Bulletin No. 242 Series B, Descriptive Geology, 47

DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY

CHARLES D. WALCOTT, DIRECTOR

GEOLOGY OF THE HUDSON VALLEY BETWEEN 

THE HOOSIC AND THE KINDERHOOK

BY

T. NELSON DALE

WASHINGTON

GOVERNMENT PRINTING OFFICE

1904

CONTENTS.

Page.

Letter of transmittal...................................................... 7

Introduction............................................................. 9

Literature ............................................................... 10

Topography .............................................................. 11

Areal geology .............................................................. 12

Lower Cambrian ............................... ..................... 13

Fossil localities................................................... 13

Petrography ..................................................... 14

Stratigraphy ..................................................... 17

Areal and structural relations ..................................... 29

Beekmantown shale .................. ............................... 30

Fossil localities................................................... 30

Petrography ..................................................... 31

Stratigraphy and areal and structural relations ..................... 31

Hudson shale and Hudson schist...................................... 33

Fossil localities................................................... 33

Petrography ..................................................... 35

Stratigraphy ..................................................... 36

Areal and structural relations ..... ............................... 37

Eensselaer grit....................................................... 39

Petrography ..................................................... 39

Stratigraphy ..................................................... 40

Areal and structural relations ..................................... 40

Resume" of the formations ............................................. 43

Structural geology........................................................ 44

Structure sections ................................................ 44

General structure.................................................. 44

Discussion and conclusions.......................:........................ 47

Three crustal movements ................................... ...... 47

Three conglomerates ............................................. 48

Minor oscillations................................................. 49

Absent formations................................................ 49

Equivalent formations............................................ 50

Denudations ..................................................... 51

Extent of the Lower Cambrian land surface........................ 52

Extent of the basal Silurian beds .................................. 53

Historical geology............... 1........................................ 53

Economic geology .................................... .................... 55

Subjects for further investigation .......................................... 57

Index .... .............................................................. 59

ILLUSTRATIONS.

Page. 

PLATE I. Geological map of the Hudson Valley between the Hoosic and the

Kinderhook .................................................. 12

II. Microscopical sections of typical rocks: A, Cambrian sandstone; B, 

Cambrian shale; C, gritty beds in Cambrian shale; D, Ordovician 

(Hudson) grit; E, Silurian (Rensselaer) grit.................... 20

III. Structure sections, A,B, C....................................... 46

FIG. 1. Oldhamia (Murchisonites) occidens (Walcott)...................... 13

2. Organic impressions in quartzite from the Lower Cambrian shale..... 14

3. Calcareous sandstone with brecciated limestone or dolomite beds..... 15

4. .Diagram section of hill a half mile west of East Nassau.............. 18

5. Diagram section of ridge southwest of Hoag Corners, in Nassau ...... 21

6. Diagram section of ridge east of Tackawasick Creek, in Nassau....... 21

7. Diagram section across western edge of Rensselaer Plateau, in Nassau. 21

8. Diagram section across Curtis Mountain, in Nassau.................. 23

9. Diagram section across Ashley Hill, northeast of Riders Mills, in

Chatham....................................................... 24

10. Diagram section a mile south of Ashley Hill, in Chatham ........... 24

11. Diagram section 2 miles south west of WestSandlake, inEastGreenbusli. 25

12. Diagram section 2 miles east of Defreestville, in North Greenbush.... 25

13. Diagram section across the Cambrian and Ordovician at Troy, by

Foerste ........................................................ 26

14. Columnar section of the Cambrian at Troy, by Foerste .......... .... 26

15. Diagram section near Speigletown in Lansingburg .................. 27

1.6. Diagram section across the Cambrian and Ordovician in the Poesten

Kill at Troy.............................................. ...... 27

17. Diagram section across the fault near Schodack Landing............. 28

5

LETTER OF TRANSM1TTAL.

DEPARTMENT OF THE INTERIOR, 

UNITED STATES GEOLOGICAL SURVEY,

Washington, Z>. <?., May 11,1904..

SIR: I have the honor to transmit herewith the manuscript of a 

report on the geology of the Hudson Valley between the Hoosic and 

the Kinderhook, by T. Nelson D.ale, and to recommend its publication 

as a bulletin.

Very respectfully, C. W. HAYES,

Geologist in Charge of Geology. 

Hon. CHARLES D. WALCOTT,

Director United States Geological Survey.

GEOLOGY OF THE HUDSON VALLEY BETWEEN THE 

HOOSIC AND THE KINDERHOOK.

By T. NELSON DALE.

INTRODUCTION.

This paper treats of a strip of the Hudson Valley between the 

Hudson River on the west and the Rensselaer Plateau and the Taconic 

Range on the east. It is roughly bounded on the north by the Hoosic 

and on the south by the Kinderhook, and has an area of about 315 

square miles, situated mostly in Rensselaer County but parti}7 in 

Columbia County, N. Y.; it includes a portion of the area of the 

Cohoes, Troy, and Kinderhook sheets of the topographic atlas of the 

United States Geological Survey.

This area presents several geological problems which have long been 

in process of solution. These are: The delimitation and age of the 

 several formations, the order of their local deposition, and their present structural relations. These problems would be easily solved but 

for the rarity of fossil localities and the obscure character of many of 

the fossils, the petrographic similarity of beds belonging to several 

formations, the minor overturned folding which marks almost the 

entire belt, the reverse faulting in places, and the general prevalence 

of glacial deposits.

The publication of this paper carries out a design originated by 

Prof. Raphael Pumpelly, while in charge of the Archeandivision of the 

United States Geological Survey, to carefully study a belt, from 20 to 

40 miles wide from north to south, extending from the highly metamorphic zone of the Green Mountain range in Massachusetts to the 

zone of unaltered sediments at the Hudson River. Monograph XXIII 

of the United States Geological Survey, on the Green Mountains in 

Massachusetts (1894), and the writer's paper on the Rensselaer Plateau 

in New York (1893), marked the execution of the more important part 

of this plan, and the present paper completes it.

This paper does not claim to be exhaustive, but is intended to facilitate more minute explorations by others, as well as the extension of
10 GEOLOGY OF HUDSON VALLEY. [BUM,. 2-12.

the work southward and northward. It is offered as a contribution 

chiefly to the stratigraphy of the region, paleontological investigations 

having been made entirely subsidiary to that and having been confined to the reference of fossils to paleontologists for determination.

The paper presents mainly the results of three months' field work 

done by the writer, assisted by Mr. Louis M. Prindle, in 1893, and 

also of a month's work, without his assistance, during 1890, 1891, 

1894, and 1895, of another month's work in 1898 and 1899, and of 

about three weeks' work in 1901, in all equivalent to eight and thr.eefourths months' field work by one person. On the map (PI. I) are 

shown several important fossil localities, some hitherto unpublished, 

discovered by Mr. Charles D. Walcott prior to 1890, some fossil 

localities discovered by Ford in Troy, and several localities either 

discovered or located in Troy and Nassau by Mr. August F. Foerste 

during a three weeks' reconnaissance made in 1892 and in a few days 

of 1890. Mr. Foerste submitted a report of his detailed work about 

Tro}r to Professor Pumpelly, from which a few quotations and figs. 13 

and 14, which embody his general results, have been taken. Figs, i, 

5, and 6 are from Mr. Prindle's note book. Paleontological determinations have been credited in their places. Mr. Rudolf Ruedeniann's 

published graptolite localities on the Deep Kill'and at Schaghticoke 

are specially designated on the map.

The extension of geological field work by this Survey in recent 

years through the Cambro-Ordovician belt, along the west side of the 

Taconic Range, in Washington County, N. Y., and Rutland County, 

Vt., has thrown much light on the relations of these formations in the 

Hudson Vallejr, and will facilitate the interpretation of the phenomena 

to be described.

LITERATURE.

Omitting the maps and descriptions of the early surveys, the modern 

geological literature of this tract is as follows, arranged in chronological order:

1. FORD, S. W. Notes on the Primordial rocks in the vicinity of Troy, N. Y.: Am. 

Jour. Sci., 3d ser., vol, 2, pp. 32-34,1871.

2. FORD, S. W. Note on the discovery of a new locality of Primordial fossils in 

Rensselaer County, N. Y.: Am. Jour. Sci., 3d ser., vol. 9, pp. 204-206,. 1875.

(See also other paleontological articles by the same author in vols. 11, 1876, and 

19, 1880, of same journal.)

3. FORD, S; W. On the age of the glazed and contorted slaty rocks in the vicinity 

of Schodack Landing, Rensselaer County, N. Y.: Am. Jour. Sci., 3d ser., vol. 28, pp. 

206-208, 1884.

4. FORD, S. W. Observations upon the great fault in the vicinity of Schodack Landing, Rensselaer County, N. Y.: Am. Jour. Sci., 3d ser., vol. 29, pp. 16-19, 1885.

5. BISHOP, I. P. On certain fossiliferous limestones of Columbia County, N. Y., 

and their relation to the Hudson River shales and the Taconic system: Am. Jour. 

Sci., 3d ser., vol. 32, pp. 438-441, 1886.
DALE.] LITERATURE. 11

6. WALCOTT, CHARLES D. The Taconic system of Emmons and the use of the 

name Taconic in geologic nomenclature: Am. Jour. Sci., 3d ser.,vol. 35, pp. 229-327, 

395-401, and map, pi. 3, 1888.

7. BISHOP, I. P. A new locality of Lower Silurian fossils in the limestones of 

Columbia County, N. Y.: Am. Jour. Sci., 3d ser., vol. 31, pp. 69-70, 1890.

8. WALCOTT, CHARLES D. Correlation papers, Cambrian: Bull. U. S. Geol. Survey 

No. 81, p. 98 and footnote on p. 283, 1891.

9. DALE, T. NELSON. The Rensselaer grit plateau in New York: Thirteenth Ann. 

Kept. U. S. Geol. Survey, pt. 2, pp. 291-340 and map, pi. 97,1893.

10. WALCOTT, CHARLES D. Discovery of the genus Oldliamia in America: Proc. 

U. S. Nat. Mus., vol. 17, No. 1002, pp. 313-315, 1894.

11. ELLS, R. W. The Kensselaer grit plateau: The Ottawa Naturalist, vol. 9, pp. 

9-11, Apr., 1895. 

12. DALE, T. NELSON. Structural details in the Green Mountain region and in 

eastern New York: Sixteenth Ann. Kept. U. S. Geol. Survey, pt. 1, pp. 551, 554, 564, 

568, 1896.

13. DALE, T. NELSON. The slate belt of eastern New York and western Vermont: 

Nineteenth Ann. Kept. U. S. Geol. Survey, pt. 3, p. 188 (Description of thin sections

of Hudson grit from Troy and East Greenbush), 1899.

14. DALE, T. NELSON. A study of Bird Mountain, Vermont: Twentieth Ann. Kept. 

U. S. Geol. Survey, pt. 2, pp. 21, 22 (On the age of the Rensselaer plateau, in reply 

to Doctor Ells), 1900.

15. RUEDEMANN, RUDOLF. Hudson River beds near Albany and their taxonomic 

equivalents: Bull. 42 New York State Mus., vol. 8, Apr., 1901.

16. RUEDEMANN, RUDOLF. Trenton conglomerate of Rysedorph Hill and its fauna: 

Bull. 49 New York State Mus., pp. 1-114, 1901.

17. DALE, T, NELSON. Structural details in the Green Mountain region and in 

eastern New York (second paper): Bull. U. S. Geol. Survey No. 195 (Plano-convex 

limestone concretions from Nassau, Rensselaer County, N. Y.), p. 12, -1902.

18. ULRICII, E. 0., and SCIIUCIIEKT, CHARLES. Paleozoic seas and barriers in eastern 

North America: Rept. of the New York State Paleontologist. I'o/ 1901, 1902, pp. 633- 

672.

19. RUEDEMANN, RUDOLF. The graptolite (Levis) facies of the Beekmantown 

formation in Rensselaer County, N. Y.: Rept. of the New York State Paleontologist 

for 1901, pp. 546-574, 1902.

20. RUEDEMANN, RUDOLF. The Cambric Dictyonema fauna in the slate belt of 

eastern New York: Rept. of the New York State Paleontologist for 1902, pp. 934-958, 

1903.

21. DALE, T. NELSON. Taconic physiography: Bull. U. S. Geol. Survey No. 

(in preparation).

TOPOGRAPHY.

The most salient topographic feature in this tract is the line of hills 

bordering the horizon on the east, and ranging in height from 1,200 

to 1,400, rarely to 1,600, feet above sea level. This is the western 

edge of a plateau only a third of whose area appears on the map. 

Along the central part of the eastern edge of the tract here mapped 

this plateau is 3 miles wide, but in Grafton, at the north, and 

in Nassau, at the south, the plateau front recedes farther eastward. 

South of this plateau a somewhat irregular mass of hills, belonging to 

the Taconic Range and ranging from 800 to 1,150 feet above sea level, 

advances westward as far as Chatham. Between the point where the
12 GEOLOGY OF HUDSON VALLEY. [BUM, 242.

northern edge of the plateau turns eastward and the Washington 

County line there are no highlands.

The lowland is marked by numerous more or less oval hillocks, usually from 100 to 200 feet high, and mostly of glacial < . -ff ,ii. Twt 

conspicuous isolated hill masses, Mount Rafinesque in Brunswick (1,10'"« 

feet), with the adjacent Rice (or Bald) Mountain (925 feet) in Lansing 

burg, and Curtis Mountain (Dnsenbery Ridge) in Nassau (1,180 feet), 

rise from 500 to 600 feet above the lowland. The lowland drops gradually from the 600- and YOO-foot levels at the east to the 250-foot level 

at the .west in a distance of 7 to 11 miles, and within another mile 

descends to tide water. The drainage is all to the Hudson. The principal streams, beginning at the north, are the Hoosic, the Poesten Kill, 

the Wynant Kill, the Moordener Kill, and the Kinderhook. Numerous 

smaller streams enter the Hudson directly, having cut deep ravines in 

the terrace-capped shales which form its eastern bank. The Hoosic, 

near Schaghticoke, has cut a canyon nearly 200 feet deep through similar materials. The Poesten Kill, which drains a large part of the 

plateau, flows through a deep incision in its western edge, and has cut 

a small gorge 2| miles east of the Hudson and another at Troy. Owing 

to the glacial deposits and river terraces outcrops occur chiefly along 

the watercourses.

For the general physiography of the 'region the reader is referred 

to the writer's forthcoming "Taconic Physiography 1 ' (No. 21, p. 11).

AREA:L GEOLOGY.

The principal geological traits of the strip are shown on the map (PI. 

I). There is a central longitudinal Cambrian belt, consisting mainly of 

shale, extending from the Washington County line to Chatham Center and beyond, which is from If to 11 miles wide. This Cambrian 

belt includes, however, two outliers of upper Ordovician age, one covering about three-fourths of a square mile in North Greenbush, the 

other about 9 square miles, including Mount Rafinesque and Rice 

Mountain, and situated partly in Brunswick, Pittstown, Lansingburg, 

and Schaghticoke. This Cambrian belt is bordered on the west by the 

upper Ordovician shale and grit through which the Hudson flows, the 

boundary between the two formations being probably a fault. At 

the north the Cambrian belt narrows, and is bordered on both sides 

by Ordovician shale and grit. Ordovician areas likewise recur at 

the south, alternating with Cambrian strips, and also in places along 

the foot of the plateau. South of the plateau Ordovician schist, the 

metamorphic equivalent of the shale and grit, constitutes the Taconic 

Range and merges into these at the west. There are also a number of 

very small areas of Beekmantown shale (lowest Ordovician) overlying 

the Cambrian. Finally, the Rensselaer grit, with its interbedded slate
U.S. GEOLOGICAL.SURVEY BULLETIN No.242 PL. I

fcWJHINGTON ! _CO. ,

MAP OF

THE HUDSON VALLEY

BKTW.EKN

HOOSIC RIVER

AND

KINDERHOOK CREEK

BT X NELSON DALE 

Sc«le of miles

Scale of kilometers

O I 23456

CHIEF OUTCROPS 

Sandstone and limestone breccia

< I ^ i iypieal red and dreeti shale 

0 [with small quartzlte beds

Graptolites (Trenton) 

Tveritoii fossi

A Oldhatiiia occidens 

A Ruedemanris localities

 Possible fault 

Strike

JULIUS O1 EN & CO. LITH.N.Y.
DALE.] AREAL GEOLOGY. 13

and shale, representing the basal part of the Silurian, constitutes the 

plateau, besides an outlying lenticular area of 4£ square miles in 

Nassau and Chatham, another of half a square mile near North Nassau, 

and a much smaller area resting on the Ordovician schist near Spencertown in Austerlitz, 12 miles south of the plateau. 

Each of these formations will now be described in detail.

LOWER CAMBRIAN. 

FOSSIL LOCALITIES.

The map shows 30 localities of Cambrian fossils, all Lower Cambrian (Olenellus fauna), according to determinations by Ford, Walcott, 

or Foerste. The fossils usually occur in small limestone beds in the 

shale. In places the limestone is made up so 

exclusively of Olenellus fragments as to deserve 

the name Trilobite limestone. In some places 

pteropods are frequent; in others, brachiopods.

Besides these there are 5 localities where the 

calcareous alga or nullipore, Oldhamia (Murchisonites) occidens Wale., has been found. These 

are designated by a separate symbol on the map. 

(See paper No. 10, p. 11. Mr. Walcott's figure 

is here reproduced fig. 1.) The description of 

the localities, sent to him by the writer for inclusion in that paper and therein published, is here 

repeated:

The Oldhamia was first found in reddish shales associated 

with greenish shales and beds of quartzite, ranging from 1 

to nearly 22 inches in thickness, at a sawmill dam midway 

between Burden Lake and Nassau Pond, in the township 

of Nassau; again in similar rocks about 2 miles farther up J

gle frond. Natural size. Possiblyanullipore. LowerCambrian. From the gorge of the' 

Poesten Kill, 2i miles east of 

Troy. Copied from Proc. Nat. 

Mus., vol. 17,1894, p. 314, fig. 1.

the same stream and 1$ miles south-southeast from the FIG. i. oidhamia (Mnrchisonsouth end of Burden Lake. It occurs also on the Moor- ites)ocddcns( Walcott). Asindener Kill, about 1} miles northeast of Schodack depot, in 

the township of Schodack, and in great abundance in the 

gorge of the Poesten Kill, If miles east of Troy, near the 

Eagle Mills [Millville] road, along the right bank of the 

river, which there flows south. The Oldhamia is here associated with various trails, and both cover large surfaces of the rock.

Still another Oldhamia locality is about a mile east of Nassau village, 

between two road corners, on the north side of the road. The fossil 

will probably also be found near the South Schodack railroad crossing 

and at many other points. The locality near Troy is the most accessible and the most likely to reward collectors.

Mr. Walcott regarded this Oldhamia as closely related to the Oldhamia antigua-oi the Cambrian of Ireland, but "the determination of
GEOLOGY OF HUDSON VALLEY. [BULL. 242.

the geologic horizon" as "somewhat uncertain." His assignment of 

the reddish shale to '' the post-Lower Cambrian and pre-Trenton " was 

based mainly upon the writer's interpretation of the stratigraphy at 

that time, when the reddish shale seemed to him to overlie the Lower 

Cambrian fossiliferous limestone. The determination of the precise 

position of this reddish and greenish shale with beds of quartzite of 

various thickness with reference to the Lower Cambrian limestone is 

attended with no little difficulty. The reddish color is not a safe 

guide in this region, for such shale is sometimes associated with 

black graptolite shale and is then of Trenton-Hudson age. It is 

also interbedded with the Rensselaer grit, and then belongs to the 

Oneida and Medina. But in places it also occurs below the Lower

Cambrian fossiliferous 

limestone. The stratigraphic reasons for finally 

assigning the Oldhamia 

shale to this last position 

will be given under'' Stratigraphy."

The same series of alternating red and green shale 

and small quartzite beds is 

also marked by annelid 

trails and casts of bifurcating impressions which have 

as yet no chronological or 

paleontological importance. These casts are,

however, here quite char- Fro. 2. Fossil casts of organic impressions in quartzite from the . , .

Lower Cambrian shale in brook bed a mile north of Poesten-ftCteriStlC 01 the Series, 

kill village. Redrawn from a photograph taken by Dale ^yrflJQh also Carries the Oldand Foerste. , . _.. ,.. liarma. Jbig. 2 will serve

to convey an idea of their general appearance and dimensions. As 

the forms stand out in relief on the quartzite surfaces the impressions themselves must have been made on the clay surfaces and then 

filled with sand, which has become quartzite or grit. The more important outcrops of this typical shale are indicated on the map.

PETROGRAPHY.

Certain rocks of the Lower Cambrian have such marked characteristics as to deserve special notice. A metamorphic olive grit, usually 

weathering a light brick red, crops out at a few points, and is also 

typical of this formation in Washington County. (See p. 179 of the 

paper No. 13, p. 11, for microscopical description.) It occurs one-half
BALE.] PETROGRAPHY. 15

mile east of Lake Ida, in Troy, and also north of its eastern end; onehalf mile southwest of Wynantskill; at the milldam in Raymertown; 

at Brunswick Center; in Lansingburg, at Oakwood Cemetery, on the 

north side of the outlet of the pond, where it contains organic impressions and is in contact with the Ordovician shale; and at a point a 

mile south of Grant Hollow.

Still more characteristic of the Cambrian, and of much more frequent occurrence, is a calcareous sandstone .and an associated limestone 

breccia. (See pp. 183, 184 of No. 13, p. 11, for a description of this 

sandstone as it occurs in Washington County.) This rock usually consists of roundish quartz grains held together by a cement of crystalline 

and granular calcite or of dolomite. On the weathered surface these 

grains stand out in relief and are slightly opalescent. They are even 

noticeable in the loose stones of the rye fields, and may be taken as 

an almost infallible indication of Cambrian age. Associated with 

these quartz grains is an occasional grain of plagioclase. Pebbles of 

carbonaceous-siliceous shale or of chloritic shale are quite characterFIG. 3. Sketch of a specimen of calcareous sandstone with 

small brecciated limestone or dolomite beds, typical of the 

Lower Cambrian of Rensselaer County. About one-third, 

natural size. Locality, south of Lake Aries, in North Greenbush. From Sixteenth Ann. Kept., pt. 1, p. 569.

istic of this rock. There are also oolitic calcareous spherules from 

0.12 to 0.75 mm. in diameter, which are sometimes ferruginous, suggestive of rhizopods, and grains of limestone consisting of similar 

spherules. A microscopical drawing of the rock is shown in PI. II, 

A (p. 20).

This sandstone very often includes beds of bluish fossiliferous 

limestone from one-half to 1 inch thick, which are generally brecciated, probably because of their greater rigidity under lateral compression than the intervening sandstone. (See fig. 3, which is taken 

from p. 569, fig. 99, of paper No. 12, p. 11.) The abutments of the 

grade crossing a mile south-southwest of the Lansingburg reservoir 

are built of this material and exhibit well its general character.

This sandstone is frequently associated with (either passing horizontally into or underlain at no great interval by) a quartzite in which 

the cement is either very slightly calcareous or sericitic. Both sandstone and quartzite are apt to be traversed by a network of veins and 

veinlets of quartz, which, owing to the rapid weathering of the CaCO., 

of the cement, project on its surface., This sandstone crops out in
16 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

Oakwood Cemetery in Lansingburg, and continues north northeast for a 

mile to a hillock, known locally as "Diamond Rock," on account of .its 

abundance of quartz crystals; these occur in association with such veins.

The more important outcrops of the olive grit and of the calcareous 

sandstone and breccia are shown on the map, PL I. Outcrops of the 

latter at which fossils were found are, however, designated simply as 

fossil localities.

A limestone conglomerate deserves notice. Two miles south of 

Schodack Landing (Coxsackie quadrangle), or 7 miles west-southwest 

from North Chatham, the Cambrian shale and limestone form a cliff 

about 70 feet high (fig. 17, p. 28). Near the top is a bed about 10 

feet thick, the lower part of which is a brecciated limestone, but 

the upper resembles a conglomerate; and it looks as if the brecciated 

limestone had for a while been exposed to wave action. The pebbles are limestone carrying Lower Cambrian fossils, but the cement 

is shaly. Some of the pebbles have pitted surfaces. This bed is 

capped by a few inches, of coarse-grained limestone also carrying 

Lower Cambrian fossils. At Ashley Hill, a mile northeast of Riders 

Mills, in Chatham, the brecciated; Cambrian limestone seems also to 

pass into a conglomerate, and the pebble-like nodules are likewise 

pitted from the impression of the quartz grains of the matrix. This 

pitting will be found explained and illustrated in pp. 312, 313, and fig. 

24 of paper No. 9, p. 11. Foerste traced similar pebbles in the Cambrian shale at Troy to small limestone beds which had undergone a 

process of brecciation, slip cleavage, and partial solution. (See p. 

569, fig. 100, of paper No. 12, p. 11.) Such "pebbles" might also be 

accounted for by a .concretionary process taking place in sediments 

which were partly calcareous and partly argillaceous; or, finalty, by a 

slight crustal movement exposing the limestone to wave action during 

a brief period and then submerging it again. The applicability of 

the first two theories should be carefully tested before resorting to an 

explanation involving geographical changes. It is, however, quite 

possible that such changes did occur here in Lower Cambrian time, 

and that in some localities there are true conglomerates a, in others 

autoclastic ones.

A greenish shale, occasionally slightly reddish or blackish,, covers 

a number of square miles of the Cambrian area. In places it underlies and is interbedded with the fossiliferous limestone. Under the 

microscope it is a very fine-grained aggregate of muscovite and 

chlorite scales, angular quartz grains, rarely plagioclase grains, with 

brownish dots which are probably limonite. The direction of the bed- 

"ding is shown by bands of quartz grains, but the bedding foliation is 

crossed by an incipient slip cleavage, so that the, muscovite scales

aWalcott, Charles D., Paleozoic intraformational conglomerates: Bull. Geol. Soc. America, vol. 5, 

pp. 191-198, Pis. V-VII, 1894.
DALE.] PETBOGKAPHYo . 17

appear as if arranged in two directions, at a large angle to each other. 

PI. II, B, shows a microscopical drawing of this shale. The ledge from 

which the specimen came has bedding planes striking N. 5° E. and 

dipping 35° W., crossed by a cleavage foliation striking N. 7° W and 

dipping 70° E., besides vertical joints striking N. 70° E. In consequence of these three systems of partings the rock weathers into sticklike fragments, and this mode pf weathering is very common in this 

 shale. The economic importance of this will be shown under "Economic geology." The microscopical composition and structure of this 

shale indicate that it would probably not have required a vastly 

increased amount of compression to transform it into schist.

This shale is very frequently interbedded with quartzose beds, weathering rusty-brown, from one-half inch to 2 inches thick. These little 

beds, when examined microscopically, prove to range from an almost 

pure quartzite to a dolomitic quartz grit. With the quartz grains, 

which are generally angular, are always a few of plagioclase and of 

zircon, and sometimes scales of muscovite and of chlorite and grains of 

tourmaline. The cement varies in quantity and in material, being 

sometimes purely siliceous, or partly siliceous and partly calcareous or 

sericitic, and sometimes entirely dolomitic. There are also black particles, probably graphite, and there is limonite staining from the 

decomposition of pyrite or carbonate. A typical section of the more 

gritty beds is shown in PI. II, 0.

There remain to be described certain greenish coarse and fine 

quartzite beds interbedded with the red and green shale bearing Oldhamia occidens. These differ little from those just described except 

in the occasional abundance of chlorite or chlorite-schist areas or fragments. Belonging to the same series are beds of massive quartzite, 

from 8 to 50 feet thick, of similar character, but including here and 

there small beds of quartz conglomerate, in which the pebbles measure 

up to one-fourth .and even one-half inch in diameter, and occasionally 

a pebble of dark-greenish slate.

The reddish shale associated with all these quartzite beds varies much 

in the amount of its hematite and, therefore, in the intensity of its 

color. In the gorge of the Poesten Kill, a little east of Troy, and also 

in other places, the color is purplish. In the hill mass west of Burden 

Lake the red is deep. The green shales owe their color to chlorite, 

the purplish ones probably to chlorite and hematite, and the blackish 

ones, naturally, to carbon.

STRATIGRAPHY.

The paleontological evidence as to the age of these beds having been 

given, and their petrographical features shown, they will now be examined stratigraphically. At the outset, however, it must be stated that

Bull. 242 04 2
18 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

it is impossible to determine their total thickness, because they consist 

so largely of closely folded and easily weathering shale and because 

there are so few deep cuts across them. When a bed of quartzite disappears beneath the shale, there are no means of identifying it and fixing 

its position in a series which includes several such beds. A number 

of detail sections of the Cambrian beds follow, which will afterwards 

be generalized in tabular form. Their relations to the Cambrian series 

of Washington County, N. Y., and of the Green Mountain range, in 

Massachusetts and Vermont, are shown in the table on page 43 and are 

discussed on page 50.

About a half mile northwest of East Nassau the Kinder-hook turns at 

a right angle to flow south between two steep hills. The eastern hill 

consists of Rensselaer grit, but the western one of thick beds of quartzite and thin-bedded red and greenish shale, which, for reasons to be 

given, are all regarded as being Lower Cambrian. Fig. 4 represents a 

diagrammatic cross section of this hill. It shows two thick beds of

PIG.. 4. Diagram section of first ridge west of Kinderhook Creek and Snake Hill, in Nassau. 

Dotted beds, quartzite; lined beds, shale. Height, about 200 feet. Quartzite, about30 feet 

thick.

quartzite and two masses of shale. The lowest of these shale beds is 

red, and the upper contains small beds of quartzite. This same series 

recurs 2 miles.north-northeast along the strike, making up the ridge 

on the east side of Tackawasick Pond, :wnich"continues 2 rniies north 

to Hoag Corners. The structure of this ridge is complex. At the 

extreme north it consists of a simple syncline of massive quartzite 

underlain by red shale, as shown in fig. 5 (p. 21). About a half mile south 

a small anticline of the same rocks appears east of this syncline, and 

'within another half mile another syncline is added east of that anticline. Combining the observations made at all points the structure of 

the whole ridge appears to be approximately as shown in fig. 6 (p. 21), 

and thus, like that shown in fig. 4, consists of two thick quartzite beds 

separated by red shale, and the lower quartzite also underlain by red 

'shale- There is considerable variation in the. thipkness of the quartzite; the bed sometimes divides into smaller ones, and,the.se. unite again 

farther on. The folds here have a marked northerly pitch and have 

been greatly eroded.
PLATE II.

19
PLATE II.

MICROSCOPICAL SECTIONS OF TYPICAL ROCKS.

A. Microscopical drawing of two thin sections of calcareous sandstone typical of the 

Lower Cambrian of Rensselaer County, showing roundish quartz grains (unshaded), 

grains of concretionary limestone containing quartz grains, grains of granular limestone or dolomite (finely dotted), large ferruginous concretions, and a small grain of 

plagioclase, all in a matrix of crystalline calcite with some large'plates of calcite.

B. Microscopical drawing of thin section of greenish shale typical of the Lower 

Cambrian of Rensselaer County, from near Nassau village. The section crosses three 

minute beds, two of which are made up largely of quartz grains (unshaded particles). 

Direction of bedding shown by arrow. The position of some of the muscovite and 

chlorite scales (black particles) shows an incipient cleavage. Two grains of plagioclase 

(banded).

C. Microscopical drawing of a thin section of a small gritty bed typical of the Lower 

Cambrian shale of Rensselaer County, from one-fourth mile north of Lake Ida, in 

Troy, showing angular quartz grains (unshaded), three plagioclase grains, and two 

zircon grains, in a matrix mainly of sericite.

D. Microscopical drawing of a thin section of grit typical of the Hudson formation of 

Rensselaer County, from 1£ miles south of Grandview Hill, in Greenbush, showing 

angular quartz grains (unshaded), grains of plagioclase and .orthoclase, two grains of 

zircon (lower left corner), one large grain of quart'zite, presumably of Cambrian 

origin, and some carbonaceous matter (black), all in a matrix of fine argillaceous 

material with considerable calcite (finely dotted areas).

E. Microscopical drawing of a thin section of Silurian grit typical of the Rensselaer 

grit, from the western edge of the plateau, showing large and small angular grains 

of quartz (unshaded), four grains of plagioclase, one grain of microcline, one of 

orthoclase, and several grains of ilmenite (?), all in a matrix of sericite and chlorite.

20
U. S. GEOLOGICAL SURVEY

 - V' i"H''.'> 3'-; *-'k*v 'i ~~s*' !» - ' ' V"-'"'^.. '>Jf l.l'i -i mm

v *^> ^v v ^(

' / :;
DAtE.J STRATIG&APHV.

The north-south hollow through which runs the road from East 

Nassau to Hoag Corners separates this last ridge from another east of

w

FIG. 6. Diagram section of ridge southwest of Hoag Corners, in Nassau. Dotted beds, quartzite; lined beds, reddish shale containing small beds of quartz!te with casts of organic impressions, etc.

it. Upon this is situated the Coonradt farm. This ridge is separated 

from the edge of the Rensselaer Plateau by still another hollow.

FIG. 6. Diagram section- showing the general structure of the ridge between Tackawasick 

Creek and Pond and the Rensselaer Plateau, in Nassau. Dotted beds, quartzite; lined beds, 

shale. Height, about 200 feet.

This ridge also consists of two thick beds of quartzite, each of which is 

both underlain and overlain by red and green shale with small quartzFIG. 7. Diagram section across the western edge of the Rensselaer Plateau and the second 

ridge east of Tackawasick Pond, in Nassau, showing the surface relations and the probable 

structural relations of the Lower Cambrian quartzite and shale (Gl), the Hudson limestone 

and shale (Oh), and the Silurian'Rensselaer grit (Sr). Dotted beds (61), quartzite; lined 

beds, red and green shale with small quartzite beds with organic impressions. Height of 

western ridge, 90 feet.

ite beds having casts of organic impressions. (See fig. 7.) The section 

has been extended eastward across a small hillock in the adjoining 

hollow to the edge of the plateau.
22 GEOLOGY OF HUDSON VALLEY. [BULI, 242.

A similar series is also exposed on Curtis Mountain, better known 

locally as Dusenbery Ridge. This can best be observed by ascending the mountain from the saddle between two road forks a half mile 

south of the western part of Tackawasick Pond. There is first a 40-foot 

bed of quartzite dipping steepty west and 90°, with red shale under 

it on the east, followed on the west by 50 to 70 feet of reddish shale 

with small quartzites with similar dip; then at the head of a ravine 

there is a ledge, several hundred feet long, of reddish and green shale 

with small quartzites capped by another bed of quartzite, 15 feet thick, 

with a low westerly dip. Higher up, after an interval, comes greenish 

shale with steep westerly dip, recurring at the summit, where it forms 

an open syncline capped by a slightly calcareous quartzite bed, 10 feet 

thick, with a gentle southerly pitch. Now, descending the ridge on 

the west, there is a large body of greenish shale with easterly dip, 

followed, near the road which skirts the crest on the west, by a bed of 

quartzite, about 40 feet thick, dipping 45° E., underlain by shale 

and small quartzites. Within 80 feet of the road is still another bed 

of quartzite, nearly 10 feet thick, with like dip; and west of that road 

in a brook (a mile southwest of Tackawasick Pond) is the typical red 

shale with small quartzites dipping 45° E. and 80 feet thick. These 

two beds of quartzite with the alternating shale can be traced 1£ 

miles north along the crest of Curtis Mountain. A similar series with 

like dip, evidently belonging to the western part of the same syncline, 

crops ouk li miles south of this last locality, between a small brook 

crossing the road to Nassau about 3 miles east-southeast of that 

village, and a corner east of it where three roads meet. Here an upper 

quartzite, 20 to 25 feet thick, dipping from 45° to 50° E., is underlain by 30 to 40 feet of red and green shale with small quartzites, 

and these again by another bed of quartzite 8 to 20 feet thick. The 

same series, but on the eastern side of the syncline, is again exposed 

on the east side of Curtis Mountain a mile south of the section. Unfortunately the relations are obscured there by overturning and by 

the coming in of. other folds. The general structure of the Curtis 

Mountain syncline is shown in tig. 8.

Ashley Hill, in Chatham, between Riders Mills and Brainard, lies in 

the direction of the strike of the syncline on Curtis Mountain. The 

relations there, however, become perplexing, owing either to faulting or 

to the syncline being close and followed on both the east and the west by 

anticlines. Indications of an anticline in the southern part of Curtis 

Mountain, east of the syncline, have just been pointed out. There is a 

bench west of the crest of Ashley Hill with a fine exposure of limestone breccia and conglomerate, about 20 feet thick and one-fourth mile 

long, with the fauna of the Olenellus zone. a This breccia is associated

. a See, for petrography, p. 15, and also pp. 312-314 and map, PL XCVII, of paper No. 9, p. 11.
DALE.]. STRATIGRAPHY. 23

with grayish and black shale. At the western edge of the bench is the 

typical calcareous sandstone with a westerly dip, while east of the 

fossiliferous belt is a noncalcare.ous quartzite, probably of the same 

horizon. In following the strike of the fossiliferous beds northward, 

down along the ravine to the Kinderhook, the breccia disappears, but 

the associated black and gray shale crops out occasionally. The calcareous quartzite occurs on both sides of the ravine, with a dip varying according to the overturn of the syncline or as the axis of either 

adjacent anticline is crossed. This quartzite recurs li miles northnortheast of Ashley Hill, along the east-west road on the north side of 

the Kinderhook, and appears to be the same rock as that capping the 

southward-pitching syncline at the top of Curtis. Mountain, 2£ miles 

north-northeast of Ashley Hill, from which the fossiliferous limestone 

would thus appear to have been eroded. In the northern part of the 

bench on Ashley Hilfthe calcareous quartzite is underlain on the east 

by a mass of grayish shale, and this by a bed of massive quartzite, 45 feet

FIG. 8. Diagram section across the southern part of Curtis Mountain (Dusenbery Ridge), in 

Nassau, showing the relation of the two thick quartzite beds and the red and green shale 

with small quartzite beds to the calcareous quartzite syncline at the top. Height, about 

400 feet.

thick, dipping 70° W. Farther south, owing probably to an overturn, the dip changes to 55° E., and the gray shale there apparently 

underlies the massive quartzite. Still farther south is a small outcrop 

of noncalcareous granular quartzite, already referred to and regarded 

as the continuation of the calcareous, quartzite, and lying east of the 

fossiliferous bed. East of this is a space of 550 feet of the typical 

red shale and small quartzites, with the usual casts; 480 feet of these 

dip steeply east, but the last TO feet are greatly contorted .and have 

folds pitching 60° S."

East of these are about 150 feet of green shale, then the massive 

quartzite, 40 feet thick, dipping 65°-70° E., and forming the crest of 

the hill. About 300 feet farther east is another thick bed of quartzite, dipping 25° E. The gist of all these data is that there is here a 

bed of calcareous quartzite underlain by shale, and this by two beds 

of massive greenish quartzite with intervening thicknesses of shale, or 

by pne bed of quartzite .doubled in an anticline, the whole closely

a See p. 552 and fig. 75 of paper No. 12, p. 11.
24 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

resembling the series.on Curtis Mountain, but here.overlain by the 

fossil if erous limestone breccia and conglomerate. The general structure 

of Ashley Hill thus appears to be that shown in fig. 9. That there 

is a syncline on the western side of the hill is shown by the easterly dip 

of a bed of quartzite, 8 feet thick, along the highway a half mile west 

of the top. . About a mile south of Ashley Hill and three-tenths of a mile west 

of Rayville station, in Chatham, is another important locality. Its

FIG. 9. Diagram section across Ashley Hill, northeast of Riders Mills, in Chatham, Columbia 

County, showing the relation of the upper massive quartzite bed and the red shale with 

small quartzite beds to the calcareous quartzite (2) and the fossiliferous Lower Cambrian 

limestone breccia (61).

stratigraphy is shown in fig. 10. Here are two small synclinal hillocks 

separated by an anticlinal hollow. The fossiliferous Lower Cambrian 

limestone, about 100 feet thick, is underlain by gray and red shale 

with small quartzite beds. The eastern sj^ncline has a 5-foot bed of

FIG. 10. Diagram section across the hillock a mile south of Ashley Hill, in Chatham, Columbia County, showing the relation of the quartzite (dotted bed) and of the red shale (R) and 

green shale (G) to the fossiliferous Lower Cambrian limestone (61). Height, 60 feet.

brecciated limestone below the red shale, and this is underlain by 

gray shale with quartzite beds from one-half inch to 2 inches thick. 

West of these hillocks is a bed of calcareous sandstone dipping 

toward and probably under them. This tends to corroborate the interpretation of the structure of Ashley Hill as to the relations of the sandstone to the fossiliferous beds.

At a small limestone quarry in East Greenbush, 2 miles south-southwest of Lake Aries and 2 miles southwest of West Sandlake, a mass of
DALE.] STRATIGRAPHY. 25

Lower Cambrian bluish limestone or dolomite and calcareous quartzsandstone, interbedded with dark-gray shale, and a mass of gray 

shale in contact with it on the east, all dip steeply west; and 200 feet 

west another outcrop of the same limestone dips east, and there is 

also easterly dipping shale south of it. These outcrops, taken altogether, indicate the structure shown in fig. 11. Among the limestone 

strata are large disk-shaped, veined concretions (septaria). Similar 

Cambrian beds in Nassau contain plano-convex .concretions which are

mofeet

FIG. 11. Diagram section 2 miles southwest of West Sandlake, in East Grecnbush, showing 

the relation of the Lower- Cambrian limestone (61) and gray shale.

not veined. See paper No. 17, p. 11. The eastern limb of this sy ncline 

is again exposed about 800 feet south, but there with an easterly dip. 

At a small quarry about 1£ miles west of Lake Aries, on the south 

side of the road which follows the north side of the lake, the calcareous sandstone'and limestone breccia, with the Olenellus fauna, is in 

contact on the west with greenish shales for one-fourth of a mile along 

the strike. That this shale here overlies the limestone seems probable from the presence of a small anticline in the limestone along the

. 100 f ee-t .'

W

FIG. 12. Diagram section 2 miles east of Defreestville, in North Greenbush, showing two 

interpretations of the relations of the greenish shale to the Lower Cambrian fossil iferous 

limestone (61),

road, as well as from the almost horizontal dip of the limestone on the 

east side of the knoll. About 200 feet east of the quarry the shale 

crops out again, dipping east under beds of calcareous sandstone. The 

lower part of this shale has small quartzite beds with casts of organic 

impressions (fig. 12). The evidence as to the relations here is not conclusive. The figure shows two hypotheses: According to 1 the sandstone would underlie both masses of shale, but according to II it would 

overlie the shale with quartzites and underlie that at the west without
26 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

quartzites. There is also a third possibility that there is no repetition 

of beds, but two calcareous and two shale beds. -

Foerste found that the Cambrian fossil iferoiis beds east of Troy,

w

FIG. 13. Diagram section by Foerste, but slightly modified, showing the probable general 

relations of the Lower Cambrian fossiliferous limestone ( 1) at Troy to the red and green 

shale (lined beds) and to the Hudson shale (Oh).

between the 200- and the 400-foot levels, constitute two synclines and 

two anticlines, underlain by reddish and greenish shale and separated 

from the Ordovician beds by the overthrust, as shown 'in fig. 13. He

i.i.i.'. 1 . 1 . 1 . 1

'i I I i i i I I L

15 feet

A few feet 

I0-20feet

100 feet +

FIG. 14. Columnar section by Foerste, showing the Lower Cambrian series exposed at Troy. A, red and green shale, in places"with small quartzite beds. B, 

light-blue dolomitic limestone intercalated asflne layers and sometimes forming 

"brecciation pebbles" in the shale. C, shale with or without limestone beds. 

D and E, quarto sandstone more or less calcareous, sometimes replaced by sandy 

shale. F, light-blue dolomitic limestone.

also gives the following section, fig. 14, as representing the Cambrian 

series of that vicinity.

If the Cambrian beds be followed northward, a different series is 

found. From Oakwood Cemetery to the vicinity of Melrose the olive
STRATIGRAPHY. 27

grit, already referred to under "Petrography," crops out occasional \y 

between the Ordovieian shale and the Lower Cambrian sandstone, giving a cross section approximately like that shown in fig. 15. This, 

olive grit occurs also at Rayraertown associated .with the same sandstone. Its exposures near Lake Ida at Troy would bring it, by overw

FIG. 15 Diagram section near Speigletown in Lansingbnrg, showing the general relations of the olive grit (G) to the Lower Cambrian sandstone (61) and the Hudson shale 

(Oh).

turned folding, under the red and green shale with annelid trails 

and Oldhamia, which in turn underlies the fossil if erous Cambrian 

limestone.

The following section, fig. 16, embodies the writer's observations at 

and below the dam in the Poesten Kill at Troy. Here reddish, purplish,

w

Fault

FIG. 16. Diagram section across the dam in the Poesten Kill at Troy, showing the relation 

of the Hudson shale (Oh) to the Lower Cumbrian red, purple, and green shale (1) and the 

relation of these to the sandstone bed with Hyolithesand Hyolithellus (2). Height, 100 feet.

and greenish shale underlies a sandstone bed carrying the Olenellus 

fauna, as determined by Mr. Walcott. This colored shale with trails 

closely resembles that occurring about 2 miles northeast of this 

locality, which carries Oldhamia.

To these sections should be added one at the well-known locality 2 

miles south of Schodack Landing, i. e., 7 miles west-southwest from
28 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

North Chatham, described by Ford (see paper No. 4, p. 10), as it throws 

much light on the thickness and order of the Lower Cambrian beds. 

(See fig. IT.) The section combines the observations at the cliffs, where 

the thrust plane is not exposed, with those made a third of a mile north, 

where, however, the beds dip more steeply, the Cambrian 50° and the 

Ordovician 55°. The dip of the beds in the figure is taken from the 

cliffs.

These sections will serve to convey a general idea of the Cambrian, 

stratigraphy in this region. Its main features consist of a series of 

fossiliferous limestone beds, alternating with shale and sandstone, and 

carrying the Olenellus fauna, underlain by gray, red, or purple and 

green shale, as shown in figs. 11, 14, and 17. On Ashley Hill (fig. 9) 

this shale is underlain by a calcareous quartzite, and also near Kayw

FIG. 17. Diagram section showing the relation of the Lower Cambrian Milestone 

(B, C, D) and shale (A) to the Hudson shale (Oh) as exposed at two localities 

near Schodack Landing in Eensselaer Comity. B, bedded limestone and nodular 

limestone in shale (Olenellus fauna). C, Conglomerate with a brecciated limestone stratum below it. The pebbles have Olenellus fauna. I), Coarse-grained 

limestone bed with Olenellus fauna.

ville station (fig. 10). North of Troy this shale is underlain by an 

olive grit with or without the intervening quartzite. On Curtis Mountain (fig. 8) the calcareous quartzite is underlain by three horizons of 

shale, alternating with two of quartzite. These appear again in the 

ridge south of Tackawasick Pond (fig. 4) and in that east of it (figs. 5 

and 6J. The red, purple, and green shale which underlies the fossiliferous limestone at Troy (fig. 16) probably belongs to the same horizon 

as that which 2 miles east of that city carries the Oldhamia. The 

red and green shale with casts and Oldhatnia, in Nassau, is petrographically identical with that which is interbedded with, the two 

massive quartzite beds (figs. 4, 5, 6, 7, 8, and 9).

All the data in sections 4 to 17 are combined in the following table, 

to which estimates of thickness, based upon measurements at various 

localities, have been added, as well as references to the figures.
DALE.] STEATIGEA.PHY. 29

Table showing the Lower Cambrian series as exposed in Rensselaer County and part of

Columbia County, N. Y.

Serial 

letter.

.1 

I

H

G 

F

E

D 

C

. B 

A

Description of strata.

Thin-bedded limestone, or dolomitic 

limestone, in varying alternations 

with black or greenish shale and 

calcareous quartz sandstone. Some 

of the limestone beds brecciuted 

within the sandstone or shale and 

forming brecciation pebbles, in 

places, however, beach pebbles.

Greenish, reddish, purplish shale, 

in places with small beds of more 

or less calcareous quartette. 

At Troy, in upper part a 2£-foot bed . 

 of calcareous sandstone.

Granular quartzite, in places a calcareous sandstone.

Olive grit, metamorphic, usually 

weather! ng reddish ; absent at south.

Greenish, or reddish and greenish, 

shale with small quartzite or grit 

beds.

Massive greenish quartzite, in places 

very coarse.

Reddish and greenish shale with 

small bedsof quartzite or grit (rarely 

up to 5 feet thick).

Massive greenish quartzite, in places 

very coarse.

Reddish and greenish shale with 

small beds of quartzite or grit, from 

1 to 12 and, rarely, 24 inches thick.

Evidence.

.Figure.

12 ?.................

9, 10, 11, 12, 13, 14,17. 

10, 11, 13, 14, 16, 17..

8, 9, 10 ..............

15...................

7, 8, 9.............:.

4, 6, 7, 8, 9 ..........

4, 5, 6, 7, 8 ..........

4, 5, 6, 7; 8 ..........

4,5,6,7,8 ...:......

Fauna.

Olendlue fauna .....

Oldhamia, annelid 

trails.

Hyolithcs and Hyolithellns.

Traces of V ..........

Castsof impressions, 

Oldhamia.b

Casts of impressions, 

Oldhamia.

Casts of impressions, 

Oldhamia.

Estimated 

thickness.

Feet. 

50

'< 20-200

25 V-100+

ld-40 

18-50 

05-535

10-50 

30-80

8-40 

50-80

"Usually 50. '> Oldhamia occurs in A, C, or E, and quite possibly in all three. 

Minimum, 286. Maximum, 1,225+.

AREAL AND STRUCTURAL RELATIONS.

The greenish and reddish shale which makes up the greater part of 

the Cambrian area belongs to the several shale horizons A, C, E, H, I, 

and J. The shales of these horizons can be distinguished only where 

they corne in contact with either the fossiliferous limestone or the 

two beds of massive quartzite. As some areas of Beekmantown shale 

may yet be found, here and there, within the Lower Cambrian area, the 

age designation of that area on the map should not be strictly interpreted. The finest exposures of the reddish and greenish shale with 

small quartzites having organic impressions (horizons A, C, E), which 

either carry Oldhamia or are likely to do so, are in the eastern half of 

the Cambrian area as indicated on the map. Most of the exposures 

of the massive quartzite of horizons B and D are in the township of 

Nassau.

There is a considerable area of the greenish shale with small 

quartzite and small limestone beds, extending from a point 2 miles 

northeast of Melrose, on the west, to Tomhannock and Valley Falls
30 GEOLOGY OF HUDSON VALLEY. . [BULL. 242.

on the east, and north to the Washington County line and beyond, 

which is regarded as belonging to the Cambrian. Mr. .Ruedemann's 

Upper Cambrian fossil locality at Schaghticoke (paper No. 20, p. 11), 

for reasons given on page 31, is regarded as being in an outlier of 

Beekmantown.

As the Middle Cambrian is absent and the Upper Cambrian essentially so, the Lower Cambrian is here unconformably related to all the 

formations which adjoin it as well as to the outliers which rest upon 

it. On the Avest it appears to be thrust over onto the Hudson by a 

fault which is clearly present near Schodack Landing on the south 

and at Bald Mountain, in Greenwich, on the north, but which may be 

inconsiderable here, and, in places, disappear altogether, being simply 

an unconformity and an overturned fold. The observed relations of the 

Lower Cambrian to the Hudson have been shown in figs. 13,15,16, and 

17, and they will be further considered in the study of that formation. 

Its relations at one point to the Rensselaer grit are shown in fig. 7, 

and will also be further described under that heading. Its relation to 

the Beekmantown will be considered more fully under the next heading.

BEEKMANTOWN SHALE. 

FOSSIL LOCALITIES.

Mr. Prindle found some graptolites in very small grayish arenaceous 

layers, interbedded with small layers of finely banded quartzite, cropping out on either side of the road running from West Sandlakc to 

Defreestville, about a mile southwest of Lake Aries, in North Greenbush, and again in similar rock at a point about 2| miles north-northeast of the first locality and a mile south of Wynantskill, in the same 

town. These were referred to Mr. Charles Schuchert, who identified 

them provisionally as Graptolithus quadribrachiatiis (Hall), G, bryonides (Hall), G. Mfidus (Hall), Clonograptus flexilis (Hall), C. near 

6'fl^ra (Hall), Dictyoneina murrayi (Hall), D. near irreyulare (Hall), 

and pronounced them "faunalty much like the Quebec (Levis) graptolite zone." Mr. Prindle soon afterwards found similar rocks with 

similar graptolites at a point a mile southwest of Wynantskill, and 

again at another point 1£ miles west-southwest of that village. In 

1895 the writer found some graptolites at a point 2 miles northeast 

of Raymertown village, in Pittstown, in small micaceous, calcareous, 

quartzose, finely banded, grayish beds covered with trails. These Avere 

referred to Mr. R. R. Gurley, who identified them as Dichograpsus 

sp., Dichogra/psus?', and Tetrograpsus or Dichograpsus, and called the 

horizon Calciferous, i. e., Beekmantown.

Mr. Ruedemann's new graptolite localities in the Deep Kill, east of 

Grant Hollow, in Schaghticoke (paper No. 19, p. 11), appear to be in one 

or two masses of Beekmantown shale separated from the Hudson shale
DALE.] ' BEEKMANTOWN SHALE. 31

on the west by an outcrop of Cambrian breccia, noted by the writer 

in 1899. " Typical Cambrian rocks occur also one-fourth of a mile southwest, and three-tenths of a mile northeast. The fauna of his eastern 

outcrop, which measures 40 feet from east to west and is separated 

from the western one by 825 feet of drift, he regards as Beekmantown 

or Chazy, and in any case as more recent than that of the other. This 

eastern outcrop may be continuous with i. e., its beds may. pass 

under the Hudson outlier to which Rice Mountain belongs.

In some shale at Schaghticoke Mr. Ruedemann found Dictyonema 

flcd>elliforme(l&ichwa,\d}&nd Clonograptusproximatus (Matthew), which 

he regards as Upper Cambrian (see paper No. 20 on page 11), but on 

page 936 he observes:

It is evident that there was no difference or break whatever in physical conditions 

from the time of the deposition of these Cambrian beds to that of the lower Siluric 

beds.

- As these forms are not quite conclusively or exclusively Upper 

Cambrian, and as the genera Olonograptus and Dictyonema occur 

mingled with Beekmantown graptolites a mile southwest of Wynantskill, as shown on page 30, this fauna is regarded'as essentially Beekmantown, with possibly a few surviving Upper Cambrian forms. 

This locality is, therefore, shown on the map as occurring in a small 

area of Beekmantown shale resting upon the Lower Cambrian. It 

should be added that the surfaces of the fossiliferous Beekmantown 

beds in North Greenbush are marked by coarse branching casts of 

organic origin. 

All these localities are shown on the map.

PETROGRAPHY.

The finely banded quartzite beds which mark this horizon, when 

examined microscopically, prove to consist of angular grains of quartz, 

with rare fragments of plagioclase and occasional scales of muscovite. 

The banding is due to fine stringers of sericite stained with limonite 

and containing here and there what appear to be carbonaceous particles. These undulating stringers of sericite are from 0.12 to 0;62 

mm. apart. In places the beds are very calcareous. The associated 

grayish and greenish shale was not examined microscopically. Outwardly it resembles the Cambrian shale of the same colors.

STRATIGRAPHY AND AREAL AND STRUCTURAL RELATIONS.

Several areas of Beekmantown shale are shown on the map. That 

on the so'uth side of Mount Rafinesque, in Brunswick, and three of 

those in North Greenbush, were identified 'only petrographically. 

rMore minute exploration may bring others to light. From the relative position of the areas in North Greenbush to the Cambrian fossil
32 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

localities, the outlier of Hudson shale with Normans Kill graptolites is 

probably surrounded and underlain b}r Beekmantown shale, and that 

by the Lower Cambrian. Its structure would be a complex syncline. 

Near Wynantskill, however, the Beekmantown seems to occur in a 

narrow fold. In Pittstown the area! relations indicate a westwardly 

overturned anticline of Beekmantown from which the Hudson has 

been eroded. Whether the Beekmantown always intervenes hero 

between the Lower Cambrian and the Hudson is uncertain. The map 

indicates the formation only where it has been identified.

The exposures of Beekmantown shale are not sufficiently satisfactory 

to be represented in sections. At the first-mentioned locality, which 

is about 200 feet west of the tollgate, the greenish-gray shale, with 

small beds of finely banded quartzite, measures about 100 feet across 

the strike, followed on the west by 93 feet of similar shale not banded, 

which may be Cambrian. The whole series is in minor folds more 

or less overturned to the west. The fossils were found 25 feet east 

of the boundary between the two varieties of quartzite. The situation 

of the outcrop west of the tollgate in relation to the Normans Kill graptolite locality north of the road, and of this to another outcrop of 

Beekmantown east of it, indicates a synclinal structure here for the 

Beekmantown, with the Hudson shale overlying. At the second locality (south of Wynantskill) the outcrop is about 80 feet wide from east 

to west; the beds strike N. 25° E, and are in minor folds. Limestone, probably Cambrian, occurs in close proximity. . At the locality 

a mile southwest of Wynantskill from 30 to 40 feet of this shale and 

.quartzite overlie the fossiliferous Cambrian limestone.

At the locality northeast of Kaymertown, in ascending the brook 

from the road on the west, the following series is crossed: Green shale 

with small quartzite beds, lindertying light-green, red, and purplish 

shale, striking N. 30° E. and dipping 45° E. These colored beds 

are covered with trails, etc. Farther up comes red shale with small 

calcareous quartzite beds. In a gulley a few hundred feet north of 

the creek is an outcrop of typical Hudson grit. Farther up the main 

creek is the gray shale with small calcareous quartzite beds containing Beekmantown graptolites. About a half mile north, in the 

direction of the strike, is the black Hudson shale with graptolites, 

and 40 feet west of this is the red and green Hudson shale which 

was crossed at the beginning of the section.

In all of these localities the close proximity of the Beekmantown 

beds to both the Lower Cambrian and the Hudson beds is noticeable. 

This signifies: (1) An unconformity between the Lower Cambrian and 

the Beekmantown by the absence of the Middle Cambrian and, as far 

as present evidence goes, of the Upper Cambrian also. (2) An unconformity between the Beekmantown and the Trenton, the Chazy being
HUDSON SHALE AND SCHIST. 33

absent, if not the base of the Trenton also. Mr. Ruedemann is not quite 

sure of the Chazy age of the Deep Kill fossils (his zone C), but is sure 

of the Chazy age of the fossils in certain limestone pebbles in the conglomerate of Rysedorph Hill (see pp. 89, 107, of paper No. 16, p. 11), 

and Chazy limestone beds have not yet been found in this tract.

The thickness of the Beekinantown shale at the localities described 

in this paper is roughly estimated at about 50 feet. As there is a 

possibility that some of the green shale without banded quartzites 

and without, fossils belongs to this formation, this estimate should be 

taken as a minimum. Mr. Ruedemann estimates it as high as 200 or 

300 feet on the Deep Kill (p. 550 of paper No. 19, p. 11).

HUDSON SHALE AND HUDSON SCHIST.

As the schist of the Taconic Range is the metamorphic equivalent of 

the shale and grit of the valley, they will all be here treated as one 

formation. 

FOSSIL LOCALITIES.

Twenty-five fossil localities are shown in the Hudson areas. The 

fossils collected at the locality one-half mile southwest of Lake Aries, 

in North Greenbush, were identified by' Mr. Charles Schuchert as 

Diplogra/ptus cf. angustifolius. From a point a mile north-northeast 

of that he identified Didymograptus Sagittarius, Lasiograptus mucronatus, as well as Diplograptus cf. angustifolius. Graptolites also occur 

a half mile west of this last place. From a place on the north bank of 

the Hoosic, a mile west of Schaghticoke., he identified Climacograptus 

bicornis, and from the locality near the paper mill on the Moordener 

Kill, three-fourths of a mile north-northeast of Castleton, in Schodack, 

the following: Didymograptus Sagittarius, Diplogra2)tus cf. angustifolius, Lasiograptus mucronatus, Dicellograptus sextans, Dicranograptusramosus, Ciimacograptusbicornis, and C.parvus. a

Graptolites were also found at the five-localities indicated in Pittstown 

and two in Schaghticoke, near Melrose. They were found in 1890 by 

Foerste south of and in the railroad cut between 1 and 2 miles north 

of Chatham. (See PI. XCVI1 of paper No. 9, p. 11.)

In the Boston and Maine Railroad cut near the Deep Kill, a mile 

southwest of Melrose, in Schaghticoke, a very thin calcareous bed in 

the Hudson shale carries brachiopods, crinoids, and polyzoa.

There are also important conglomerates in these shales. The R}rsedorph Hill locality'in East Greenbush has been exhaustively described 

by Mr. Ruedemann. (See paper No. 16, p. 11.) Mr. Prindle, when 

visiting this locality in 1893, noted that the pebbles of the conglomerate

a Ruedemann gives from this locality: Diplograptusfoliacens, D. angustifolius, Ciimacograptusbicornis, 

Lasiograptus mucronatus, and Corynoides calicularis. (See p. 644 of paper No. 15, p. 11.)

BulJ.242 04 3
34 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

were a blue limestone, that the cement on exposed surfaces was yellowish, and that both pebbles and cement were f ossilit'erous. On Van Denburg Hill, in Schodack, about 5£ miles south-southwest of Rj^sedorph 

Hill, is a limestone breccia (and conglomerate ?) containing Ordovician 

brachiopods and crinoids.

On the Moordener Kill, 200 feet upstream from the graptolite 

locality already mentioned, Mr. Prindle noted 1-foot blocks and small 

fragments of limestone conglomerate in a dark-gray fossiliferous shale. 

The pebbles of this conglomerate, as well as its cement, contained 

Ordovician brachiopods and crinoids. Two hundred feet farther upstream a similar bed of1 conglomerate was found, producing a waterfall 10 feet high. He was unable to determine whether this was a 

lenticular mass within the shale or the core of an anticline.. Here a 

vertical cliff of shale 200 feet high, containing similar pieces of fossiliferous conglomerate, forms the right bank of the stream. About 200 

feet farther upstream, and 50 feet below the upper falls, is a third bed 

of conglomerate, 12 feet thick, also carrying brachiopods. Between 

this point and the falls is a fourth bed, separated from the last by 

about 25 feet of shale. About 500 feet beyond the upper falls Mr. 

Prindle found a fifth mass of conglomerate, 50 feet thick, in the shale. 

This} like the others, contains pebbles of bluish fossiliferous limestone 

in a brownish cement. It afforded, however, no clue to its structure. 

Mr. Ruedemann describes two of these conglomerates and gives a list 

of fossils showing both pebbles and cement to be of Trenton age. ft It 

was not determined whether these conglomerates were distinct beds or 

repetitions of one or more beds. A half mile northeast of Schodack 

depot, on the same kill, the Hudson grit and shale contain thin beds, 

with crinoids and polyzoa.

Passing now to the Ordovician on the east side of the Cambrian belt, 

there are several fossiliferous limestone localities, one at the foot of 

the Rensselaer Pfateau in Nassau, a half .mile northeast of Tackawasick 

Pond, the structural relations of which are shown in fig. 7 (p. 21). This 

locality was first described on pp. 311, 312, and the map PI. XCV1I, of 

paper No. 9, p. 11. The fossils found here by Foerste were Trenton: 

" Monticulopora, Murchisonia, Calymene, an orthis of 0. plicatella 

type, and crinoid stems." This limestone contains a bed of gray shale, 

and this shale recurs, at the south. Both are, therefore, regarded as 

Trenton.

Another locality is in Chatham, about midway between Sutherland 

Pond and the Chatham and Lebanon Valley Railroad. This appears 

to be .about a, mile east of one of Bishop's localities and is probably connected with it. (See p. MO of paper No. 5, p. 10). The limestone is 

interbedded with greenish rusty shale and dolomite. A poorly pre-

" See pp. 544-546 of paper No. 15, p. 11,
HALE.] HUDSON SHALE AND SCHIST. 35

served gastropod and a loosely laminated Stromatocerium, as determined by Mr. E. 0. Ulrich, were found here. A wall by the road 

here is made of fossiliferous limestone. Adjacent to this locality on 

the east and south is grayish-greenish shale. This limestone seems 

to recur a half mile south of Old Chatham, in a hillock known as 

Tonys Nose, there also associated with dolomite. At the top, limestone fragments, apparently from an' outcropping grayish-greenish 

shale, contain traces of fossils. Between these two localities is a ridge 

composed of two thick beds of quartzite, alternating with red and 

green shale with small quartzites, typical of horizons B, C, D, E, of 

the Lower Cambrian series.

The last locality is one of Bishop's, li miles north of Chatham, 

where Foerste obtained Leptaena sericea, a Murchisonia, a Pleurotomaria, etc. (See p. 315 and PI. XCVII of paper No. 9, p. 11.) 

Bishop mentions from here, and from a point a mile south, besides the 

above, Strophomena alternata, a doubtful Maclurea, an Ophileta, an 

undeterminable Orthoc&ras, and the polyzoon, Ptilodycta. The Hudson grit, a half mile west of Schaghticoke, on the south bank of the 

Hoosic, and again a half v mile south of Schodack depot, on the 

railroad, has organic impressions preserved as casts, somewhat similar 

to those occurring in the quartzite beds of the Lower Cambrian series.

PETROGRAPHY.

The unaltered part of the Hudson formation consists of black, gray, 

greenish, and reddish shale1, with interbedded grit; black, whiteweathering, cherty-looking beds; limestone, and limestone conglomerate; and in places small beds of quartzite.

The most typical and significant of these rocks is the grit. This is 

a loose aggregate of angular grains of quartz, plagioclase feldspar, 

scales of muscovite, and graphite, together with particles of several 

clastic rocks, all held together by a carbonaceous, calcareous, and 

rarely sericitic cement. As the writer has already published microscopical descriptions of this rock, based upon a number of thin 

sections/' it will be sufficient, in order to convey an idea of its general 

character, to add a microscopical drawing (PI. II, D} and also to call 

attention again to the significant occurrence in it of grains of clastic 

rocks. A description of a thin section of this grit from a point 100 

feet below the dam in the Poesten Kill, at Troy, is here repeated from 

paper No. 13, p. 11. The rock contains grains of quartzite, limestone 

with veins of calcite, grains consisting of quartz fragments, muscovite 

scales without orientation, chlorite, and rutile needles (which indicate 

a slate in parallel section, or else a shale), a grain of micaceous quartzite, a grain of stratified carbonate rock with quartz grains i. e\,

a See pp. 187,188 of paper No. 13, p. 11.
36 . GEOLOGY OF HUDSON VALLEY.

quartzose limestone or dolomite and a grain of slate with aggregate 

polarization, containing quartz grains, chlorite, and tourmaline.

At the Avestern foot of Rice Mountain, 1£ miles south-southwest 

from Grant Hollow and about 700 feet southeast of the road corner, in 

the town of Scbaghticoke, a small excavation has exposed Hudson grit, 

strata, about 30 feet thick, containing a few inches of conglomerate, the 

pebbles of which scarcely exceed one-sixth of an inch in diameter. 

These pebbles prove to be mostly fine-grained dolomite, but there are 

also pebbles of slate, carbonaceous shale, carbonaceous sandstone, 

cryptociystalline quartz, vein quartz, and plagioclase and orthoclase feldspar. The grains of clastic rock show that during the 

deposition of the Hudson grit certain slates, shales, limestones, dolomites, quartzites, and sandstones were above water at no very great 

distance. At a quarry south of the Poesten Kill, in Troy, the grit contains minute globular masses of anthracite, each surrounded by a film 

of chalcedon}'.

The cherty-looking beds referred to crop out at several points. At 

Grand view Hill, in East Greenbush, this rock consists of a carbonaceous matrix containing- angular fragments of quartz and plagioclase and scales of muscovite. Its weathering white may be due either 

to the loss of carbon or to the kaolinization of a fine f eldspathic cement.

In a small ravine 2 miles west-southwest of East Greenbush, south of 

the Boston and Albany Railroad crossing, the Hudson shale contains 

small irregular beds or nodules of fine-grained calcareous quartzite, in 

which the particles are angular and almost entirely quartz, with an occasional grain of plagioclase or zircon or a flake of muscovite.

The metamorphic part of the Hudson formation consists of the sericite-schist which constitutes the Taconic Range. This has been so 

often described a that it will be sufficient to. state that it is sometimes 

black from the presence of graphite, or -greenish from the abundance 

of chlorite, or purplish from the addition of hematite. In Chatham the 

transition from shale to schist, in passing from the west to the east, 

is so gradual that it is often difficult in the field to determine whether 

a given rock is a shale or a phyllite. In Austerlitz, a quarter of a 

mile south of Redrockrthe schist contains a bed of slightly chloritic 

quartzite, 20 feet thick, with pebbles of quartz up to an eighth of an 

inch in diameter.

STRATIGRAPHY.

The general structure of the strip of the Hudson formation between 

the Hudson River and the Cambrian boundary, in at least its narrower 

part, is shown at a quarry between Troy and South Troy, where an 

acute anticlinal core, slightly overturned to the west, forms the center 

of a mass of shale and grit about 400 feet wide, measured across the

a see pp. 303-306 of paper No. 9, p. 11, and Mon. U. S. Geol. Survey, vol. 23, pp. 182-184.
DALE.] HUDSON SHALE AND SCHIST. 37

strike. At the north end of the quarry the east limb of the fold dips 

60° E. and the west limb 80° E., but at the south the anticline is 

nearly erect. The folds in the wider part, however, are not all of this 

character, for at an old quarry a half mile southwest of Defreestville, 

or 2 miles northeast of Rensselaer, a gentle anticline of grit and shale, 

about 100 feet in diameter, is exposed.

The order and thickness of the Hudson beds are difficult to determine. This is in consequence not only of the frequent overturned 

folding, as shown above, but also because of the horizontal transition 

of red and green shale into each <5ther and probably of several other 

members of the series, the interbedding, the possible difference in age 

indicated by different graptolite faunas, as shown by Ruedemann (paper 

No. 15, p. 11), and also the unconformities shown by the limestone 

conglomerates (paper No. 16, p. 11).

The following table embodies such approximations as to the order 

and thickness of this formation as the data, obtained during these 

studies and from the literature, seem to warrant:

Table showing the Hudson formation as exposed in Rensselaer County and the northeastern 

part of Columbia County, N. Y.

Description of strata.

Black shale with arenaceous limestone, etc. «

Black and gray shale 

with interbedded grit.c

Similar shale with limestone and limestone conglomerate.

weathering, "chertylooking" shale. «

ish shale, with small 

quartette beds.e '

Fauna.

(Diplogr. amplexi- 

\ caulis.k

fNormans Kill 

\ graptolite fauna.

(Trenton fauna in 

1 limestone and 

I cement of conI glomerate.^

Estimated 

thickness.

Feet. 

1,200-2,500?

Age.

Trenton.

Metamorphic 

equivalent.

Sericite-schist, 

black, green, or 

purple, in places 

with greenish 

quartette up to

20 feet thick.

Estimated 

thickness.

Feet. 

1,000-2,000

a See Ruedemann, pp. 635-537, stations 24, 25, 26, of paper No. 15, p. 11.

6 See as above for other fossils.

c Rarely with small beds of quartette.

dThe pebbles of this conglomerate contain Trenton, Chazy, and Lower Cambrian fossils. See 

paper No. 16, p. 11, and Ford, paper No. 3, p. 10.

eThe vertical relations of the colored shale and' the black siliceous shale to each other and to 

the black arid gray shale with Normans Kill graptolite fauna are not clear. They are all intimately 

associated. The greenish shale sometimes includes small limestone beds.

AREAL AND STRUCTURAL RELATIONS.

The Hudson formation, as shown on the map, occurs on both sides 

of the Lower Cambrian belt, and it also forms two isolated areas of 

more or less complex synclinal structure within and upon it. Some 

of its structural relations are shown in tigs. 7, 13, and 15-17. The 

Hudson beds are frequently separated from the Lower Cambrian by a 

few feet of Beekmantown shale. Whether this shale always intervenes in eastern New York has not yet been determined. In any case,
38 GEOLOGY OF HUDSON VALLEY. (JOJL-L.M&.

it is here unconforinably related to the underlying formations either 

by the absence of the Chazy and the Middle Cambrian, very probably 

also of the Upper Cambrian, or by the absence of these and the Beekmantown, and in both cases possibly also by the absence of the lowest 

Trenton. An unconformity to older sedimentary formations is indicated by the pebbles and grains of slate, limestone, dolomite, and quartz - 

ite within the grit, as shown under "Petrography," and this has also 

been paleontologically corroborated by the conglomerate interbedded 

with the grit, the pebbles of which contain Lower Cambrian and Chazy 

fossils.

That the relations on the west side of the Cambrian belt are not 

only those of unconformable deposition but of a more or less continuous overthrust is rendered somewhat probable from the situation ofthe overthrust near Schodack Landing (fig. 17) and of that at Bald 

Mountain a in Greenwich, 47 miles north-northeast of the former, as 

well as from the general direction of the Cambro-Hudson boundary 

between them. It is to be noted also that at the outlet of the pond in 

Oakwood Cemetery in Lansingburg the black cherty beds of the 

Hudson underlie the olive grit (horizon F) of the Lower Cambrian, 

from 11.0 to 340 feet of the Lower Cambrian being absent either through 

faulting or through pre-Hudson erosion.

For these reasons it is assumed that in consequence of a westwardly 

overturned fold, which is frequently ruptured, the Lower Cambrian 

here usually overlies the Hudson i. e., the Trenton or middle part of 

the Ordovician. The east-west course of the Cambro-Hudson boundary east of Van Denburg Hill corresponds roughly to a change in the 

strike of the Hudson beds. It is uncertain whether the overthrust 

follows this bend or maintains its northerly course or is interrupted.

The isolated mass of Hudson shale in Brunswick, Lansingburg, and 

Pittstown, amply identified by graptolite localities and by the typical 

black and red shale, grit, and cherty-looking beds, is almost surrounded by typical Cambrian beds with several fossil localities. It 

has Beekmantown beds at two points, one on either side of it. The 

reason for drawing the boundary here different from that on Mr. Walcott's map b is that the shale with small beds of quartzite which crops 

out north of the graptolite shale has a general resemblance to the 

Cambrian shale, although no Lower Cambrian fossils have as yet been 

found north of the latitude of Tomhannock village in the area of this 

map. 'The east-northeast to west-southwest.trend of Mount Ratinesque 

is due to change in the strike of the Hudson shale. Less than a mile

aSee paper No. 6, p. 11; Walcott, C. D., Am. Jour. Sci., 3d ser., vol. 35, p. 317, fig. 12. The continuation of this fault was retraced in 1902 by Mr. Fred H. Moffit, then the writer's assistant, from Bald 

Mountain, Greenwich, in a northerly direction 10 miles into Argyle.

b See PI. Ill of paper No. 6, p. 11.
BALE.] RENSSELAER GRIT. 39

east of Chatham Center there is an outcrop of the black cherty-looking 

beds and red shale of the Hudson formation striking N. 10° E., but 

a mile farther southeast the gray shale of the Cambrian crops out. At 

Maiden bridge, 4 miles north-northeast of the first of these localities, 

the following series is exposed in the bed of the Kinderhook: Beginning 

on the east, 40_feet of gray shale and grit, 24 feet of black shale and 

limestone, followed by over 70 feet of shale, with a few calcareous 

beds and coarse, gritty beds. As the age of these beds is uncertain 

and as the area between them and the outcrops east of Chatham Center was not explored, there may be a tongue of Hudson-Trenton 

extending up this valley. This area has therefore been left uncolored.

The relations of the Hudson formation to the overlying liensselaer 

grit of the Silurian are shown in the section, fig. 7 (p. 21), which crosses 

the contact of the two formations in Nassau, near Tackawasick Pond, 

and on the map, PI. I (p. 12), which shows an outlier of typical Rensselaer grit and conglomerate resting upon the Hudson schist 2 miles 

northeast of Spencertown, in Austerlitz.

The small mass of unfossiliferous limestone southeast of Pike Pond, 

in Nassau, is probably of Hudson (Trenton) age also, and immediately 

underlies the grit of the plateau. It may be continuous with that 

about 3 miles south.

RENSSELAER GRIT. 

PETROGRAPHY.

With the exception of faint annelid trails at one point, no fossils 

have as yet been found in this formation. Its petrography has been 

already so fully treated in print that little need be added. a Its petrdgraphic characteristics, in brief, are as follows: A dark-green, tough, 

generally thick-bedded, often calcareous, crystalline, granular rock, 

with visible quartz and feldspar grains, and traversed by veins of 

quartz, in places of epidote and calcite. This rock alternates with 

beds of purplish, reddish, or greenish slate or shale. The grit itself 

contains microscopical grains of quartz, orthoclase, plagioclase, and 

microcline feldspar, biotite, garnet, tourir.aline, zircon, magnetite, 

ilmenite, and epidote, in a cement of chlorite, muscovite, quartz, calcite, epidote, and pyrite. In some places the grit contains beds of 

conglomerate up to 4 feet in thickness, with pebbles of quartz, orthoclase, plagioclase, microcline, granitoid gneiss or granite (with the 

same feldspars), fine-grained-gneiss, and rarely chloritized diabase or 

gabbro, together with pebbles of the following sedimentary rocks: 

Quartzite (white, black, or red), greenish phyllite, siliceous shale and 

fine grit (carbonaceous, and sometimes calcareous, with angular grains 

of quartz, plagioclase, microcline, and scales of muscovite), granular

a See pp. 306-310 and PI. C of paper No. 9, p. 11.
40 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

and crystalline limestone, and cryptocrystalline quartz (with grains of 

plagioclase, muscovite scales, rutile, calcite, and quartz veins). The 

diameter of these pebbles does not usually exceed an inch, but the 

quartzite sometimes attains 2 inches, the limestone 4, and the gneiss in 

one case measured 12 by 8 by 3. a PI. II, E (p. 20), shows a microscopical drawing of the typical Rensselaer grit, and illustrates particularly the difference between its cement and that of the Hudson grit. 

In the outlier, which extends from East Nassau to Old Chatham, the 

matrix of the grit is sometimes reddish, .and where greenish the rock 

approaches a quartzite. Although the massive Cambrian quartzites 

(horizons B, D) are generally greenish and sometimes pass into conglomerates, they can usually be distinguished from the Rensselaer grit 

by 'their cement being mostly quartz and their grains and pebbles 

entirely quartz, with the exception of an occasional one of feldspar or 

slate.

STRATIGRAPHY.

The total thickness of the grits on the plateau was estimated at about 

1,400 feet, but it may be a little greater. The portion of the plateau 

described in this paper consists of minor folds with a north or northnortheast trend. Some of these folds are exposed in the gorge of the 

Poesten Kill, between Barberville and a point a mile east of the village 

of Poestenkill. 6 Several folds are also crossed on the road leadingnortheast from Sandlake.

The outlier south of North Nassau consists of -two masses, which at 

the north are separated by a swampy interval. Each of these consists 

of a syncline followed on the east b}^ an anticline, but the entire outlier 

is probably made up of three anticlines and four synclines in alternation. (See PI. Ill, Sec. (7, p. 46.) The north end of the outlier west of 

East Nassau is a syncline.

The Rensselaer grit south of Alps village in Nassau strikes N. 70° E. 

and dips 50° to 60° NW. From this point the strikes in the adjacent 

Cambrian gradually curve southward for over 2 miles and in the 

outlier south of. North Nassau resume their normal direction.

AREAL AND STRUCTURAL RELATIONS.

The relations of the Rensselaer grit are peculiar. Along the greater 

part of its western boundary it is bounded and underlain by the Lower 

Cambrian, and these relations reappear in the greater part of the large 

outlier in Nassau and Chatham and-in the smaller one near North 

Nassau. In places, however, as near Tackawasick Pond (fig. 7), it overlies the Hudson (Trenton shale and limestone), and the outlier in Austerlitz lies upon the Hudson schist. Such relations signify: (1) That

«The dimension of 23 inches given on p. 308 of paper No. 9, p. 11, was an error. 

bSee figs. 34, 35, 36, and 37 on pp. 325-327 of paper No. 9, p. 11.
RALE.] RENSSELAER GRIT. 41

the Rensselaer grit is later than a part or the whole of the Hudson 

formation, and (2) that it was deposited in places upon a Lower Cambrian surface upon which the Hudson beds had never been deposited 

or from which they had been eroded.

That similar Lower Cambrian surfaces were above water during the 

deposition of the grit at no great distance is shown })j the presence of 

quartzite pebbles within the grit. One of these conglomerate beds, 

with pebbles of quartzite an inch in diameter, occurs within a mile 

northeast of Tackawasick Pond, but the evidence from the pebbles 

shows that the grit was also uriconformable to formations containing 

greenish phyllite, siliceous-carbonaceous sha'le or grit, crystalline 

limestone, and cryptocrystalline quartz. These may all have come 

from Lower Cambrian beds, but the black siliceous grit pebbles 

resemble the Hudson grit as much as they do the black pebbles of 

the Cambrian sandstone. In common' with the Cambrian quartzite 

and the Hudson .grit, the Rensselaer grit contains quartz, feldspar, 

and zircon fragments from the older crystallines. Its pebbles of 

granite and gneiss are still more conclusive on this point, and the 

large granite '' pebble" shows that these older crystallines were not 

far distant.

Finally, two contacts along the western boundary of the grit will be 

described in detail. One of these is a half mile north of Hoag Corners, in Nassau, about 400 feet east of the road to Alps. A large 

outcrop of grit, striking N. 35° W. and dipping 40° E., is underlain by red and green shale, without small quartzite beds, and probably also belonging to the Rensselaer grit formation. About 150 

feet west of the shale is the typical red shale of the Cambrian, with 

small quartzites, striking N. 15° E. and dipping 90°. This interval 

of 150 feet without outcrop may be occupied either by the Trenton 

limestone and shale, as it is If miles south (fig. 7, p. 21), or by the 

Cambrian shale. (See PI. Ill, Sec. (7, p. 46.)

The other, 11 miles north-northwest of the first, is in the town of 

Brunswick, where the road from Eagle Mills (Millville) toward Davitt Pond crosses the geological boundary. This contact is 3 miles eastsoutheast of Millville, where the road bends from a south-southeast to 

an east-northeast course. There are large outcrops of the red and 

green shale with small quartzites, with trails, etc., typical of the Lower 

Cambrian horizons A, C, E. At the road bend this shale dips 45°-70° 

E., and measures over 1()0 feet along the road, which crosses it diagonally. ' In contact with it on the east is a series of alternating small 

beds of reddish and greenish shale and fine-grained grit or quartzite 

of uncertain position. On the east side of, and in contact with, this 

series is a bed of typical Rensselaer grit 3 feet thick, with large pebbles of quartz, etc., dipping 90°, and followed by the usual alternations 

of shale and grit. The following measurements of this series of small
42 GEOLOGY OF HUDSON VALLEY. [BOLL. 242.

beds; intervening between the typical Rensselaer grit beds and the 

typical Lower Cambrian beds, were taken, and thin sections were prepared of beds marked 1 to 7, in order to determine how nearly the 

Rensselaer grit approaches the Lower Cambrian. The names attached 

to these beds are based upon these microscopical determinations.

Measured section at contact of Rensselaer grit and Lower Cambrian in Brunsivick, 8 miles 

east-southeast of Eagle Mills.

Thin 

section.

n

fi

5

4

3

2

1

Description of strata.

<!>

Kensselaer grit and interbedded shale or slate ......................

Rensselaer grit ....... .................................. ..........

Red and green shale and small beds of Rensselaer grit. ..............

Bed of roundish quartz grains in a cement of chlorite with some secondary quartz ........'.............................,.. .^ .........

Bed of angular quartz and plagioclase grains in a cement of chlorite.. 

Red and green shale ............. ............ ........I...... .......

Rensselaer grit, thin bedded, with some shale ......................

Red shale with small quartzite beds, with trails, etc., typical of horizons A, C, E, of Lower Cambrian. ...............................

Thick- - 

ness.

Feet. in.

Indef.

4 6

3 4

7 6

2

8 4

1

3 6

L 1 2

3 4

0 3-4 

3 6

5 0

50 0

This piece of investigation thus shows that the Rensselaer grit, the 

basal part of the Silurian, lies at this point immediately upon the red 

shale series classed as Lower Cambrian.

Finally, attention should be called to the significance of the position 

of the three outliers with reference to the plateau. The northern one 

is opposite the eastward recession of the edge of the plateau, and the 

western sides of both larger outliers are in about the same longitude 

as the most westerly part of the plateau in Poestenkill. This indicates 

that the southern prolongation of the plateau once extended at least 

that far west, while the third outlier in Austerlitz shows that the Rens-. 

selaer grit extended at least 7 miles south-southeast of the second 

outlier, or 12 miles south of the plateau itself. On the west side of 

the first road east of Tackawasick Pond, in Nassau, there appears to be 

still another outlier of Rensselaer grit, but it is too small to enter upon 

the map.
DALE.] AftEAL GEOLOGY. 43

RESUME OF THE FORMATIONS.

In the following table all the stratigraphical results from the study of 

the four formations are brought together and generalized. This table 

differs in important respects from that on pages 332, 333 of paper No. 

9, p. 11, in which the Hudson shale and the Berkshire schist were 

unintentionally represented as not equivalent, and in which the relations of the Rensselaer grit to the Cambrian west of the plateau were 

not given at all.

Tabular resume oj the formations.

Period. Formation. Equivalent. General description.

Thickness in 

feet.

Silurian.

Ordovician.

Rensselaer grit.

(In places rests uncomformably on 

Lower Cambrian.')

Hudson shale or 

Hudson schist.

Oneidaand Medina.

Trenton.

Cambrian.

(U nconformity. 

Chazyabsent.and 

lowest Trenton?)

Beekmantown (Calciferous).

(Unconformity. 

Upper and Middle Cambrian 

absent.)

Lower Cambrian.

Part of Stockbridge 

limestone.

Part of Stockbridge 

limestone, Greenwich slate of 

Washington Co., 

N. Y., Vermont 

formation of Massachusetts and 

Vermont.

Dark-green metamorphic grit with 

interbedded reddish and greenish 

shale or slate and conglomerate, 

containing pebbles of quartzite, 

marble, black siliceous shale,grit, 

phyllite, all of Lower Cambrian 

age, some of them possibly of 

Ordovician age; also pebbles of 

gneiss and granite of pre-Cambrian origin.

Black, gray, greenish, and reddish 

shale, the black with Normans 

Kill graptolite fauna, and like 

the gray, interbedded with grit; 

black siliceous shale, one or several beds of limestone Conglomerate, the pebbles of which carry 

Trenton, Chazy, and Lower Cambrian fossils. The gray shale in 

places with limestone having 

fossils of Trenton age. In the 

corresponding metamorphic zone 

sericite-schist with occasional 

thick beds of quartzite.

Greenish-gray shale, with small 

beds of finely banded quartzite, 

sometimes calcareous and micaceous, carrying "Levis graptnlites" and Dictyonema and Clonograptus.

Alternating beds of limestone, black 

or gray shale, calcareous sandstone; the limestone often brecciated and in places a conglomerate, all with Olenelhis fauna.

The above underlain by reddish and 

greenish shale with Oldhamia and 

Hyolithes, and these in places 

by an olive grit or a sandstone 

passing into quartzite. The lowest beds exposed are reddish and 

greenish shale with thin quartzite beds, carrying Oldhamia, etc., 

interbedded with two beds of 

greenish quartzite, each 8 to 50 

feet thick.

1,400

1,000- 

2,000+

50+

1,225+
44 GEOLOGY OF HUDSON VALLEY. [BOLL. 242.

STRUCTURAL GEOLOGY.

STRUCTURE SECTIONS.

Section A, PI. Ill, shows the unconformable relations between the 

large synclinal outlier of Hudson shale and the Lower Cambrian; also 

that between the Silurian Rensselaer grit and the Lower Cambrian, as 

well as the overthrust at the west which has brought the Lower Cambrian on to the Hudson. The section involves three periods of folding, one at the close of the Lower Cambrian, another at the close of the 

Ordovician, and still another which metamorphosed and folded the 

Silurian beds. That these last two movements were not identical, i. e., 

that the Ordovician beds were folded before the Silurian beds, is shown 

by the well-known unconformable relations between the Ordovician 

and the Silurian at a number of points in,the Hudson Valley. a

As the Silurian movement in New York seems to have been confined 

to an emergence causing a slight retreat of the shore line, and as both 

Silurian and Devonian beds in conformable relations are powerfully 

folded at Becraft Moun tain, scarcely 25 miles south west of the Rensselaer 

Plateau, b the movement which affected the Silurian grit of Rensselaer 

County does not date further back than the close of Devonian time, 

and may have occurred as late as the close of the Carboniferous.

Section B, PI. Ill, crossing the smaller synclinal outlier of Hudson, 

repeats essentially the features of Section A. In both it is assumed 

that the unconformity between the Beekmantown and the Trenton 

represents merely an emergence followed by a period of denudation. 

In both sections the "minor folds in the broad Cambrian area are necessarily largely hypothetical.

Section #, PI. Ill, shows mainly the general structure of the small 

outlier of Silurian resting upon the Cambrian.

GENERAL STRUCTURE.

The general structural features are: The westwardly overturned 

folds which mark a large part of the area; the presence of an anticline 

of this character, the rupture of which resulted here and there in an 

overthrust at the west; east of this a synclinal axis running through 

both of the Ordovician outliers, with a complex anticline east of it. 

The most important inference, however, to be drawn from the sections 

is the presence of three periods of folding: The Lower Cambrian one, 

which raised some parts of'the Cambrian area above water; that at the

aSee Davis, William M., The nonconformity at Rondout, N. Y.: Am. Jour. Sci.,3d ser., vol.26, 1883, 

p. .389. Van Ingen, Gilbert, and Clark, P. Edwin, Disturbed fossiliferous rocks in the vicinity of 

Rondout, N. Y.: Report New York State Paleontologist for 1902, 1903, p. 1176. Darton, N. H., Preliminary report on the geology of Ulster County, N. Y.: Rept. State Geologist o f New York for 1893, p. 357.

&See Grabau, Amadeus W., Stratigraphy of Becraft Mountain, Columbia County, N. Y.: Rept. New 

York State Paleontologist for 1902, 1903, p. 1030.
PLATE in.

45
PLATE III.

STRUCTURE SECTIONS.

A. Section from near Quackenkill, in Grafton, to the Hudson 2 miles north of 

Lansingburg.

B. Section from a point 2 miles east of Sandlake to the Hudson 2 miles south of 

South Troy.

0. Section in Nassau from the western edge of the Rensselaer Plateau to a point a 

mile south-southeast of Burden Lake.

In these sections l=Lower Cambrian; Ob=0rdovieian, Beekmantown; Oh= 

Ordovician, Hudson; Sr=Silurian, Rensselaer grit. Scale, one-half inch=1 mile.

46 -
U. S. GEOLOGICAL SURVEY 

Mount Rafinesque

Oh C)b

(A)

WNWHudaon 

River

(S)

(C)

SBCTIONS ALONG THE LINES A.B.A
DALE.] DISCUSSION AND CONCLUSIONS. 47

''close of the Ordovician, which not only folded the Hudson and the 

Beekmantown beds, 'but also modified and faulted the Lower Cambrian folds; and one at the close of Devonian or Carboniferous time, 

which folded and metamorphosed the Silurian grit, and which must 

also have modified both the Ordovician and the Cambrian folds. The 

sections also imply the existence, in places, of a Lower Cambrian 

land surf ace in Ordovician time, which became partially submerged in 

Silurian time.

DISCUSSION AND CONCLUSIONS.

The paleontological, petrographical, and stratigraphical observations, given in detail, and summarized in the table and the sections, 

speak for themselves. It remains but to discuss some of their general 

bearings and to draw a few brief conclusions. This will be done under

c5

separate topics.

THREE CRUSTAL MOVEMENTS.

The evidence of the crustal movement (1) at the close of the Lower 

Cambrian along the western side of the Taconic Range is not confined 

to the unconf ormable areal relations of the Lower Cambrian and Ordovician in Columbia, Rensselaer, and Washington counties," nor to the 

pebbles containing Lower Cambrian fossils found by Ruedemann in 

conglomerates of Hudson (Trenton) age and partially confirmed by 

the occurrence of grains of clastic rocks in the Hudson grit, but is 

made conclusive by the structural unconformity of the two formations 

recently observed at the north end of the Taconic Range in Rutland 

County, Vt. 6

The Taconic or Green Mountain movement (2), which folded the 

Ordovician beds at Rondout and other places in Ulster County, and 

also in Orange County,c where the Silurian beds lie on their eroded 

edges, also folded and faulted the Hudson shale of this part of the 

Hudson Valley, and folded and metamorphosed the Hudson beds of 

the Taconic Range.

To the post-Devonian or Carboniferous movement (3), which folded 

both Devonian and Silurian beds at Becraft Mountain, in Columbia 

County, must be assigned the folding and the metaniorphism of the 

Silurian grit of the Rensselaer Plateau. A similar movement metamorphosed Devonian fossiliferous beds at Bernardston, Mass., on the 

west side of the Connecticut Valley, about 50 miles east of the west 

edge of the Rensselaer grit deposit-/' and that movement may possibly

a For Washington County see PI. XIII and pp. 290, 2!»1 of paper No. 13, p. 11.

&See Dale, T. Nelson, The geology of the north end of the Taconic Range: Am. Jour. Sci. 4th ser., 

vol. 17, Mar. 1904, p. 185, and map, PI. XI.

cSee Hies, Heinrich, Geology of Orange County: Fifteenth Ann. Kept. State Geologist of New York, 

1895, PI. XX.

rfSee Emerson, Benjamin K., Geology of old Hampshire County, Mass., Gomprising Franklin, 

Hampshire, and Hampden counties; Chapter IX, The Bernardston series of m(ppe.r. De.vonj/Ul rocks,, 

and PI. IV: Mon. U. S. Geol. Survey, vol. 29, 1898.
48 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

have extended across the Green Mountain crystalline axis and tfre 

Taconic synclinorium to the Rensselaer Plateau. Traces of a secondary 

crustal movement have been found here and there in the schist of the 

Taconic Range in the form of secondary cleavage foliations, sometimes 

plicated or followed by the formation of'fresh sericite. a

THREE CONGLOMERATES.

The lowest of these occurs within the Lower Cambrian beds, and 

implies a temporary emergence sufficient to expose the beds to wave 

action and thus to form beach pebbles. The next consists of limestone 

pebbles within the Hudson shale. It implies a temporary emergence 

during Ordovician time; and the paleontological evidence obtained by 

Ford andJRuedemann from the pebbles shows that Lower Cambrian, 

Chaz}', and Trenton rocks were above water during that part of Trenton time. Whether these Trenton pebbles came from a distance or 

from limestone beds formed in situ and then exposed to wave action, 

as in the case of-the Lower Cambrian conglomerates, may be difficult 

to determine.

The third conglomerate is that of the Rensselaer grit, formed in 

Silurian (Upper) time. Its pebbles show that Cambrian quartzites 

were then above water at no very great distance; that slate, carbonaceous shale and grit, and marble, of Cambrian or Ordovician age, 

were likewise above water; also that detritus from coarse granites 

and fine gneisses was being brought into the sea near by. The distance of the plateau from the crystallines at the northwest (about 25 

miles) b and at the east (11 miles), and the large size of one of the 

granite pebbles (12 by 8 by 3 inches), raise a difficult}7" here. Mr. 

G. K. Gilbert's suggestion that there may have been a pre-Cambrian 

mass in the center of the plateau that supplied these pebbles, 

which became concealed by the later beds of the grit or by drift or 

swamp, is valuable. Such a pre-Cambrian mass occurs at Stissing 

Mountain, 40 miles south-southeast of the Rensselaer Plateau and 

about 15 miles west of the Green Mountain crystallines. Furthermore, the presence of such a crystalline core in the plateau would 

help to account for the metamorphism of the grits, as the crystalline 

core of the Green Mountain axis accounts, in part, for the metamorphism of the Paleozoic sediments on either side of it. Such a core would 

furnish a buttress against which the grits have been pressed and thus 

metamorphosed.

aSee Mon. U. S. Geol. Survey, vol. 23, p. 143, Case IV; p. 151, Case VIII; also pp. 321-324 of paper No. 

9, p. 11 of this bulletin; p. 564, fig. 566, of paper No. 12, p. 11 of this bulletin.

6 See Blerrill, Frederick J. H., Geological Map of New York, Exhibiting the Structure of the State 

as far as Known, 1901.
DALE.] DISCUSSION AND CONCLUSIONS. " 49

MINOR OSCILLATIONS.

Thus, in addition to the three main crustal movements, the Cambrian 

and Ordovician conglomerates indicate a minor oscillation in Lower 

Cambrian time and another in Trenton time. There was also an 

emergence at the close of Beekmantown time, for the Hudson lies 

in places immediately upon the Beekmantown, the Chazy being 

absent. The full thickness of this formation in the Lake Champlain 

region is estimated at 890 feet/' Mr. Ruedemann's doubtful determination of Chazy graptolites in a 40-foot outcrop at the Deep Kill can 

not suffice to substantiate the presence of a formation representing 

such a lapse of time as is implied in the deposition of 890 feet of 

limestone.

The writer in 1901 found in the town of Shoreham, in Addison 

County, Vt., a small anticlinal hill of Potsdam overlain by theTrentonUtica, the Beekmantown and Chazy being absent. Such minor oscillations seem to have marked the entire Hudson-Champlain region 

during Paleozoic time.

ABSENT FOEMATIONS.

The formation which, owing to unconformity, is not at all represented within this area, is the Middle Cambrian. The Upper Cambrian and the Chazy are also practically absent, besides possibly the 

lowest Trenton. Of these the Upper Cambrian, or Potsdam proper, 

occurs around the southern border of the Adirondack mass, 25 miles 

north-northwest of Troy, and the Chazy about the. same distance.in 

north-northeast and north-northwest directions, and probably also 

forms part of the Stockbridge limestone, 20 miles northeast and 

southeast of Troy. The significance of the absence of these formations is that the Lower Cambrian was here a land surface at least during Middle Cambrian time, and that the Beekmantown was also a land 

surface during Chazy time, and may possibly have remained so during 

very earl}7" Trenton time.

The absence of the Middle Cambrian fauna agrees with the structural 

evidence of movement, which involved the Lower Cambrian beds, in 

pointing to the existence of a land surface' here during Middle Cambrian time. But the absence of exclusively Upper Cambrian fossils, as 

well as the mingling of the equivocal Dictyonema with Beekmantown 

graptolites, indicates the submergence of the Middle Cambrian land surface in Beekmantown time and the consequent immigration of Beekmantown graptolites along with the Dictyonema which may have survived from the Upper Cambrian. Messrs. Walcott and Schuchert, to

aSee Brainard, Ezra, The Chazy formation in the Champlain Valley: Bull. Geol. Soc. America, vol. 

2.1891, p. 293.

Bull. 242 04 4
50 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

whom this question has been submitted, agree in the opinion "that the 

data at hand are not clearly sufficient to determine whether or not the 

mingling of the Dictyonema with the Beekmantown graptolites indicates the continuance of Middle Cambrian land into the later portion 

of the Upper Cambrian time."

EQUIVALENT FORMATIONS.

xThe entire Lower Cambrian series, shown in the tables on pages 29 

and 43, is regarded as the offshore but shallow-water equivalent of the 

Lower Cambrian conglomerate, quartzite, schist, and dolomite which 

border the Green Mountain pre-Cambrian axis (Vermont formation 

and basal part of Stockbridge limestone of Monograph XXIII). It 

is assumed that sediments of Lower Cambrian age forming the base 

of the Taconic synclinorium are continuous from Hoosac Mountain to 

Troy, with a possible interruption by an island of pre-Cambrian within 

the area of the Rensselaer Plateau, but that the character of these 

sediments changes with the distance from the highlands of pre-Cambrian time and with the westward decrease of metamorphism. The 

Lower Cambrian series is also regarded as equivalent to the Greenwich formation of Washington County, N. Y., and Rutland County, 

Vt., where, however, the moderate metamorphism and the regularity 

of the compression which attended the crustal movement at the close 

of the Lower Cambrian changed the shale into slate, and where also 

the basal part of the formation as exposed in Rensselaer County (horizons A to E of table on p. 29) does not appear to be exposed. a

The Beekmantown of the Hudson Valley is regarded as the equivalent of the Beekmantown part of the Stockbridge limestone. That 

formation represents the upper part of the Lower Cambrian, the Beekmantown, the Chazy, and the lower part of the Trenton. The Stockbridge limestone usually disappears from east to west under the 

Hudson schist of the Taconic Range, owing, it is now thought, to the 

presence of a Lower Cambrian shore line there and to the overlapping 

of that limestone along that shore line by the Hudson schist (Berkshire schist) during a submergence which took place in Trenton time. 6 

As the fossiliferous Trenton limestone along the west edge of the plateau in Nassau is associated with shale, it probably belongs to the 

Hudson formation and not to the Stockbridge limestone. For these 

reasons the Beekmantown shale of the Hudson Valley, although 

equivalent to the Beekmantown part of the Stockbridge limestone, is 

regarded as belonging to different basins which were separated by an 

island (?) of Lower Cambrian.

The Rensselaer grit is regarded as the equivalent of theOneida and

a See table opposite p. 178 of'paper No. 13, p. 11. 

&See op. cit. on north end of Taconic Range.
DALE.] DISCUSSION AND CONCLUSIONS. 51

the Medina. Its estimated thickness of 1,400 feet compares fairly well 

with the estimates for these formations in western New York of 1,158 

feet,ffl and in Pennsylvania of 1,125 feet. 6

DENUDATIONS.

One of the marked features of the region is the repeated denudation which it has undergone. Passing by the denudation which 

accompanied the minor emergence that produced the Cambrian conglomerate, the first important denudation began in Lower Cambrian time and continued during Middle and Upper Cambrian. 

Upon the eroded Lower Cambrian surface the Beekmantown and 

Hudson shales were deposited. But as both the Hudson (Trenton) 

grit and the Rensselaer grit (Oneida-Medina) contain pebbles of 

Lower Cambrian age, denudation of a portion of the Cambrian surface must have gone on in Ordovician and early Silurian time. Omitting the denudation which accompanied the minor emergence implied 

in the Ordovician conglomerate, there is the unconformity between 

the Beekmantown and the Trenton, representing a time interval sufficient for the deposition of 890 feet of limestone in the Champlain 

region, during which much denudation must have taken place. It is 

uncertain, however, whether the absence of the Beekmantown shale 

from so large an area of Lower Cambrian is to be attributed to the 

denudation of Chazy time or to a later one. The next important 

denudation followed the Green Mountain movement and affected the 

Hudson shale and schist. As the Hudson shale (e. g., at Rondout 

and Becraft Mountain) was eroded before the deposition of the Silurian, it follows that the transition from the Ordovician to the Silurian 

was not simply attended by a retreat of the sea consequent upon the 

folding and elevation of the Ordovician beds, but that after these 

folded beds had been eroded there occurred a sufficient submergence 

to bring the sea back again over the denuded Ordovician surfaces east 

of the Hudson, at least ao far as the eastern edge of the Rensselaer 

Plateau.

As the Rensselaer Plateau lies in some places upon Hudson beds and 

in others upon Lower Cambrian beds, it is evident that where it overlies 

the Lower Cambrian that surface had either been denuded of its Ordovician beds or else formed part of the Cambrian surface which had 

remained above water during Ordovician time and which became submerged in the Silurian transgression. It may not be possible to 

determine which of these two possibilities is a probability.

aProsser, Charles S., The thickness of the Devonian and Silurian rocks of central New. York: Bull 

Geol. Soc. America, vol. 4, p. 117. 

t> Lesley, J. P., Second Geol. Survey of Pennsylvania, Final Report,
52 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

But there was also a third denudation, which began at the close of the 

Oneida and Medina and which eventually severed the Rensselaer Plateau 

from the outlying masses in Nassau, Chatham, and Austerlitz. The two 

outliers of Hudson, lying in the same synclinal axis, must have once been 

continuous. It is a question whether the denudation which removed the 

intervening mass of Hudson shale and thus reexposed the old Cambrian land surface was that which occurred between the Ordovician 

crustal movement and the Silurian transgression, or whether the postSilurian denudation did the major part of the work. In this case, as 

the time interval since the post-Devonian or Carboniferous crustal 

movement was so much greater, it seems probable that the work was 

done mostly during the third period of denudation, although at the 

beginning of that period a certain thickness of Silurian would have to 

be removed before the partially eroded Ordovician surface could have 

again been reached.

EXTENT OF THE LOWER CAMBRIAN LAND SURFACE.

The Lower Cambrian land surface was bounded on the north and 

northwest by the sea which formed the Upper Cambrian (Potsdam) 

deposits about the Adirondack mass and on the east side of Lake 

Champlain, but the data require a Lower Cambrian land surface during Ordovician time not very distant from the conglomerate bed at 

Rysedorph Hill, nor from the Hudson grit in general. Such a surface would have to lie east of the axis of the two outliers. If the 

Cambrian area in Pittstown and Brunswick be followed around the 

northern end of the plateau it will be found to connect with one which 

terminates near the village of Cambridge in Washington Countjr." 

There appears to be a continuous Lower Cambrian surface at least 

from the Columbia County line to Cambridge, a distance of about 35 

miles, and in width from 2 to 4 miles, which is the distance between 

the plateau and the Hudson outliers or masses on the west. As the 

northwestern part of the Rensselaer Plateau lies on the Lower Cambrian it is possible that the area west of a line running north-northwest 

from North Nassau under the plateau to Potter Hill, in the town of 

Hoosic, may have, in Ordovician time, formed part of the Cambrian 

land surface. In that case the width of that surface would have been 

2 to 3 miles greater. But the data also require a Cambrian land surface during Silurian time on the landward side of the Rensselaer grit. 

As the Silurian transgression presumably came from the southwest, 

this Cambrian area would have to lie north of the plateau, and it. 

would also have to be south of Cambridge. It would thus form the 

northern part of the area just outlined.

a See map, PI. XIII, of paper No. 13, p. 11.
DAW.]' DISCUSSIONS AND CONCLUSIONS. 53 

EXTENT OF THE BASAL SILURIAN BEDS.

The Rensselaer grit of the plateau and its three outliers mast needs 

have been originally connected and also continuous with other Silurian 

deposits. The geographical relations of the Rensselaer grit to the Silurian formations west of'the Hudson River are shown on the Lower 

Hudson, the Hudson-Mohawk, and the Central sheets of Men-ill's 

geological map of New York. ft It will be noticed that the northern 

edge of the Rensselear Plateau is in nearly the same latitude as the 

boundary between the Silurian (Oneida-Medina) and the Ordovician 

(Hudson) in Herkimer County, and that its southern part is in line 

with the southern continuation of the same boundary along the Kittatinny Mountain. The plateau thus lies at the apex of the angle formed 

by the receding shore line of Silurian and Devonian time, as indicated 

by the outcrops. The west-northwest and east-northeast strikes at 

the north end of the plateau and the east-northeast one in the Hudson 

shale on Mount Rafinesque are either related to the general moN^emeut 

which resulted in the general east-west course of the boundary 

between the Ordovician and the Silurian across the State of New York 

or else are due to transverse folding. For all these reasons it may be 

assumed that the grit mass now forming the plateau was near the end 

of the Silurian bay; but in the Taconic Range, in the northern half of 

Rutland County, Vt.,. about 57 miles north-northeast of the northern 

edge of the plateau, lies another mass of grit and conglomerate, also 

containing pebbles of Cambrian quartzite and also overlying the Hudson schist, but only about 500 feet in thickness, and covering not quite 

4 square miles. 6 The bay of Silurian time may thus possibly have 

sent an arm up the Champlain Valley.

HISTORICAL GEOLOGY.

With the aid of these conclusions the main outlines of the geological 

history of this portion of the Hudson Valley maj7 be tentatively drawn. 

As the presence of a core of pre-Cambrian granite and gneiss within 

the Rensselaer Plateau area is not yet established, geological history 

does not begin here until after the Cambrian transgression, arid it 

begins with the presence of the Lower Cambrian sea, with its fauna 

chiefly of trilobites, brachiopods and pteropods, and a flora abounding in Oldhamia, if it be a plant. The sediments were alternately 

sandy, clayey, and calcareous-organic. The sea was shallow and there 

was one slight emergence of short duration during a general gradual 

subsidence. At the close of Lower Cambrian time a crustal movement 

folded these sediments, and the sea retreated northward, northwestward, and possibly in other directions. The new land surface became'

"Op. cit. b See paper No. 14, p. 11.
54 GEOLOGY OF HUDSON VALLEY. [BULL. 242.

exposed to atmospheric erosion during Middle and Upper Cambrian 

time. Toward the close of Upper Cambrian time, at least the western 

part of this Cambrian land surface became submerged and the Beekmantown graptolites, together with some surviving Upper Cambrian 

forms, appeared. This submergence was of relatively short duration, 

and an emergence took place during Chazy time which may have lasted 

into early Trenton time, Avhen another submergence occurred. Another 

great series of sandy, clayey, and calcareous sediments was then 

deposited, also upon a shallow subsiding sea floor. An abundant 

graptolite fauna (Normans Kill) flourished, and at intervals a Trenton 

fauna of tetracorallia, crinoids, gastropods, polyzoa, brachiopods, trilobites, etc. a One or more brief emergences and submergences occurred 

in places during this time, resulting in the formation of conglomerates, the pebbles of which show that limestone rocks of Lower Cambrian, Chazy, and Trenton age were above water at no great distance. 

At the close of Ordovician time the powerful crustal movement 

which formed the Taconic Range folded the Trenton and Beekmantown 

sediments and with them refolded and faulted the Lower Cambrian sea 

bottom. The metamorphism attending this movement extended to 

the western foot of the Taconic Range. The sea retreated southward 

and westward. A period of denudation set in which affected the 

Ordovician beds and still further eroded the Lower Cambrian areas 

(islands?), which had remained unsubmerged during Ordovician time. 

Then came the Silurian transgression, which again submerged the 

Ordovician areas and part of the still exposed Lower Cambian area. 

The Silurian sea formed a bay, the wider part of which seems to have 

terminated in the region of the Rensselaer Plateau. The sediments 

deposited at this time were alternately clayey and sandy, with occasional pebbly beds, the pebbles of which came from pre-Cambrian

coarse granites and fine gneisses above water at no great distance, and 

also from Lower. Cambrian quartzites and from slate, shale, grit, 

and marble of Lower Cambrian or Ordovician age. The land areas 

from which the Cambrian pebbles came were probably north of the 

plateau.

These Silurian beds may have become exposed to denudation soon 

after their deposition, owing to a slight emergence and the retreat of 

the shore line in the Silurian bay. However that may have been, at 

the close of Devonian or of Carboniferous time these beds were folded 

and somewhat metamorphosed, and this movement also affected the 

Ordovician sea bottom. The region has been greatly denuded since 

Devonian time, and this denudation was greatly facilitated by one or 

more uplifts and finally by glacial action. The extent of this denudation is shown by the outliers of Hudson shale and Rensselaer grit,

a See p. 101 of paper No. 16, p. 11.
DAM]. filStfOKlCAL AND ECONOMIC GrEOLOGY. 55

and still more by the isolation of the three masses of Rensselaer grit 

from other Silurian deposits of the same age.

This region thus shows the effects of three transgressions (Lower 

Cambrian, Ordovician, and Silurian), three or more minor recessions 

and advances of the sea (one in Lower Cambrian and one or more in 

Trenton), of three crustal movements (Lower Cambrian, Ordovician, 

and Devonian or Carboniferous), and of four periods of denudation 

(at close of Lower Cambrian, of Beekmantown, of Trenton, and in postSilurian time), besides those attending the minor recessions in Lower 

Cambrian and Trenton time, The history of this portion of the Hudson Valley was eventful indeed.

The facts presented will also be found to have some bearing upon 

1 the geographic-paleontologieal theories recently set forth by Messrs. 

Ulrich and Schuchert. (See paper No. 18, p. 11).'

ECONOMIC GEOLOGY.

i

The rocks of this tract have thus far proved of little economic value.

The Cambrian limestone breccia, when in beds of sufficient thickness,

makes a good building stone of unique appearance. The Hudson grit

is used for foundations. The carbonaceous-siliceous shales of the

Hudson formation, quarried near Grand vie>v Hill, are useful for country

roads, and the shales of all the formations are serviceable for application to sandy roads. The red shales of the Lower Cambrian (horizons

A, C, E, of table on p. 29), quarried west of Burden Lake, and of the

I Silurian Rensselaer grit have been used in the manufacture of putty

i and paint. The coarser beds of the Rensselaer grit, with their dark-

 f green matrix and occasional white, reddish, and bluish pebbles, become

a beautiful rock when polished a and would answer for indoor decora1M tion. Efforts to utilize it for outdoor purposes have failed because of

^ the small percentage of lime in the matrix, the surface of which, under

continued exposure, thus acquires a spongy texture.

 .; But the chief economic value of these formations lies in their relation 

to agriculture. The greenish shale of the Lower Cambrian (horizons

v C, E, H), which covers so many square miles of the valley, owing to 

its numerous planes of bedding, cleavage, and jointing, and to the

j action of rain, changes of temperature, and frost, breaks up into 

roughly quadrangular, stick-like fragments which gradually pass into 

a clayey subsoil and soil. Upon this, rye, which is one of the chief 

products of Rensselaer County, and is cultivated as much for its straw 

as for its grain, tlirives. Specimens of soil and subsoil of this origin, 

from typical rye lands in this county, were submitted in 1894 to Prof. 

Milton Whitney, of the United States Department of Agriculture, for 

mechanical analysis. The results of the analyses are as follows:

u See PI. C of paper No, 9, p. 11, for a colored lithograph of polished specimens.
56 GEOLOGY OF HUDSON VALLEY. [BULL. 242.-

Mechanical analysis of soils from Rensselaer County, N. Y.

Moisture in air-dry sample. .......:.....,...........:..............:...............

Fine sand (0.1-0.25 mm.) . ..........................................................

Silt (0.01-0.05 mm.) ................................................................

Fine silt (0.005-0.01 mm. )................................... J. .....................

Clay (0.0001-0.005 mm.). ...-...............................:........................

Material larger than 2 mm ..........................................................

"Fine earth " ......................................................................

1721, 

soil.

Per cent. 

2.48

8.17

7.03

4.66

4 fi4

3.93

19 47

OS 07

6.51

8.58

38.00

62.00

100.00

1722, 

subsoil.

Per cent. 

2.02

6.42

7.71

4.33

3.74

3.59

19.00

3d 17

8.21

10.60

22.00

78.00

100. 00

Professor Whitney, in a letter to the writer, offered the following 

remark on these analyses:

I think it is not hard to point out the reason why this soil is considered poor and 

why it is not adapted to wheat and grass. If the soil were composed wholly of the 

fine earth and had none of the coarse material of the undecomposed shale, the soil 

itself would contain, according to our analysis, 8.53 per cent of clay and the subsoil 

10.60 per cent. This would be much less than is necessary for a good wheat land, 

except in cases where there is a large amount (45 per cent or over) of silt. The 

samples would be considered too light in texture for wheat or grass and not sufficiently retentive of moisture. These have, however, about the same texture as good 

fruit land with us, especially adapted for peaches. When we consider, however, 

that this fine earth represents-only about 62 per cent of the soil and 78 per cent of 

the subsoil, while the remaining 38 per cent in one case and 22 per cent in the other 

is coarse, inert material, it \yill be seen that the actual amount of clay in the soil is 

very much less than would be indicated by the mechanical analyses of the fine earth. 

Instead of there being 10 per cent of clay in the subsoil there would be very 

much less than this, and too little, I should say, to give the proper supply of water 

to the staple agricultural crops.

As a matter of observation, rye seems to have such an affinity for 

this Cambrian shale that the stalks will grow almost on a bare ledge of 

it. Under the microscope this shale is seen to consist largely of 

potash mica (see PI. II, j?), and as the ash of the grain contains 32.10 

per cent and that of the straw 22.56 per cent of potash a there may 

be a slight chemical relationship between the supply of potash by the 

soil and its requirement by the plant, which, added to the permeability 

and other physical properties of the soil, makes it peculiarly favorable 

for the cultivation of rye.

The region also affords an illustration of the effect of the uneconomic 

use of geological and topographical conditions i. e., of unwise defora Strassburger, Noll, Schenck, and Schimper, Lehrbuch der Botanik, 2d ed., Jena, 1895, p. 147.
DALE.] SUBJECTS FOE FURTHER INVESTIGATION. 57

estation/' The Rensselaer Plateau is the natural source of water supply 

for towns along the east shore of the Hudson for a stretch of 20 miles, 

but it was deforested over a half century ago, with the effect of 

diminishing the quantity and lowering the quality of the supply.

SUBJECTS FOR FURTHER INVESTIGATION.

These geological studies indicate the directions in which further 

investigations are needed. These are:

(1) Very minute exploration of the Rensselaer Plateau area for a 

pre-Cambrian mass.

(2) The determination of the structure of the bed or beds of limestone conglomerate in the Moordener Kill, in order to ascertain whether 

there was more than one emergence in Hudson time.

(3) A careful search for Beekmantown graptolites in the areas 

mapped as Lower Cambrian, with a view to determining-the exact areal 

extent and the thickness of the Beekmantown formation.

(4) Further search for fossils in the belt of shale with small quartzite beds which lies between Schaghticoke and Valley Falls and extends 

north to the Washington County line.

(5) Search for favorable points for the measurement of the Lower 

Cambrian shale horizons A, C, E, H, with a view to making a more 

nearly correct measurement of the thickness of the Lower Cambrian 

exposed.

(6) The extension of the areal and structural work, thus begun, into 

Columbia Count}7 to that point where the Ordovician areas on each 

side of the Cambrian meet, and also northward into Washington 

County.

"See p. 299 of paper No. 9, and a quotation from Spafford in paper No. 21, in list on p. 11 of this 

bulletin.

INDEX.

A.

Algffi, occurrence of....................... 13

Alps, rocks near............... ............ 40

Analyses of soils, results of.. ............. 65-56

Aries, Lake, calcareous sandstone near,

figure showing ................. 16

fossils near ............................ 30,33

rocks near ............................. 24-26

sections near, diagrams snowing ..... 25

Ashley Hill, rocks near.... ......... 16,22-24,28

sections at and near, diagrams showing ............................. 24

Austerlitz Town, rocks in ................ 36

Bald Mountain. See Rice Mountain.

Becraf t Mountain, folding at ............. 44, 47

folding at, Grabau, A. W., cited on .. 44 

Beekinanto wn shale, character of ........ 43

equivalent of .......................... 43, 50

folding of .............................. 44-47

fossils in . .......... ..................... 30-31

occurrence of.................... 12,39,30,38

petrography of ........................ 31

relations of .............. I....- 31-33,37-38,43

stratigraphy of. ....................... 31-33

thickness of __...._-..........--.....--_ 33

Beekmantown time, conditions in........ 49

Bibliography, table of .................... 10-11

Bishop, I. P., cited on fossils of Columbia

County, N.Y. ................. 34,35

Brachiopods, occurrence of......... 13,34,53,54

Brainard,Ezra, cited on Chazy formation. 49 

Brunswick Town, rocks in ............ 38,41^2

Burden Lake, rocks near ................. 17

sectionnear ........................... 46

C.

Calymene, occurrence of ................. 34

Cambrian, Lower, crustal movement, occurrence of .................... 47,53

Cambrian, Lower, denudation, extent of. 51 

Cambrian, Lower, fossils, localities of ... 13-14 

Cambrian, Lower, limestone, relations

of, diagrams showing... 24,25,26,46 

Cambrian, Lower, oscillation, occurrence

of .............................. 49

Cambrian, Lower, rocks, character of... 16,43 

conglomerate in....................... 48

Dale, T. Nelson, cited on .......... 14,15,16

discussion of. .......................... 13-30

equivalents of ......................... 43,50

Page. 

Cambrian, Lower, rocks, Foerste, A. F.,

cited on........................ 16,26

folding of .....I----------------------- 44-47

occurrence of.................... 12,16,31,35

petrography of........................ 14-17

relations of.......... 14,21,27,30-32,37,43,44

Ruodemann, R., cited on.............. 31

sections of, diagrams showing ....... 18,

21,23,24,25,26,27,28 

stratigraphy of......-.-..-..-...-..... 17-29

table showing..................... 29

thickness of ........................ 17-18,28

value of.............:...-.............. 56

Cambrian, Lower, sandstone, microscopical sections of, figures showing ............................. 20

Cambrian, Lower, shale, organic impressions in, figure showing........ 14

Cambrian, Lower, time, conditions in... 50,

51,52,53 

conditions in, Schuchert, Charles,

cited on........................ 49-50

Walcott, Charles D., cited on..... 49-50

Cambrian, Middle, rocks, absence of..... 30,

32-33,38,49

Cambrian, Middle, time, conditions in. 49,53-64 

Cambrian, Upper, rocks1, possible occurrence of........................ 31

probable absence of.......... 30,32-33,38,49

Cambrian, Upper, time, conditions in... 53-54 

Carboniferous crustal movement, occurrence of........................ 47

Castleton, fossils near.I................... 33

Chatham, fossils near..................... 33,35

rocks near ...:......................... 38-39

Chatham Town, fossils in................. 34

rocks in............................. 22-24,36

Chazy formation, Brainard, Ezra, cited on 49 

equivalent of.......................... 50

occurrence of.......................... 31,49

probable absence of............. 32-33,38,49

Ruedeinann, R., cited on.............. 49

thickness of............................ 49

Chazy time, conditions in................. 49,54

Clark, P. Edwin, cited on unconformities............................. 44

Climacograptus bicornis, occurrence of. 33 

parvus, occurrenceof................. 33

Clonograptus, occurrence of.............. 43

flexilis (Hall), occurrence of.......... SO

proximatus (Matthew), occurrence of 31 

near Salteri (Hall), occurrence of.... 30

59
60 INDEX.

Page.

Cohoes atlas sheet, portion of, in area discussed, mention of............ 9

Columbia County, portion of, in area discussed, mention of ............ 9

Conglomerates, occurrence of............. 48

Coonradt farm, section at, diagram showing ............................. 21

Corynoides calicularis, occurrence of.... 33

Crinoids, occurrence of................... 34,54

Crustal movements, Emerson, B. K., cited

on -.........-...---....-..--..-- 47

occurrence of.....^.................... 46-47

Curtis Mountain, elevation of-..... .... 12

rocks at and near ....^................ -22,28

section of, diagram showing.......... 23

D.

Dale, T. Nelson, cited on Green Mountain region..................... 25

cited on Hudson formation ........... 35,36

cited on Lower Cambrian rocks. - - 14,15,16 

cited on Oldhamia fossils ............. 13-14

cited on olive grit..................... 15

cited on Rensselaer grit........J._ 34,35,39

cited on sandstone, calcareous_. _ 15 

cited on unconformity................ 47

fossils found by......... ...--_....... 30

oscillation, traces of, found by ....... 49

photograph taken by., figure drawn

from........................... 14

Barton, 1ST. PL, cited on unconformities.. 44 

Davis, Wm. M., cited on unconformities. 44 

Deep Kill, fossils near................ 30-31,33,49

Deforestation, loss from .................. 56-57

Defreestville, fossils near................. 30

rocks near............................. 37

section near, diagram showing....... 25

Denudations, extent of-.--...-............ 54-55

occurrence of.......................... 51

Devonian bees, metamorphism of........ 47

thickness of, Lesley, J. P., cited on... 51 

Prosser, C. S., cited on............ 51

Dichograpsus sp., occurrence of.......... 30

Dicranogi-aptus ramosus, occurrence of . 33 

Dictyonema, occurrence of............ 43,49,50

labelliforme (Eichwald), occurrence

of............................... 31

murrayi (Hall), occurrencecf........ 30

near irregulare (Hall), occurrence of. 30 

Didymograptus Sagittarius, occurrence

of............................... 33

Diplograptus angustifolius, occurrence

of............................... 33

cf. angustifolius, occurrence of....... 33

f oliaceous, occurrence of.............. 33

sextens, occurrence of ............._ 33

Drainage of area discussed, features of.. 12 

Dusenbery Ridge. See Curtis Mountain.

E.

East Greenbush, rocks at................. 36

East Greenbusb Town, rocks in.......... 24-25

East Nassau, rocks near .................. 40

Economic geology. See Geology, economic. 

Elevations, character of .................. 11-12

Emerson, B. K., cited on crustal movements ....................... 47

Erosion. See Denudation.

F.

Faulting, Ford, S.'W., cited on........... 28

occurrence of..................... 9,28,30,38

See also Overthrusts. 

Field work, extent of ..................... 10

Foerste, A. F., cited on Lower Cambrian

rocks........................... 16,26

figure cited from ...................... 26

fossil determinations by ................ 13

fossils found by.................. 10,33,34,35

photograph taken by, figure drawn'

from .......................... 14

Folding, occurrence of--..-..... --..--- 9,38,54

periods of.............................. 44-47

Ford, S. W.,cited on fault near Schodack

Landing ....................... 27-28

cited on Hudson formation........... 37

cited on Trenton- conditions .......... 48

fossil determinations by .............. 13

fossil localities discovered by......... 10

Formations, age of ........................ 9

character of--....-..--.-.....-.---.... 9

relations of ............._..... ..... 9

resume of............................... 43

" table of ............................ 43

Fossils, determinations of, by Foerste,

A.F............................ 13

determinations of, by Ford, S. W.... 13

byGurley, R. R ......... ....... 33

by Schuchert, Charles ............ 30,33

by Walcott, 'Charles D ......... 13-14,27

discovery of, by Dale, T. Nelson...... 30

by Foerste, A. F............. 10,33,34,35

by Ford, S. W ..................... 10

by Walcott, Charles D............ 10

obscure character of.................. 9

Fossils and fossil localities, occurrence of 13-14, 

16,30-31,33-35,39,43,49 

Fossils of Columbia County, Bishop, I. P.,

cited on........................ 34,35

Fossil localities, Ruedemann, R., cited on. 30,33

G.

Gastropods, occurrence of...... ..... 34-35,54

Geological history of . area discussed,

sketch of....................... 53-55

Geological map of area discussed ........ 12

Geological Survey, work of............... 9,10

Geology, economic, discussion of......... 55-57

problems of ........................... 9

summary of ..................... 12-13,44-47

Gilbert, G. K., cited on Silurian conditions ......_.-......-..-....-. 48

Glacial deposits, occurrence of........... 9

Grabau. Amadeus W., cited on Becraft

Mountain folding ............. 44

.Grafton Town, section in, diagram showing ............................. 46

Grant Hollow, rocks at and near......... 15,36

Graptolites, occurrence of....... 30,33,49-50,54

Graptolittius bifidus (Hall), occurrence

of,... ............... -.....- 30

bryonides (Hall), occurrence of...... HO
INDEX. 61

Page.

Graptolithus quadribrachiatus (Hall),

occurrence of.................. 30

Green Mountain crustal movement, occurrence of.................... 47

Green Mountain Range, metamorphic

zone of-..-......-...-.--...-.-- 9

Green Mountain region, Dale, T. Nelson,

cited on........................ 25

Greenwich slate, equivalent of........... 43,50

Greenwich Town, fault in....--....--.--. 30

Grit, olive, Dale, T. Nelson, cited on...... 15

occurrence of............._...- 14-15,27-29

relations of ............................ 27

Gurley, K. E., fossils identified by ....... 30

H.

Hematite, 'Variations in amount of....... 17

History, geological, sketch of ............ 53-55

Hoag Corners, rocks near................. 41

section near, diagram showing....... 21

Hoosic River, fossils on.................... 33

Hudson formation, character of....... 35-36,43

conglomerate in....................... 48

Dale, T. Nelson, cited on.............. 35,36

discussion of........................... 33-39

equivalent of .......................... 43,50

folding of _.,..._....._......-._.-:..... 44-47

Ford, S. W., cited on................... 37

fossils in ............................... 33-35

occurrence of.......,..--.-...-..... 30-32,38

petrography of ........................ 35-36

relations of....... 21,26-28,30-32,37,41,43,44

relations of, section showing ......... 46

Buedemann, R., cited on.............. 37

stratigraphy of........................ 36-37

value of - .-..-._-.---..-.---.---.-..---- 55

Hudson grit, microscopic section of...... 20

Hudson Valley, portion discussed, area

and boundaries of............. 9

Hyolithellus, occurrence of............... 27

Hyolithes, occurrence of....'..-_....__,... 27,43

I.

Ida, Lake, rocks near .................. 14-15,27

Investigations, further, need of .......... 57

subjects for......................... 57

K.

Kinderhook atlas sheet, portion of, in

area discussed, mention of._ 9 

Kinderhook Creek, loc«ition of ........... 12

sections at and near..............._.. 18,39

diagram showing.................. 18

L.

Lansingburg Town, rocks in .......... 15-16,38

section in ........................... 27

Lasiograptus mucronatus, occurrence of. 33 

Leptcena sericea, occurrence of........... 35

Lesley, J. P., cited on thickness of Devonian and Silurian rocks....... 51

Levis graptolites, occurrence of.......... 43

Lower Cambrian. See Cambrian, Lower.

 M. Page.

Maclurea, occurrence of............... _ 35

Maiden Bridge, section ut ................ 39

Map, geological, of area discussed........ 12

Medina formation, equivalent of......... 43,50

reddish shale of........................ 13-14

Melrose, fossils near....................... 33

rocks near............................. 29

Merrill, F. J. H., cited on geology of New

York................. ....... 48,53

Microscopical sections of typical rocks .. 20 

Middle Cambrian. See Cambrian, Mi ddle. 

Millville, rocks near....................... 41-42

section near .................._...... 42

Moifitt, F. H., fault traced by ............ 38

Monticulopora,occurrence of............. 34

Moordener Kill, fossils on.............. 13,33,84

location of............................. ' 12

.Murchisonia, occurrence of............... 34,35

N.

Nassau, fossils near....................... 13

rocks near'.-........................... 40

NaHsauTown, fossils in................... 13

rocks in....................... 25,28,29,40,41

sections in .......................... 18,21,46

New York, geology of, Merrill, F. J. H.,

cited on.................'....... 48,53

Normans Kill fauna, occurrence of ... 37,43,54 

North Greenbush Town, fossils Jn ....... 30,33

rocks near.............................. 31

sections in ............................. 25

Nullipores, occurrence of................. 13

O.

Oldhamia (Munchisonites) occidens 

Wale., Dale, T. Nelson, cited 

on.............................. 13-14

figure showing ........................ 13

occurrence of.............. 13-14,27,29,43,53

Walcott, Charles D., cited on......... 27

Ole uellus fauna, occurrence of ........... 13,

22-23,25,27,28,43 

Oneida formation, equivalent of...... 43,50-51

r.ddish shale of ....................... 13-14

Ophileta, occurrence of................... 35

Orange County, geology of, Eies, H., cited

on.............................. 47

Ordovician denudation, extent of........ 51

occurrence of.......................... 61,54

Ordovician grit, microscopical section of. 20 

Ordovician rocks, character and relations of.......................... 43

folding of......-- ..-.-......-...:.. 44-47

occurrence of....................... 12,27,34

Ordovician time, conditions in .;...... 51,53-54

Orthis cf. plicatella, occurrence of....... 34

Orthoceras, occurrence of................ 35

Oscillations, finding of traces of, by T.

Nelson Dale.................... 49

occurrence of.......................... 49

Overthrusts, occurrence of.... _........ 38,44

See also "Faulting.

P. 

Paleozoic conglomerates, Walcott,

Charles D., cited on........... 16
62-- INDEX.

. Page.

Petrography of Beekmantown shale.._"._ 31 

of Hudson formation.-...--....-..-... 35-36

of Lower Cambrian rocks .-.. .... 14-17

of Eensselaer grit..................... 39-40

Pike Pond, rocks near..........:.......... 39

Pittstown Town, fossils in................ 33

rocks in...---.....-..-..-..-........... 38

Pleurotomaria, occurrence of ..._...... 35

Poesten Kill, fossil from .................. 13

location of ............................. 12

organic impressions near, figure of... 14 

rockson and near ....-....'...... 17,35,36,40

section on, diagram showing.-.-..... 27

Polyzoa, occurrence of ................... 54

Post-Devonian crustal movement, occurrence of.-...-.-....--..-.-...-. 47

Post-Lower ' Cambrian rocks, reddish 

shale of .........................13-14

Post-Silur-ian denudation, extent of...... 51

Post-Silurian time, conditions in......... 51

Potash, occurrence of...................... 56

Potsdam formation, occurrence of....... 49

Pre-Trenton rocks, reddish shale of...... 13-14

Prindle, L. M., aid by ..................... 10

information gained by. ............ 30,33-34

Prosser, C. S., cited on thickness of Devonian and Silurian rocks..... 51

Pteropods, occurrence of................. 13,53

Ptilodycta, occurrence of................. 35

Pumpelly, Raphael, plan of............... 9

Quackenkill, section near, diagram showing ............................. 46

Quartzite, organic impressions in, figure

of................................ 14

Quartzose beds, occurrence and character of............-.-.--'.-.. .. 17

B.

Raflnesque, Mount, elevation of.......... 12

rocks near .............................. . 31

trend of................................ 38

Raymertown, fossils near ................ 30

rocks near.......................... 15,27,32

Bedrock, rocks at.-...-.....-..--.-...--.- 36

Bensselaer, Hudson formation near....... 37

Bensselaer County, portion of, in area discussed, mention of ............ 9

soil of ............-.-.....-..-.-..--.... 55-56

analyses of......................... 56

Bensselaer grit, character of .......... 39-40,43

conglomerate in.-..-.-.....--..-..-..- 48

Dale, T. Nelson, cited on........... 34,35,39

discussion of............................ 39-42

equivalents of ........................ 43,50-51

folding of.............................. 47

foasilsof................................ 39

metamorphism of..............;...... 47-48

microscopical section of............... 20

occurrence of.......................... 12-13

petrography of........................ 39-40

relations of...................... 21,39,40-42

section showing ................... 46

stratigraphy of........................ 40

Page. 

Bensselaer grit, thickness of .......... 40,50-51

value of................................ 55

Bensselaer Plateau, boundaries of..--.-.. 11 

deforestation of....................... 56-57

fossils at foot of ........................ 36

rocks of................................ 32-13

sections at and near..__.-__-_-.--_.... 46

Bice Mountain, elevation of.............. 12

faults at and near.................. 28,30,38

rocks at-..--..-..-......--..--.----.... 36

Bies, Heinrich, cited on geology of Orange

County......................... 47

Buedemann, Rudolf, cited on Chazy formation......................... 49

cited on conglomerate formations ... 34,48 

cited on fossil localities ....-..-..--.-. 30,33

cited on Hudson formation ........... 37

cited on Lower Cambrian rocks...... 31

publication by.-..-.-..--.--.--.-..-... 10

Butland County, Vt., geological work in. 10

Bye, growth of.-..-......-..-..--....-..-. 55-56

Bysedorph Hill, fossils at................. 33

Buedemann,B.,cited on .............. 33

S.

Sandlake, rocks near...................... 40

section near...........-...--......-.... 46

Sandstone, calcareous, character of...... 15

Dale, T. Nelson, cited on.............. 15

occurrence of......._......-..- ,15-16,23,29

specimen of, figure showing._....__-. 15

Schaghticoke, fossils at and near... 30-31,33,35 

fossils at and near, Buedemann, B.,

cited on --...-.-..--...-..-.-..- 33 

rocks at-------.---.-.--..- --.-.----.-.- 36

Schaghticoke Town, fossils in ............ 33

Schodack, fossils near..................... 34

Schodack Landing, fault near......... 28,30,38

rocks near.-..-......-..-..-.....-..... 27-28

section near........-.---..-.-......-... 28

Schodack Town, fossils in.............. 13,33,34

Schuchert, Charles, cited on Lower Cambrian conditions...-......-.-.- 49-50

fossils identified by.................... 30,33

Sections, geologic, figures showing....... 46

Sections, microscopical, of typical rocks. 20 

Sediments, deposition and character of.. 53-54 

Septaria, occurrence of................... Hu

Shale, greenish, character of.............. 16:-17

occurrence of.......................... 16

Shale, reddish,occurrence of.......... 13-14,29

relations of............................ 29

variations in color of.................. 17

Shoreham, Vt., rocks near................ 49

Silurian grit, microscopical section of... 20

Silurian rocks, character and relations of. 43

extent of.-..-.---.-.-------.-.--. ------ 53

folding of--..-..-.--. --....---.--. 47

occurrence of......_.........--.-.---- 12-13

thickness of, Lesley, J. P., cited on.... 51

Prosser, C. S.,cited on............. 51

Silurian time, conditions in............... 48,53

conditions in, Gilbert, G. K., cited on. 48 

Snake Hill, section near .................. 18

Soils, analyses of....-.....-..---.-.-.-...- 55-66

value of......--.--.--....-..-....--.... 55
INDEX. 63

Page. ' 

Soils, Whitney, Milton, cited on.......... 56

South Troy, rocks near.................... 36-37

section near............................ 46

Spafford, , cited on deforestation... 56-57 

Speigletown, section near, diagram showing ............................. 27

Spencertown, rocks near ................. 39

Stissing Mountain, rocks at............... 48

Stockbridge limestone, equivalent of ..'.. 43,50 

Stratigraphy of Beekmantown shale..... 31-33

of Hudson formation.................. 36

of Lower Cambrian rocks ............ 17-29

of Kensselaer grit..................... 40

Stromatocerium, occurrence of.......... 34-36

Strophoinena alternata, occurrence' of... 35 

Sutherland Pond, fossils near ............ 34

T.

Tackawasick Creek, fossils nea r.......... 34

rocks near................ ...... 22,28,40-44

sections at and near................... 21

Taconic crustal movement, occurrence of 47,54 

Taconic Eange, character of.............. 12

schist of................................ 33

Taconic system, Walcott, Charles D.,

cited on........................ 38

Tetracorallia, occurrence of.............. 54

Tetrograpsus, occurrence of.............. 30

Tomhannock, rocks near ................. 24

Topography, discussion of................ 11-12

Trenton formation, base of, probable ab-.

sence of.................. 32-33,38,49

. equivalentof .......................... 43,50

occurrence of ........................... 34

relations of ............................ 40-41

Trenton-Hudson period, reddish shale of. 13-14 

Trenton oscillation, occurrence of........ 49

Trenton time, conditions in............ 48,50,54

conditions in, Ford, S. W., cited on .. 48 

'' Trilobite'' limestone, occurrence of.... 13

Trilobites, occurrence of.................. 53,54

Troy, fossils near......................._ 13

Hudson grit from, description of..... 35,36

rocks near........... 14-15,17,27,28,29,36-37

Page. 

Troy, section at, diagram showing....... 27

Troy atlas sheet, portion of, in area discussed, mention of ............ 9

Troy Town, section in .................... 26

U.

Unconformities, Clark, P. Edwin, cited

on.............................. 44

Dartori, N. H., cited on................ 44

Dale, T. Nelson, cited on.............. 47

Davis, Wm. IV., cited on .............. 44

occurrence of .......... .. 30,32-33,38,43,44

Van Ingen, Gilbert, cited on.......... 44

Upper Cambrian. See Cambrian, Upper.

V.

Valley Palls, rocks near................... 29

Van Denburg Hill, fossils on .............. 34

Van Ingen, Gilbert, cited on unconformities............................. 44

Vermont formation, equivalent of ....... 43,50

W.

Walcott, Charles D., cited on Lower Cambrian conditions.... t .......... 49-50

cited on Paleozoic conglomerates .... 16

cited on Oldhamia fossils ............. ] 3-14

cited, on Olenellus fauna .............. 27

cited on Taconic system .............. 38

figure cited from...................... 13

fossil determination by............ 13-14,27

fossils found by. ............... ...'.... 10

map by, mention of.................... 38

quoted on Oldhamia fossils ........... 13-14

Washington County, geological work in. ]0 

Water supply, injury to .................. 57

West Sandlake, fossils near............... 30

rocks near ............................. 24-25

Whitney, Milton, analyses by ............ 55-56

cited on soils of area discussed ....... 56

Wynants Kill, fossils near ................ 30

location of............................. 12

rocks near ... ....................... 32