposit, like those 

of the Wheatfield group, lies in the beds of passage between the 

quartzite and the limestone. Crumpled slate is exposed in a little 

knoll about 1^ miles southwest of the mine and one-half mile west of 

the Center Hotel; just west of this knoll quartzite appears with dips 

toward the southeast beneath the slate. In the road-metal quarry 

along the wagon road on the east side of the slate knoll, Mesozoic 

conglomerate rests upon the slate, with its stratification dipping 

gently southward. Half a mile east of the mine southward-dipping 

quartzite forms the prominent hill south of the reservoirs above the 

wagon bridge over Angelic Creek. Immediately south. of this 

quartzite knoll, slates and limestones may come in above the quartzite before the diabase is.reached, but their presence or absence can 

not be determined because of the existing mantle of surface debris. 

It is suggested that other ore beds like the one formerly mined may 

.exist along the northern Avail of the diabase both east and Avest of the 

Raudenbusch mine. On the west the question could be readily settled by running crosscut tunnels toAvard the diabase and drifting 

either along the contact or, perhaps better, along the hanging Avail of 

green slate, Avhich Avill probably be encountered before the intrusive 

rock is reached.

Suggestions for prospecting eastward from the Raudenbusch mine 

will be deferred until after the Island mine has been described.
38 MAGNETITE DEPOSITS IK PENNSYLVANIA.

FRITZ ISLAND AND VICINITY. 

ISLAND MINE.

The Island mine is situated 2 miles south of Reading, at the north 

end of Fritz Island, in Schuylkill River. The old workings are very 

near the edge of the Mesozoic belt, and are thought to have penetrated the Paleozoic limestone which lies beneath the Mesozoic strata. 

Large masses of diabase are present in the vicinity and dikes of the 

same rock were encountered in the mines (PL V). The geologic 

features of the mine may be summarized from the account by D'lnvilliers.a

The ore was encountered through the washing away of some 

ground by high water during the winter of 1850-51. In opening the 

mines and extending the workings underground it was found that 

the ore occurs in a magnesian limestone, with associated shales of a 

sea-green color like those at the Raudenbusch mine, and that the 

ore-bearing strata are capped over by a limestone conglomerate.

Diabase is here and there the foot wall, but beneath the ore there 

is, more commonly, a decomposed sandstone, regarded as of Cambrian age, and therefore similar to the quartzite outcropping in the 

knoll about half a mile to the north. The ore pinches and swells, as 

in the Boyertown mines, the maximum recorded thickness being 22 

feet. Horses or wedges of limestone are found with ore occurring 

on either side. The strike of the" deposits is nearly east and west, 

and though the general dip seems to be toward the north, in places 

at an angle as great as 40°, locally the ore stands vertical or even 

dips toward the south. Slope No. 1, beginning on the outcrop, is 

231 feet deep, being inclined at the top about 62° and averaging 

about 46°. Three levels were run eastward from the slope, passing 

under the bed of the river and under a small island in the eastern 

channel, known as Yost Island. West of the shaft the two lower 

levels were carried about 150 feet, which brought them beneath the 

east end of the open pit (PI. VII). The gangways are about 60 

feet apart, the upper one being about 50 feet below the surface.

Considerable stoping was done above the lowest level. In the 

bottom of the mine, 125 feet east of the slope, the ore was found to 

branch and was followed by two drifts*which came together 175 feet 

beyond. Irregularity of dip is shown by the vertical attitude of the 

vein in the-middle level 300 feet east of the slope. Diabase was encountered beneath the ore in all the drifts, and a crosscut from the 

.bottom level revealed a leader of ore on the south side of this dike. 

The dike is somewhat more than 100 feet thick, and its south wall 

nearly vertical. The ore lying south of the dike dips to the south 

and is thought to be the same vein as that opened by slope No. 2 and

a Second Geol. Survey Pennsylvania, Kept. D3, 1883, pp. 333-342.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. VII

LEGEND

3L-.--.-j_---;c-i: Upper drifts 

Middle drifts 

=^E=^^= Lower drifts

From atlu to Report D 5

Second Geological Survey of Pennsylvanta

MAP OF FRITZ ISLAND IRON MINES,. BERKS COUNTY, PA.
BERKS COUNTY DEPOSITS. 39

worked to a depth of about 100 feet above the crosscut from slope 

"No. 1. The position of slope No. 2 is about 300 feet northwest by 

west from No. 1.

In 1883 slope No. 2, which is sunk through rock, was down 122 

feet on a dip of 40° to 55°, averaging -perhaps 45°, but the direction 

of slope is not stated.

The open-cut workings seem to have had considerable importance, 

although no record has been found concerning the features which 

they exhibited. The old pit extends east and west and is nearly 300 

feet in lenth.

NNW. SSE.

FIG. 4. Sketch section at north end of Fritz Island.

The average daily production of the mine in 1883 was 25 to 30 

tons, amounting to about 10,000 tons per year; At that time only 

one slope, No. 1, was being operated. The total yield up to 1883 

was estimated at 250,000 tons.

The general relations of the different rocks, indicated by the foregoing description are shoAvn in fig. 4. Apparently there is a wedge 

of Paleozoic limestone lying between diabase dikes on the south and 

northward dipping conglomerate on the north, but it is not known 

whether the ore bodies followed the bedding of the inclosing rocks 

or not. On Fritz Island the thin edge of the wedge has been removed

SSE.

Paleozoic 

FIG. 5. Sketch section along river bank east of -Fritz Island mines.

by erosion, and the same relation probably exists near, the towpath 

on the east side of the Schuylkill, where, as reported, ore was discovered in a prospect shaft. Farther east, however, the Paleozoic rocks 

seem to be capped over by Mesozoic strata in some such manner as 

indicated in fig. 5. In the two figures just mentioned a fault is 

shown between the Mesozoic and Paleozoic areas, because the northerly dip of the conglomerate makes it difficult to see how this boundary could be formed by simple overlap. At many places the nature 

of the northern boundary of the Mesozoic is a vexing question, for 

though overlap is locally observable, elsewhere there is strong evidence of fault displacements of considerable amount.
40 MAGNETITE DEPOSITS IE' PENNSYLVANIA.

Future mining on Fritz Island is not likely, as the property has 

been acquired by the city of Reading to be used, as a sewer farm, but 

even if otherwise available the fact that the old workings run out beneath the river introduces an element of danger from flooding which 

might preclude further development. From a purely geologic standpoint it seems that the deposit might be expected to show considerable 

continuity in depth, for if the ore beds already worked are not actually continuous, others might be discovered by deep prospecting along 

the contacts of the intrusive masses of diabase.

The statement is made in the report by D'lnvilliers a that mining 

toward the east was discontinued somewhere beneath Yost Island 

because of poor ventilation, so that it may be inferred that ore still 

remains at this place. The fact that ore was also found on the east 

side of the river near the towpath is a further indication favorable 

to prospecting in this direction. The rocks \vhich have furnished the 

surface debris in the neighborhood are shales, sandstones, limestone 

conglomerate, and diabase, and the ore-bearing strata can hardly 

come to the surface except in a narrow wedge-shaped area near the 

river bank. As the northeast wall of diabase is followed in a southeasterly direction, the limestones are found to become covered by a 

rapidly thickening cap of the younger strata, so that it seems that any 

ore bodies existing will be found to lie deeper and deeper toward the 

southeast. In making the above suggestion it is assumed, as elsewhere in this report, that ore will not occur except near the intrusive 

rock, and that important bodies are not likely to be found where the 

diabase is in contact with other than calcareous strata. The only exception to this rule which has been noted is at Boyertown, where the 

Black vein and the East vein are both some distance away from the 

diabase intrusion.

EAST BANK OF SCHUYLKILL RIVER.

On the east side of the Schuylkill, as on Fritz Island, the diabase 

is not a solid mass, two dikes being separated from the main body 

lying to the south by strips of Mesozoic shale. If these dikes continue 

downward and penetrate the ore-bearing limestones separately, crosscut tunnels would seem to be justified in order to explore all their 

walls, and also that of the larger intrusive mass beyond. This supposition is suggested by the occurrence of ore on both sides of the 100- 

foot dike in the Island mine.

It would seem that if due care is taken to avoid breaking into the 

old Island mine workings, further prospecting from the east side 

of the river will be Avarranted by the probability of finding ore 

bodies similar to those formerly worked on Fritz Island. The known

a Second Geol. Survey Pennsylvania, Kept. D3, 1883,'pp. 337-338.
BEERS COUNTY DEPOSITS. 41

presence of qre near the river bank would apparently justify a shaft, 

from which tunnels could be run as suggested above. Prospecting 

in this manner would probably be more satisfactory than by a series 

of drill holes.

WEST BANK OF SCHUYLKILL RIVER.

West of the river the presence of deep surface wash makes it impossible to determine whether the fields below the wagon road are 

underlain entirely by diabase or in part by sedimentary rocks Diabase is exposed opposite the north end of Fritz Island, but from 

the existence of two outlying dikes east of the river and at least one 

on the island, all with apparently east-west courses, it may very 

well be that this outcrop belongs to a mass lying north of the, main 

intrusion. The question whether this is so or not is important and 

could be settled at slight cost by running two or'three short tunnels

from the bank of the western channel above the Fritz Island bridge. 

It is believed that if any other rock than diabase is found there would 

be a good chance- of discovering ore bodies like those of the Island 

mine by systematic prospecting. It is perhaps not likely that limestone conglomerate will be encountered, but if it should be present 

it would only be necessary to turn northward and penetrate this cap 

in order to reach the Paleozoic strata. If any ore should be found 

it would be desirable to determine how many outyling dikes of 

diabase exist and too explore carefully all contacts.

ESTERLY MINE.

About 4 miles due east of the Fritz Island mine and 2 miles south 

of Jacksonwald, on the W. Esterly farm, a small deposit of magnetite was once worked. William G. Rowe, of Reading, is authority 

for the statement that this mine furnished between 3,000 and 4,000 

tons of ore. It was opened to a depth of 125 feet by a 58° slope inclined toward the north, the drifts being run about 250 feet to the 

east. About 600 feet southeast of the Esterly slope an opening 

known as the Bishop shaft was sunk for 150 feet and a north crosscut driven for 200 feet, .ending in garnet rock. A bore hole from 

the bottom of this shaft reached limestone conglomerate at about 

300 feet.

The Esterly vein lies between a hanging wall of diabase and a foot 

wall of metamorphosed shale. The diabase is an intrusive sill included in northward-dipping strata. In the neighborhood of the 

intruded rock there has been considerable baking, and here and there 

such metamorphic minerals as garnet, hornblende, and magnetite are 

found. These minerals, with some chlorite, are present in the material on the old mine dump, and the silicates evidently occur in 

close association with the magnetite of the ore. Some limy material
42 MAGNETITE DEPOSITS IN PENNSYLVANIA.

is to be noted, but no pure limestone; it seems, therefore, that this 

ore was formed by the replacement of shales under the mineralizing 

influence of the diabase.

The diabase is the outer of two concentric curving sills which follow the bedding of the Mesozoic shales and sandstones, here thrown 

into a rather sharp synclinal fold (PL V). The ore bed lies on the 

lower contact of the sill and, like it, strikes conformably with the inclosing rocks, nearly east and west, with a dip of about 50° N. The 

deposit may be imagined to have considerable downward extent, 

though of course its continuity in this direction can not be affirmed. 

Along the strike it is rather short, as not more than 100 feet west of 

the slope carbonaceous and limy shale is exposed along the road, and 

though the situation is very near the diabase contact no magnetite 

has been developed.

No other magnetite is known to have been found along either side 

of this arm of the sill, -but Mr. Kowe states that specimens have been 

plowed up in the fields near Spring Creek, between the northern 

arm and Stonersville. Though some prospecting "was done in this 

vicinity, no magnetite was found in bed rock. It is possible that the 

mineral may have been float from a deposit situated near the diabase 

Avail on the hill slopes above the creek, though it may have been derived from a pocket lying in the limestone conglomerate which covers 

considerable ground on the west side of Spring Creek south of the 

Reading turnpike.

In this place the strata of limestone conglomerate dip rather 

steeply to the southwest. This dip would carry them beneath the 

diabase sill, but the outcrops are so far from those of the diabase 

that it seems hardly likely that any important body of ore will be 

found in this rock, at least near the surface. In depth the conglomerates may be cut by the diabase, and if so there would be a chance 

for ore bodies in them and likewise for the occurrence of pockets at 

some distance from the intrusive rock.

On the surface shales probably come between' the conglomerate 

strata and the diabase, as they do in the vicinity of the Esterly mine, 

though the hill slope above Spring Creek on the south, and next to 

the conglomerate outcrops farther north, is hidden by an unbroken 

mantle of soil and diabase fragments. In the fields above the wagon 

road, however, the position of the diabase wall may be closely estimated from the presence of a sharp rise in the profile of the hill, and 

the contact could be reached almost anywhere by short tunnels.

In view of the fact that only limestone beds have thus far been 

found to yield really important ore deposits of the Cornwall type, 

it can not be urged that this contact is a particularly favorable place 

for prospecting, though it is undoubtedly the most likely place for ore 

occurrence in the neighborhood. No general recommendation that the
BERKS COUNTY DEPOSITS.. 43

diabase contacts should be prospected through their entire length 

seems warranted, though the discovery of ore at any locality would 

naturally lead to a rather careful search at other points.

Both arms of the two horseshoe dikes closely approach and probably actually reach the northern edge of the Mesozoic area, and inasmuch as limestone occurs everywhere north of the boundary it would 

seem that ore bodies might be expected at the localities where the 

diabase and limestone come together. It is believed, however, that the 

diabase does not intrude the limestone at any of these places, but instead that the Paleozoic and Mesozoic rocks come together along a 

fault which has developed since the younger strata in the synclinal 

fold were invaded by the tAvo sills of diabase.

BOYERTOWN DEPOSITS. 

GENERAL DESCRIPTION.

The mining operations which have been carried on at Boyertown 

have developed the existence of five apparently separate bodies.of 

magnetic iron ore, all of which exhibit the form of somewhat irregular layers of varying thickness. These ore layers seem to follow 

rather closely the stratification of a set of limestones and limy shales 

which constitute a transition between " No. I" sandstone and " No. 

II " limestone of the Paleozoic section, as given in the publications of 

the Second Geological Survey of Pennsylvania. In stratigraphic 

position these beds correspond with the ore-bearing strata at the 

Wheatfield and Fritz Island mines.

The mine openings are situated near the northwest edge of the 

Mesozoic belt, and the workings have shown that the three bestdeveloped ore bodies lie immediately beneath a Mesozoic basal conglomerate composed of limestone fragments up to an inch in diameter 

set in a paste of red clay. This conglomerate bed, with a general 

southwest-northeast strike, dips toward the southeast, and beneath 

it the Paleozoic strata are so tilted that they lie in nearly parallel 

position. The two other ore bodies occur well within the limy beds 

of the Paleozoic at contact of a mass of intrusive diabase (PL VIII). 

The ore bodies just beneath the conglomerate are here called the East 

vein, the Hagy (sometimes known as the Eckert) vein, and the Warwick or Black vein. The deposits in contact with the diabase are 

known as the Rhoades and Blue veins. The East vein was worked 

from two inclined shafts situated southeast of Walnut street and 

known as Phoenix upper and middle slopes. The Hagy vein, outcropping south of the Eeading road in the outskirts of town, was 

first worked by means of an open excavation knoAvn as the Hagy pit, 

afterwards by the so-called Eckert slope, and finally by the lower 

Phoenix or California slope. The Warwick vein has been worked
44 MAGNETITE DEPOSITS IN PENNSYLVANIA.

both from the Warwick shaft and from the two shafts of the Gabe] 

mine. In the latter mine it was called the Black vein. A body of 

ore ecountered in the lower workings of the California mine and 

known as ore ISTo. 2 is believed by the writer to represent the northward extension of the Warwick vein. The Blue vein has been found 

only in the Gabel mine. The Rhoades vein has been opened from the 

surface at several places and also by means of two tunnels from the 

California slope.

It is suspected that connection may eventually be established between the Blue and Rhoades veins, also that the Warwick and Hagy 

veins are parts of a once continuous ore body separated by a fault. 

These points and. the possible relation between the East vein and 

the Hagy vein are discussed on pages 58-60. The relative positions of 

the several mines are indicated on the map (PI. VIII).

The strata which carry the deposits occur in a narrow strip lying 

between the region of gneisses and sandstones northwest of Boyertown and the Mesozoic area on the southeast. The length of this 

strip is at least 2 miles and possibly somewhat more, but all the 

known ore bodies occur within a distance of less than half a mile.

The situation of the deposits with respect to the Mesozoic rocks is 

similar to that of the Cornwall, Wheatfield, and Fritz Island deposits. Like all of these, they are associated with intrusive diabase, 

and though this association is somewhat less obvious at Boyertown 

than elsewhere it is sufficiently evident to justify the conclusion that 

the ores have been formed under the influence of the invading rock, 

as at Cornwall and other localities where ores of a similar type occur.

GEOLOGY OF THE DISTRICT.

BoyertoAvn is situated near the northwest end of a roughly oval

valley, 9 miles long from southeast to northwest, and about 5 miles 

wide. Ridges formed either by diabase sills or by sandstones and 

shales baked and hardened by the intrusive rock define this valley 

on three sides, the remaining or northwest side being formed by the 

Reading Hills, which are composed mainly of ancient gneisses, but 

contain also limestones and quartzites.. From the ridges the strata 

dip toward the interior of the valley, which is thus structurally, as 

well as topographically, a broad basin. It is one link in a chain of 

four similar basins that extend nearly to Delaware River. Each of 

these basins is rimmed by diabase, the outcrops of which are nearly, if 

not actually, continuous. The great extent of the diabase, the continuity of its outcrop, and the persistency with which the intrusive 

rock follows the structure of the inclosing strata lead to the belief 

that it forms a practically unbroken sheet beneath all the basins that 

are surrounded by its outcrop. The basin here discussed is not com-
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. VIII

SURFACE MAP OF BOYERTOWN MINES, SHOWING RELATIVE POSITION OF ORE BODIES ON LEVEL SURFACE 400 FEET BELOW TOP OF

GABEL NO. 1 SHAFT.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. IX

Imile

GEOLOGIC SKETCH MAP OF VICINITY OF BOYERTOWN, BERKS COUNTY, PA.
BEEKS COUNTY DEPOSITS. 45

pletely rimmed by the igneous rock, but it seems probable that the 

two existing gaps, one near Boyertown and the other 3 miles to the 

northeast (PI. IX and fig. 10), are to be explained on the supposition 

thatiiR these places the invading rock was, not able to force its way 

far Q&ough upward to reach the present surface of the land.

Just .south of the mines the Avestern slope of Gabel Hill is formed 

by diabase, which marks the northward termination of a curving mass 

of intensive rock that follows the base of the ridge and the valley of 

Ironstone Creek to Colebrookdale station and farther south connects Avith the rim-rock sills on the southwest side of the synclinal 

basin described aboA^e. The sedimentary rocks adjacent to this diabase 

have been greatly metamorphosed, and Gabel Hill, together Avith the 

ridge running southward from it, has been preserved from erosion 

by the indurated nature of the shales and sandstones of which they

are composed. The originally red sandstones have been bleached to 

a doll white or yelloAV. A feAV outcrops suffice to show that the strata 

strike parallel with the course of the sill and Avith the crest of the 

ridge and dip to the east and southeast toAvard the interior of the 

basin. North and east of the blunt end of the diabase outcrop a fe\v 

exposures of sandstone have the natural red color of the Mesozoic 

strata and show no induration. In the WarAvick mine, hoxvever, and 

in both shafts of the Gabel mine limestone conglomerate lying above 

the black ore is someAvhat metamorphosed, garnet and hematite being 

developed in it. These minerals occur also in boAA^lders both of limestone and siliceous conglomerate on Gabel Hill. The surface distribution of the metamorphic effects conforms so closely Avith the 

extent of the diabase that the presence of common metamorphic 

minerals in the conglomerate that occurs in the mines points definitely 

to the presence of intrusive rock near by. To judge, hoAveA7er, from 

the descriptions of D'lnvilliers ° and Willis 6 the instrusive rock is 

absent from most parts of the mines. Small dikes Avere noted in the 

WarAvick mine and diabase is knoAvn to lie beneath the Khoades vein 

and in the Gabel No. 1 Avorkings beneath the Blue A^ein. Willis, shoAVS 

this rock as the foot Avail of both the last-named veins, and indicates 

its presence in the crosscut tunnel from the 496-foot level of the WarAvick mine, which Avas opened in search of the Blue vein. It is 

thought probable that a rather direct underground connection may 

exist between the Gabel Hill deposits near BoyertoAvn and the masses 

of the same rock occurring northeast of New Beiiinville, and also betAveen the latter and the diabase that outcrops east of Sassamansville. 

From scattered exposures strata corresponding Avith those Avhich 

carry the ore layers are knoAvn to extend about one-half mile south-

" Second Gcol. Survey Pennsylvania, Kept. D3, vol. 2, pt. 1, 1883. 

6 Tenth Census, vol. 15, 1886.
46 MAGNETITE DEPOSITS IF PENNSYLVANIA.

west and 1 mile northeast of the mines, and they may continue considerably farther north beyond New Berlinville, beneath the alluvial 

wash of the swampy lands along the railroad. Shales including a 

dark carbonaceous layer have been revealed by an old pit in a field 

between the Reading turnpike and the railroad about half a mile 

north of the California slope, and shales broken down by surface 

weathering are exposed on both sides of the same road just where 

the trolley track leaves it and turns up the valley of Ironstone Creek. 

Decomposed shale was revealed in excavations for cellars made'in 

1906 on the south side of the road between the exposures last mentioned and the engine house at the California mine, and a few lumps 

of iron ore were found mixed, with the clay. This material was 

apparently, undisturbed, though it is possible that it may have been 

waste from the mines. A prospecting shaft situated between 500 

and 600 feet northeast of Philadelphia avenue along the strike of 

the East vein showed the presence of carbonaceous shale which is 

reported to have been similar to some of the material associated with 

the ore, and which very likely represents the ore horizon, as the limestone conglomerate occurs near by. Fragments of similar limy and 

carbonaceous shale containing a little pyrite which came from a 

 slope half a mile farther northeast, on the east side of the railroad 

track opposite the clay pit and brick kilns, may still be found scattered over the field. A hole was drilled near by, but no details of 

this prospecting have been obtained. The clay used in the brick 

Avorks near New Berlinville station is weathered shale, and in places 

where the decomposition is not complete the rock closely resembles 

that which outcrops southwest of the California mine along the 

Reading turnpike. North of New Berlinville no exposure of shale 

has been noted, though it probably occurs west of the railroad between the track and the narrow band of quartzite that is represented 

on the geologic map of the Reading and Durham hills accompanying 

the Berks County report by D'lnvilliers. From the mines northeastward to New Berlinville the shales and accompanying limy beds are 

overlapped by the Mesozoic strata, the strike of which, though variable from place to place, runs in general nearly parallel with the 

strip of Paleozoic rocks. The dip in both sets of rocks is toward the 

southeast and, as already noted, the strata lie nearly parallel. From 

the Rhoades mine toward the southwest the diabase sill appears to 

separate the strata of the ore-bearing group from those of the 

Mesozoic almost as far as the Gresh limestone quarry, a short distance east of which the sill turns southward into the Mesozoic area. 

At the quarry baked Mesozoic shales are seen almost in contact with 

the massive blue Paleozoic limestone. The hill above the quarry is 

covered with fragments of whitened and indurated sandstone.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. X

RHOADES ESTATE 

n SHAFT

too zoofeet

GENERAL PLAN OF WORKINGS AT BOYERTOWN MINES, BERKS COUNTY, PA.
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 369 PL XI

Gabel No. 1 shaft Surface

\

X

G.552-::-

B

Gabel No. 2 shaft

Tunnel about 50 feet south of section

\

\

N 

\ 

\

665'

100 0

I___I 100 200 feet

CROSS SECTION AT BOYERTOWN MINES (ALONG LINE A-B, PL. X).
BEKKS COUNTY DEPOSITS. 47 

THE AVORKINGS.

All the mines of the Boyertown group were flooded when the writer 

visited the locality, arid for this reason no first-hand information concerning the underground, geology of the ore deposits enters into the 

present descriptions. The facts available in regard to the geology of 

' he mines are those recorded by Willis and D'lnvilliers, whose descriptions are quoted below. For the map of the workings which forms 

PI. X acknowledgment is due the former engineer and superintendent 

of the Phoenix mines, Mr. J. H. Harden, of Phoenixville, by whom 

it was in part drawn from original surveys and in part compiled from 

data furnished by the several companies which formerly owned the 

mines. The workings of the 640-foot level of Gabel shaft No. 2 have o

been added to Mr. Harden's map from notes of a survey in possession of W. H. Dechant, successor to the practice of Kendall Brothers, 

civil engineers, formerly located at Reading. The cross sections of 

the mines (Pis. XI-XV) have been constructed from the data afforded 

by the mine maps, with the aid of sketches made by Mr. Harden. 

Their purpose is to show the general attitude of the veins, and they 

do not take account of the many existing irregularities of thickness.

DESCRIPTIONS BY

The Phoenix mines present the simplest structure. Two inclines, having an 

average slope of 46°, are sunk on the ore, between a hanging wall of Mesozoic 

red sandstone and a foot wall of dark-gray limestone. Drifts * * * have 

been driven off on either side of the incline and the ore removed by stoping. 

The bed varies from 7 to 12 feet in thickness, and near the hanging wall there 

is usually a selvage of chloritic slate, which comes down in mining. The strike 

is quite regular, about northeast and southwest, and the beds have the apparent 

prospect of continuing indefinitely in. either direction ; just southwest of the 

lower incline the bed is pinched out, however, and no exploration has been made 

to ascertain whether it continues or not.

A shaft, known as Eckert's, * * * was sunk a short distance northeast of 

the California incline, and " Eckert's vein " was opened by it. The Phoenix company owns part of the mineral right on this " vein," and the California incline 

was sunk through rock to develop it and " Rhoades's vein," which was known 

by surface workings.

* * * The northeast drifts of the California mine reach the southwest end 

of Eckert's ore, while two long crosscuts have been driven through limestone to 

Rhoades's deposits. Eckert's is like the Phoenix in geological relations, but 

strikes nearly north and south, with a dip to the east.

Rhoades's vein strikes at right angles to the Phoenix, southeast and northwest, and dips northeast; it has a hanging wall of limestone and foot wall of 

trap, and in this resembles the deposit opened by the Gabel shaft [Blue vein] ; 

the ores obtained from the two openings are also very similar, and the differences of strike and dip are hardly sufficient in so disturbed a corner to render it 

improbable that they belong to the same deposit.

"Tenth Census, vol. 15, 1886, pp. 229-231.
48 MAGNETITE DEPOSITS IN PENNSYLVANIA.

. The lowest working in the California mine, on Eckert's vein, is 218 feet from 

the surface at the top of the incline; the dip is about 45° toward the east. This 

drift is 240 feet from the Warwick shaft, measured on the map. Ore was first 

struck in that shaft at a depth of about 400 feet, probably 425 feet below the 

top of the California incline.

A dip of 38° to 40° would place a southern extension of Eckert's vein in the 

position of the ore cut in the Warwick shaft. It does not follow that the ore 

body is continuous from the Warwick workings up to the California drifts. 

In fact, the trap which lies west of the Warwick shaft and that penetrated in 

the long crosscut toward the Gabel mine render it very improbable that there 

is an undisturbed body of ore here; but it does seem probable that the Warwick, the Eckert, and perhaps the Phoenix beds, which all have a red-sandstone 

hanging wall and a limestone foot wall, are disturbed portions of the same 

originally connected bed.

FIG. 6. Plan of upper or 496-foot level, Warwick mine, after Willis. 1, Diabase; 2, Mesozoic sandstone ; 3, limestone; 4, limestone mixed with ore ; 5, magnetite ore.

A special map is herewith given of the Warwick mine [fig. 6]. It is opened 

in the most disturbed portion of the belt, and'the apparent development of two 

parallel ore beds, together with the exceptional facilities afforded by the kindness of Captain Polkinhorn, led to careful study of it. In the long drift on 

the middle level, toward the south, there is a well-defined limestone foot wall. 

The hanging wall of red sandstone is also uninterrupted; but between the two, 

and especially in the northern end of the mine, the limits of the ore are very 

ill defined. The wall is usually mixed limestone and ore, and mining is left 

off simply when the proportion of ore to limestone becomes too small to pay.

Where the ore body turns southward the upper, bed of ore approaches the 

lower bed, and it.will probably be found that there is but one extending southeastward beyond the next turn in the Gabel property. The variations in thethickness of the ore bed and the positions of the associated limestone, red sandstone, and trap are given in the accompanying special map.
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. XII

Drift 33 feat northeast

100 100 200 feet _i

CROSS SECTION AT BOYERTOWN MINES (ALONG LINE C-D, PL. X).
BERKS COUNTY DEPOSITS. 49

Accepting the inference that the Warwick, Eckert, and.Phoenix deposits have 

originally formed parts of one bed, though now disturbed and separated by 

"pinches," it is difficult to understand how the Blue (Gabel) vein and the 

Rhoades vein can ever have been part of that bed.

The foot wall of the Phoenix and the Eckert mines is apparently tilted, but 

otherwise a little-disturbed and . continuous stratum. Away from the trap, 

which has confused the deposit near the Warwick shaft, the limestone foot wall 

is in that mine also well defined. The long cut driven from the Gabel bed to 

the large deposit in the south end of the Warwick mine passes through 175 

feet of limestone. The same material lies uninterruptedly between the Eckert 

and the Rhoacles beds. Hence it seems highly probable that there are here two 

distinct deposits of ore. With this in view, it would be interesting to know the 

results of exploration north of the Phoenix mines.

DESCRIPTIONS BY D'lNVILLIERS.

The following descriptions of the several mines are abridged from 

D'lnvilliers's account of the Boyertown mines:

Phoenix upper and middle slopes? These slopes are 350 feet apart 

and both work the same body of ore, averaging from 12 to 15 feet 

in thickness, though at many places swelling into bunches three times 

as large in different portions of the different gangways. The dip 

of the ore averages about 45° SE. The upper slope is 353 feet deep, 

vertical measurement, its top being located 6 feet higher than Gabel 

shaft No. 1. The lowest drift is driven on this slope from the bottom for about 150 feet each way northeast and southwest, but the 

courses have never been surveyed, and consequently could not be 

located. Forty-three feet vertically above this is the middle drift, 

likewise driven each side of the slope about 160 feet northeastward 

and 300 feet southwestward to the middle slope. The upper drift 

is 267 feet below the. surface and 43 feet above the middle gangway, 

and has been driven each way about 300 feet, connecting on the southwest with the middle slope, as on the lower'level. 6

The top of the middle slope is at the same elevation as the upper 

one, and it is about 310 feet long, with two levels corresponding and 

connecting with the upper and middle levels on the upper slope. The 

middle slope Avas driven in rock, but the upper slope was driven on 

ore all the way, and as the ore body here is much softer than in the 

middle slope a great deal of trouble and expense has been necessary 

to keep the slope in repair. This has led to its proposed abandonment. 

and to the erection of permanent buildings at the middle slope, from 

which all future mining will probably be carried on. These improvements were hardly consummated when the dull times of 1880 and

0 D'lnvilliers, E. V., Geology of Berks County: Second Geol. Survey Pennsylvania, Rept. 

D3, 1883, pp. 314-316.

6 This level was afterward extended to a distance of about 500 feet northeast of the 

slope and reached beyond Philadelphia avenue, according to the statemnet of Richard 

Richards, former foreman of the Phoenix company.

54370 Bull. 359 08 4
50 MAGNETITE DEPOSITS IN PENNSYLVANIA. /

1881 led to the closing of all the mines, and the two upper slopes are 

still filled with water [1883]. It is likewise proposed here to further 

test the property toy driving northward from the slope to prove the 

presence or absence of the underlying blue ore bed.a

The true foot wall in both these slopes is an altered syenite carding 

thin seams of earthy magnetite with dull luster, in many places 

massed or bunched, and showing but little crystallization. 6 The 

syenite is filled with pink feldspar nodules, hornblende, and epidote, 

all distinctly stratified. In the upper slope, however, a dark greenish-black unctuous limestone layer is found at many points between 

the main body of the ore and the true foot Avail, much of it carrying 

chert in large masses. The top wall is a decomposed, light greenishgray, serpentine limestone, slaty and carrjdng crystals of pyrite. The 

ore rock is generally an impure conglomerate limestone carrying 

masses of dull-colored crystalline limestone, serpentine, and magnetic 

ore, but the bulk of it is a green to black dolomite with coatings of 

calcite. The ordinary run of the mine shows a mixture of magnetic 

iron ore, with limestone and minute crystals of iron pyrites diffused 

through the mass. Locally the pyrite occurs in large and well-defined crystals.

Phoenix lower slope, or California mine.0 The developments here 

consist [1883] of a slope about 300 feet long, from which three levels 

have been driven toward the northeast for the purpose of working 

the Hagy ore bed, and two toward the southwest to meet the Rhoades 

vein. The lowest level was driven first for about 50 feet through a 

dark quartzose sandy rock of a bluish color. The course of the gangway being thought to be turned too much toward the east to strike 

the ore, the next 50 feet was driven more to the north, likewise through 

rock, until at a distance of 110 feet from the foot of the slope ore was 

struck. The original northeast course was resumed and carried 

through ore for 50 feet more. The gangway at the time of visit 

showed a chamber fully 22 feet wide, without showing foot or hanging walls. The dip of this western body of black ore is probably 

toward the southeast at a steep inclination.

The middle drift is about 40 feet vertically above the lowest, and in 

driving northward from the shaft the same characteristics were met 

 as already noted in the lower level. The drift is not parallel to the 

lower level, but turns somewhat more toward the northeast. For the 

first 30 feet it passed through rock, beyond which the ore body was 

met in a rather pinched condition.

The upper level is driven northward from the slope about 176 feet 

vertically below the surface of the ground. It extends for about 80

0 Mr. Richards states that this exploration was made, but that no ore was found. 

6 Compare with statement of Willis, p. 49. 

c D'lnvilliers, E/ V., op. cit., pp. 308-311.
U. S. GEOLOGICAL SURVEY

E

BULLETIN NO. 359 PL. XIII

Surfac

100 ,100

In Gabel workings,section runs 

nearly parallel with strike of veins

x « 

Drift 25rsoutheast

200 feet

G. 552

W

W,

CROSS SECTION AT BOYERTOWN MINES (ALONG LINE E-F, PL. X).
BERKS COUNTY DEPOSITS. 51

feet along the south line of the old Eckert open cut, and the ore body 

pinches toward the northeast.

Exploration has been carried on south of the slope, where the workings consist of a .rock tunnel driven southwestward for about 200 

feet at a depth of about 176 feet through a mixed micaceous and 

quartzose rock to the Khoades vein, which strikes about S. 25° E. 

and dips a little east of north at an angle of 50°. A similar rock 

tunnel was driven from the middle level in a nearly parallel direction, and from its extremity a raise has been opened to strike the vein 

on the upper level. A fine face of ore 30 feet thick is exposed in this 

middle level, but, owing to its inferior quality as compared with the 

Hag}' ore, work has been suspended [1883], The thickness of this 

bed varies greatly, as is the case throughout all the mines. The 

gangue is.similar to that of the Hagy mine, being mostly silica, lime, 

and magnesia, but the ore is leaner in iron and carries more Sulphur 

and a little copper, being identical in composition and physical 

attributes with the blue ore of the Gabel mine. In the Gabel mine 

the Blue vein is separated from the overlying Black vein by 150 feet, 

more or less,® of impure limestone, but the Hagy and Khoades veins 

are divided by a rock which is apparently a rotten quartzose gneiss, 

though the gangue of the ore itself in each place is largely limestone.6

Warwick mine. 0 The Warwick mine has three levels [1883], Avith 

numerous gangways and counter gangways, many of which have 

been long since abandoned and could not be explored. The first level 

is 420 feet vertically below the surface, the second 500 feet, and the 

third- 567 feet [corresponding with 416-foot, 496-foot, and 555-foot 

levels as given on PL X]. Two gangways were driven on the 500- 

foot level, one on the hanging wall, which is generally Mesozoic, the 

other extending toward the southeast and thence south into the Gabel 

property and showing generally a limestonce foot wall. The average 

horizontal distance between these gangways is about 50 feet, which 

would give a thickness of about 25 feet of ore, measured at right 

angles to the dip. The space between, however, is by no means entirely occupied by ore, but contains numerous horses of serpentine, 

limestone, and greenstone, as well as many occurrences of pinching 

Adhere-the foot and hanging walls come together. Pinching is particularly noteworthy in the north gangway, where about 150 feet 

from the shaft the ore is only from 3 inches to 1 foot, and again at 

the end of the gangway, where the ore is entirely cut off.

The ore is found everywhere to lie in lenticular-shaped bodies, 

thinning o out in the line of strike and swelling tu to immense bunches in

" One hundred and sixty feet, as measured on the map.

6 To judge from the workings on the 176-foot level of the California mine, the horizontal distance hetween the Hagy vein and the Rhoades vein is ahout 175 feet, but the 

two veins strike in very different directions in fact, at an angle to each other of ahout 

45°. A. C. S.

° D'lnvjlliers, E. V., op. cit, pp. 320-324,
52 . MAGNETITE DEPOSITS IN PENNSYLVANIA.

the center, variously mixed with limestone, with which it seems to 

be here and there intimately interstratified. A fine illustration of 

this relation was furnished in the lower [454-foot] level of the Gabel 

mine, where in a piece of limestone 6 inches thick there were four 

bands of interstratified Ore from £ to 1 inch thick.

From the 500-foot level to a point 90 feet out from the shaft a 

crosscut was driven S. 40° W. in search of the Blue vein found in 

the (jabel mine. It is probable that this bed exists in the extreme 

southwest corner of the Warwick tract, but, except at lower levels, it 

would not pay to stope it, as it must within a short distance pass into 

the adjacent properties.

The crosscut was not driven far enough to reach the Blue bed, for 

the slight development of this vein in the Gabel mine shows that it 

has a decided tendency to bear toward the northwest, in the direction 

of the lower Phoenix slope. The crosscut was closed, at the time the 

mine was examined, but it was said to have been carried first through 

10 feet of limestone, then 4 feet of ore, and for 143 feet through 

quartzose sandstone.*

From a point beneath the railroad to the boundary with the Gabel 

property the south gangway on the 500-foot level is driven through 

limestone and ore, the former being the general foot wall and dipping 

about 35° SE. A great deal of ore has been obtained from stopings 

carried up from this gangway along the foot wall. Masses of calcite, 

bearing clusters of pyrite, are seen in numerous places accompanying 

the ore.

Close to the property line the north edge of an immense body of ore 

appeared, and in parting the drift to work it the ore was found to 

be fully 40 feet thick. The absence of connected surveys led to the 

continuation of both drifts into the Gabel property, from which fully

8,000 tons of ore was eventually extracted. A magnificent pillar of 

excellent black ore still remains as the support to the roof of this immense chamber. A crosscut from the foot to the hanging wall was 

in ore for its entire length.

Inspection of the lowest 567-foot level in this mine [555-foot level 

of PI. X] will show that two gangways have been opened, connected 

in two places by crosscuts.

In the two parallel gangways driven eastward from the shaft to 

meet the ore body a considerable mass of limestone was driven 

through, extending as far as 125 feet from the shaft, after which ore 

was encountered to the Mesozoic conglomerate hanging wall, dipping 

here 50° to 55° a little south of east. The last 60 feet of the southern 

of these two drifts was entirely in ore, which here spreads out to a 

pinch within about 30 feet to the northeast along the main gangway, 

branching off from the north crosscut. The quality of the ore here

a The rocks through which this tunnel was run are shown by Willis as diabase.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. XIV

G. 356^ \

\

Surface

H

100 0

\ \ I I I

100 200 feet

702'

\ \ \ x 

s \

454

*« 

\\\ \

\\\ \

\\

W.416 \ v Workings 55 feet northwest of..section

'W.496'

W,

W. 683'

CROSS SECTION AT BOYERTOWN MINES (ALONG LINE G-H, PL. X).
BEBKS COUNTY DEPOSITS. 53

was excellent, but it was soon cut off by the meeting of the limestone 

and the Triassic measures [conglomerate]. To the south-southeast, 

along the hanging-wall gangway, the ore gradually thins away, and 

about 60 feet below the south crosscut it ranges from 3 inches to 1 

foot. This pinch corresponds closely in position and character to 

that already mentioned as occurring on the 500-foot level, and the 

gangways are essentially parallel. The pinch on the hanging-wall 

gangway extends for 50 feet, to a point where the gangway makes 

a decided turn toward the S. 40° E.; here another body of ore was 

encountered, 10 feet thick and swelling into the hanging wall, but 

pinching again in about 35 feet. This ore was stoped up for about 

40 feet, where it was found to extend back over the pinch, thus showing the presence of bulging and thinning on the line of dip. The 

S. 40° E. course extends for 120 feet to a point under the railroad,

where the gangway turns southward and shows a limestone top. 

Sixty feet beyond, a greenstone dike was encountered similar to that 

occurring in several places in this and in the 500-foot level along 

a line from this point, to the shaft. These dikes are noAvhere of great 

thickness, and generally dip to the northeast. Where diabase is 

present it usually forms a true foot wall, no ore being found beyond 

it, but in the 567-foot level in the hanging-wall gangway it partakes 

more of the character of a horse, having ore on both sides.

The foot-wall -gangway on this level is almost entirely in ore, in 

many places with a very steep dip and in one place even overturned. 

Inspection of the mine map will show that the f oot-Avall gangway of 

the 567-foot level lies very nearly underneath the foot-wall gangway 

on the level above. On both levels the gangways have a general 

curve convex toward the east, and toward the south the dips become 

lower and lower until near the Gabel property line they do not average over 35° and here and there fall to 20°. Because of the low dip 

in the southern part of the mine most of the stoping has been confined to the 500-foot level.

A little development has been made on the 420-foot level, but here 

the dip of the vein 'carries the ore beyond the property limits within 

a short distance, so that no extensive work has been done.

Gabel mine.a A vertical section through the Gabel No. 1 shaft 

shows 

Feet. 

Banded shales, sandstones, and conglomerate, with a layer

of altered inud rock about 5 feet thick at the bottom___ 180 

Black bedded ore, folded and broken, and consisting mostly

of calcareous breccia __ _________________ 26

Limestone__________ _ : _________ 150

Blue ore bed (measured across the bedding 20 feet)_____ 55 

Chloritic rock or greenstone [probably diabase]________ 74

0 D'lnvilliers, E. V., op. cit., pp. 328-330.
54 MAGNETITE DEPOSITS IN PENNSYLVANIA.

The mine has two levels, the upper 180 feet [160?] and the lower 

474 feet [454]. Some development was carried on in the upper level 

close to the shaft, but the ore was greatly mixed with a light-green 

limestone gangue and in addition was greatly broken and folded. 

The underlying limestone was similar to that found in the Warwick 

mine, being mostly a serpentine-green limestone of a.light color, but 

the gangue-rock limestone is much darker and in places black from 

the contained ore.

While mining in the upper level the Gabel Company became convinced of the trespass that had been made on its property through 

the 500-foot level of the Warwick mine. From the 474-foot level a 

main gangway was started toward the southeast, in which the blue 

bed was struck 30 feet from the shaft. This ore extended for 33 

feet, the vein dipping about 60°. At the Blue vein the course of the 

gangway was turned somewhat to the left, and the remaining part 

of the gangway was entirety in limestone, at first dipping rather 

steeply but afterward flattening as the Black vein was approached. 

About 175 feet beyond the hanging wall of the Blue vein the foot 

wall of the Black vein was struck. The gangway came into the 

Warwick Company's stopes, which had been driven up from its 500- 

foot level on a dip of about 35°. In the Gabel shaft the two ore beds 

and the strata which lie between them all dip about 45° S. 55° E.

The ore beds in the Gabel mine are like those in the other shafts. 

They occur in masses and bunches 40 feet thick, which pinch out to 

mere leaders and are therefore by' no means continuous bodies of ore. 

The ores, however, show one difference, in that they are harder and 

more compact than in the other mines, probably on account of their 

proximity to the Gabel Hill dike, which may have exerted some influence in altering their physical properties.

From the 474-foot level two gangways have been driven in the 

foot wall of the Black ore bed. Owing to its great thickness here and 

large limestone partings, stoping has been carried up almost to the 

shaft, where the Black vein was cut 180 feet below the surface, thus 

proving the identity of the brecciated bed there found with the magnificent body of ore in the lower part of the mine.

The Warwick gangwaj7 s have likewise been extended along the 

hanging wall ["new red" that is, limestone conglomerate], but 

not from the 500-foot level, being started from the stopings above. 

These drifts along the hanging wall, as well as those on the foot wall, 

have been carried a considerable distance to the south, two of them 

being at least as far out as the barn. These gangAvays exhibit the 

tendency of the ore body to swing around Gabel Hill.

Some stoping has been done on the Blue ore bed, but the inferior 

quality of this ore delays its extended development. The company 

intends [1883] to sink another lift in the near future, from which
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. XV

K

SN N ^ Open pit J

100 109 200 feet

CROSS SECTION AT BOYERTOWN MINES (ALONG LINE K-L, PL. X).
BERKS COUNTY DEPOSITS. 55

it will drive to the southeast, thus opening a third level on this 

valuable ore tract. [See 552-foot level, PL X.]

A crosscut was driven from the 474-foot level toward the southwest into the hill, but the ore was found to be cut off in this direction 

by the diorite dike which outcrops on the north side of Gabel Hill.

LATER DEVELOPMENTS.

The descriptions which have been given include the tunnels and 

shafts opened before 1883. Between that year and 1893 the workings 

of the various mines were considerably extended. Gabel shaft No. 1 

was carried to a depth of about 570 feet, and on the 552-foot level a 

crosscut was run to the Blue and Black veins, giving stoping ground 

of 9.8 feet vertically below the next level above. Gabel shaft No. 2 

was sunk to a depth of 665 feet. The shaft encountered the Black 

vein at about 640 feet, but the thickness of the ore body can not be 

stated. The workings from the shaft comprise two short drifts in 

the ore body. The northerly drift, about 55 feet long, is connected 

by a raise with the 552-level of Gabel No. 1 mine. The southerly 

drift is 25 feet long and from its end a crosscut tunnel penetrates the 

foot wall. The length of this tunnel is about 360 feet. About 35 

feet from its end short drifts, which extend to the right and left, are 

supposed to follow the hanging wall of the Blue vein. Unfortunately no person was found who had worked in this tunnel, and its 

depth below the surface is not accurately knoAvn. Between shaft No. 

1 (where the ore was first cut at a depth of about 180 feet) and shaft 

No. 2 the Black vein had been proved as a continuous layer for about 

800 feet in the direction of dip. On the trespass level the drifts in 

ore within the Gabel property were about 250 feet long, and from the 

Warwick shaft the vein had been followed for 400 feet before crossing the property line.

The Blue vein lies below the Black vein somewhat more than 100 

feet, measured normal to the bedding, or from 160 feet to 325 feet 

measured along the various crosscuts. It has been mined on the 

dip to the height of about 375 feet and on the strike to a maximum 

length of about 250 feet. On the 640-foot level neither vein had 

been fully developed when mining was suspended. To judge from 

the course of the Blue vein in the higher workings, it is not likely to 

extend more .than a short distance into the Warwick plot. All of 

shaft No. 1 below the Blue vein that is, below a level about 400 

feet from the top is supposed to be in diabase (greenstone of D'lnvilliers's description), though no positive statement to this effect was 

made either by Willis or by D'lnvilliers.

No information has been procured in regard to the behavior of 

the ore bodies in the southernmost workings of Gabel No. 1 mine, but 

the fact that none of the drifts were extended for more than 200 feet
56 MAGNETITE DEPOSITS IN PENNSYLVANIA.

from the crosscut may indicate that both veins come to an edge in 

this ground. In view of the uncertainty which exists on this point 

it would be safer to lay out any exploration for the veins at lower 

levels southeast of the shaft rather than south or southwest.

In the Warwick mine two lifts were sunk after 1883. On the 610- 

foot level the vein was found to be double (as on the 555-foot level), 

and both the foot-wall and hanging-wall leads were developed by 

drifts extending southward nearly to the property line.

An extension of about 120 feet would connect the foot-wall gangway with the 640-foot level of the Gabel mine. On the 610-foot level 

a crosscut 200 feet long which was run into the foot wall nearly to 

the property line failed to locate the Blue vein, but nothing is known 

concerning the rocks penetrated. Unless diabase was encountered 

it would seem to be worth while, in view of the present control of 

both the Gabel and Warwick tracts by the same company, to continue this tunnel to the diabase, for in the Gabel mine, at about the 

same elevation, the horizontal distance between the Black and Blue 

veins was about 325 feet. In the eastern drifts of Gabel No. 1 1 mine 

the manner in which the Blue vein curves toward the north and the 

fact that the drift on the 552-foot level if continued in its course 

would pass nearly under the end of the drift on the 454-foot level 

suggest that in this ground the Blue vein stands very steeply.

In a search for the Hagy vein two tunnels were run into the hanging wall on the 610-foot level about 100 feet east of the shaft. 

Though the vein was not located, it is probable that it may yet be 

discovered by extending the exploration toward the north or northwest. This point is referred to again on page 59.

The workings, on the Warwick 683-foot level, so far as is shown 

on the map (PL X), comprise a gangway 200 feet long, apparently 

on the foot wall of the vein, and two crosscuts, one into the foot 

wall and the other started toward the hanging wall. No data have 

been procured concerning the ore body on this level, and the nature 

of the rock encountered in the lower part of the shaft is not known. 

It may be suggested that if the Warwick shaft penetrated any considerable mass of diabase there can be no further probability of 

encountering either the Blue vein or the Rhoades vein on the lowest 

level, as the foot wall of both is the Gabel Hill intrusive mass. On 

the other hand, if the main mass of diabase has not been encountered 

there is still a chance of finding ore by locating and exploring the 

diabase contact.

In the California mine the workings now reach a vertical depth 

of 390 feet, two levels having been opened below the 200-foot level, 

which was the lowest in 1883. Just beneath the old sump a body 

of ore was encountered which was known as ore No. 2. On the 305- 

foot level, where the same bed was. struck about 20 feet from the
O. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. XVI

PLAN OF CALIFORNIA AND WARWICK MINES AT BOYERTOWN, PA., SHOWING POSITION OF FAULT.
BERKS COUNTY DEPOSITS. 57

slope, it extends for about 30 feet along the drift and is reported to 

be 18 to 20 feet thick. On this level about 45 feet beyond ore No. 

2, or 95 feet distant from the slope, the Hagy vein Avas encountered. 

Along the hanging wall it was mined for 125 feet. On the 390-foot 

level ore No. 2 was cut about 75 feet from the slope and it continued in the drift for about 30 feet, with a maximum thickness of 

about 20 feet. Fifty feet farther on the Hagy vein appears and, 

being cut diagonally, continues for about 90 feet in the drift. This 

vein has been stoped from the 390-foot level to the bottom of the 

Hagy pit, or about 500 feet along the dip.

In the California mine the southernmost workings in the 390-foot 

level on ore No. 2 are about 60 feet distant from the Warwick 

shaft and about 30 feet higher than the 416-foot level of the latter 

mine on which the Warwick vein was first opened. The proximity 

of these workings leaves little doubt that ore No. 2 and the Warwick vein are parts of the same ore body, as has been commonly 

supposed by persons most familiar with these mines.

PRACTICAL CONCLUSIONS.

Facts are not at hand to warrant an unreserved statement of the 

relation existing between ore No. 2 and the Hagy body; at the same 

time, it is thought that they are probably parts of a single vein which 

lias been separated by faulting. The existence of a fault is surmised 

from the knowledge that in the Warwick mine limestone conglomerate forms the hanging wall of the vein at least as deep as the 555- 

foot level, whereas in the upper levels of the California mine the 

same rock lies above the Hagy vein. If, then, the Warwick vein 

holds its position just beneath the conglomerate as it extends upward 

into the California mine, and if the Hagy vein holds its position 

beneath the conglomerate as it extends downward from the 200-foot 

level to the 390-foot level there can be no doubt that both the ore 

layer and the overlying conglomerate have been offset along a fault 

break. The same conclusion would follow if it were found that conglomerate forms the hanging wall both of ore No. 2 and of the Hagy 

vein on the 390-foot level of the California mine. The horizontal 

displacement along the fault appears to be about 125 feet (Pis. VIII 

and XVI).

On the assumption that there is a fault and that the Hagy vein continues to dip about 65°, as noted on the map (PL X) at the end of 

the 390-foot level, California mine, the positions of the foot wall on 

the 555-foot, 610-foot, and 683-foot levels will be approximately 

as shown by PI. XVI.

On the 390-foot level in the California mine, according to Mr. 

Richards, exploration was carried in lean ore for 50 or 60 feet toward
58 MAGNETITE DEPOSITS IN PENNSYLVANIA.

the north along the strike of the vein. This makes it appear that 

mineralization dies out in this direction. A similar decrease in 

values having been found in a 100-foot westerly drift from the 

middle slope, the intervening ground has been judged to be barren. 

Whether it is really so or not of course can not be decided without 

actual exploration, but the existence of a fault break or of several 

breaks between the workings of the .California mine and those of the 

Phoenix mine on the East vein is strongly suggested by the relative positions and different strikes of the Hagy and East veins. 

A good idea of these features may be obtained from the plan giving 

the projected positions of the several veins on a level surface 400 feet 

below the top of Gabel No. 1 shaft (PL VIII). Mr. Richards states 

that on the lowest level of the workings on the East vein good 

ore continued east of the upper slope about 100 feet, beyond which 

lean ore was penetrated for perhaps 50 feet. On the middle level, 

43 feet vertically above, mining was continued toward the east for 

150 feet, and on the upper level, 43 feet higher, good ore was found 

for fully 500 feet. The total length of the ore body on the upper 

level was about T50 feet. Corresponding roughly with the bottom 

of the minable ore, which is found farther and farther west as depth 

is gained, the upper edge lies more than 100 feet east of the middle 

slope on the upper level, about 25 feet east on the middle level, and 

some distance west of the slope at the bottom of the mine. It is thus 

apparent that, in addition to its southeastern dip, the ore shoot 

pitches toward the south, and also that if this pitch continues the 

ore body must pass into the block of ground bounded by Third street, 

the mineral-reserve line, and the railroad. How far it may persistin this direction can not be suggested. It may or may not extend as

far as the ore horizon remains unbroken.

It is strongly suspected, as already stated, that at least one displace-. 

ment of the ore horizon that is to say, the surface between the limy 

strata and the limestone conglomerate exists between the middle 

slope and the workings of the Hagy vein of the California mine. 

Three faults with horizontal displacements equal to that of the fault 

supposed to exist between the Warwick and Hagy ore bodies would 

suffice to throw the ore horizon from the place it occupies in the California mine into the observed position of the East vein. (See fig. 7.) 

If the Hagy vein is ever found in the lower workings of the Warwick mine, further prospecting in the direction of the estimated 

downward extension of the East vein would seem warranted. The 

intervening block of ground may not contain workable ore near the 

surface, but is perhaps more likely to carry ore bodies as depth is 

gained, because the mineralizing waters which produced the ore are 

believed to have come from below.
BEE.KS COUNTY DEPOSITS. 59

The chances of finding the Hagy and East veins above the lowest 

level of the Warwick mine are thought to fully warrant explorations 

along the lines of the foregoing suggestions, but the ground that offers 

the strongest inducement for exploration is that which lies beyond 

the Warwick and Gabel workings in the direction of the dip of the 

Warwick ore body. No extended argument is needed to show the 

advisability of testing the further persistence of an ore body like the 

Warwick or Black vein, which has been followed along its course 

almost continuously (though swelling and pinching) for 1,000 feet 

and along its dip for 800 feet, with no signs of failure in the lowest 

levels that have been opened. The map and cross sections (Pis. 

X-XV) which accompany this report afford adequate data for laying

FIG. 7. Ideal sketch showing possible type of structure in ground between Hagy vein 

and East vein. Datum of plan, 400 feet below top of Gabel No. 1 shaft.

out an advantageous plan of prospecting the veins by means of the 

diamond drill.

The theory which has been developed concerning the origin of the 

Boyertown ore bodies is based on the analogies between these deposits 

and those of similar character at other places in the State, each of 

which exhibits a close dependence on adjacent bodies of intrusive 

diabase. It is noteworthy that all the ore bodies except the East 

vein lie just beyond the termination of the diabase sill which occurs 

along the northwest side of Gabel Hill. Apparently underground 

the sill dips with the bedding of the invaded rock and the edge 

which it presents toward the north pitches steeply in such a direction 

that it passes beneath the Warwick and Gabel workings. The Blue 

vein in the Gabel mine appears to follow the upper surface of the 

sill, but the Khoades vein seems to lie against its blunt edge. In the
60 MAGNETITE DEPOSITS IN PENNSYLVANIA.

Gabel mine more than 100 feet of limy strata lie between the diabase 

and the conglomerate which caps the Black vein, but all indications 

on the surface favor the conclusion that the conglomerate extends 

northward almost if not actually to the walls of the diabase. As in 

the mine it appears that the diabase follows the stratification of the 

limy beds, the near approach or actual contact of the conglomerate 

and the diabase at the surface signifies one of two things either that 

the intrusive mass cuts across the stratification above the point where 

the contact is penetrated by Gabel No. 1 shaft, or that the parallelism 

between the stratification of the Paleozoic and Mesozoic rocks, which 

apparently exists elsewhere in the mine, does not hold in this place. 

A plausible suggestion of what the relations may be in depth is

Gabel shaft No. 1

10ft. 100 JOO__BOOfeet

FIG. 8. Sketch section illustrating possible relation of Black vein to buried edge 

of a diabase sill at Gabel mines.

illustrated in fig. 8. The presence of several sills south of Boyertown, as shown on the sketch map, the manner in which these sills 

terminate, and the probable existence of an underlay of diabase 

beneath the structural basin which has been described all suggest 

the validity of the assumption that one or more buried sills exist 

in the region southeast and east of the Boyertown mines.

The emergence of a minor intrusion of diabase near West Swamp 

Creek, 1 mile northeast of New Berlinville, and of a great mass east 

of Bechtelsville suggest that the edges of the sills representing the 

upward limit of intrusion on the northwest side of the synclinal basin 

probably lie at no great depth and not very far back (southeast) of 

the boundary between the Mesozoic area and that occupied by the
BERKS COUNTY DEPOSITS. 61

older formations. If the presence of the buried sills in this vicinity 

were known to be a fact, and if the place could be determined where 

any one of them penetrates strata corresponding to those in which 

the Boyertown deposits occur, the existence of a series' oif iron-ore 

deposits in the limy strata near the diabase might be suggested. 

The absence of knowledge on these two points leaves the whole 

question in the light of a speculation, with the hazards rather too 

great to justify recommending the expenditure which would be required to make a practical test. The imaginary position of the

FIG. 9. Geologic sketch map of vicinity of Boyertown, showing 

imaginary position of edge of buried sill.

upper edge of the supposed sill is shoAvn in plan on the sketch map, 

fig. 9.

DEPOSITS SOUTHWEST OF BOYERTOWN.

South of the Boyertown mines the northwest slope of Gabel Hill 

is formed by diabase, the hill itself and the connecting ridge for a 

mile or more toward the south being formed by baked and indurated 

shales and sandstones. At the surface this mass of diabase ends as 

an apparently blunt wedge south of the ground in which the ore 

deposits have been found, and as nearly as can be determined, it comes 

to the surface just at the base of the Mesozoic beds where they overlap on the ore-bearing strata. ^ In this position the diabase, having the 

form of a sill, extends for three-fourths of a mile southwestward and
62 MAGNETITE DEPOSITS IN PENNSYLVANIA.

then, turning down the valley of Ironstone Creek, cuts back into the 

Mesozoic area. The western' edge of this sill has not been seen at any 

place because it comes to the surface beneath a mantle of loose debris, 

but its eastern contact was encountered at the old Brower iron mine 

on the hill slope opposite the upper end of Wren's ice pond, about 

half a mile southwest o°f the Khoades mine. The Brower ore at this 

place was discovered in a post hole.

Richard Richards, of Boyertown, who had charge of this property 

in 1857 and 1858, states that he extracted more than 2,000 tons of magnetite ore from an irregular layer having a northeast-southwest strike, 

a dip of 35° or 40° SE., and a maximum thickness of about 8 feet. 

The mine was worked by means of a tunnel and two shafts, and ore 

was stoped from two levels to a depth of about TO feet and to a length 

on the strike of about 50 feet. Examination of the locality shows that 

the ore layer occurred very near if not exactly in contact with the 

upper side of the diabase sill, under a hanging Avail of flinty baked 

shale or sandstone. Taken by itself the occurrence of ore at this place 

is an all but evident instance of ore segregation during igneous or socalled contact metamorphism, and considered in the light of the many 

like deposits closely associated with intrusive diabase at other places 

it must be accepted as a deposit of this variety.

About 300 yards southwest of the Brower mine, back of the J. Wren 

house, a short tunnel with its mouth in diabase was started toward the 

contact, but no information has been obtained concerning what was 

found at this place, nor concerning a shaft lying between the Wren 

tunnel and the.Brower mine, shown on the topographic map of the 

Second Geological Survey of Pennsylvania.

About one-fourth mile southwest of the Rhoades mine, on the hill 

slope about 50 feet above the level of the railroad track, a shaft 

(known as the Rhoades and Grim shaft) has been sunk to a depth of 

40 or 50 feet, to judge from the material on the dump. Nothing but 

diabase seems to have been encountered at this place. East and somewhat north of ,this shaft a tunnel of unknown length was run into 

Gabel Hill, but no person was found having any knowledge of this 

work. The mouth of the tunnel is situated very near the eastern or 

upper edge of the diabase sill, and it seems that Mesozoic strata must 

have been penetrated.

It is not at all unlikely that other masses of ore like those of the 

Brower mine exist along the east contact of the sill, but as no limy 

strata are known to occur on the upper side of the diabase, this ground 

is not regarded as offering much inducement for prospecting. West 

of the diabase, conditions are probably more favorable, on the supposition that the strata which carry the Boyertown veins are here in 

contact with the under side of the sill, but the valley of Ironstone 

Creek is not a favorable place for making excavations, and it seems
BERKS COUNTY DEPOSITS. 63

that any exploration of the under side of the diabase should be undertaken by means of the diamond drill.

DEPOSITS NORTH OF BOYERTOWN.

About 2 miles north by northeast of Boyertown there has been some 

exploration for iron ore on the south side of the group of diabase 

hills southeast of Bechtelsville. The position of two shafts is shown 

on the topographic map of Berks County, issued by the Second Geological Survey of Pennsylvania, though no essential data are given 

in the Berks County report beyond the statement that some excellent

Old mines and prospects

FIG. 10. Geologic sketch map of region northeast of poyertown.

ore was taken from an opening known as the Gilbert shaft. The 

shafts mentioned were not found during the present investigation, 

but from their indicated position they are situated within Mesozoic 

strata, which come up onto the diabase rock from the south.

The diabase covers a roughly triangular area of nearly 2 square 

miles, which lies between West Swamp Creek and a tributary known 

as Middle Creek. From the southeast corner of this area'an arm extends for about 1| miles toward the southeast. The mass of diabase 

is nearly surrounded by Mesozoic strata, which appear to lap onto it 

from the east and from the south. (See fig. 10.) On the northwest
64 MAGNETITE DEPOSITS IN PENNSYLVANIA.

the structural relations are obscure, but from the rock fragments 

scattered over the fields the Mesozoic rocks are known to be present 

along the base of the hill above the wagon road to a point within 

one-fourth mile of the bridge across West Swamp Creek. Near the 

turn in the road, a short distance northeast of this bridge, blue Paleozoic limestones are exposed, and above them baked shales, which may 

belong to the Mesozoic. This shale seems to dip toward the hill at a 

low angle, as if it would pass beneath the mass of diabase which 

outcrops a short distance up the slope. The blue limestone is not 

metamorphosed to any marked degree.

On every side of the diabase the Mesozoic rocks, including shale, 

sandstone, and limestone conglomerate, have been considerably baked, 

and this induration extends in places as far as one-half mile from the 

contact. Loose fragments of limestone conglomerate containing 

abundant spangles of hematite may be found at several places along 

the ridge east of Middle Creek, and similar material is abundant on 

the hill slope about 1 mile southeast of Eshbach. On the south side 

of the diabase hills both specular hematite and magnetite were noted 

in material revealed in a cutting along the east-west road a few 

hundred yards west of the crossroads 1£ miles northeast of New 

Berlinville. This locality is near one of the old prospecting shafts 

mentioned above.

Although the presence of hematite in the baked rocks which surround the diabase shows that certain conditions favorable for the 

formation of ore existed, it does not seem that any large bodies of ore 

are likely to be encountered in the Mesozoic strata. The exposures 

are not sufficient to indicate how much limestone conglomerate exists 

in the neighborhood, but it is probably not present in any such

amount as at Dillsburg, York County, where magnetite ore deposits

are associated with beds of this rock in the vicinity of diabase 

intrusions.

Near the diabase there is only one exposure of the Paleozoic limestone which is known to occupy the valley lying west of the diabase 

hills, so that almost nothing is known of the structural relations of 

this rock to the Mesozoic strata and to the diabase. It is probable, 

however, that the limestones are here overlapped by the Mesozoic 

strata in. much the same way as in the vicinity of the Boyertown 

mines, and if this is so there is a possibility that the ore bodies may 

exist in depth beneath the Mesozoic rocks which occur west of the 

diabase mass. Though this point could be readily tested by a series 

of drill holes along the western portion of the diabase area, such exploration would be regarded as a hazardous project from a practical 

standpoint.

Iron ore is said to have been extracted from workings known as 

the Fegley mine, situated well within the diabase area on the north
BERKS COUNTY DEPOSITS. 65

side of the little brook about one-fourth mile north of the Gilbert 

shaft. A suggestion concerning the manner in which the ore occurs 

in this place was obtained from material on the dump at the tunnel 

mouth. A large fragment of diabase wa.s found, on one side of which 

there was a coating of ore 1 inch thick composed of crystalline magnetite intergrown with a minor amount of feldspar. Appearances 

indicate that the magnetite was segregated in a crevice traversing 

the diabase. There is no sharp division between the rock and the 

ore, a fact which suggests that the magnetite and accompanying 

feldspar may have been deposited by vaporous solutions derived from 

the deeper-seated part of the diabase mass shortly after the period of 

intrusion.

In many places the diabase intrusions in the Mesozoic area contain 

very considerable amounts of magnetite as a mineral constituent, 

but this is the only place that has come to the writer's attention where 

magnetite has been found segregated in a definite vein inclosed by 

the igneous rock. This occurrence has a bearing on the general problem of the genesis of deposits of the Cornwall type, affording good 

evidence that the diabase rock could have been the actual source of 

the ore-forming solutions as well as of the energy which caused the 

circulation of the mineralizing waters. Elsewhere, though the influence of the diabase intrusions is everywhere noteworthy, it has not 

been possible to show definitely that the solutions have emanated 

from the intrusive rock.

A shallow pit has been sunk in search of copper ore in a road-metal 

quarry beside the wagon road half a mile west of Congo post-office, 

near the end of the arm of diabase which extends toAvard the southAvest from the main triangular area. In the Avails of this pit may be 

seen a veinlet about an inch Avide, composed mainly of hornblende and 

feldspar containing scattered bunches of chalcopyrite. The hornblende of the vein appears to have groAvn out from the Avails of a 

crevice, and the material of the vein is thus closely knit to that of the 

inclosing rock, as in the magnetite vein described above. It is suggested that this veinlet \vas formed in a manner similar to that suggested for the magnetite vein. In a recent paper on the copper 

deposits of NCAV Jersey by J. V. Lewis* the source of this metal is 

believed to have been the diabase intrusions Avhich in.each place are 

associated Avith the ore occurrence.

JONES MINE.

The Jones mine, also knoAvn as the Warwick mine because it was 

formerly Avorked by the Warwick Iron Company, is situated about 

three-fourths of a mile east of Joanna station and 1^ miles nortlrwest

" Copper deposits of the New Jersey Trlassic: Econ. Geology, vol. 2, 1907, pp. 242-257. 

54370 Bull. 359 08 5
66 MAGNETITE DEPOSITS IN PENNSYLVANIA.

of Elverson, on the Wilmington division of the Philadelphia and 

Reading Railroad. (See PL XVII.) This mine is in Berks County, 

about 4 miles west-northwest of the Warwick mines in Chester 

County. Part of the description of the Jones mine by H. D. Rogers 

is here given: a

The chief mine is an open excavation covering rather more than 5 acres, and 

there is another to the south of it covering about 1 acre [Kinuey mine]. Magnesian limestone bounds the ore on the northern edge of the principal excavation. Here there is a mine shaft 180 feet deep * * *. The shaft enters the 

limestone at a depth of 50 feet, and a boring 20 feet from the bottom of the 

shaft is still in this rock.

A dike of trap rock cuts the ore-bearing strata near the southern side of the 

pit and produces, phenomena precisely identical with those caused by the trap 

dikes in the Cornwall-Lebanon mines, converting the ore to a more highly 

crystalline form and endowing it partially with magnetism. As in every such 

instance, the ore is richest and purest adjacent to the trap rock. This is 

equally the case in the southern or smaller mine. The strata dip N. 30° W. 

at about 20°; and in the northern bank of the large mine we may perceive the 

Auroral limestone regularly overlying the upper beds of the Primal slate, containing or consisting of the ore. * * * In this mine, as in that of Cornwall 

and that'of Lebanon, some of the ore contains a small amount of copper.

FIG. 11. East-west structure section, Jones mine (along line A.-E, PI. XVIII).

A large-scale topographic map of the vicinity of the mines by J. H. 

Harden (reproduced here as PL XVIII) accompanies the report by 

D'lnvilliers on the geology of Berks County, but no description of 

the mine is given in the text. However, something of the geology and 

structure of the mines is indicated in cross sections which accompany 

the map. These data have been used in constructing the revised cross 

sections here given (figs. 11,12, and 13).

The Jones mine and the smaller Kinney mine adjacent lie in the 

isolated area of Paleozoic limy strata, which are supposed to belong 

near the base of limestone " No. II " of the Pennsylvania section. As 

at Boyertown and Cornwall, there is apparently interbedding of limestone and limy shale, the latter being largely changed to ore, while the 

former exhibits a very moderate degree of metamorphism. Though 

the pit is now flooded, it is known from dips recorded on the Harden 

map that in the Jones workings the ore strata are considerably cona Geology of Pennsylvania, vol. 1, 1858, p. 182,
BULLETIN NO. 359 PL.XVII

Mesozoic rocks Paleozoic limestone Quartzite

(Paleozoic except near mine, at this 

point probably metamorphosed Mesozoic

Diabase Gneiss

SKETCH MAP SHOWING GEOLOGY IN VICINITY OF JONES AND WARWICK MINES, BERKS AND CHESTER COUNTIES, PA.
BERKS COUNTY DEPOSITS. 67

torted, the general direction of dip, however, being 

toward the west-northwest. In the northern pit 

the ore. dips 16° N. 55° W. "Above the ore is a 

limestone bed conformable to it, about 12 to 15 feet 

thick, and above that still is a conformable lightgreen earthy shale." a

The ore-bearing strata are overlapped on the 

north by reddish Mesozoic conglomerate, containing large quartzite pebbles. East of the large 

mine the nature of the -bed rock can not be determined, but presumably the limy strata run put 

for several miles in this direction. On the State 

Survey geologic map of Berks County the " No. 

II " limestone is represented as a narrow strip extending through the Jones mine toward the eastnortheast as far as Hopewell furnace, and though 

no outcrops are to be found it is very likely that 

these strata underlie the accumulation of surface 

debris along the topographic depression which 

separates the red conglomerate and sandstone hills 

on the north from the quartzite hills on the 

south.

Two bodies of diabase occur on the south side of 

the Jones pit and are exposed along the edge of 

the excavation. Between them are limy strata in 

the southwest corner of the pit, and these beds probably extend through to the Kinney mine. South 

of the Kinney pit quartzite fragments occur in 

the soil, and near the railroad crossing this rock 

may be seen in place. It is not known whether the 

quartzite belongs to the Mesozoic or to the Paleozoic " No. I " sandstone. .The area which it occupies is limited on the west and east by the masses 

of diabase. The western mass is exposed along 

the railroad for about one-half mile; the other 

may be traced eastward to the falls of French 

Creek and for several miles beyond. The mass of 

diabase represented on the Berks County, map just 

north of Joanna station was not visited by the 

writer. Several minor masses of diabase, dividing the ore, were encountered in the mine workings. The sketch map (PI. XVII) shows the 

distribution of the,various rocks in the vicinity of 

the Jones and Warwick mines.

(/>

"Willis, Bailey,. Tenth Census, vol. 15, 1886, p. 225.
68 MAGNETITE DEPOSITS IN PENNSYLVANIA.

The iron minerals of the Jones ore are magnetite and pyrite, and 

some of the ore contains chalcopyrite. In the richer material the 

magnetite and pyrite occur in more or less crystalline form, accompanied by calcite or dolomite, the whole forming a rather granular 

aggregate. Such ore does not betray its origin; but lean material, of 

which there is a great amount on the old dumps, shows clearly that 

the iron minerals have been formed by a chemical substitution or 

replacement of limy strata. Blocks may be seen showing all degrees 

of replacement and still retaining their stratification. Brecciation 

and cross veining, which are noteworthy features at Cornwall, are 

not observed in the material from the Jones mine. As at Cornwall, 

chlorite'is an abundant mineral in the waste, but only minor amounts 

of this mineral occur in the usable ore. A few blocks of limestone 

containing small garnets were noted.

The important role of the intrusive diabase as an element in the 

local geology is shown by the extent of the rocks indicated on the 

geologic sketch map (PL XVII). The writer believes that the segregation of the ore resulted from the intrusion of this rock, though 

evidence sufficient to establish this theory has not been found. That

ore minerals were being deposited after the diabase had 

been injected is indicated by 

the presence of magnetite, 

pyrite, calcite, and chlorite in

FIG. 13. East-west structure section, Kinney Cracks in the igneOUS rock and

mine (along line E-F, PI. xviii). entirely surrounding fragments 

of it. Blocks showing these relations, which presumably came from 

one of the minor masses of diabase encountered in the workings, 

were found near the engine house, on the north side of the Jones mine.

From existing descriptions it appears that the overlapping Mesozoic strata are separated from the ore body by barren shale and limestone, a relation which makes it difficult to.believe that the leaching 

of these ferruginous sediments could have furnished the iron for this 

large ore body and which leaves the way open for the suggestion that 

the diabase was the source of the mineralizing waters and of the iron 

that they contained.

The discussion of the possible occurrence of -other ore deposits in 

the vicinity will be deferred until the detailed geologic map of the 

district is available. Professor Bascom, of Bryn Mawr College, is 

now engaged in studying the geology of the Honeybrook quadrangle, 

in which the mines are situated.

The following note is copied from Frazer:.°

On the lands of the Warwick reserve, 2 miles southeast of the Joanna furnace 

and about li miles east of Morgantown and \ mile south of the narrow belt of

o Frazer, Persifor, jr., Second Geol. Survey Pennsylvania, Kept, CCC, 1877, p. 237.
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. XVIII

TOPOGRAPHIC MAP OF VICINITY OF JONES AND KINNEY MINES, BERKS COUNTY. PA.
BERKS COUNTY DEPOSITS. 69

limestone which leaves the large Lancaster limestone tract and passes through 

Morgantown, * * * in Berks County, is an exploitation for ore. * * * 

The material thrown out of the pit appears to be an altered mud rock, alongside of which occurs ore very like that of Cornwall and some of that from 

Dillsburg.

WARWICK MINE.

The old workings of the Chester County Warwick mine are situated just east of Warwick, formerly known as St. Marys. (See PL 

XVII.) The deposit appears to have been nearly exhausted prior 

to 1875, although there was some mining as late as 1882. Little can 

be made out by an examination of the ground at the present time, but 

such features as can be observed correspond with the following description published by H. D. Rogers in 1858: °

This extensive and interesting body of iron ore, situated just southeast of 

St. Mary's Episcopal Church, is in reality not a genuine lode or igneous intrusive vein, though the ore derives some of its characters from intrusive igneous 

action, but it is a bed or deposit at the base or very near the base of the middle 

secondary red sandstone, which here laps upon the gneiss. The explored extent 

of this bed, hitherto penetrated only near its outcrop, or where the overlying

FIG'. 14. Structure section at Warwick mine, Chester County.

1, Diabase; 2, gneiss.

After H. D. Rogers.

strata are shallow, is already very great, amounting to many acres. The ore 

deposit observes everywhere a very gentle dip, and seems to undulate in two 

or three waves across the tract which includes it. A somewhat conspicuous 

anticlinal change in the dip occurs to the south and southwest of the present 

main engine shaft by which the mines are dried, and there is every indication 

that the ore basins are both south and north of this saddle. Though the basin 

to the'south of it is intersected, and the ore in one place cut off or thrown out 

to the surface by the intrusion of a wide dike of trap rock, there is strong 

reason to infer that the ore occupies a comparatively wide though perhaps 

shallow basin, north and northeast of the engine shaft [fig. 14].

Besides this intrusion of trap, there seems to exist here injections of serpentine and other mineral matters, and at one point, just by the southwest margin 

of the ore bed, there exists a very singular intrusion of mineral matter penetrating the ore and altering, in a remarkable manner, the conglomeratic layers 

which here constitute the southeast border of the red sandstone formation, 

This rock is greatly baked and changed in aspect, includes numerous spheroidal 

bunches of segregated crystalline mineral matters (some of them in the form 

of hollow geodes), and is intersected besides with numerous strings, or little 

veins. In these spheroidal nests occur beautiful linings of crystallized epidote 

and other minerals, and bunches of large crystals of the fine variety of garnet 

called meleuite. The list of the minerals occurring here is not extensive. The

a Geology of Pennsylvania, vol. 2, 1858, pp. 708-709.
70 MAGNETITE DEPOSITS IN PENNSYLVANIA.

conditions under which they present themselves are such as strongly to impress 

the geological observer with the notion of their having been introduced chiefly 

in a vaporous state, or by sublimation, for in many of these hollow spheroids 

we can detect no connection whatever between the interior or even the exterior 

walls of the geodes and any external veins or filaments of injected matter, such 

as any other theory would demand for the introduction of the materials of the 

crystalline minerals here so curiously insulated.

The bed of iron ore for which this locality is chiefly noted is of very variable 

thickness, fluctuating from 1 or 2 to 9 or even 17 feet. As illustrating the 

general levelness of this undulating deposit, it may be stated that in no place 

has it been required to sink deeper than about 60 feet to reach the ore, while 

generally the covering is so thin that the ore is conveniently procured by merely 

stripping off a thickness of a few feet or yards of loose disintegrated rock. The 

average richness of this ore may be stated at about 45 per cent of metallic 

iron, though much of it exceeds 50 per cent. It is somewhat sulphurous; and 

when care is not employed in selecting it for smelting, and in the after 

processes, it tends to produce a hot-short or red-short iron, but when carefully 

manufactured it yields an excellent metal. The annual product of the Warwick 

iron mines for fifteen years was not less than 4,000 tons, and the average yield 

for the past twenty years has been 6,000 tons. In the year 1853 the amount 

mined reached 12,000 tons. These ore pits have been wrought for the last one 

hundred and twenty years, and there would seem to be at present really more 

ore within sight than there has ever been before at any one time. The present 

average cost of mining this ore is about $1.50 per ton. * * *

This ore is intermediate in its physical characters and aspect between the 

true brown hematite and the magnetic oxide of iron. As, on the' view of its 

having been originally hematite but subsequently altered by igneous action, we 

might naturally anticipate, those portions of it which have undergone the highest degree of metamorphic influence are of a gray'color, quite crystalline,, and 

partially endowed with magnetic force, whereas the less altered parts are nearly 

in the condition of a compact, closely cemented hematite. Minutely interstratified with this ore there occurs more or less earthy matter, apparently laminae 

of indurated slate or shale; and when the layers of this rock are thick, and they 

disperse the ore, they interfere materially with the economical prosecution of 

the mine. This slaty or earthy matter tends, furthermore, by intimately mixing 

itself in with the finer granular ore, seriously to reduce the richness of the 

mingled mass in iron.

Specimens of the metamorphosed conglomerate described by Rogers 

may be found in the old mine pits. Green hornblende and brown 

garnet, calcite, pyrite, specular hematite, and magnetite are among 

the secondary minerals observed. Epiclote was not noted. No geologist familiar with the common metamorphic alterations of sedimentary rocks adjacent to intrusive igneous masses can see this 

material without regarding it as a product of contact metamorphism 

involving the action of heated water. In the writer's opinion the 

features of the ore specimens which have been examined do not suggest that the magnetite of the Warwick deposit has been produced 

from brown hematite by heat metamorphism, as proposed by Rogers, 

but it seems that hematite, magnetite, and pyrite must have been 

introduced into their present situation and must have been formed 

contemporaneously.
YORK COUNTY DEPOSITS. Tl

In conformity with the general theory concerning the origin of 

other deposits of the Corn Avail type, it is suggested that'the ore minerals were introduced by'solutions sent into circulation by the intrusive diabase that occurs north of the mines. This view is justified 

by the baked condition of the M.esozoic .strata throughout the strip 

whiclj lies south of the diabase mass and by the observed alteration 

of the conglomerate rock, so well described by Rogers. There is no 

evidence to show whether the iron was leached out of the Mesozoic 

strata or was furnished by the igneous rock.

The geologic relations observed at the Warwick mines continue for 

some distance both east and west. It is thought not improbable that 

similar ore deposits may exist at other points, between the east-west 

mass of diabase and the south edge of the Mesozoic strip which marks 

the overlap of the sandstone upon the ancient gneisses. Bodies of 

iron ore may lie in a position similar to that of the Warwick deposit 

and still not extend far enough south to have been brought to light 

along the edge of the Mesozoic strip. If erosion had been only 

slightly less than what is actually observed in the neighborhood of 

the old mines the edge of the ore deposit would not have been stripped 

of its cover and would not have been discovered except by some 

chance excavation of considerable .depth. On the other hand, the 

removal of a little more cover elsewhere along the line of overlap 

might .have revealed deposits similarly situated, of which, under existing conditions, there are no surface indications. Although it is 

regarded as possible that systematic drilling might lead to the discovery of new ore deposits in the ground indicated, the undertaking of 

such extensive explorations as \vould be required can hardly be recommended as a business venture at the present time.

About 2|- miles east of the Warwick mines and just north of 

Knauertown indications of iron ore were prospected many years ago. 

The geologic position is identical with that of the Warwick deposit. 

' On the basis of the theory that the mass of diabase which lies north 

of this place has been the inciting cause of the deposition of iron minerals, it is not unreasonable to expect that these indications may lead 

to a better deposit of ore at a greater depth beneath the hill.

YORK COUNTY DEPOSITS.

GENERAL STATEMENT.

Iron ores like those of the Cornwall mines occur at several localities in northern York County. The principal group of mines is situated about 1 mile east of Dillsburg, and a second smaller group is 

located just south of Yellow Breeches Creek near Grantham crossing, 

on the Philadelphia and Reading Railroad. Specular hematite with 

some associated magnetite has been worked at Minebank schoolhouse,
72 MAGNETITE DEPOSITS IN PENNSYLVANIA.

about 2 miles southwest of Wellsville, and minor pockets and indications of ore have been found at various other localities. Most of 

these occurrences had been discovered prior to 1873 and are described 

or mentioned in Report CC of the Second Geological Survey of 

Pennsylvania a and in .the Annual Report for 1886. 6

In 1907, Avhen the writer visited the field, no mining was being 

done, so that such data as could be collected concerning these interesting deposits have been procured from examinations of the surface 

and from conversation with persons familiar with the underground 

operations. Since the publication of the reports mentioned above 

only two new mines have been opened, but considerable ore has been 

taken from several of the old ones.

Two opinions have been expressed in published descriptions regarding the geologic position of the Dillsburg deposits. They have 

been held on the one hand to lie in Mesozoic rocks and on the other to 

occur in Paleozoic strata, as at Cornwall. Detailed study of the general region now shows that all the deposits are inclosed by the younger 

set of rocks, as stated by D'lnvilliers.

The Grantham mines lie very near the edge of the Mesozoic area; 

those of the Dillsburg group are situated from 1^ to 2^ miles within 

the northwest boundary, and the mine southwest of Wellsville lies 6£ 

miles within the Mesozoic belt. (See PI. XIX.) No bodies of ore 

and no strong indications of ore occurrence have been found except 

where the strata have been greatly metamorphosed or baked in proximity to intrusive masses of diabase. This association points definitely, as do all other occurrences of iron ore of the Cornwall type, to 

the belief that the ores are connected in origin with the intrusion of 

the diabase. However, the mere presence of diabase in a locality is 

by no means sufficient to insure the presence of ore near by; otherwise, 

York County would be unsurpassed as an ore field because of the 

great extent of the diabase masses within her borders. The scattered 

or limited occurrence of ore deposits points to a second condition as 

essential to the formation 'of ore, and it is believed that this condition 

is the presence of calcareous (or lime-bearing) rocks in the vicinity 

of intrusive masses of diabase. In all the more important mines of 

the Dillsburg group and at Grantham beds of limestone conglomerate 

are found in the workings. At Minebank, also, crystallized limestone 

is to be found in the mine waste. At Dillsburg many pockets of ore 

which were mined out years ago and one bed continuous for nearly 

500 feet at the surface (McCormick long cut) appear to have been 

inclosed in baked sandstone. Though there is now no evidence that 

limestone occurs in these workings, it is possible that the masses of

0 Frazer, Persifor, jr., Report of progress in the counties of York, Adams, Cumberland, and Franklin. 1877, pp. 201-230.

6 Ann. Kept. Geol. Survey Pennsylvania for 1886, pt. 4, 1887, pp. 1501-1514.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. XIX

^T 4* 4""4-u1f\ *^

4. 4- 4 44- -

h T T »" ' -V T-j~= --=Jp____"t'_'_-^-" / *l ' ' ", * ' ' ' "^

44 44 4 4 ' 4 «V" ~47~4Nv£{;4 4 fr. 4 4 4 4 

4 4 + 4 4 4 4 4)W----^ //^,| 44 44-44 

,44444 4 4 //4 -+ 

4 I'-r ^ 4 4 4 4 4-y4*- j>_

 //j; 44+4 + f_.±^/+ + +'.

4 4 4 4 4 4 4 4

+ 4\4 +)lr 4 4 4x^4- 4+4

,Ttt T 1- 1- T 1- 1

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4 miles

Mesozpic red sandstones 

and shales

Diabase Mines and prospects . 

GEOLOGIC SKETCH MAP OF MESOZOIC AREA NEAR DILLSBURG, YORK COUNTY, PA.

Limestone conglomerate 

(ITits roek occurs in 

several of the mines}
YOBK COUNTY .DEPOSITS. 73

ore represent original bodies of limestone conglomerate which have 

been converted into iron' ore by chemical replacement.

In the vicinity of the Dillsburg mines there are no natural exposures of limestone conglomerate and only along the Philadelphia 

and Reading tracks near Grantham can this rock be seen at the surface near known ore bodies. In drill holes near the old McCormick 

workings at Dillsburg the occurrence of limestone has been recorded.

Exposures of rock in place in this region are very few in number, 

but the distribution of the diabase and of the Mesozoic rocks as a 

whole can be recognized from the presence of residual bowlders or 

broken fragments in the soil. It is not possible, however, to decipher 

any. details concerning the make-up of the sedimentary formation. 

It is supposed that there may be several beds of limestone conglomerate separated from each other by sandstone and shales, but only the 

presence of the latter can be ascertained from inspection of the soil. 

Everywhere the materials of the surface debris show evidence of the 

baking which the rocks have undergone. The absence in the vicinity 

of the mines of fragments from the limestone conglomerate is no 

doubt due to the great solubility of this rock compared with the overwash of the more resistant baked sandstone fragments.

Limestone conglomerate outcrops at several places west and southwest of Dillsburg, showing that here it is an important element in 

the constitution of the Mesozoic formation. In the foothills of South 

Mountain, northwest of Beavertown, fully 50 feet of the rock is exposed in a large quarry. This quarry has been opened around a 

sink hole, into which a small brook disappears. A series of sinks 

may be followed from this place for nearly a mile toward the northeast. Though the sink holes suggest that the conglomerate continues 

as the bed rock in this direction there are no exposures, because of the 

heavy over-wash derived from the mountain slope, and it is possible 

that a strip of the Paleozoic limestone sets in between the quartzites 

of South Mountain and the Mesozoic beds, which lie to the east. In 

this situation either the limestone conglomerate or the older limestone would be liable to contain underground watercourses and to 

give rise to the observed sinks. At a .quarry on the west side of the 

York Springs road, about 1 mile from Dillsburg, 12 or 15 feet of 

conglomerate are seen lying between a stratum of red sandy shale, 

and massive beds of metamorphosed conglomerate may be seen a 

mile southwest of this quarry, at the eastern base of the diabase hill, 

along an abandoned railroad grade. The same rock is said to have 

been found in several dug wells in the northern and western parts 

of Dillsburg. A drilled well at the creamery penetrated 80 feet of 

conglomerate, and at this depth encountered an open cavity. This 

well overflows during wet seasons. The only exposure noted within 

the borough limits is just south of the mine railroad at the eastern-
Y4 MAGNETITE DEPOSITS IN PENNSYLVANIA.

most street crossing. The occurrences which have been mentioned 

strongly suggest that west of Dillsburg the 'broad valley, occupied by 

Dogwood Run and its southern tributaries is underlain by limestone 

conglomerate. It seems probable also that beds of the same rock are 

present beneath the meadows east of Dillsburg, between the town and 

the mines. This is suspected because the conglomerate is known to 

occur both east and west of the flat, and because the presence of this 

soluble rock would be a favorable condition for the development of 

just such a broad basin as exists.

It may be mentioned incidentally that the presence in the soil of 

debris derived from the-South Mountain rocks shows that Dogwood 

Run formerly flowed across this depression and joined Yellow 

Breeches Creek by way of Fishers Run.

The geologic sketch map (PL XIX) shows the general position of 

the boundary between the Mesozoic area and the older formations of 

South Mountain, and also the approximate distribution of the diabase intrusions in the Dillsburg region. The close association of the 

ore with the masses of igneous rock is well brought out by the indicated positions of the mines and prospects of the district.

DILLSBURG MINES. 

INTRODUCTION.

The Dillsburg ore field has a greater extent than any of the other 

districts which furnish ore of the Cornwall type. Ore has been taken 

from more than 30 openings, including open pits and underground 

mines, and these workings are distributed over a zone nearly 1^ miles 

long and from one-fourth to one-half mile wide.

The animal output of the Dillsburg mines has never been large and 

the aggregate of the ore shipped is probably less than 1,500,000 tons, 

the period of production having been about sixty years. The ores 

have not been in general or constant demand, mainly because they 

are high in sulphur, but also because their iron content is low in comparison 'with that of Lake ores. They compare favorably, however, 

with the Cornwall ore, the use of which has been on the increase for 

many y'ears. Like the Cornwall ore they must be roasted before 

going to the blast furnace, except when they are mixed in rather small 

proportions with other ores. The fact that the Dillsburg ore has 

found even a limited market at various times during the last twenty 

years is sufficient ground for believing that if the mines can be shown 

to be capable of further output no serious difficulty need be expected 

in disposing of the product. The mines have been worked mainly 

by individual owners and lessees without sufficient capital to carry 

development far enough ahead of extraction to justify "operation on 

a large scale. Could the ore fields be brought under the control of
U. S. GEOLOGICAL SURVEY BULLETIN NO. 359 PL. XX

t. LOGAN

2. COX

3. PRICE

4. GROVE

s. BELL

6. KING

7. JAUSS

7a. ALTLAND

8. SMYSER

9. UNDERWOOD

10. LONGNECKER

11. MCCORMICK

Mesozoic sandstones and shales Diabase 

with local beds of limestone conglomerate 

1000 o 1000 2000 feet

Contour interval 10 feet

GEOLOGIC AND TOPOGRAPHIC MAP OF DILLSBURG ORE FIELDS

1908
YOBE; COUNTY DEPOSITS. 75

interests strong enough to explore the deposits adequately and, if preliminary work should warrant, to develop them on a large scale, it 

seems likely that they might be brought, again into successful operation. Even a moderate tonnage, if assured for a period of years, 

might warrant the maintenance of roasting furnaces, or, what might 

prove more advantageous, the installation of some concentrating 

process to raise the grade of the ore as it comes from the mine. Geologic considerations favor the persistence of the deposits in depth arid 

point to the probability that ore bodies in addition to those IIOAV 

knoAvn might be discovered by systematic prospecting.

It is hoped that the present description and the geologic map of 

the district (PI. XX) that has been prepared may aid in the future 

development of the deposits.

DESCRIPTIONS OF MINES.

Logan mine. The shaft of the Logan mine, Avhich is the most recent opening in the district, is located about 200 feet north of the 

Avagon road leading from Dillsburg to StevenstoAvn. It is situated 

just within the outcrop of a diabase sill about 200 feet Avide, which 

crosses the road east of the forks. Mr. Logan, the owner of the 

property, Avas encouraged to open at this place through having observed a strong magnetic attraction determined with a dipping 

needle. The bottom of the diabase is evidently inclined toward the 

north at a IOAV angle, for it is said to have been penetrated at a depth 

of 32 feet. Mr. Logan reports that 7 feet of ore was encountered 

just under the diabase, and that the floor is'limestone conglomerate. 

The ore bed and the inclosing rocks dip toward the north. The 

mine Avas operated for a short time only, so that the extent of the ore 

body is not knoAvn.

North of the shaft the surface slopes gently toward a small stream 

fed by a spring between the tAVO forks of the wagon road. Sandstone fragments observed along the depression occupied by this stream 

indicate the presence of a strip of sedimentary rock, which, as it is 

traced toAvard the east, curves to the south and crosses the right-hand 

road just Avest of the church. It is thought that this band of sandstone may run doAvn the ravine and across Fishers Run to join a 

similar band AAT hich sets in from the Avest, but this connection can not 

be established from observation. North of the sedimentary strip 

diabase appears at the surface and continues Avithout interruption to 

the vicinity of the Jauss and King mines.

South of the diabase intrusion penetrated by the Logan shaft there 

is a considerable strip of sedimentary rock, beyond Avhich appears 

another somewhat wider diabase band. These tAvo masses of diabase 

come together southeast of the mine. Still farther south there is yet 

another band of sedimentary.rock, and beyond this is the large mass
76 MAGNETITE DEPOSITS I3ST PENNSYLVANIA.

of diabase forming the group of hills south and east of Stevenstown. 

As already noted, this diabase extends westward to Dillsburg.

Inasmuch as limestone conglomerate occurs at the old Price pit, 

and also in the Logan mine 1,300 feet to the east, there is reason 

to believe that the mass of diabase which lies immediately north of 

both mines is a sill conforming more or less closely with the stratification of the sedimentary rock into which it has been injected. The 

limestone conglomerate dissolves under the action of the weather, so 

that its presence can not be determined by inspection of the surface 

debris. It is very likely that it extends along the contact with the 

diabase between the Logan and Cox openings, and west of the Price 

pit, perhaps as far as the next north-south wagon road. There is 

nothing to suggest how far it may extend toward the east and southeast beneath the diabase sill.

The masses of diabase occurring south of the Logan mine are probably sills, and other beds of conglomerate may be associated with 

them. If this is the case, it seems very likely that other ore deposits 

may be present in the country south of the Price, Cox, and Logan 

mines. Though it may be suggested that surface indications should 

betray the presence of any considerable deposit of ore in this part of 

the district, the surface debris is here apparently so thick and so 

liable to have moved for some distance that the weathered portions 

of ore beds might very well have been entirely covered. This is 

particularly true of the strip of sedimentary rocks which lies north of 

the Logan shaft. Both sides of this strip would seem to offer likely 

situations for the occurrence of iron-ore deposits. The Logan ore 

was discovered by means of the dipping needle. This instrument may 

prove of value in further exploration of this ground.

Cox mine. The Cox mine is situated about 950 feet west of the

Logan shaft, just south of the same diabase sill. The mine was in operation when the Dillsburg field was visited by D'lnvilliers, whose 

report ° may be summarized as follows:

At the Cox mine, on the Price farm, the engine house is situated 

just north of the public road. The ore bed'is mined by means of a 

slope about 300 feet long on a bed of magnetic ore dipping about 25° 

a little west of north. Near by is an abandoned slope descending 

nearly due north for 280 feet, and in a shaft 125 feet north of the 

engine house the ore bed was struck near this slope at a depth of 

about 40 feet. The ore so far as developed seems to lie in a deposit 

shaped like a shell, the top and bottom of the shell coming together 

and pinching out the ore on all sides along the strike, as well as along 

the dip. The average thickness of the bed is 5^ to 6 feet, though in 

places it swells to 9 feet. ' Generally it has a gray dolerite trap for a 

hanging wall and a sandy bastard limestone for a foot Avail; but

0 Ann. Kept. Geol. Survey Pennsylvania for 1886, pt. 4, p. 1504.
YOEK COUNTY DEPOSITS. 77

there seems to be no very persistent character for either. The western side of the deposit is more mixed in character than the eastern, 

and in places the trap wall seems to stand almost vertical, squeezing 

the ore into a narrow compass. The foot wall in many places appears more like white baked slate rock than like limestone, but contains some lime. In April, 1887, ore was being mined at the rate of 

25 tons per day.

West of the slope a small open cut exhibits a bed of rather sandy 

ore, from which perhaps 200 tons have been taken.

Price mine. A large pit situated about 250 feet west of the Cox 

slope is known as the Price mine. The mine is said to have been 

opened about 1855 and the ore is reported to have been 6 feet thick. 

Fragments of limestone conglomerate may be seen in a small pile of 

waste in the pit. The edge of the diabase sill passes just north of 

the pit and the dip of the rocks is evidently toward the north, as at

the Logan shaft and Cox slope. Instead of being in actual contact 

with the diabase the ore body appears to have been separated from 

the mass of igneous rock by. intervening beds of sedimentary rock. 

The sedimentary area between the two sills of diabase is much narrower in the vicinity of the Price mine than farther east. The 

southern sill comes to a blunt termination in the field northwest of 

and across the road from the schoolhouse.

Grove mine. About 1,400 feet due west of the Price pit is the mouth 

of the Grove slope, which was opened in 1873. The dip of the rocks 

is given in Report CC as 24° N. 10° E. Though rock resembling 

weathered trap is said to occur at the mouth of the slope, the present 

writer was not able to find any evidence of other material than sandstone and shale in the vicinity. In the wagon road north of the 

opening exposures of baked, shale are to be seen dipping about 20° N.

About 400 feet south of the slope is an old excavation, doubtless an 

ore pit, but no information'has been procured concerning what was 

found at this place or when the opening was made. The edge of the 

east-west diabase mass passes about 300 feet south of the pit.

Prospects near the Price farmhouse. Mr. Logan, the present owner 

of the Price farm, states that a bore hole put down in the .swamp east 

of the farmhouse encountered ore at a.depth of 75 feet. This hole appears to have been located north of the boundary of the main mass 

of diabase, and the ore probably lies on the under contact of the intrusive rock. Inspection of the geologic map will show the position 

of this occurrence with reference to the strip of sedimentary rock 

occurring north of the Logan mine. It seems that if the diabase contact follows the stratification in this vicinity ore may occur to the east 

as Avell as near the Price house, although, as stated previously, the 

continuity of the sedimentary strip across the creek is not proved.
78 MAGNETITE DEPOSITS IN PENNSYLVANIA.

Indications of ore have been found 700 feet northwest of the farmhouse, just at the edge of the diabase, where the boundary curves 

toward the north. No other signs of ore are known to have been 

found between this point and the Bell mine.

Bell mine. The Bell mine, which was opened in 1875, is situated 

about midway between the Price pit and the Underwood group of 

workings. It was last worked about 1902, at which time the pillars 

of ore were robbed and the mine finally abandoned. From a statement 

by Frazer a that bowlders of hard limestone were encountered in the 

upper 25 feet of the discovery shaft just north of the entrance to the 

working slope, it is judged that the ore lies beneath limestone conglomerate. This suggestion is corroborated by the presence of conglomerate .in the mine waste, but there can be little doubt that the 

mass of diabase lies at no great distance above the ore body.

FIG. 15. Plan and sections of Bell mine, near Dillsburg. From Ann. Kept. Pennsylvania Geol. Survey for 1885, p. 566.

The mine was worked by a slope a short .distance south of the main 

diabase area. The course of the slope is N. 10° E. and its inclination 

is said to be about 20°, though the cross section given in fig. 15 indicates a lower angle of inclination. In 1883 the slope was about 875 

feet long, but it was afterward extended 200 feet or more. The ore 

body is said to have had the form of a rather well-defined shoot f ollowing the dip of the inclosing strata, but limited on both sides along 

the strike. The maximum width is stated by D'lnvilliers & to have 

been 60 feet, and at 875 feet from the mouth of the slope the bed was 

10 to 12 feet thick. In fig. 15 the ore is shown to be cut out on the 

east by diabase (see PL, XX), and from the relations shown it may

"Frazer, Persifor, jr., Second Geol. Survey Pennsylvania, Rept.. CC, 1877, p. 218, 

"Ann. Kept, Geol, Survey Pennsylvania, pt. 4, for 1886, 1887, p. 1505,
YORK COUNTY DEPOSITS. 79

.4- ..+

though

bearing stratum

FIG. 16. Surface plan at Bell mine, near Dillsburg, 

showing probable structure.

This point may be worthy of investibe that the ore body occurs adjacent to a roll in the bottom of the 

diabase mass where this rock locally cuts across the strata (fig. 16). 

The course of the diabase boundary at the surface is favorable to 

this sugge'stion.

If the suggested structure is borne out by the facts, it is not likely 

that other ore bodies exist 

toward the east, where diabase would be encountered, 

nor toA\7 ard the west, where, 

present, the oreis probably .not mineralized.

Although it is reported 

that the bottom of the 

slope is not in ore, it niay

be that one of the sides of 

the shoot has been encountered rather than its bottom, 

gation at some future time.

When the mine was abandoned the slope was 1,100 feet in length. 

About 200 feet south of the Bell slope is an old slope stated by 

Frazer a to have been 180 feet long. From a point 125 feet down the

slope there is a 50-foot drift to the east, 

and from the bottom another 75 feet 

long to the west. Exposures at the 

.mouth of the slope show fine-grained 

sandstone as the hanging wall. The 

nearest diabase is that of the main mass, 

the edge of which lies about 100 feet to 

the northeast.

King and Jauss mines. The King 

mine is situated on the east side of 

Fishers Run, about 3,300 feet north of 

the Price mine and 2,100 feet northeast 

of the Bell slope. The Jauss shaft 

(fig. 17) is situated near the east bank 

of the creek, .750 feet northwest of the 

King workings. The shafts of these 

two eastern mines were located by dipneedle indications. They were started in diabase, but at moderate 

depth both encountered ore associated with sedimentary rocks/ The 

strata dip toward the north, so that it would appear that they must 

come to the surface south of the shafts. Nevertheless, the presence of 

these sediments would not be suspected from examination of the sur50 o_____SO_____loofeet

FIG. 17. Survey of workings at 

Jauss mine, near Dillsburg, made 

in 1888.

<* Frazer, Persifor, jr., Second Geol. Survey Pennsylvania, Kept. CC, 1877, p. 218.
80 MAGNETITE DEPOSITS IN PENNSYLVANIA.

.face, because their outcrop is obscured-by an over wash of diabase soil. 

Just north of the railroad track, however, on the west side of the creek 

and about 800 feet from the Jauss shaft, a patch of sediments may be 

inferred from the occurrence of sandstone fragments in the soil. It 

seems probable that these two masses of sedimentary rock may be connected, but the surface is covered to such an extent that nothing positive can be made out. It is entirely possible also that the sediments 

of the western patch may extend farther west than is indicated on 

the map (PL XX), for in this direction there is a broad swale in 

\vhich the presence of diabase soil may be misleading as to the actual 

extent of the intrusive rock. The trend of the two sedimentary strips 

is in the direction of the Longnecker shaft on the west and toward 

an embayment in the outer boundary of the diabase area on the east. 

Along this general line the main mass of diabase is seen to be partly 

divided by intercalated sandstones and shales. Whether this separation becomes more or less extensive in depth can not be judged, but 

from the fact that in the Longnecker workings the bedded rocks apz'oofeet 

FIG. 18. General -structure section at Jauss mine, near Dillsburg (along line A-B, fig. 17).

pear to rise to a crest beneath the diabase, it seems possible that the 

dividing masses may extend farther along the strike underground 

than is apparent from surface indications, and that they may even 

connect with one another.

It might be worth while to explore the western patch of sedimentary rocks mentioned above. If this is ever done it may be assumed 

that the northern contact with the diabase dips, toward the north, as 

at the Jauss mine. On this basis the. best scheme for proving the 

ground would be to sink shafts or bore holes just within the diabase 

area in order to catch the contact on the dip. The lower contact of 

the bedded tfocks might also be explored both in this vicinity and 

south of the Jauss mihe. A cross section showing the supposed structural relations in the vicinity of the Jauss mine is given in fig. 18. It 

is supposed that a section through the western sedimentary patch 

would be very similar,
YOKK COUNTY DEPOSITS. 81

The following notes concerning the King mine are abstracted from 

Frazer: a

The shaft, which was sunk in 1876, passes through 23 feet of soil 

and diabase, beneath which there was 9 feet of ore. Toward the east 

a drift 20 feet long encountered an oblique wall of diabase on the 

south side. Between this wall and indurated sandstones on the north 

the ore formed a wedge-shaped mass. From the end of this 20-foot 

drift a slope was opened upward until clay was encountered. The. 

course of this slope (N. 3° E.) and its angle of inclination (22°) give 

the apparent direction and amount of the dip of the ore bed. From 

the bottom of the slope a drift was run N. 5° E. for a distance of 50 

feet, following a fault showing slickensides. Along this gangway the 

fault rock is a broken-up mixture of sandstone and trap rock. About 

20 feet east of the slope indurated sandstone exhibits a dip of .23° 

in a direction N. 40° W., but the dip of the vein is reported to be 

N. 10° W.

The Jauss shaft is situated just west of Fishers Run, at the eastern 

terminus of the branch railroad. The shaft was sunk at a point 

where the dip needle showed a marked magnetic attraction. About 

.72 feet of diabase was penetrated before the 7-foot ore bed was encountered. The floor of the mine is limestone.conglomerate." As 

depth was gained the ore bed was found to thicken along tke dip, and 

in the lowest A\7 orkings, 205 feet below the surface, a .large body of ore 

is reported. Stoping was carried about 30 feet above the point where 

the ore was cut through by the shaft. A survey made in 1888 shows 

the mine workings as extending 270 feet northwest of the shaft. In 

this distance the ore bed falls 133 feet, giving an average inclination 

of nearly 50 feet per 100, or about 30°. The dip appears to be someAvhat steeper in the lower than in the upper workings.

Material on the waste pile shows that some of the ore at least has 

been formed by replacement of limestone conglomerate, though most 

of the material intimately associated with the ore is a light-green rock 

which appears to be an altered shale. Although no fragments of any 

rock except diabase are to be seen in the field south of the shaft, there 

can be little doubt that the sedimentary rocks which accompany the 

ore would be found beneath a relatively shallow cover of soil. On the 

geologic map (PI. XX) a strip of sediments is indicated as extending 

southeast to the King mine.

Altland mine. Just where the switch of the Bell mine joins the 

main track there are three shafts, two north and one south of the railroad. These constitute the Altland mine, concerning which the notes 

in the following paragraph are condensed from the description by 

D'lnvilliers: b_________________________

0 Frazer, Persifor, jr., op. ctt, p. 21.2.

"Ann. Kept. Gcol. Survey Pennsylvania for 1886, pt. 4, 1887, pp. 150G-1507.

54370 Bull. 359 08 6
82 MAGNETITE DEPOSITS IN PENNSYLVANIA.

This mine lies northwest of the Bell- mine and is opened by a shaft 

62 feet deep, from the bottom of which a slope extends northward 

on the ore bed. This bed evidently lies geologically higher than the 

one worked at Bell's. Its outcrop was formerly worked a short distance south of the shaft. The shaft encountered ore at 57 feet and 

the slope is driven northward on a 23° dip for about 125 feet, the 

ore bed ranging from 4 to 7 feet in thickness. All along the slope 

the hanging wall seems to be a fine-grained trap, in places carrying 

small crystals of iron pyrites and here and there nodules of lime. 

But in the drifts at the bottom of the slope for 25 feet on each side 

an indurated slate rock wedges in between the trap and the ore, 

forming the hanging wall. The ore body seems to have a lenticular 

shape, as at the Cox mine, being thickest at the slope and thinning 

rapidly both east and west. The upper workings are confined to the 

vicinity of the slope, but at the bottom the ore bed has a Avorkable 

thickness for a greater distance along the strike. The ore is rather 

micaceous.

From the surface distribution of the diabase, so far as it can be 

made out, the Altland ore seems to lie some distance below the bottom, 

of the main diabase mass. It is possible that the trap mentioned by 

D'In~villiers is a thin eastward extension of the sill shown on the 

geologic naap (PL XX) as ending west of the Longnecker tract. 

If this is the case, the Altland bed and the ore formerly worked at 

the Smyser pit probably correspond in stratigraphic position, and 

other ore shoots may exist beneath. Also, if the Smyser and Altland 

beds occupy the same stratigraphic horizon, the strike of the strata 

is diagonal to the contact of the main diabase, which is therefore 

slightly crosscutting in this vicinity, just as it is farther northwest, 

near the Underwood workings. From this conclusion it would seem 

worth while to seek for ore along the strike of the ore bed east of 

the Altland mine. At the contact with the diabase the structural 

conditions would be like those which have been deduced for the Bell 

deposit.

Smyser mine. The Snryser open pit is situated about 450 feet 

west of the Altland workings, and, as already stated, the ore bed 

 probably corresponds in position with that in the Altland mine. 

The Smyser deposit was opened in 1852, and 3,000 tons of ore are 

reported to have been won from it. Although the ore is said to have 

rested upon a saddle of diabase, the nearest diabase which can be 

determined from surface observations is the sill which passes north 

of the pit. This sill appears to end a short distance west of the 

Longnecker switch, though it is possible that it may extend somewhat farther east.

. A small body of ore said to have been uncovered in the railroad 

cut just west of the road crossing, about 500 feet distant from the
YOBK COUNTY DEPOSITS. ' 8.3

Smyser pit, was never opened. It apparently lies in lower strata 

than those at the Smyser pit.

Bowlders of ore may be found in the cultivated field about 400 

feet north-northeast of the Smyser pit and 200 feet north of the 

dwelling house. This locality is apparently inside the diabase area, 

but it seems possible that an irregularity in the bottom of the diabase 

mass has brought a small patch of sediments to the surface. If this 

supposition is correct, the occurrence of ore at this place is favorable 

to the view that ore deposits will be found in many places beneath 

the diabase when extensive explorations are undertaken.

Underwood workings. The most productive ground of the Dillsburg field has been the northeasterly 35 acres of the Underwood 

property and the near-by portions of the McCormick tract on the 

north and the Logan tract on the east. On the Underwood tract 

there are five large open pits and several smaller excavations, all of 

which were exhausted previous to 1874, and four deep mines, which 

have been abandoned since 1887. ' ;

The southernmost of the Underwood workings are two pits situated about 500 feet northwest of the Smyser pit, on opposite sides 

of the north-south wagon road. These two openings are doubtless 

on the same ore body, which they have developed for about 400 feet 

along its course. Though the depth of the workings is not known, 

the ore must have been followed for some distance on a northerly 

dip, because there are depressions about 175 feet north of the western 

opening which appear to be the result of the caving in of underground 

workings. The narrow diabase sill which passes north of the Smyser 

pit touches the south side of the western opening, and just north of 

 the pits is another sill which, strikes northeast and west. The second 

sill can not be traced east of the wagon road, though it may extend 

for some distance in this direction. The two sills approach each 

other toward the west and finally unite. The main diabase contact, 

running from southeast to northwest, passes near the northeast corner of the eastern pit and the strike of the ore bed is evidently diagonal to this contact and also to the course of the southern sill, but it 

is nearly parallel with the trend of the northern sill.

The next openings, to the northwest, are two large pits in which 

the general line of excavation runs from the outlying sill on the southwest diagonally across to the main contact on the northeast. The 

boundary of the main diabase area crosses the northeastern of the 

two pits, which is said to have been the first mine opened in the Dillsburg field. These pits must have furnished a very large amount .of 

ore. In 1873 a shaft was sunk in the bottom of the eastern pit (Derrick shaft), and is said to have passed through 25 feet of diabase and 

28 feet of ore. The ore body is known to have been worked for a 

distance of 250 feet northeast of the shaft and it probably connects
84 MAGNETITE DEPOSITS IN PENNSYLVANIA.

with the ore worked in the three deep mines lying immediately to the 

north. Between the open pits and the Underwood slope the ore bed 

apparently lies very flat. Limestone was encountered in the workings from the Derrick shaft.

About 600 feet northwest of these pits there is another large pit, 

the longer axis of which trends northeastward, nearly parallel with 

the diabase contact, which lies about 50 feet to the southeast. Waste, 

apparently derived from these workings, contains limestone and 

masses of garnet rock. A shaft was sunk about 50 feet beyond the 

southwest end of the pit, but Avhether or not ore was mined from this 

opening is not known.

Farther north there are two large pits between the one just described and the McCormick property line. In both of these the 

strike of the ore bed is slightly south of east. Nothing can be seen 

of the rocks which inclose the ore and it is not known to what depth 

the deposit was excavated.

Between the three western pits of the Underwood group and the 

edge of the diabase mass many small ore pockets were mined out at 

the surface, but the only important excavation in this part of the 

tract lies in the angle of the diabase boundary, about 300 feet south 

of the big McCormick pit. In the northeast corner of this excavation thin-bedded layers of baked sandstone may be seen dipping 

N. 80° E. at an angle of about 20°. "The ore evidently passes under 

this sandstone, which therefore lies between the ore and the diabase 

seen on the east side of the pit.

Of the three deep mines on the Underwood tract which remain 

to be described, the oldest was opened by the so-called Underwood 

slope, the position of which is shown on the maps (PL XXand fig. 19). 

The following notes on this mine are condensed from Frazer's 

report: a

The slope sinks due north at an angle of 28°. Ore was not followed from the surface, but was reached at a depth of 26 feet. Diabase is exposed at the mouth of the slope, and the ore, where first 

encountered, is said to have been 18 feet thick. The dip of the ore 

beds is steeper in the lower workings than in the upper part of the 

mine. The foot wall is sandstone intermixed with limestone; the 

hanging wall is diabase. The distance between the walls varies 

from 6 to 30 feet. Three levels have been opened. On the first 

level, at 120 feet, drifts extend 100 feet east and west of the slope. 

The second level, at 180 feet, was opened 90 feet east and west, and 

the third level, at 200 feet, was opened 110 feet east and 120 feet 

west. The ore body was developed by raises about 20 feet apart, 

extending from level to level.

0 Second Geol. Survey Pennsylvania, Kept. CC, 1877, pp. 207-208.
YORK COUNTY DEPOSITS. 85

Apparently referring to this same slope, D'lnvilliers states in his 

1886 report* that the workings were carried down 500 feet but were 

abandoned. He also says that the slope was carried down with the 

true hanging wall (that is, diabase) on top; but within a comparatively short distance the bed forked into an upper and a lower seam, 

with a wedge of slaty sandstone between. The gangways driven east 6 

from the slope showed the ore being rapidly cut out by the convergence of the walls, and the drifts were continually kept turning 

toward the northeast in order to keep within the ore body. The 

Jbest ore is said to have occurred near the place where the bed

FIG. 19. Plan and section of Underwood and Longnecker mines, Dillsburg, showing

probable trend of ore bed.

pinched; and where the bed is thickest the ore is mixed with slaty 

limestone layers and carries iron pyrites.

. In April, 1887, the mine was worked by a shaft 96 feet deep which 

is said to have passed through three ore beds the first at 38 feet, 

7 to 8 feet thick and rather lean; then 14 feet of sandstone; 8 feet 

of good ore; 26 feet of sandstone; and the bottom ore bed, 15 to 20 

feet thick. These extensive workings lie entirely east of the old 

slope. As in the other mines, the foot wall is a hard white calcareous sandstone, and the hanging wall is diabase; but between the

0 Ann. Kept. Geol. Survey Pennsylvania for 1886, pt. 4, 1887, p. 1508. 

6 This word is west in the original, but the concurrence of the words "west" and 

" northwest" in this sentence makes it unintelligible as it stands.
86 MAGNETITE DEPOSITS IN PENNSYLVANIA.

walls lenticular masses of sandstone and slate wedge into the ore 

body. It is no doubt due to the swelling of such wedges that the 

three beds of ore were found in the shaft. The middle bed, which 

has been somewhat largely developed, is said to lie between beds 

of altered sand rock. In the lowest bed immense chambers have 

been opened where the ore swells localty; but where the bed is 15 

to 20 feet thick it contains seams of limestone and bowlders of barren 

rock. The two upper beds are regarded as splits from the lowest or 

main bed. The mine may have furnished from 20,000 to 25,000 tons 

of ore, averaging 40 per cent of iron.

The last mine opened on the Underwood tract is described by 

D'lnvilliers a under the heading " Longnecker mine," a name now applied to the mine on the Logan tract. The writer was not able to 

determine the location of this opening, which is said to lie a little 

east of the Underwood mine.

According to D'lnvilliers, the shaft is 95 feet deep and the slope 

extending from its bottom has reached the McCormick line and is 

probably from 400 to 450 feet long. On the east four gangways 

have been driven toward the Longnecker mine, and from the bottom 

of the slope a gangway has been driven 150 feet west toward the 

Underwood mine. About 50 feet from the slope, in a stope above the 

west gangway, the ore in places is 20 to 30 feet thick. No new 

features are presented in this mine, and it may be considered that the 

ore is an extension 400 feet farther to the east of the Underwood 

bed. It may be, however, that there are two ore lenses which overlap 

each other.

,The apparent relations of the ore and the diabase, so far as they 

may be judged from the recorded descriptions of the Underwood 

slope, are illustrated in the cross section (fig. 19).

The position of the section is 90 feet east of the Underwood slope 

and its direction is north and south.

Longnecker mine. The mine now known as the Longnecker was 

formerly called the Logan mine. It was opened by the owner of 

the property, J. N. Logan, in 1874. The shaft was located from 

dip-needle indications, but 27 feet of diabase was penetrated before 

the ore was cut. Diabase soil and bowlders cover the surface near 

the mine, and it is evident that the ore must lie beneath the mass of 

this rock. Material on the mine dump shows that limestone conglomerate is present in the workings.

The ore bed is said to have been 20 feet thick at the shaft and to 

have averaged 10 feet in the mine. From the bottom of the vertical 

shaft, 51 feet deep, a slope toward the north starts at an inclination 

of 28% but flattens somewhat as depth is attained. Mr. Logan

a Op. cit, pp. 1509-1510.
YORK COUNTY DEPOSITS. 8T

states that the Avorkings extend about 300 feet north of this shaft 

and that the east drift of the lowest level is 190 feet long. The extent of the workings in 1885 is shown by the plan (fig. 20). Considerable work has been done since this survey was made. The 

vertical section which accompanies the plan does not correspond 

with the relations as they are stated above, but it is reproduced as

PLAN

Average thickness of ore bed from A to B about 10 feet

Average dip of bed and slope about 20°

Floor and roof a compact hard sandstone

Breast at B in good ore, with a horse of hard sandstone dipping N. 35

Breast at C, same sandrock but thinner

Trap wall at bottom of shaft dips 30°

Shaft VERTICAL SECTION ALONG SLOPE

^

50 100 feet + +"

FIG. 20. Plan and cross section of Longnecker mine, on Logan 

tract, Dillsburg. From Ann. Rept. 'Second Geol. Survey 

Pennsylvania for 1885, p. 568.

originally drawn. From the inclination of the slope the ore bed 

should outcrop about 50 feet south of the shaft, but at this place 

the surface rock is undoubtedly diabase. The map shows that the 

underground workings reach a point fully 100 feet south of the 

shaft, so that the under side of the diabase must lie nearly flat south 

and southwest of the shaft, as it does in the ground south and southeast of the Underwood slope. In the vicinity of the shaft the bottom
88 MAGNETITE DEPOSITS IN PENNSYLVANIA.

of the diabase takes an abrupt dip toward the north, as in the Underwood mine, so that both the Longnecker shaft and the Underwood slope appear to have penetrated the ore bed just at the angle 

where the steeper dip begins.

The very considerable extent of the ore bed shown by the Underwood and Longnecker workings furnishes a strong reason for believing that the Logan tract offers good ground for further development. The Underwood tract seems to have been completely worked 

out, though from the statement that the Longnecker workings extended north to the McCormick line it seems possible that the same 

bed of ore continues into the McCormick tract. A consideration of 

all the deep mines of this vicinity, however, suggests that the actual 

trend of the ore is toward the northeast, so that future discoveries 

are more likely to be made in the Logan tract than elsewhere. The 

boring which was made in the McCormick pit appears to be not 

deep enough to reach the extension of the Underwood ore. It is 

reported that a boring was made about 1,500 feet north of the 

Longnecker shaft, but no record of this work is available.

McCormick mines. On the McCormick tract, situated north of the 

Underwood tract, there are three large pits and several small openings, all of which were abandoned before 1875. No large masses of 

diabase are present near most of the excavations, but the largest pit 

is situated at the western edge of the main diabase, about 200 feet 

north of the pit in the angle of the diabase boundary on the Underwood tract. This large pit is said to have been opened about 1850, 

and it is apparent from the fact that its area is nearly 12,000 square 

feet that it must have furnished a large amount of ore. The size of 

the vein is not recorded, but the longer axis of the excavation trends 

somewhat north of east, showing that the strike of the ore bed is in

that direction. The position of the slope by which the mine was 

worked indicates that the strata have the usual dip toward the north. 

Frazer states a that a shaft was sunk from the bottom of the pit to 

a depth of 140 feet, and that about 100 feet north of the pit a 20-foot 

slope was put down 60 feet on the vein of ore, which was 4 feet thick 

at the bottom. He gives the following record of a drill hole in the 

large pit: 6

Record of bore hole No. 5, sunk in McGormick & Co.'s old Txink.

	Feet.

Soil________________________-_________- 8. 84

Green sandstone .17

Iron ore_____!___________ .17

Gray sandstone___ - 4.50

White sandstone_______ 6.17

Reddish-green sandstone 12.08

« Second Geol. Survey Pennsylvania, Kept. CC, 1877, p. 214. 6 Op. cit., p. 216.
YORK COUNTY DEPOSITS. 89

	Feet.

Black (?) trap.__________^___.___________ 23.07

Gray sandstone_____________________.______ 3.25

Iron ore______________________________ 3.25

White sandstone__________.____ ___________ 5.00

Iron ore______________________________ 1. 33

White sandstone_________________________ 11.00

Limestone and flint_______________._________ 6. 00

Limestone and fire clay___________________ 10.00

Red sandstone _________.____________,___ 14.00

Green sandstone_________________________ 4.00

White sandstone___. _____________________ 9.00

Green sandstone___.__________._____________ 3. 00

Iron ore__________.._____________________ 2. 00

Sandstone________ ____ ___________ _____ 2. 00

Sandstone and ore_-________________-_______1 3. 00

Limestone and flint_ . 6.50

Ore and sandstone_______________________ .50

Green sandstone______ ______ _ _____ 5. 00

White sandstone________ 5.00

Green sandstone___________________ _____ _ 6. 00

White sandstone________________ _ 1.00

Gray trap______________________._________ 2. 00

White sandstone_________________________ 2.00

Limestone______________ 3.00

Gray sandstone_____ _ - 4. 50

Red sandstone_____-________ 4.00

White sandstone____________ __ _____ 4.00

Red sandstone_______________ 1. 00

White sandstone__! ___-. ___ 4. 00

Red sandstone______ ._______ __ 3. 00

White sandstone________________ ______ 4.50

187.83

It is evident from the above record that the mass of diabase which 

outcrops east of the pit does not dip beneath this ore body. The contact of the diabase with the stratified rocks might be supposed to be 

highly inclined and strongly crosscutting, except for the fact that 

about 400 feet toward the southeast, at the bottom of the Longnecker 

slope, the lower surface of the diabase is not more than 200 feet deep. 

It seems probable, therefore, that this lower surface dips rather 

gently toward the east or northeast. The most likely situation for 

a continuation of the ore body would be where the northward-dipping 

strata meet the eastward or northeastward dipping bottom of the 

diabase.

Though the drill-hole record shows thin layers of ore at five horizons and limestone at three horizons, it is not likely that strata equivalent to those containing the ore in the Underwood deep mines have 

been reached. If these beds continue with the same dip that they 

have in the Underwood slope, their position would be about 450 feet 

from the surface beneath the McCormick pit.
90 MAGNETITE DEPOSITS IN PENNSYLVANIA.

The second McCormick pit is a long, narrow excavation situated 

just north of the property line, about 200 feet farther west. (See 

fig. 21.) Nothing is known of this ore layer beyond the fact that itstrikes slightly north of west. The pit is about 50 feet north of the 

nearest Underwood pit.

 The McCormick long cut lies about 300 feet northwest of the large 

pit and 230 feet north of the excavation last mentioned. Though 

there are some small openings beyond, the long cut is the northernmost of the formerly productive mines of the Dillsburg field. The 

ore bed was opened for a distance of 325 feet along the strike and

o

O

N

A

Hole No. 2

Hole No. 1

Hole No. 3

Hole No. 4

100 200 300 400 SOOfeet

FIG. 21. Sketch map showing situation of pits and test holes on 

McCormick tract, Dillsburg.

small openings were made at several places west of the main cut. 

The following notes are taken substantially from Frazer: a

A dolerite, which occurs in this mine at the surface and appears 

to constitute the top rock of the ore, dips N. 5° W. from 27° to 34°. 

Two slopes were driven to find the ore. The upper one followed 

the vein in between well-defined walls at a normal angle to the inclination of the sandstone layers. The upper sandstone was continued 

in the deep, but the foot wall was cut out by a dike of diabase. The 

lower slope, of about 30° to 45°, was continued for 180 feet and passed 

through the ore, which appeared to be a very irregular deposit. In 

1875 it was nearly exhausted.

"Second Geol. Survey Pennsylvania, Kept. CC, 1877, p. 215.
YORK COUNTY DEPOSITS. 91

Near the west end of the cut, fine-grained baked sandstone may be 

seen to form the hanging wall, but no evidence was found on the surface that diabase is present near the mine. The sketch map (fig. 21) 

shows the position of the several bore holes, the records of which, 

here given, are taken from Frazer: a

Record of bore hole No. 1, north of McGormick long cut.

	Feet

Clay_________________________________ 4

Sandstone _______________________________ 8

Clay___L ___________ ,. _______________________ 2

Bastard limestone _________________________ 9.5

Sandstone __________________________ ___ 9. 5

Tra&________________________________ 9

Unknown, about_________ _________ __ 20

Brown sandstone _____ - 12

Iron ore_______________ __ ___ _____ 6

Sandstone __________ _ 4

Lean iron ore_________ __ 4

88 

Record of bore hole No. 3, north of McCormick long cut.

	Feet.

Clay__________________________________ 4

White sandstone_____ ___________________ 6

Red sandstone___________________________ 7

Trap _________________________________ 17. 5

Black and green sandstone________ ___ _____ 4

Brown sandstone ______ ___ 1

Green sandstone_______ ___ ___ ____ 8

White sandstone______________ ___ _ ___ 1.5

49 

Record of bore hole No. //, southeast of McCormick long cut.

	Feet. 

Clay___________________________________ 2

Gray sandstone__________i______________ 8

Red sandstone______________1__________ 7

Unknown ___:__________________________ 10

White sandstone___________..___________ 7.5

Greenish-white sandstone____________________ G. 16

White sandstone ______________i__________ _ 6.41

Green sandstone________ ___ _ _ ____ 2. S3

Red sandstone _______ __ _________ .50

Black (?) trap____________________________ 16.08

White (?) trap___________________________ 6.66

Ore ___________________________________ 1. 50

White sandstone_______________________ 22.25

Green sandstone________ ___ _ ____ 13.16

Red and white sandstone_ 6.00

116. 04

'Op. cit, pp. 215-216.
92 MAGNETITE DEPOSITS IN PENNSYLVANIA.

Hole No. 1, located about 110 feet north of the long cut, evidently 

penetrated the ore bed, which was mined from the surface. The record of hole No. 2 is not given. To judge from the known dip of the 

strata, hole No. 3, about 50 feet north of the cut, must also have passed 

through the horizon where the ore body should be, though no ore was 

reported. The 9^-foot bed of limestone encountered in hole No. 1 

probably outcrops north of hole No. 3. The record of hole No. 5 is 

given on pages 88-89.

The position of two small pockets of ore about 200 feet north of 

the east end of the long cut is indicated on the map -(PI. XX). A 

small quantity of ore is said to have been mined from a shaft 1,200 

feet northeast of theslong cut in the northeast angle of the crossroads.

The position of this shaft is very near the boundary of^the main 

mass of diabase.

Mr. Logan states that thin seams of magnetite, or of specular 

hematite, have been found at several points in the fields of his home 

farm, about half a mile northwest of the McCormick long cut. In 

this vicinity there are several minor bodies of diabase, but the shales 

and sandstones are not generally baked, as they are in the neighborhood of the old mines.

DIABASE INTRUSIONS WEST OF THE MINES.

The present examination of the geologic features of the Dillsburg 

field has revealed the presence of several bodies of diabase on the 

western slope of the hill on wrhich most of the old mines are situated. 

The intrusions, which are four in number, appear .at the surface as 

narrow bands, and though the relation which they bear to the inclosing rocks can not be observed, they are probably sills, more or less 

closely conforming with the bedding of the rocks which incase them. 

One of the bands is the westward and northwestward extension of the 

two narrow strips of diabase which cross the wagon road just south 

of the Underwood pits and come together about 500 feet west of the 

road. Where the two forks merge the band is 250 feet wide, though 

it becomes narrower toward the west. Its observed length is about 

2,500 feet, but its western termination is not seen because of the deep 

soil in the meadows between the ore fields and Dillsburg. The three 

northern bands extend eastward nearly to the brow of the hill. The 

middle band runs northwestward for 800 or 900 feet, to a point where 

it appears to terminate, though this is not certain, for the surface 

debris in this vicinity is greatly mixed. The other bands may be 

traced toward the northwest until they are lost under the meadow 

soil. The northernmost band may be followed nearly to the wagon 

road, as shoAvn on the map (PI. XX).

On page 94 reasons are given in support of the suggestion that beds 

of limestone conglomerate which occur in the vicinity of Dillsburg
YORK COUNTY DEPOSITS. 93

may extend eastward and underlie the meadows between the town and 

mines. If any such continuity of conglomerate layers actually exists, they must traverse the ground occupied by the*four diabase sills. 

From what has been learned concerning the geology of the Dillsburg 

deposits, it seems that the possibility of beds of limestone conglomerate being locally in contact with these intrusions makes all of this 

ground worthy of careful exploration. The absence of ore indications in the soil can not be considered conclusive evidence against the 

existence of ore bodies, as the ore is known to break down completely 

under long-continued action of the weather, and as on the hill slope 

the earthy material resulting from the superficial disintegration of 

an ore body would be hidden more completely than on nearly level 

ground because of the gradual downhill movement of the rock fragments and soil.

PRACTICAL CONCLUSIONS.

A practical question to which an unqualified answer can not be 

given is Avhether or not deposits of magnetic iron ore may yet be 

found in HCAV localities in the Dillsburg district. It seems unlikely 

that new ore bodies will be discovered from surface showings encountered in tilling the soil, as in the earlier days of the district. Four 

of the ore bodies have been discovered by means of the magnetic dipping needle, and others may yet be found in the same way. In this 

connection, though no magnetic observations were made during the 

present investigation, it may be pointed out that in using the magnetic needle difficulties may arise from the attraction due. to masses 

of diabase, for it is well known that this rock possesses magnetic 

properties in certain places. On the other hand, it seems possible 

that there may be ore bodies which the needle will not detect.

Whatever may be the truth on the foregoing points, their consideration is secondary to the understanding of the geologic features of the 

district, the presentation of which is the object of this report. From 

a purely geologic standpoint, deposits of ore like those which have 

already been worked might be expected to occur west of the ore fields 

along the borders of the several diabase intrusions near Dillsburg. 

The particular feature which distinguishes this part of the district 

and makes it seem more likely that ore deposits may be present here 

than at other places in York County where large masses of diabase 

occur is the existence of beds of limestone conglomerate. This rock 

is so closely associated with the ore bodies of the mines already 

worked that its presence must be regarded as one of the favorable 

conditions for ore occurrence, and where it comes into contact with 

diabase the chances for finding ore seem worthy of attention.

The mile-wide band of diabase which runs east and west just 

south of the ore fields narrows somewhat and assumes a northwest-
94 MAGNETITE DEPOSITS IN PENNSYLVANIA.

erly trend about 1 mile southeast of Dillsburg. The southern part 

of the town is underlain by the mass of intrusive rock, but here the 

band makes another turn, this time sharply toward the southwest, 

and it continues in this general direction for about 8 miles to its termination a mile or more northwest of York Springs. Southwest 

of Dillsburg minor indications of ore have been found at several 

points along the borders of this intrusion, and at two places small 

bodies of ore have been mined, as already noted. It is not possible 

to show the presence of limestone conglomerate at any of these 

places, though outcrops at several points show that beds of the rock 

are present beneath the low meadows between Dillsburg and Beavertown. There can be little doubt that the limestone conglomerate and 

diabase actually come together in several places, though the contact 

may lie some distance beneath the surface.

On the geologic map (PL XIX) the position of known outcrops of 

limestone conglomerate has been shown. At the quarry beside the 

Dillsburg-York Springs road, 1 mile southwest of Dillsburg, a heavy 

bed of the conglomerate dips toward the southeast, so that if the diabase, which lies east of the road, is a crosscutting mass, as seems likely, 

the stratum should come into contact with the igneous rock in this 

direction. Though baking of the sediments does not extend as far 

as the quarry, the presence of ore at the surface one-fourth mile to 

the south shows that solutions capable of depositing iron were active, 

and the chances that the conglomerate bed is mineralized at the contact seem worthy of consideration.

One mile southwest of the quarry mentioned in the foregoing 

paragraph, limestone conglomerate has been exposed at the eastern 

base of the diabase hill along an abandoned railroad grade. Here 

a considerable degree of metamorphism is shown by the presence of

silicate minerals in the conglomerate, but no iron minerals have been 

introduced. The absence -of ore in this place is possibly to be charged 

to the small size of the diabase intrusion lying immediately west.

It is impossible to discover the attitude of the strata betAveen the 

outlying body of diabase just mentioned and the long dike which 

extends southwest of Dillsburg, but the rocks are much baked as the 

edge of the dike is .approached, and beds of limestone conglomerate 

are likely to exist beneath the surface debris. In the event of a successful outcome of future explorations in other localities, it may yet 

be thought desirable to determine whether or not limestone conglomerate occurs in the vicinity of this southwest dike, and if it is found, 

to .explore those places where it is likely to come into contact with the 

diabase. The existence of ore at the Bender mine and of ore indications about half a mile southeast of that opening shows at least that 

mineralizing waters were active in the neighborhood.
YOEK COUNTY DEPOSITS. 95

The dike or sill of diabase which crosses Dogwood Run northwest 

of Dillsburg has been traced in a northwesterly direction and 

found to connect with the wide intrusion south of the Grantham 

mines. Exposures of limestone very near the diabase are seen in the 

wagon road near the gristmill, in a railroad cutting near the upper 

end of the mill pond, and along the creek above the pond.

The attitude of the main diabase mass can not be made out, but 

in the railroad cutting it is evident that the limestone is cut across by 

several irregular intrusions of the igneous rock. The limestone 

where seen is not greatly metamorphosed, though the lack of red 

color in the soil indicates that the associated shales and sandstones 

are considerably altered. The diabase mass forms a prominent hill 

lying north and Avest of the creek, and from the contour of this hill 

it is judged that the intrusion does not form the floor of the broad 

valley east of Beavertown. In the area between the diabase hill and 

South Mountain there are no rock exposures, except in the quarry 

above Beavertown. This opening has been made about a sink, and 

50 feet of limestone conglomerate has been exposed. Other sink holes, 

extending in a northeast direction, suggest that the same stratum 

continues for fully a mile in a northeasterly direction along the edge 

of the Mesozoic belt. Beds of conglomerate may come into contact 

with the diabase beneath the deep mantle of soil on the west and 

northwest slopes of the hill, so that this ground may be worth prospecting.

. In the neighborhood of Dillsburg the body of diabase which has 

been under consideration lies well within the Mesozoic area, but 2 

miles north of town it lies between Mesozoic strata on the southeast 

and Paleozoic limestone on the northwest. In a limestone quarry 

one-half mile south-southeast of the D. and M. Junction the limestone 

and diabase are seen almost in contact. The fact thaf the limestone 

shows no evidence of having been affected in any way by the diabase 

suggests that in this place the two rocks have been brought together 

by a fault. Though this structure can not be proved from the features 

to be seen in this quarry, there are strong reasons for believing that 

the boundary between the Mesozoic area and the older rocks of the 

valley and of South Mountain is formed by a profound fault for at 

least 25 miles southwest of the Susquehanna and for some distance 

east of that river. The probability that this fault exists and that 

movements have taken place along it since the intrusion of the diabase 

removes the contact with the Paleozoic limestones from consideration 

as a place in which ore bodies are to be expected.

Inasmuch as it is wholly impossible to estimate the thickness of 

the Mesozoic strata in the vicinity of Dillsburg or to judge either the 

distribution of the rocks which lie below these beds or the subter-
.96 MAGNETITE DEPOSITS IN PENNSYLVANIA.

ranean forms and courses of the intrusive mass of the diabase, no suggestions can be made concerning the possibility of ore deposits being 

present beneath the Mesozoic formations.

GRANTHAM MINES.

On the south side of Yellow Breeches Creek, near Grantham crossing, are situated three old mines, known as the Landis or Fuller, the 

Porter, and the. Shelley. Outcrops in the railroad cuts and material 

on the mine dumps show that the deposits at this place occur in 

Mesozoic strata, which include beds of limestone conglomerate. 

North of Yellow Breeches Creek the bed rock is Paleozoic limestone, 

and just south of the mines diabase appears. This diabase is part 

of an intrusive mass of important size, extending westward and 

southwestward to the vicinity of Dillsburg and eastward for 4 miles 

or more to join a great mass of the same rock which forms the group 

of high hills between Dillsburg and Mount Airy. Just south of 

Grantham the intrusion is about 1 mile wide. Eastward from Rosegarden, its northern boundary is an irregular, waving line, which has 

not been traced in detail beyond Grantham. Near the mines the 

strata adjacent to the diabase are undoubtedly considerably disturbed, as is indicated by varying dips in the old workings. It 

seems, however, that the average ore-bearing beds decline gently 

toward the south and pass beneath the diabase, so that the latter 

forms a general hanging wall over the deposits. The Landis and 

Porter openings are situated just at the edge of the diabase, and at 

the Shelley mine a shaft is said to have penetrated diabase lying 

just above the ore. One mile up the railroad track from Grantham, 

at Kosegarden, diabase is seen along the tracks, and one-third mile 

farther west Paleozoic limestone appears only a short distance beyond the last 'outcrop of the igneous rock. Here, then, the diabase 

comes into contact with the older rocks. In the field south of the 

railroad debris revealed by gullies cut into the hill slopes shows the 

presence of sandstone beneath the diabase. These sandy beds can 

continue toward the west for a short distance only, for undoubted 

Paleozoic limestone is again observed very near the diabase on the 

highway just south of the crossroads. In the valley of the small 

brook which joins the creek at Rosegarden is an old prospecting 

shaft, situated at the south edge of the diabase mass. No indications 

of ore are to be seen in the material on the dump, but the amount 

of material thrown out indicates that considerable work was done 

at this place. The rock excavated is mainly a hard baked shale.

Northeast of Grantham, on the north side of the creek, is a mass of 

diabase which may have been separated from the main mass by the 

erosion of the .creek channel. On the south side of this mass, in the 

wooded ravine about one-half mile east of the railroad, there is an old
YORK COUNTY DEPOSITS. 97

prospect pit in which baked sandstone occurs. Along the railroad 

track the diabase is to be seen in contact with Paleozoic limestone, 

but as the latter is not notably metamorphosed at this place it is 

thought that the contact is not an intrusive one, but that a fault has 

brought .these two rocks together. This suggestion brings up the 

general structural problem presented by the northerly boundary of 

the Mesozoic belt throughout the State, discussion of which will 

not be attempted here.

In the fact that they occur between beds of limestone conglomerate 

arid overlying diabase the ore deposits near Grantham resemble several of the deposits of the Dillsburg group, the same relation being 

observed in the Underwood, Longnecker, Jauss, Price, and Logan 

workings.

In the absence of any adequate data concerning the amount of iron 

ore that has .been extracted from these mines and the degree of persistence shown by the ore bodies in the ground opened, it is difficult 

to judge whether prospecting in the vicinity for other deposits would 

be advisable or not. From a purely geologic standpoint conditions 

similar to those existing near the known ore bodies may be supposed 

to extend for a considerable distance both east and west of the old 

openings. The place to look for ore is evidently just beneath the 

diabase, and where conglomerate is present under the igneous rock 

ore is likely to be found. The most feasible way to make a test is by 

a line of drill holes located just within the boundary of the diabase 

area. Perhaps the most attractive scheme of prospecting would be 

to determine by means of the drill whether or not the deposits already 

known extend beyond the old workings in the direction of the dip.

The following data concerning the three old mines at Grantham 

are condensed from Frazer's report: a

The Landis mine was opened about 1863. A tunnel from the railroad and close to the banks of the creek enters a steep bank due 

south for 200 feet. Two drifts lead off west and east of the main 

tunnel. The hanging wall is diabase, dipping 24° N. 25° W.

Operations at the Porter mine were begun in 1855. In 1875 the 

excavation was reported to be about 40 feet deep and 14 feet below 

the water in Yellow Breeches Creek. Ore was loaded from the pit 

into carts. The ore bed is said to have been from 3 to 6 feet thick, to 

have been opened for 25 feet along the strike, and to have dipped 30° 

toward the creek.

At the Shelley mine 20 feet of diabase is reported above the ore. 

The ore bed was 10 feet thick and rested upon " Potomac marble "; 

that is, upon limestone conglomerate.

a Second Geol. Survey Pennsylvania, Rept. CC, 1877, pp. 220-222. 

54370 Bull. 359 OS- 7
98 MAGNETITE DEPOSITS IN PENNSYLVANIA.

Frazer regarded the inclosing rock of the Porter ore as probably 

Paleozoic limestone. Though the rock exposed in the near-by cutting along the railroad was thought by him to be "Auroral limestone," the present writer is confident that it is limestone conglomerate belonging to the Mesozoic belt. These strata dip toward the 

south at a low angle. A thin sill of diabase is seen in contact with 

the calcareous rock, which is considerably metamorphosed.

The following notes are given by D'lnvilliers: a

The old Fuller or Landis mine is owned and worked by Mr. 

Shelley, who states that a shaft 80 feet deep passed through diabase 

to a chimney-shaped bed of ore dipping north-northeast. The same 

ore was struck 100 feet farther east by a 40-foot shaft, in which the 

ore also dips toward the creek. According to Mr. Shelley, .there are 

four or five beds here, separated by short intervals of hard rock of a 

white color, and not unlike a baked slaty sandstone. In April, 1887, 

preparations were being made to sink on the outcrop of a lower bed 

showing about 100 yards south of the shaft.

Immediately across a narrow ravine to the east of this opening a 

large amount of ore was formerly raised by Mr. Fuller, and the 

operation is supposed to have been stopped owing to the occurrence 

of " Potomac marble," which cuts out the ore for a considerable extent through the mine and along the railroad. This rock shows 

largely through the field and along the track, where an abandoned 

cut developed a large body of soft surface ore, resulting from the decomposition of the bed, 5 to 8 feet thick, which was encountered in 

the bottom of the pit. Mr. Shelley says that there are 13 acres in 

this property through which no pinching in the ore beds occurs, so 

far as developed.

MINES SOUTHWEST OF WELLSVILLE.

The so-called " Minebank " workings are situated about 2 miles 

southwest of Wellsville, and about 6£ miles from the northwest 

boundary of the Mesozoic belt (PI. XIX). The most prominent 

feature in the local geology is a mass of intrusive diabase, which 

appears at the surface in an elliptical area about 2| miles long and 

1 mile wide. This diabase is surrounded by shales and sandstones 

which are bleached and baked in the vicinity of the igneous rock. 

The general strike of the strata is northeast and southwest, and dips, 

wherever observable, are toward the northwest, usually at moderate 

angles.

The " Minebank " deposit appears to be a layer conforming to the 

strata by which it is inclosed. It has been opened by a series of pits 

and shafts extending from .southwest to northeast for a distance of 

about 1,000 feet along the strike of the outcrop, and indications of

"Ann. Kept. Geol. Survey Tennsylvania for 1886, pt. 4, 1887, pp. 1513-1514.
YORK COUNTY DEPOSITS. . 99

ore were found in explorations beyond the northeasternmost and 

largest.mine, which is situated back of the schoolhouse. Although a 

narrow dike of diabase is said to have been encountered in one of the 

mines, the main intrusion lies some distance northwest of the ore 

cropping. The dip of the strata which inclose the ore is toward the 

diabase. The waste to be seen on the mine dump consists mainly of 

baked shale and fine-grained sandstone. Specimens may be seen in 

which joints crossing the stratification contain films of micaceous 

hematite. Lumps of solid ore may be found composed either of 

hematite and magnetite together, or of hematite alone. Some of the 

.micaceous ore, which looks like specular hematite, yields a black 

powder instead of the red powder, which is characteristic of hematite, 

.and is attracted by the magnet. A mass of similar ore is reported to 

have been mined out years ago from one of the Phoenix mines at

Boyertown. Several blocks were noted which were composed of crystalline limestone and specular hematite with a sprinkling of chalcopyrite. .A study of this material leaves little doubt that the iron 

mineral has been deposited through some process of chemical substitution. From the presence of the limestone it may be thought that 

the ore layer was formed by the replacement of a limestone stratum 

interbedded with the shales and sandstones which are the common 

rocks of the region. Whether this be true or not, there can be little 

doubt that the ore was introduced through the agency of hot water 

or gases, impelled by the adjacent intrusive mass of diabase. From 

the description given below it appears that the mineralizing solutions 

followed the narrow dike or sill of diabase which was encountered 

in the mine. Though showings of ore have been reported at several 

places in the vicinity of the large diabase mass, no minable body of 

ore has been discovered aside from the one at Minebank.* 

The following data are abstracted from Frazer's report: 6 

Ore was first discovered in the vicinity of the present workings 

about 1805. Prospecting in 1872 led to the opening of the Altland 

shaft, which passes through 5 feet of soil, then 25 feet of lightgreenish hard sandstone, below which a 6-foot bed of micaceous ore 

was encountered. Beneath the ore was blue to gray sandstone, similar to that above except for being harder. The ore was followed by 

a slope until a diabase dike was encountered. The dip measured on 

the sandstone is 31° to 35° N. 30° W. A second shaft was sunk in 

the same.year, about 120 feet north of the first. In 1875 the gang- 

.ways along the ore had a total length of about 500 feet. The ore lies 

.between the sandstone in regular layers, varying from 6 inches to 

7 feet in thickness, with occasional sandstone partings. It is in many 

places found cutting into the diabase. The boundary between the 

latter and the sandstone is very clearly defined. Ore had been found

" Second Gcol. Survey Pennsylvania, Rept. CC, 1877, pp. 231-23$. 

"Op. cit., pp. 235-236.
100 MAGNETITE DEPOSITS IN PENNSYLVANIA.

on the nortlnvest side of the dike, but up to 1875 not in paying quantities. Sixty feet down the slope and 50 feet northwest of it both 

the sandstone and the diabase dip 30° NW. The diabase is here 4 

feet thick. Thirty feet north of the shaft, 2 or 3 yards of rock in 

contact with the dike showed no ore, but the vein had been proved 

from this point to the surface. The ore is very micaceous.

BENDER MINE.

Near the York Springs road, about a mile southwest of Dillsburg, 

are two old pits from which iron ore was formerly extracted. One of 

these is situated, east of the road, very near the boundary of the intrusive diabase, at the south end of an embayment of sedimentary 

rocks. No exposures of rock in place are to be seen near this opening, but limestone conglomerate and red sandy shale occur in the 

quarry beside the road less than one-fourth mile to the north. The 

mine is reported to have been a small one. The second mine, known 

as the Bender property, is located about one-fourth mile farther 

southwest, on the west side of the wagon road. This deposit is said 

to have been opened in 1849, in which year 200 tons of ore was extracted. In 1873 about 80 tons of ore was mined from a so-called 

pocket averaging 5 feet thick, lying under 7 feet of stripping. The 

mine was worked entirely by open pit.0

In the neighborhood of the Bender pit irregularly shaped masses 

of extremely hard and dense green rock may be found lying upon 

the surface or embedded in the soil. This flinty material is a much 

baked sedimentary rock, probably a limy shale or impure limestone 

in its original state. Some of the specimens examined are composed 

almost entirely of massive garnet; others contain considerable colorless pyroxene. Bowlders of this rock may, be found in an area 

300 to 400 feet long and about 100 feet wide. Soil derived from diabase is present on all sides of this patch, so that the strata with which 

the ore is associated evidently form an isolated mass, surrounded by 

the intrusive rock. The locality is near the west side of the diabase 

intrusion, here about one-half mile wide, which runs northeastward 

to Dillsburg and thence southeastward and eastward to join the great 

mass which forms the group of high hills between Stevenstown and 

Mount Airy. Southwest of Dillsburg this band of diabase has been 

followed for about 8 miles.

Flinty rock like that described above occurs on the east side of the 

diabase about a mile south of the Bender pit, but in this vicinity indications of ore are not known to have been found. From the occurrence of limestone conglomerate in the valley west of the Bender mine 

it seems possible that a bed of this rock may have been replaced in 

the formation of the ore deposit.

0 Second Geol. Survey Pennsylvania, Rept. CC, 1877, p. 226.
INDEX.

Page. 

Altland mine, description of................. 81-82

Basalt, flows of.............................. 9

Bell mine, description of..................... 78-79

plan and sections of, figures showing..... 78,79

Bender mine, description of.................. ICO

Berks County, ores of..................... 12,29-71

ores of, analyses of....................... 11

Black vein, relations of, figure showing....... GO

See also Warwick mine. 

Blue vein, location of........................ 43,55

Boyertown, fault near........................ 58

fault near, position of, plate showing..... 56

geologic inap-of.......................... 44

geology near............................. 44-46

maps near............................ 44,61,63

mines of, sections of, plate showing....... 46

workings of, plate showing 46,48,50,52,54,56 

ore deposits of........................ 12,43-61

ore deposits near......................... 61-C5

prospecting near......................... 57-61

Browcr mine, description of.................. C2

California mine, description of.... 47-48,50-51,50-58

plan of, plate showing.................... 56

Cambrian quartzites, occurrence and character

of................................ 8

Cambro-Ordovician limestones, occurrence

and character of.................. 8

Casper mine, ores of.......................... 28-29

Chester County, ores of....................... 12

Cobalt, occurrence of......................... 11

Conglomerate, occurrence and character of. 18,43,73 

Congo, copper near........................... C5

Cornwall, mines near, geologic map of........ 20

ore deposits at........................... 17-28

distribution of........................ 17-19

erosion of............................ 21

extent of............................. 21-28

intrusions in......................... 19

structure of.......................... 20-21

surface relations of................... 17-18

See also Cornwall ore body, 

ore deposits near......................... 23-29

ores of................................... 11

analyses of........................... 11

Cornwall district, geologic map of............ 18

ores of................................... 17-29

structure sections of, plate showing.... 20

See also Cornwall. 

Cornwall ore body, description of............ 22-23

Cox mine, description of..................... 76-77

Diabase, intrusions of................. 9-10,passim

intrusions of, map showing. .............. 8

relation of, to ores............. 10,12,16,passim

Page. 

Dikes, occurrence and character of........... 9-10

Dillsburg, geologic map near................. 72,74

mines near.............................. 71-75

description of........................ 75-92

diabase-near......................... 92-93

map of.............................. 74

ores of................................... 11,12

conclusions on....................... 93-96

D'lnvillfers, E. V., on Altland mine......... 81-82

on Bell mine............................ 78

on Boyertown mines.................... 49-55

on Cox mines............................ 76-77

on Grantham mines..................... 98

on Island mine.......................... 38,40

on Randenbusch mine.................... 30

on Underwood workings................. 85

Drill holes, records of........................ 24

East vein, location of........................ 43

structure near, map showing............. 59

workings on.. I'.......................... 43

Eckert vein, location of...................... 43

workings on.......................... 43,47-49

Esterly mine, description of................. 41-43

Faulting. See Folding and faulting.

Fegley mine, ore from....................... 64-65

Folding and faulting, prevalence of.......... 8

Frazer, Persiflor, on Bell mine............... . 79

on Grantham mines..................... 97

on Jones mine vicinity...'................ 68-69

on McCormick mines.................... 88-92

on Minnebank mine.................... 99-100

. on Underwood workings................. 84

Fritz Island, geologic map of................. 38

ore deposits on and near................. 38-41

sections on, figures showing.............. 39

Fritztown station, geology near............... 30

Fuller mine. See Landis mine.

Gabel mine, description of................ 47,53-56

geology of............................... 45

plan of, plate showing................... 44

section of................................ 53

figure showing........................ 60

Geology, description of...................... 7-10

Gilbert shaft, ore from....................... 63

Grantham mines, description of.......:.. 72,96-98

Grove mine, description of.................... 77

Hagy vein, location of................... 43,57-59

structure near, map showing............. 59

workings on............................. 43

Harden, J. H., map by...................... 47

Hummelstown, ores near.................... 29

Igneous rocks, occurrence and character of... 9-10 

Iron, source of............................... 13-16

101
108 INDEX.

Page. 

Island mine, description of.................. 38-40

Jauss mine, description of................... 79-81

plan of, figureshowing................... 79

section of, figure showing................ 80

Joanna station, oras near.................... 12

Jones mine, description of................... 65-69

geologic map of.......................... CO

map of.................................. 68

sections of, figures showing.............. 60,07

King mine; description of.................... 79-81

Kinney mine, geology of..................... 60-68

map of.................................. 66

section of, figure showing ............... 66-67

Knauertown, ores near...................... 71

Lancaster County, geology in................ 20

Landis mine, description of.................. 96-98

Lebanon, ore deposits near. See Cornwall. 

Lewis, J. V., on New Jersey copper.......... 65

Logan mine, description of............. ... 75-70

Longnecker mine, description of............. 88-88

sections of, figures showing.... ... ..... 85,87

McCormick mines, description of............ 88-92

map of, figure showing................. 90

sections in............................ 88-99,91

McCreath, A. S., analyses by................ 11

Mesozoic rocks, occurrence and character of. 8-9

occurrence and character of, map showing. 8,74

Metamorpbjsm, occurrence and character of. 14-16

relation of, to ores..................... 13,15-16

Mill Ridge, geology of........................ 26

Minnebank. ore deposits near......... 71-72,98-100

Newark group. See Mesozoic rocks.

Nova Scotia, ores of......................... 12

Ordovician shales, occurrence and character of 8 

Ore deposits, occurrence and character of. 10,16-17

ores of. See Ores. 

Ores, analyses of............................. 11

composition of........................... 11

distribution of........................... 12

geologic relations of....".................. 12

metamorphismof........................ . 16

origin of................................. 13-16

See dso partkuhr mines,

Paleozoic rocks, occurrence and character of. 8 

Peckitt, Leonard, analyses by............... 11

Phoenix mines, description of................ 47-51

Porter mine, description of.................. 96-97

Price farm, prospects on..................... 77-78

Price mine, description of.................... 77

Page. 

Pyrite, occurrence of......................... 10

Raudenbusch mine, description of........... 36-37

Reading, geologic map near.................. 30

ores near................................ 12

Replacement deposits, occurrence and character of.................................... 13

Reservoir, ores near......................... 23-24

Rhoades and Ginn shaft, description of...... 62

Rhoades vein, location of.................... 43,47

workings on............................. 44,47

Richards, Richard, on Boyertown mines.... 57,62

Rogers, H. D., on Jones mine............... 66

on Raudenbusch mine......./..;..'....-. '36

on Warwick mine.......................... G9-70

Rowe, W. G., on Esterly mine.............. 41j'42

Ruth mine, section at, figure showing....... 31

Schuylkill River, ore deposits on............ 40-41

Scope of paper.................. p ........... 7

Second Geological Survey of Pennsylvania,

on Paleozoic rocks............... 8

Sedimentary rocks, description of........... 8-9

Shale, occurrence and character of........... 45-46

Shelley mine, description of................. 96-98

Sinyser mine, description- of................. 82-83

South Mountain, geology at................. 73-74

Underwood workings, description of......... 83-86

- section of, figureshowiog................ 85

Warwick mine (Berks Co.), description of... 43-

45,48-49,51-53,56

map of, figure showing.................. 48

plan of, plate showing--.................. 56

vein of, location of....................... 43,57

Warwick mine (Chester Co.), description of.. 69-71 

geologic map of.-......................... 6&

section of, figure showing................ 69

Wellsville, mines near...................... 98-100

'Wheatfield. group, description of............. 29-30

diabase and, relation of.................. 30

geologic map of.......................... 32

ore deposits of, distribution of........... 34-36

ores of, character of........................ 31,35

structureat.............................. 31-34

figure showing................... 31,32,33

Willis, Bailey, on Boyertown mines......... 47-49

York County, mines of, description of...... 74-100

ore deposits in.......................... 71-100

ores from................................ 12

analyses of.......................... 11

0