DEPARTMENT OF THE INTERIOR

BULLETIN

OP THK

UNITED STATES

3STo. 53

WASHINGTON ,

GOVERNMENT PRINTING OFFICE 

 1889

BULLETIN" N° 53 , PL SVWTBCKET LIGHT

MAP

OF THE

ISLAND OF NANTUCKET

SHOWING THE

DISTRIBLmON OF GLACIAL AND POST-GLACIAL, DEPOSITS

ey

S.S.SHALER. 

Scale Ijl30,000

C oatour interval 2 0 feet.

Post-glacial deposits . Swamps.

Kame andmoraiiie 

Frontal terrace.

 ... .- ibm ..._ Nevr-r's ._. - .-.. ~f Hi-ail ; r~-.--- ..- .. ____ -j __ J

UNITED STATES GEOLOGICAL SUBVEY

J. TV. POWELL, DIRECTOK

THE

GEOLOGY OF KANTUCKET

BY

WASHINGTON

GOVERNMENT PRINTING OFFICE , 

1889

CONTENTS.

Page.

Letter of transmittal ........................................................ 9

Prefatory note ...................................................._....-...... 11

General form of Nantucket ..................................... .......... 11

General geological struc ture................................................. 15

 Origin of tlie detrital materials .............................................. 26

Fossiliferous deposits........................................................ 28

Fossiliferous deposits of Sankaty Head................................... 30

Succession of geological events .:............................................ 42

Post-glacial changes of Nantucket .......................................... 47

Recent changes on the coast of Nautucket.................................... 49

"Vegetation of Nantucket .................................................... 52

(603) 5

ILLUSTRATIONS.

Page. 

PI. I. Geological map of Nantucket Island.......................... Frontispiece

II. Aspect of kame moraine on the northern border, near Shemo Point.. 16

III. Kame valley, with dome-shaped hill, looking south, on north road,

near Shemo Point............................................... 18

IV. Topography of kame moraine in central district, near north end of

Long Pond, looking north....................................... 20

V. East branch of Hummock Pond, looking south ..................... 22

VI. Junction of karae moraine and terrace plain on Gibbs Pond; Siasconset in distance................................................... 26

VII. Sankaty Head, looking north from a point 150 yards south of lighthouse .-.--...--......................'........................... 30

VIII. View of co.ast escarpment 500 yards north of Sankaty light......... 40

I.. Aspect of north shore, from near upper end of Long Pond, looking east. 46

X. Split pebbles, resembling stone implements ........................ 50

Fig. L Diagrammatic horizontal section of small spit on Coatue Beach...... 13

2. Diagrammatic section through Coatue Beach......... ........... 15

3. Generalized section of Squam Head ................................ 16

4. Section at Weewocket............................................. 16

5. Section on border of Lily Pond..................................... 16

6. Section from Coatue Bay to the ocean.............................. 17

7. Diagrammatic section across valleys in sunken plain................ 20

8. Diagrammatic section showing positions of bowlders on surface of

glacial plain near Gibbs Pond ................................... 21

9. Section of submerged swamp on north shore........................ 28

10. Section at Sankaty Head .......................................... 32

11. Diagrammatic section of beds at Sankaty Head .................... 39

12. Section 500 yards south of beds at Sankaty Head ................... 41

13. Section showing apparent beach line, near Gibbs Pond ............. 45

14. Kameseast of Nantucket village................... ................ 45

15. Section of shore east of Surf Side, showing beginning of coast apron. 50

16. Profile across Great Head, showing dunes .......................... 51

(605) 7

LETTER OF TRANSMITTAL

U. S. GEOLOGICAL SURVEY,

ATLANTIC COAST DIVISION,

Cambridge, Mass., April 26,1888.

SIR : I have the honor to transmit herewith a report on the geology 

of the island of Nantucket. This report embodies a portion of the work 

which I have done in connection with the general study of the Atlantic 

coast line. Although part of a much more extended inquiry, it seems 

well to publish the results contained in this memoir in advance of my 

general report for the reason that the region constitutes a distinctly 

bounded field and also because the problems considered in this report 

have an important bearing on work which is in the hands of other divisions of the Survey.

Very respectfully, your obedient servant,

1ST. S. SHALER,

Geologist in charge. 

Hon. J. W. POWELL,

Director U. 8. Geological Survey, Washington, D. C.

(607) 9

GEOLOGY OF THE ISLAND OP NANTDCKET.

BY NATHANIEL S. SHALEE.

PREFATORY NOTE.

The island of Nantucket occupies a position which makes its structure of great interest to the geologist. It lies near the extreme southeastern point of a great salient of lands and shoals forming the southern front of New England. This district, unlike the main-land of New 

England, exposes none of the older rocks; it is composed of sands, 

gravels, and clays which were brought into their present position during 

or immediately before the last Glacial Period. It should be noted that 

the island of Nantucket is but a small fragment of a vast sheet of this 

glacially transported matter. The greater part of Plymouth County, 

Mass., the whole of Cape Cod, the larger portion of Martha's Vineyard, 

and the whole of Long Island, with all the many islands and islets 

at its eastern extremity, are the dissevered remains of a great shelf 

formed of the debris brought to its present position by the glacial ice 

and by the streams of water which flowed beneath it.

Owing to its extreme southeastern position the island of Nantucket 

affords evidence concerning the history of the ice sheet which can not 

be obtained at any other point on the coast: it has, therefore, seemed 

worthy of the detailed studies which will be presented in this report.

The general form and structure of the island will be first considered: 

after that the relations of the area to the other parts of the district 

will be set forth.

GENERAL FORM OF NANTUCKET.

As will be seen from the map that accompanies this report (Plate I), 

the form of the island of Nantucket is rudely crescentic; its shape 

may be compared to that of the implement known as a bill-hook. Its 

extreme length in an east and west line is about eleven miles. The 

westernmost mile of this length is formed by a sandspit which is constantly varying in its extension. At present this sandspit has only 

about one-third of the length indicated on the map, so that the permanent part of the island may be estimated at ten miles in length. The

(609) 11
12 ' GEOLOGY OF NANTUCKET. [BULL. 53.

north and south width of the island does not at any point exceed seven 

miles, but the northern three miles of this width included in the spit 

of Great Head are made up of blown sands and detritus carried to 

its position by the currents of the sea; so that the part of the area 

which was formed during the glacial period does not exceed four miles 

in width. This measurement is also variable, for Great Head has lost 

1,400 feet in length since 1784.1 ' ,

The surface of the island, though varied, has a narrow range of 

height, the loftiest point being about ninety feet above the level of the 

sea. Through its central part there extends a series of low but extremely numerous and irregularly shaped hills of glacial drift. On the 

western part of the island this hill belt comes to the shore which forms 

a boundary of the island; on the eastern part the hills are cut transversely by the coast, forming the bluffs which face the sea from Siasconset to Squam Head. On the southern half of the island this line of 

low drift hills declines into a plain of sand, which extends with gentle 

slope from the base of the hills to the sea, terminating in a series of 

low bluffs rarely exceeding twenty feet in height.

The coast line of the island is cast in a set of very gentle curves 

united by lines of straight shore. On the southern and eastern faces 

the shores are either straight or very gently convex; on the northern 

coast the sea line exhibits no convex curves. This conforms to the general rule that long gravelly shores which face the open sea have, prevailingly, a straight or slightly convex form. (See PI. IX.)

The details of the shore line of this island present many interesting 

features, most of which can be noted in connection with the geological 

structure of the island, but some of them may best be considered in 

this general sketch of its topography. The most remarkable of these 

topographic peculiarities is that which is commonly known as Coatue, 

including the harbor and the beach of that name, and the promontory 

of Great Head.

This remarkable district exhibits a number of very singular features. 

The most notable of these are Coatue Bay and the sand beach which 

separates it from the sound on the north. Coatue Bay has the most 

puzzling configuration of bottom and of shores of any inlet on the 

North American coast. The bottom is divided into two great basins 

and a third one of lesser extent. In these basins the sea-floor slopes 

gently from the shores to considerable depths, the two greater easternmost basins having about twenty feet 'of water at low tide, while the 

barrier between them has then only about three feet of water upon it.

The configuration of the shores is even more peculiar than that of the 

bottom. On the south the boundary of the bay is quite irregular, being 

decidedly more indented than the general outer face of the island, for 

the evident reason that it has been protected by Coatue Beach from the

1 See Monomoy and its shoals, Henry Mitchell: Annual Reports of Harbor and 

Land Commissioner of Massachusetts, 1837 to 1842.

(610)
BHALEK.] GENERAL FORM OF NANTUCKET.

taction of strong waves. On the north shore of Coatue Bay the low 

dune-covered Coatue peninsula has six small crescent-shaped bays, of 

which five are very distinct in their outlines and of about the same size. 

These bays are each a little less than a mile wide, and the base of their 

curves is about two hundred yards from ,the line wrhich connects their 

promontories. From each promontory there extends for a distance of 

200 yards or more out into the bay a sandspit which is not delineated on 

the general map, but which, if represented, would add much to the peculiarity of their aspect. They are diagrammatically indicated in the appended sketch (Fig. 1). The cause of these peculiar projections is not 

plain. They are possibly due in some way to the action of the tidal currents, which sweep up the bay with much speed and move the finegrained sands with considerable ease. From a superficial inspection 

it' appears that the tidal waters are thrown into a series of whirlpools, 

which excavate the shore between these salients and accumulate the

sand on the spits.

"FIG. 1. Diagrammatic horizontal section of small spit on Coatue Beach. 

a, a, a, successive beaches; b, b, promontory.

It is evident on inspection that the process which brought about the 

construction of these bays is still in operation. On each of the little 

headlands separating the basins there are traces of very recent, if not 

still active, building out of the point toward deeper water. On three 

of the points there are small salt-water ponds placed as indicated in 

the diagram. These pools are inclosed behind a low beach wall, formed

(611)
14 GEOLOGY OF NANTUCKET. [BULL. 53.

during some great storm by the waves of the bay in which they lie.* 

The lagoons are not clearly traceable on the other points, but they all 

have the general form and structure shown in the diagram.

Coatue Beach, on the southern boundary of which lie the abovedescribed bays, is in itself a remarkable bit of shore topography. It 

clearly belongs to the class of barrier beaches such as are originated 

along coasts by the breaking of the waves in shallow water. It is evident that this beach has grown slowly and by successive and variable 

accretions; even in its narrow width we can trace a number of low walls 

which mark the line of the sea at various stages in the progress of its 

growth. The whole of these sands have been thrown up from the bottom of Nantucket Bay (Pig. 2). When we come to consider the successive changes of level of this island we shall find that this beach affords 

us evidence of some value as to the nature of these movements.

The long sand strip known as Great Head is the third element in 

this peculiar topography. This promontory is essentially like many 

others on the sandy shores of our coast. It will be observed that while 

the elevated and older portion of this spit trends in a northwest and 

southeast direction, the submerged and more recently formed portion, 

which is covered even at low water, has an axis nearly at right angles 

to this trend, and also that this under-sea part is much more irregular 

than the emerged portion. This sudden change in the direction of the 

spit may very properly lead us to the conclusion that there has been 

considerable change in the course of the currents which have swept 

these shores in recent time, a change dependent on the alteration in 

the shape of the lauds, which has in turn affected the action of the sea. 

The structure and history of this point will be hereafter considered.

In connection with the shore,line of Nantucket, we should notice the 

fresh-water system of the island. This is extremely peculiar. There is 

not a single well-defined stream on Nantucket The only approach to

brooks are a few obscure channels between ponds where the water has, 

except in times of flood, a feeble current. This absence of streams is 

due to the great porosity of the sand and gravel deposits. The fresli 

and brackish water ponds are quite numerous. They are divisible into 

two tolerably distinct classes, viz, the subcircular ponds, which are scattered irregularly through the sand-hills, and which range in size from a 

few score feet to a half a mile in diameter, and the elongate ponds, which 

lie in the long shallow troughs leading from the south slope of the range 

of sand-hills down to the Atlantic shore. With the single exception of 

Oroskaty Pond, which lies on the northern part of the island, these elongated ponds are limited to the southern shore. With trifling exceptions, 

these elongated ponds have axes which trend in the direction of about 

N. 30° E. They are larger in the western than in the eastern half of the 

island. These singularities of position depend upon their relation to 

the remarkable shallow valleys in which they lie. As will be seen in

(612)
BHALEK.] GENEEAL GEOLOGICAL STRUCTURE. 15

Soundthe later portion of this paper, their peculiar form and arrangement 

have been given them by the conditions of the Glacial Period.

The reader should note the fact that, while the 

northern shore of JSTantucket extending west from the 

harbor of that name to Matacut Harbor, presents a 

remarkably straight and unbroken face to the sea, the 

southern border of Coatue Bay or Sound is very deeply indented. The straight shore is the normal form of 

the coast line, where the materials exposed to erosion 

are of a very uniform nature, which is assaulted by 

waves of considerable power, such as break upon this 

coast in times of storm. The indented shore has the 

form which a coast composed pf such materials assumes 

when it is not exposed to the action of strong current

and powerful waves, as the inner shore of Coatue Bay

must have been exposed before the present beach was

constructed. >

These considerations of the existing and more evi- I

dent geographical features of Nantucket fairly pre- !

sent to us the problems of a geological nature which j

we shall have to consider in our study of the island, j

We shall first endeavor to determine the geological j

structure of the several parts of this area and the con- |

ditions under which the beds were accumulated ; next <

we shall try to ascertain the changes which have taken a *

place through the action of the waves and currents Ef &xtiuaxdu

of the sea j and finally we shall consider the light if

which the structure of this island may throw on the <

geological history of the shore land, of which it forms \

a part. [

GENERAL GEOLOGICAL STRUCTURE. \

t

The lowest deposit exposed on the island consists 

of a bed of clay, generally blue and compact^ scantily 

intermingled with pebbles and sand, the whole forming a deposit which is probably to be classed as till 

or bowlder clay. The mass is apparently though 

obscurely stratified. Its pebbles are occasionally 

scratched. Throughout they have the angular or 

faceted character common to glacial pebbles. When 

considerable sections are exposed, as is the case at 

two or three points, the upper deposit for fifteen 

or twenty feet is seen to be altered to a yellowish 

or grayish color, while the mass below is of the characteristic blue color of such clays. In general aspect, as well as in details of structure, this mass is indistinguishable from the ordinary till of the mainland.

(613)
16 GEOLOGY OF NANTUCKET. [BULL. 53,

except that its pebbles are always of smaller size, rarely exceeding two 

or three inches in diameter, and that it is clayey and less compact 

than the similar deposits of more northern regions. At one point on 

the northern shore of the island, about a mile west of the harbor, the 

till passes upward into a fine-grained blue clay, this overlying deposit 

being at least ten feet in thickness; but generally the clay retains itsadmixture of pebbles to the upper surface. It is best seen at Squam 

Head (Fig. 3), on the north shore, near the pumping station of the 

water-works (Fig. 4), and in the village of Nautucket (Fig. 5).

Jrnyailar- Zeddects sands cetffumonypeSSles 

S3^ ^jtotolft, bt*Kffmoter^Kun

J3lue sandy clay; 

FIG. 3. Generalized section of Squam Head.

The underlying till deposit does not rise above the level of the sea. 

save in a.small portion of the surface of the island. Along the larger 

part of the shore its upper surface is certainly below the level of the 

sea. The highest point at which it has been seen is in a clay pit worked 

for road material in the western part of the village of Nantucket. At

FIG. 4. Section at Weewocket. 

a, till-like deposit; 6, pebbly sand; c, blue clayey sand.

this point its upper surface is about thirty feet above the level of the sea.

The next highest point where it has been observed is at Sauam Head, 

on the eastern shore, where its surface is about twelve feet above the sea 

level. It is certain that at many other points in the central part of the 

island, as for instance in the promontory between the arms of HumFIG. 5. Section on border of Lily Pond. 

a, kame sands and gravels; b, bluish yellow till, very much, jointed, with a few angular pebbles.

mock Pond, it attains equal elevation; but this interior surface is so 

masked by gravelly drift, that it is not possible to determine its position with accuracy.

The surface of this till appears to be cast into very broad and low 

arch-like elevations, with lesser hummocks upon them, the principal

(614)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. II

ASPECT OF KAME MORAINE ON THE NORTHERN BORDER, NEAR SHEMO POINT.
SHALER.] GENERAL GEOLOGICAL STRUCTURE. 17

axes of which extend in a north and south direction, 

of these wide backed ridges project themselves 

above the level of the sea. One of these, perhaps 

the most extensive, rises from Coatue Bay, on the ' 

shore east of Pocomo Head, and underlies the 

lowlands about Polpis Harbor. It is traceable on 

both sides of that harbor, having at this point a

width above the water line of about one mile. On 5

tj the shores of Coatue Bay it doesjiot at any point 

rise more than five or six feet above the water 

level.^ Haifa mile south of Polpis Harbor the 

ridge may have an elevation of fifteen or twenty 

feet, and here it becomes completely masked by 

the gravel deposits. Its effect, here or elsewhere, 

is marked in the better quality of the soil, which 

shows itself in the gravelly beds as well as in the 

clay itself, for a certain amount of the underlying j 

clay deposit has been mingled with the coarser ^ ' 

detrital material, making the soil better suited -® 

for agriculture. It also affords several small j» 

springs where it intercepts the waters which sink £ 

through the gravel. 5, 

In the central part of the island there is another I 

of these undulations of the till extending through g 

the village of Nan tucket. (Fig. 5). The expos- g 

ures of the clay on the north shore and in the j? 

western border of the village are upon the ridge. ? 

It may be a continuation of this ridge or it may i 

be a separate undulation which appears in the 1 

low arched promontory between the two great p 

branches of Hummock Pond. There is probably 

a similar arch of the till below the central part of 

the island of Tuckernuck. This was not actually j 

seen, but has been inferred from the character of * 

the soil on that island. There is probably yet 

another undulation which brings the till twenty 

or thirty feet above the level of the sea, at a point 

about a mile and a half west of Siasconset; here, 

too, the evidence is derived from the character of 

the soil and the nature of the bottoms in the low 

valleys, and is also indicated by the appearance of 

water in scanty springs. There are probably yet 

other points'where the till rises above the sea 

level, but is hidden by the prevailing deep coating of the pebbly stratified drift. The diagrammatic section (Fig. 6) will give a general idea of 

Bull. 53 2

(615)

At least three 

ft*

\Stramp.

GibbsponcCr 

J.0/% aboy*} 

fsa- Zewt/,
18 GEOLOGY OF NANTUCKET. |BULL.63.

the relations of the underlying till to the sea level and to the overlying deposits of the stratified drift.

The undulating form of tbis underlying clay, the generally distinct 

boundary of its upper surface, the. apparent elongation of the arches in 

the ridges in a north and south direction, all serve to indicate that the 

mass has been worn by the glacial ice since the time when it was deposited. This view is supported, as we shall hereafter see, by the character of the deposits overlying it.

Immediately above the undulating surface of the lower clay lies a mass 

of more or less stratified sand, which the student of glacial phenomena 

at once recognizes as, in part at least, belonging to that division of the 

drift known as karnes and the terraces which commonly accompany 

them. The contour of the surface is of the most varied nature, and can 

not well be described to any one unfamiliar with this class of glacial 

accumulations. A tolerable idea of its extreme peculiarities may be 

gained from the appended diagram, which shows sections through certain parts of this surface. Most commonly it consists of a haddle of 

low hills never exceeding twenty feet in height, and with extremely irregular outlines. Generally thejT are more or less conical in figure, often 

elongated in an east or west direction to a length of from one to three 

thousand feet. Usually they are crowded together so that their bases 

are adjacent, but at some points they stand in an isolated position on 

the southern sand plain. Where they are the most crowded they have 

the steepest slope, which often rises to an angle of from 20° to 30° of 

declivity. Even where the belts are not elongated, they are often so 

arranged that their summits have an east and west alignment. Between the ridges there are often considerable trough-like valleys. In 

these valleys, which at many points appear to extend downward to or 

near the underlying till, there are occasional ponds or swamp grounds,

which have evidently been sheets of water, but have been closed by

the growth of peaty matter. Where they remain as pools, they are 

generally shallow, not exceeding twenty feet in depth and usually of 

circular outline. (See Pis. II, JII, and IV.)

Where the hills are steepest they usually are very stony, large angular blocks being scattered over their surfaces. In such cases they 

clearly belong to the class of frontal moraines. Bowlders were once 

far more numerous than at present, for the reason that they have been 

extensively gathered during the last two centuries for masonry constructions, cellars, wharves, and retaining-walls. Some hundreds of 

thousands of these are now built into the edifices of the island. In 

many places the surface of the ground is dotted over with the pits from 

which the stones have been removed. The entire absence of other building stones on Nantucket, the scarcity of good brick clay, and the cost of 

fuel for burning bricks have made it necessary to resort to these erratics 

for building materials. The result is, that this district has been more 

thoroughly stripped of its bowlders than any other known to me.

(GIG)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. Ill

VALLEY, WITH DOME-SHAPED HILL, ON NORTH ROAD, NEAR SHEMO POINT, LOOKING SOUTH.
BHAUJB.J GENERAL GEOLOGICAL STRUCTURE. 19

As before noticed, this belt of sand and gravel hills is limited to the 

central and northern portions of Nantucket; at no point does it attain 

the southern shore. The hills are relatively low on the north shore; 

they increase in height as we go southward toward the center of the 

island, and on the south they'fall away suddenly into a slightly rolling 

sand plain, which gently descends to the Atlantic shore. Near the 

foot of the hills this plain is much more rolling than it becomes at a 

little distance to the south; at most points the section from north to 

south shows a somewhat gradual passage from the base of the hills to 

a tolerably level surface near the sea.

The distribution of the sand hills within the field they occupy is not 

entirely regular; there are certain broad spaces where they do not 

occur. One of these is occupied in part by Polpis Harbor, another of 

less size by Sachacha Pond. There are several others of less extent. 

These blank spaces are common in all moraines of this type, Here, as 

elsewhere, they often form considerable valleys with ho outlet, the rainwater passing off through the interstices of the ground. They were 

probably formed by the irregular motion of the ice-front, which in its 

retreat abandoned considerable parts of the area with such suddenness 

that no morainal matter was deposited upon it. If I am right in my 

supposition that these kame moraines were deposited at a considerable 

depth beneath the sea, there is a possibility that these low spaces were 

formed by the separation of icebergs at the front of the glacier. Such 

a separation of large fields of ice would suddenly change the position 

of the glacial front.

The most peculiar feature of the southern plains is found in certain 

broad channels extending from near thefootof the sand hills to the ocean 

shore. These channels are digitate in form; the depressions are from 200 

to 800 feet in width and from 5 to 20feet in depth'; theirbottomsare very 

flat, exhibiting no trace of a stream-bed. They slope toward the sea, with 

an irregular descent of about 5 feet in a mile. Their seaward extremities are in all cases below the level of the ocean and so contain more or 

less considerable lagoons or ponds which are barred from the ocean by 

a wall beach of sand through which their waters percolate and at times 

break their way. In some cases these lakes are very small; this is particularly the case with those on the eastern extremity of the island. 

West of the meridian of Nantucket village they become larger and, in 

the case of Hummock Pond and Long Pond, they occupy nearly the 

whole of the depression in which they lie. It can not be said that any 

of these troughs extend across the whole Hue of the hills, but at their 

head there is in some instances a nearly flat surface in which they are 

lost. The lake which fills the trough of Hummock Pond (see PI. V) 

extends up to the foot of the hills. Its depression is continued to the 

north shore by a series of ponds, four in number, which are separated 

by low sand-hills and which indicate the persistence of. the excavating 

action which produced the valleys across the island. The valley of

(617)
GEOLOGY OF NANTUCKET. IIJULL. 53.

Long Pond constitutes a depression extending to within one-third of a 

mile of the northern shore, very nearly sundering the island, and the 

trough may be faintly traced across this remaining space of laud. (See 

. 7.)

Horizontal- -Scale, ££>5 JL in,. 

Vertical, ScaZ&j <5<9 = /T>z.

FIG. 7. Diagrammatic section across valleys in sunken plain.

At the point where these hollows originate in the sand hills, the hills 

are generally lower than* elsewhere and have a more or less washedaway appearance. This is especially the case just east of the village 

of Nantucket, where two of the largest of the troughs head against the 

axis of the sand hills. At this point the hills themselves are in good 

ipart wanting.

West of Long Pond the troughs hav^ 'Seen to a good extent destroyed 

toy the invasion of the sea, but we may trace them in the valleys of 

Hither Creek, Broad Creek, Narrow Creek, and Further Creek to the 

-western extremity of the island. They reappear on the island of Tuck- 

<ernuck, there being two distinct trough-like furrows of this nature on 

that island. Counting these on Tuckernuck and reckoning all the depressions on Nan tucket which can be put in this category, we have in 

all 23 of these remarkable depressions along this shore, or an average 

of about two to a mile of its east and west length. Some of these, particularly in the eastern end of Nantucket, are very small and do not distinctly extend up to the foot of the range of sand hills; still, all of them 

are manifestly of the same type and must be explained in the same way.1

We turn now to the internal structure of the sand belts and terraces. 

The sections through the sand belts are few in number and imperfectly 

reveal the structure of the mass. Where seen in section these deposits 

present a curious mixture of stratified and unstratified materials. In 

most cases the mass is throughout irregularly stratified, by far the 

greater portion of the materials consisting of sand and small pebbles 

accunimulated in irregular layers. At a few points they contain, especially near their bases, materials huddled together in the manner of 

glacial till. It is noteworthy that wherever we find a section giving a

*A further discussion of these peculiar topograpllical features may be found in uiy 

report on the Island of Martha's Vineyard, Seventh ADD. Kept. U. S. Geol. Survey, 

p. 314 et seq.

(618)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. IV

'ffi^m®*****?--- '/<.-Ar#.fc: '' ' - ^- ^ : -f/

TOPOGRAPHY OF KAME MORAINE IN CENTRAL DISTRICT, NEAR NORTH END OF LONG POND, LOOKING NORTH.
SIIALKB.J GENERAL GEOLOGICAL STRUCTURE. 21

view of the stratified beds with the adjacent till, the gravels are found 

to contain a considerable mixture of clay, which appears to have been 

derived from the grinding up of the till upon which they lie and the 

mingling of the waste with the stratified kaine deposits. Although 

there are occasionally large angular bowlders in the stratified depositsthey are much less common tban iu the surface of the hills. On a section following the contour of the surface and ten feet below its level 

there will probably be not as much as one-fourth the number of large 

bowlders that are contained on the terraces or on the surface of the 

hills. This indicates that the bowlders were brought to their present 

positions by other agents than those which accumulated the heaps of 

gravel and sand. The contact of these bowlders with the surface inmany cases seems to indicate that they have fallen with some violence 

to their present positions and have not been conveyed along the surface 

by glacial ice or currents of water. Here, as elsewhere in southern 

New England, these erratics often lie slightly embedded in the subjacent sand and gravel. It seems clear that they were brought to their 

present positions by floating ice. The greater number which are or 

were found on the surface when compared with any section of the subjacent deposits seems to indicate that the ice-rafting action continued! 

for a considerable time after the glacier retreated from this vicinity. 

(See Fig. 8.)

FIG. 8. Diagrammatic section position of bowlders on glacial plain near Gibb Pond. 

a, horizontally stratified aaud ; b, somewhat irregularly bedded sand; c, very irregularly bedded saiidIt may be incidentally noted that if these bowlders were brought totheir present positions by the ice we have from them evidence to show 

that this region was submerged during the accumulation of the kanie 

deposits. Furthermore, from the fact that there are no evidences of 

the grounding of ice rafts on the delicately molded kames we may 

presume that this surface was deeply depressed beneath the sea at the 

time when the icebergs floated above it. In the kame hills scratched 

pebbles are of rare occurrence, and where found they have but faint 

traces of their original grooves.

Perhaps the most noteworthy feature in these deposits of drift is thevery extensive decay to which the pebbles and sand have been subjected. Some of the consequences of this decay will be noted below. 

In their form and structure the drift deposits differ in no distinct way 

from the similar accummulations found in the region a hundred miles 

farther north, but in their state of preservation they present important 

differences. The decay which has attacked the pebbles is exhibited in 

the following ways, viz: (1) By the interstitial decay of the stone, which

(619)
22 GEOLOGY OF NANTUCKET. [BULL.53.

manifests itself in the crumbling of many of the varieties of crystalline 

and fragmental rocks; (2) by the dissolved look of the surface of the 

rocks which resist the interstitial decay; and (3) by the development 

of the incipient joint planes in the pebbles, so that, though they may 

be but little decayed, they often split into fragments on being removed 

from their bed.

The interstitial decay is best shown in the pebbles of crystalline rocks 

where there is no magma, or base, to bind the separate crystals together; 

in certain varieties of syenite and in the hyperite pebbles, which not 

infrequently occur in some parts of the drift, this decay is most complete. It is also manifest in the numerous fragments of sandstone and 

in many of the conglomerate bowlders. Compared with the pebbles in 

the drift in the region about Fall Eiver, Mass., these Nantucket fragments exhibit'at least twice as much of this interstitial decay.

The superficial dissolving of the pebbles is a much more conspicuous 

and peculiar feature than the interstitial disintegration. It must be an 

inattentive eye which does not mark the effect of this peculiar form of 

decay in the erratics of the drift on this island. In appearance the 

pebbles subjected to this decay may be compared to crystals of rock 

candy partially dissolved away. The surface of the bowlders becomes 

very smooth, though uneven; in some cases pebbles or crystals contained 

in it are left as rounded projections on its face. This decay is observable in a* great variety of specimens, but it is most conspicuous on the 

siliceous pebbles and appears to be limited to those which lie near the 

surface of the soil. In no case have I observed it at the depth often 

feet below, but my observations are hardly sufficient to warrant an 

opinion as to the depth below the surface at which it occurs.

It seems likely that this peculiar form, of corrosion is due to the action of the surface waters, which, by the carbonic dioxide they obtain 

from, the decaying vegetation, are able to effect a certain amount of solution of the more soluble stones. A trace of this action may be observed in the gravels on the southernmost part of the mainland north of 

Nantucket, but it is only in this island that it is a feature which quickly 

attracts the eye. In amount it is at least three times as great on this 

island as in the more northern localities. In some cases the pebbles on 

exposed portions of the surface show a small amount of erosion from the 

action of blown sand. These effects are not conspicuous and would 

hardly deserve mention were it not for the fact that it is worth while to 

discriminate between the considerable corrosion due to leaching and 

the inconsiderable amount effected by the erosive action of moving 

grains of sand.

In connection with this subject it should be noted that the bed-rocks 

of the mainland often exhibit a notable amount of decay which has 

taken place since the close of the Glacial Period. The amount of this 

corrosive action varies greatly according to the constitution of the 

rock and the extent to which it has been protected by the covering of

(620)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. V

?^v;:7-^

EAST BRANCH OF HUMMOCK POND, LOOKING SOUTH.
SHALEK.] GENERAL GEOLOGICAL STEUCTUEE. 23

the drift; but when the rock has been to any considerable degree exposed to the action of the waters corrosion has generally affected it to 

the depth of a foot or more. This process of decay is traceable in the 

northern part of New England, though in that section it is relatively 

very slight, requiring close observation to detect it. In the region about 

Boston it becomes much more evident, the diabasic rocks of that vicinity having been decayed to the depth of twenty feet or more. Along 

the shores of Narragansett Bay the decay has penetrated less deeply, 

but more generally, into the rocks, none, except those which have been 

deeply covered by till, having entirely escaped the corrosive action. 

Where the bed rocks have so far suffered from this corrosion it is to be 

expected that the pebbles in the kame and terrace drift will be found 

even more extensively altered.

The third evidence of decay is that afforded by the splitting of the 

pebbles contained in the drift. This is a tolerably conspicuous feature 

in all parts of the deposits above the level of the lower till. The fractures are of two kinds: those which have taken place in pebbles as 

they lie, the fragments remaining connected, and those which have 

taken place in a remote period before the last movement to which the 

gravels have been subjected. This recent splitting is observable in all 

the glacial drift of New England. It is especially marked in the katne 

deposits, because the agents of decay penetrate more readily into the 

debris of this description than into the less porous till. On Nantucket 

it is, however, much more conspicuous than elsewhere, so far affecting 

the pebbly beds of the island that a large part of the fragments fall to 

pieces on exposure and many others are readily shattered by a very 

slight blow. The greater prevalence of this manifestation of decay 

seems to show that these beds have been subjected to weather for a 

much longer period than the gravels of the region to the northward.

The other group of split pebbles, of which the fracturing was done 

before the fragments came to their present position, is more puzzling. Pebbles of this class present distinct fracture faces, which are 

usually in joint planes. These fracture faces are a little rounded, the 

rounding being about what is found in unpolished paleolithic implements, or that measure of roundiug which comes from a small amount 

of friction. In no case are the fragments which are separated from the 

slightly rounded pebbles found in connection with. them. In some 

-cases the edges of the stones are slightly chipped, making them appear 

like the secondary fractures which the savage implement-maker formed 

on the stones (PI. X).

At first sight a large number of these faceted pebbles look like imperfect stone implements; to my eye they closely resemble the interesting 

implement-like stones from the gravels near Trenton, N. J. It is often, 

indeed, difficult to resist the conviction that some selected specimens are 

the result of human labor. A careful inquiry, however, has led me to 

the conviction that they are all natural products. This inquiry was con-

(621) . *
24 GEOLOGY OF NANTUCKET. [BULL.5?,

ducted in the following manner, viz, gathering an extensive collection 

of these stones it was observed that they were far too common in the 

drift to make it reasonable to suppose that they had been the work of 

man. It was also evident that the range in size of these fragments was 

far too great to justify the supposition that they were of artificial origin. 

Specimens weighing 20 or 30 pounds were not infrequently observed; 

these were evidently too large to have been used as implements; others 

were found not exceeding an inch in length, which were clearly too small 

to have served any useful purpose.

Moreover, out .of a hundred specimens, on the average not over one 

t>r two were chipped in a way which it would be reasonable to suppose 

a savage would have chosen to adopt in order to bring the stones into a 

shape suitable for any of his limited needs. The gradation between the 

specimens, which are so like unquestionable stone implements that they 

would readily be accepted by the collector as the work of "the human 

hand and those which would be unhesitatingly rejected, is singularly 

complete and well calculated to persuade the unprejudiced observer that 

all the artificinl-looking fragments from the kames and terraces of Nantucket are of natural origin. It is clear that the occurrence of such 

chipped and polished fragments resembling works'of art shows us how 

careful we should be in classing as man's work fragments of stone which 

have been selected from a great many chipped pebbles.1

These chipped and somewhat polished stones may be accounted for 

in a natural way, thus: Let us suppose that the pebbles were formed 

and transported to near their present position by the glaciers during 

the first part of the ice age and left in the form of kame and till deposits for a long period during which they were exposed to the influences 

of decay. In this period of repose their incipient joints were developed; 

as the joints are now developed everywhere in the pebbles buried in 

the kame deposits. Next, in a readvance of the ice, these pebbles were

forced forward and thereby submitted to strains which separated the 

fractured portions from the mass of the more or less chipped fragments; 

the transportation led to the rounding of the exposed edges and to the 

partial polishing of the fractured surfaces. We would then have the 

pebbles in the shape in which we now find them; and the enthusiastic 

collector, selecting one in a hundred of these fragments, would suppose 

that he had discovered implements which were accumulating on the 

ground during the glacial period.

The full bearing of these observations on the discoveries made by 

Dr. 0. C. Abbott in the region about Trenton, N. J., can not be discussed

1 It seems to me that we may for the criticism of such materials make a simple rule, 

based on experience, which is as follows: Where the stones appearing to be artificially worked are mingled with many similarly chipped stones which can not be regarded as artificial, we probably have a case similar to that above cited. Where 

the supposed implements are not so mingled with similar pebbles evidently of natural 

origin we shall run little risk in classing them as artificial objects.

(622)
BHALER.I GENERAL GEOLOGICAL STRUCTURE. 25

in this memoir. It still seems likely that the collections of chipped pebbles gathered from the Delaware drift contain a large number of fragments which have been worked by human hands. However, on comparing the large and fairly representative collection of these pebbles 

contained in the Peabody Museum, at Cambridge, Mass., with specimens 

which abound at Nantucket, I am convinced that the whole problem 

requires a very careful discussion from the point of view of the geologist, as well as from that of the ethnologist.

These artificial-looking stones are found in relatively great abundance in all the pebble-drift sections exposed at Nantucket. At Sankaty Head they occur at a depth of 25 feet or so at the crest of thfc 

cliff', in positions which seem to indicate that they could not have 

slipped down from the surface. It is hardly possible to explain the 

occurrence of these fragments on the supposition that they are artificial in any way that is consistent with the demonstrated facts concerning the history of the Glacial Period. The pebbles themselves 

must have been formed during the glacial period, for the whole of this 

upper or kame drift rests upon a layer of till produced during the first 

great advance of the ice, and they are overlaid by what appears to be 

till of a later age. Apparently all the work of man on these materials, if 

indeed any such work has been done, must therefore have been accomplished in the interval between the retreat of the glacier after the first 

part of the ice epoch and the second advance of the glacier. We have 

to suppose that in this relatively brief interval savage men strewed 

the surface with chipped stones in a measure unknown in any part of 

the earth's surface, however long occupied by primitive people; otherwise, when the surface was swept by the readvancing ice sheet and 

the superficial material commingled with that which was below, forming the vast kame heaps which the glacier pushed forward to itsfront, these chipped stones would not have abounded in it as they 

do on this island, at Trenton, and probably at other points on the ice 

front.

Let us imagine the glacier to return to the present surface of "New 

England, sweeping away all the-superficial materials now resting upon 

it, and accumulating along a new ice front the de"bris which was not 

ground up in transportation. What would be the chance of finding 

in this deposit any remains of the Indians who lived during the Glacial 

Period ? Manifestly their remains would be almost inconceivably rare. 

The explorer would be probably well rewarded with a single find in a 

lifetime of search, so slight would be the chance of a fragment of art 

work surviving the accidents of a glacial journey.

The worked stones and the other substantial elements of our modern 

arts in New England would afford thousands of times as many fragments as all the stone hatchets and similar tools which the aborigines 

left on the surface of this country, and yet I doubt if the remains of 

our arts would be as plenty in the frontal moraine of a new glacial

(623)
26 GEOLOGY OF NANTUCKET. [BULL. 53.

period which should overtake us as these implement-like fragments 

which are now found at Nantucket.

One of the considerable difficulties which we encounter in assigning 

an artificial origin to these frontal drift fragments arises from the fact 

that none of them appear to be worn on their cutting edges. It may be 

said that they were used for striking blows and not for cutting bones, 

sinews, and other hard substances. If this were the case we should 

find other forms of implements which were so used, for we can not believe that there was ever a tribe of savages making stone implements 

for the single purpose of striking blows, who neglected the equally serviceable uses in which the edges of the stone would have been worn.

ORIGIN OF THE DETRITAL MATERIALS.

The mineralogical features of the pebbles of the drift in this region 

have especial interest, inasmuch as they afford some information concerning the nature of the rocks which lie to the northward of Nantucket 

but which are deeply covered by the mantle of detrital material. About 

all we may ever know concerning these deposits we shall learn from a 

study of the drift materials derivedfrom them. On this account I have 

paid especial attention to the pebbly deposits of the island. The exposures of the underlying till are so scanty and the pebbles contained 

in the exposed portion so few and small that no effort has been made to 

ascertain the variety of rocks represented in this portion of the ice-borne 

material. The only examination has been of the stratified gravels.

It should be noted that the distance to which the fragments contained 

in the bowlder clay have been carried is much less considerable than 

that to which the stratified or kame gravels have been conveyed. In 

the valley of theTauuton River, which is the nearest considerable basin 

on the mainland, the average distance to which the kame fragments 

have been carried is at least three times as far as that to which the till

materials have traveled. The result is, that the kame or stratified 

gravels give us information of a less accurate because less localized 

nature than we may obtain from the study of the fragments from the 

till.

The pebbles of the stratified gravels on Nantucket are in large part 

derived from the group of granitic rocks known, on the neighboring 

mainland; probably nearly one-half of the whole mass is of this nature. 

Of the remainder a considerable part is composed of felsites and felsite 

porphyries such as are common in the region of Boston, Mass. On the 

' eastern end of the island these porphyrite and felsite materials are 

much more abundant than on the western portion. In the region about 

Sankaty Head these porphyritic pebbles are plentifully intermingled 

with somewhat angular fragments of volcanic breccias of a type unknown to me in any part of southern New England, though they much 

resemble the ash beds and breccias of the eastern portion of the shore 

of Maine, especially those found near Eastport. Although the felsites

(624)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. VI

JUNCTION OF KAME MORAINE AND TERRACE PLAIN ON GIBBS POND; SIASCONSET IN THE DISTANCE.
8HALEU.] ORIGIN OF THE DETRITAL MATERIALS. 27

near Boston are only 60 miles away, I am disposed to believe that these 

fragments of porphyry found on Nantucket are derived from localities 

which are much nearer this island. The very angular nature of some 

of the fragments leads me to believe that they are from a field not more 

than 30 miles to the northward of the place where they are now found. 

There is a variety of stratified rocks, clay, slates, and sandstones and 

conglomerates in this drift material. The conglomerates and sandstones have the aspect of the deposits found in the Narragansett Coal 

Measures, especially those near Taunton, Mass. No distinct plant fossils 

or other organic remains have been found in these fragments, but several of the best of them show traces of carbonaceous matter, and in one 

instance a large bowlder lying near the village of Siasconset was found 

to contain faint traces of fossil plants.

Some of the bowlders of conglomerate have their pebbles much compressed, as is often the case in the mill-stone grit bed of the Narragansett coal fields, but only rarely so in the conglomerates near Boston. 

Mingled with these coal-measure pebbles is an abundance of large 

bowlders of white quartz, such as plentifully occur in veins in the much 

altered coal measures about Narragausett Bay, but which are rare in 

other parts of southern New England. Knowing that these materials 

are from a coal basin, the question arises whether they are derived 

from any part of the Narragausett field. Assuming as before that the 

direction of carriage of this drift was from the northwest, we find that the 

only part of the Narragansett basin lying in the path traversed by the 

.glacial stream which brought the pebbles to Nantucket is in the narrow strip of those rocks extending northeasterly from Taunton through 

Bridgewater up to and a little beyond the village known as Queen 

Anne's Corner, a district which lies about 50 miles from Nantucket. 

The considerable size and the nature of many of these fragments are 

much against the supposition that they have journeyed so far. I am 

inclined to believe that they are from some area of carbonaceous rocks 

not farther away than the southern shores of Cape Cod.

If we assume that the direction of the ice movement at the time when 

the Nantucket moraine was formed was at right angles to the frontal 

line of that moraine, then these materials derived from the volcanic and 

the Carboniferous rocks probably could not have come from any part of 

the Narragausett field j they must have been derived from deposits of 

that age which lie either below the surface of Cape Cod or under the 

ocean to the north or south of it. The extreme western limit whence 

they could have journeyed must have been a meridional line lying at 

least teu'miles to the east of Boston. In general it is a tolerably fair 

assumption that an extended moraine front was formed by an ice 

stream which moved down at right angles to the line of the accumulations. I am therefore disposed to believe that all the glacial waste of 

.Nantucket, except perhaps the bowlders transported by icebergs, came 

from far east of the Narragansett basin.

(625)
28 GEOLOGY OF NANTUCKET. [BULL. 53..

Besides the above-mentioned stratified rocks there is a considerable 

amount of clay slate in the pebbles of Nantucket. These slates are 

represented by small though numerous fragments. A careful search 

failed to show any distinct fossils in them ; in their physical condition 

they are more like the Carboniferous deposits of this section than any 

other deposits of this nature known to me in southern New England.

At no point on Nantucket have I found any distinct evidence of detrital matter such as might have been derived from Tertiary deposits 

like those which occur on Martha's Vineyard. This should not be taken 

as evidence that the Tertiary strata do not exist beneath this section. 

It may be that the beds of that age are deeply covered by the blue 

till, and that the last invasion of the ice was thus fended from them.

FOSS1LIFEROUS DEPOSITS.

The fossil-bearing deposits of Nantucket are confined to two small 

groups of strata; one of these con sists of fresh water peats, the other 

of areas of stratified sands containing a variety of marine species.

The fresh water marsh deposits are found, here and there, over the 

whole surface of the island. They consist of ordinary peats, and at first 

sight appear to have no special geological interest. On the shores of 

the island, however, there are, at several points, deposits of these peats 

which at present lie several feet below the level of high tide. These 

submerged fresh water peats appear to be particularly abundant in the 

sections from Tom Never's Head to Squam Head. Every heavy storm 

throws up considerable quantities of this peaty matter. The largest 

fragments are found on the beach a little south of Siasconset, but they 

may be observed at any time of storm along the whole of this eastern 

shore. The material, though not in any way changed from its original 

character, is interesting for the reason that it lies below the level of 

low tide, and also from the fact that it contains many beetles and other

insects. There is another locality where the peats appear below the 

high tide level; this is on the north shore, about one mile west of the 

harbor of Nantucket, not far from the pumping station which suppliesthe town with water. At this point the peat is disclosed at low tide,.

Fis. 9. Section of submerged swamp, north shore. 

a, swamp; Z>, ferruginous sand; c, dune sand; d, stratified drift.

and is there seen to cover an area of several thousand square feet. (See 

Fig. 9.)

(626)
.siiALEB.1 FOSSILIFEROUS DEPOSITS. 29

These submerged peat deposits contain abundant remains of insects. 

'These are most plentiful in the deposits which occur along the eastern 

face of the island.

Ait first sight it appears as if these submarine peats might have been 

formed at their present levels in pools which were originally at a distance from the sea, but to which the sea has attained by the recession 

of the shores. There can be no question that this is the way in which 

the sea has come to invade these peaty deposits, but it seems doubtful 

whether we can explain their present elevation without supposing that 

the deposits have been somewhat depressed since the time of their 

formation. Ordinary spongy peat is now forming in many existing 

pools of the island below the level of high tide for the reason that the 

bottoms of the pools of fresh water are a little below that level; but the 

crowns of living trees never lie below the high tide mark, and even the 

rushes which grow on the margins of the swamps rarely, if ever, have 

their roots as low as the tide line. In these peat deposits on the north 

and northeast shores not only are the crowns of the rushes below the 

high tide line, but at one point we find the crowns and roots of a tree ten 

inches in diameter standing in the natural attitude about two feet below 

the highest tides and in a position where it is covered by the sea water. 

The roots of this tree were sufficiently exposed to view to make it clear 

that it was in the position where it had grown. It is not possible from 

fragments to determine its species in a clear way, but it is probably a 

variety of oak.

It is not admissible for us to assume, as we may in some other cases 

where trees grow below high tide mark, that this marsh deposit has 

been depressed by the local erosion of the base on which it stands. The 

area of swamp in which it occurs has the basin shape proper to the bottom of the basin-shaped pools found elsewhere on the island. A section excavated through the swamp shows that it rests upon the clay 

underlying all such, accumulations, and that below the clay there are 

deposits of ferruginous sand. It would hare been impossible for the 

waves to cut under this section in such a manner as to lower it gently 

beneath the sea. It is equally impossible to believe that the crown of 

any of our northern species of trees would have grown below the level 

of the water. I am therefore compelled to assume that this area has 

subsided since the above mentioned tree grew. The amount of the subsidence can not be less than two feet, that being the height to which 

the tides sometimes rise above the present level of its crowns. The 

roots of this specimen or those of a similar tree are found at least 

another foot further below the level of tide line. Moreover, as the existing swamps of the island which have or very recently had trees about 

their shores lie two or three feet above the sea level, it seems safe to 

assume that the tree when it grew had its crown at least five or sjx feet 

above its present altitude.

(627)
30 GEOLOGY OF NANTUCKET. [BULL. 53.

So far as I am informed this is perhaps the clearest evidence which 

has been obtained showing recent subsidence aloug this partgf the 

New England coast. As to the date of the subsidence no evidence 

seems obtainable from this locality. The peaty matter has a very 

fresh and unconsolidated aspect. The roots of the rushes which it contains are singularly recent-looking; they are little decayed, and indeed 

seem to retain some part of their color and odor.

No other of the depressed fresh-water peats of this island exhibit 

their beds in place even at the lowest tides. They appear elsewhere 

than on the north shore to be covered by the deposits of sand, or are 

perhaps too deeply submerged to be exposed at the lowest stages of 

the tides. Still they contain fragments of roots of trees of considerable 

size, which may belong to some of the many species of shrubby plants 

which are tolerant of fresh water.

The evidence of marine deposits above the present level of the sea 

is, as has been long known, abundant on Nantucket. These deposits, 

so far as exhibited by natural sections, are limited to the east side of the 

island. This apparent limitation is probably due to the absence of 

natural sections elsewhere than on that part of the shore, for it is only 

on this eastern face of the island that we have any very extensive sections which clearly expose the stratified sands to a considerable depth. 

I am informed that at various points in and about Nantucket village 

deposits of shells have been encountered in digging the shallow wells, 

which never descend below high-tide mark. I have been unable to obtain any specimens of these fossils; but, as their presence is attested 

by Prof. Henry Mitchell, there can be no doubt that sands and gravels 

of the last stage of the Glacial Period containing scattered patches 

of fossiliferous beds, probably of the same age as those exposed at 

Sankaty Head, exist in other parts of the island.

FOSSILIFEROUS DEPOSITS OF SANKATY HEAD.

These fossiliferous beds of Sankaty Head appear in a cliff which has 

a height of about eighty feet above the high-tide mark. This cliff is cut 

through a portion of the kame gravels, which form a sort of elevated 

rolling terrace near the southern border of the true frontal moraine. 

The top of this terrace has a broadly rolling surface, and may be regarded as forming the zone of passage from the frontal moraine to the 

plain which lies on the southern part of the island. (See PL VII.)

The section at Saukaty Head is at present almost entirely hidden by 

the thick growth of grass and other plants, which have found a hold 

upon the surface since the sea has been fended from it by the considerable northward extension of the Siasconset apron-like beach. This 

is to be regretted, for the reason that it is from a geological point of 

view by far the most interesting section of the island and one of the 

most important found on the New England coast. It has been the ob-

(628) .
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. VII

SANKATY HEAD, LOOKING NORTH FROM A POINT 150 YARDS SOUTH OF LIGHTHOUSE.
8HALEK.] FOSSILIFEROUS DEPOSITS OF 8ANKATY HEAD. 31

ject of considerable study by several distinguished naturalists. In 1849 

Messrs. E. Desor and Edward C. Cabot published in the proceedings of 

the Geological Society of London a short paper giving an account of 

this locality. At that time and for many years afterwards the continued inroads of the sea preserved a fresh face on the escarpment. 1

The section as given by Messrs. Desor and Cabot is shown in Fig. 

10. It differs from any I have been able to obtain in the present condition of the escarpment in certain important parts. It will be observed 

that at the base of the section the above-named authors indicate a bed 

of brown clay of unknown thickness which rises for 20 feet above the 

sea level. Above that point to the height of 33 feet they place successive layers of sand, gravel, and clay containing fossils, still higher 

'in the section for a distance of 52 feet successive layers of sand and 

gravel without fossils, then a thin layer of peat one foot in thickness 

capped by six feet of dune sands, the whole forming an escarpment 

which rises 92 feet above the beach. The total height of the cliff as 

given by them is at least 15 feet greater than its actual altitude. It will 

be noticed also that the lower stratum of brown clay, which according to 

this section extends to a height of 20 feet above the sea level, is shown 

to be uuconformably related to the gravelly layers which appear above 

it» It was the opinion of these observers that this lower clay belonged 

to the series ot deposits which appear at Gay Head, and on this hypothesis they construct a highly ideal section, shown in Fig. 2 of their 

report, in which the Gay Head clays appear in the form of a syncline, 

the trough of which includes all the area between Sankaty Head and 

the western extremity of Martha's Vineyard. There is at present no 

trace of this brown clay at any part of this escarpment, nor was the 

thin layer one foot in thickness of tough clay, occurring according to 

their section at the height of 26 feet above the water line, found in my 

examinations. (See Fig. 10.)

The exhibition of this lower clay at the time Messrs. Desor and Cabot 

made their examination must have been clear, and the unconformity 

which they note was probably evident, as will be seen from the following extract from their report:

The strata thus enumerated seem at first horizontal, but in digging along their edges 

 we soon ascertained that they all dipped to the west, their inclination varying from 

fifteen to five degrees, the upper beds being generally less inclined than the lower ones. 

The inferior clay stratum, however, was found to differ considerably from the others, 

its dip being nearly thirty degrees to the southwest, and in some places even as much 

as forty degrees.

These circumstances induced us to examine this lower clay stratum more carefully. 

Having made ont a spot where the overlying gravel bed was seen in immediate contact with the top of the clay, wo could distinctly trace its uncouformable cleposi1 On the Tertiary and more recent deposits in the Island of Nautucket, Messrs. E. 

Desor and Edward 3. Cabot, in a letter to Sir Charles Lyell, president of the Geological Society: Quart. Jour. Geol. Soc. London, vol. 5, 1849 (proceedings), p. 340. ,

(629)
32 GEOLOGY OP NANTUCKET. [BULL. 53.

tion, the gravel being seen dying out towards the more inclined clay stratum, as 

shown in the above section taken on the side of a gully in the cliffs. * * * A

6 feet, o. Dune sand. 1 37-

5

10

2

3

1

1

4

2

20

6.

c.

d.

e.

f.

q.

h.

i.

7. i

i.

Peat.

Sand with an occasional stratum of coarse gravelFerruginous gravel.

Sand.

Worn shells.

Ser'pula.

Oysters.

Tough clay.

Homogeneous white sand.

Gravel.

Brown clay. .

Fig. 10. Section at Sankaty Head.

considerable change of level must have taken place between the> deposition of the 

clay and that of the gravel. *

This statement compels us to believe that the lower clay was exposed 

to view at the time when McoSis. Desor .and Cabot made their examination. This was probably in the year 1847. It will be noticed, as is 

indicated in the section, that a slight recession of the cliff in the direction in which, it was then rapidly wearing would carry the shore-line 

across the exposure of the brown clay, and that a wearing back of 20 

feet would in good part, if not entirely, destroy the exposure. It is 

 not improbable that this recession has taken place and that this bed 

lias disappeared from view.

This hypothesis is borne out by the results of a study of this section 

made in 1874 by Mr. S. H. Scudder, which is contained in a memoir by 

Prof. A. E. Verrill, On the post-Pliocene fossils of Sankaty Head, 

Nantucket Island.1 At the time when Mr. Scudder made his observations the clay described by Messrs. Desor and Cabot was still visible. 

As his observations differ in an important way from those made by the 

above-named gentlemen, I give his note in full :

The sands and gravels forming the bluff at Sankaty Head, Nautncket, rest at base 

upon a thick bed of light-brown sandy clay of uncertain thickness, but extending 

upward to about 20 feet above the sea level. As the beds which rest upon it dip to 

the southwest, and as the anchor brings up clay from Sankaty Head eastward for 

half a mile, this clay bed is probably of great thickness.

The brown clay is overlaid by 4 feet of gravel and coarse sand, the coarser parts 

mostly confined to three or four inches of the uppermost levels; the upper bed is 

more or less ferruginous, and hardens on exposure into a rather compact conglomerate.

1 Am. Jour. Sci., 3d series, vol. 10,1875, pp. 364-375. 

(G30)
8HALER.J FOSSILIFEROUS DEPOSITS OF SANKATY HEAD. 33

To this stratum must doubtless be referred a single specimen of a bivalve (probably a mactra), with valves half open, picked up on the bluff, embedded in a gravel 

conglomerate, and like it strongly impregnated with iron. The gravel is followed 

by about four feet of sands, subdivisible into separate beds, viz: At base, an inch or 

two of a very fine loose white sand, followed by nearly two feet and a half of a little less fine, closely packed, white sand, with irregular ferruginous streaks through 

its mass; this is covered by 9 inches of a coarse beach sand, with a still coarser sand 

in pocket; and this again by 9 inches of a very fine white sand. Above this comes a 

foot of ferruginous sand closely packed with masses of tough blue clay, much exceeding the sand in bulk, and forming the floor of the fossiliferotis beds.

These consist first, at base, of 22 inches of coarse sand, in which the oyster, quahog, and common clam are the prevailing forms, the first predominating to such a 

degree as to make the name of oyster-bed the most appropriate. This merges into 

a serpula-bed, about 28 inches in thickness, made up almost altogether of large 

masses of serpula packed in sand and almost wholly devoid of other fossils. The 

bed of worn shells superimposed on this is about 22 inches in thickness and closely 

resembles coquina, except in the entire want of adhesion between the fragments.

This bed is followed by about 10 feet of fine, white, thinly bedded sand, and this 

by the stratified drift of the island, to a depth, as estimated by Desor and Cabot, of 

42 feet. The foot of peat mentioned by them is wanting at this exact locality (though 

present a few hundred feet farther south), leaving the drift covered by five or six feet 

of dune-sand, more or less intermixed with loam below.

On following the bed of broken shells along the face of the cliff it was found to 

thin out to about a foot in thickness 25 feet on either side of the most prominent 

point, where the section was made, and which has doubtless been longer protected 

than the other parts of the bluff by the former presence of a great mass of clay next 

the water's edge, called "Antony's Nose;" beyond these 25 feet the bed of broken 

shells becomes more or less obscured by an admixture of sand, gravel, and serpula, 

and is entirely lost at 40 feet distance on either side.

The strata, from the lowermost clay to the bed of worn shells, all dip to the southwest. The uppermost beds incline along the face of the cliff three degrees to the 

south, while the inclination to the west (along the section dug out of the cliff) is 

eleven degrees, making a dip of nine degrees to the southwest. All the beds below 

this also incline eleven degrees to the west, but the inclination of their face toward the south increased gradually in passing downward until that of the upper 

edge of the lower clay reaches eleven degrees, making a southwesterly dip of this 

bed seventeen degrees to the southwest. There is no evidence of any thinning out of 

the gravel-bed, as stated by Desor and Cabot, nor of any uuconformability between 

this bed and the underlying clays; but, on the contrary, every appearance that the 

latter belong to the same continuous series as the former.

It is worthy of note that the fossils of this locality lie above the clays instead of 

in the clays, as in most of the New England localities of post-Pliocene marine shells.

It will be clearly observed that Mr. Scudder seems to have seen the 

clay, or rather sandy clay, found by Messrs. Desor and Cabot, but he 

failed to find any evidence of unconforinability between this clay and 

the overlying fossiliferous sands. It is likely, however, that the aspect 

of the section had changed a good deal in the score of years which had 

intervened between these two observations. I think it probable that 

the observations made by the earlier geologists were good in the conditions of the cliff at the time when they were made.

I am disposed to believe that this lower sandy clay is not related to 

the deposits at Gay Head, but that it represents the upper portion of 

Bull. 53 3 (631)
34 ' GEOLOGY OF NANTUCKET. [BULL. 53.

the lower till at Nantucket, which, as is shown in some parts of Squam 

Head, in the neighborhood of Polpis Harbor, on the north shore, and in 

the village of Nantucket, often contains very few pebbles, and presents 

in general the appearance indicated by the terms applied to it by the 

above-named observers. It is possible, however, that although not 

synchronous with the Gay Head deposits, it may be of the same age as 

the clays which occur on the southern shore of Chilmark.1

The most interesting portion of Professor Verrill's important memoir 

concerns the distribution of the fossil contents of this section. He 

divides this section into an upper and lower series of strata, between 

which there are considerable differences as to the character of their 

fossil contents. The exact line which separates these two portions of 

the section is not indicated save in the description given by Mr. Scudder. Inasmuch as this list of fossils is of great value to those who may 

be engaged in the study of quaternary fossils we give it in full.

List of species from the lower shell-led.

MOLLUSCA.

Tritia trivittata Adams. Common. ?.

Florida to Gulf of St. Lawrence; low water to 40 fathoms. Fossil in the post-Pliocene of Point Shirley, Gardiner I., Virginia, and southward; in the Miocene of Maryland, South Carolina; etc.

Ilyanassa obsoleta Stimpson. Common.

Florida and Gulf of Mexico to southern Maine; local in the southern part of the 

Gulf of St. Lawrence; littoral to 2 fathoms. Fossil in the post-Pliocene of Point. 

Shirley, Virginia, South Carolina, etc.

Urosalpinx cinerea Stimpson. Common.

Tampa Bay and eastern Florida to Massachusetts Bay and local farther north to 

Gulf of St. Lawrence; littoral to 10 fathoms. Post-Pliocene fossil at Point Shirley,, 

Gardiner I., Virginia, and southward; in the Miocene of Maryland.

Eupleura caudata Adams. One fine specimen.

Gulf of Mexico and eastern Florida to Cape Cod; low water to 8 fathoms. In the

post-Pliocene from Virginia to Florida; Miocene of Maryland and South Carolina.

Astyris lunata Dall. One specimen.

Alabama and Florida to Massachusetts Bay; low water to 14 fathoms. Fossil in 

the post-Pliocene of Gardiner I. and South Carolina.

Cerithiopsis Greeni Verrill. Four specimens.

South Carolina to Massachusetts Bay ; 2 to 10 fathoms.

Crepidula fornicata Lamarck. Abundant.

Gulf of Mexico to southern Maine, and local in the southern part of the Gulf of 

St. Lawrence; low water to 15 fathoms. Post-Pliocene fossil at Gardiner I., South 

Carolina, etc.; and Miocene in Maryland and South Carolina.

CrepidulaplanaSay. Common.

Distribution same as the preceding, from which, however, it is very distinct.

Crepidula convexa Say. Not common.

Distribution like the two preceding, from both of which it is perfectly distinct (although confounded with C. fornicata by Tryon and others). Fossil in the post-Pliocene 

of Virginia and South Carolina.

Odoslomia trifida Gould. Common.

New Jersey to Massachusetts Bay : low water to 5 fathoms.

1 Geology of Martha's Vineyard : Seventh Ann. Kept. U. S. Geol. Survey.

(632)
SHALBB.] FOSSILIFEKOUS DEPOSITS OF SANKATY HEAD. 35

Odostomia impressa Stimpsou. Common.

South Carolina to Vineyard Sound ; low water to 5 fathoms.

Turlonilla interrupta Adams. Several specimens.

South Carolina to Cape Cod; local farther north to the southern part of the Gulf 

of St. Lawrence, near Prince Edward Island; low water to 15 fathoms. Post-Pliocene fossil at Gardiner I. and in South Carolina.

Saxticava arctica Deshayes. Rare and small.

Arctic Ocean to Georgia; local and rare south of Long Island; low water to 50 

fathoms. Fossil in the post-Pliocene of Maine-and everywhere northward.

Mya arenaria Linne". Abundant.

Arctic Ocean (lat. 78° N.) to South Carolina; low water to 40 fathoms. Post-Pliocene fossil from South Caroliua and Virginia to Greenland and northern Europe.

Cortula contracta Say. One valve.

Florida to Cape Cod.

Ensatella Americana Verrill. Common.

Labrador to Florida; low water to 25 fathoms. Fossil in the post-Pliocene of Portlaud, Me., Point Shirley, Gardiner I.,Virginia, and South Carolina ; Miocene of Marylaud, etc.

Angulus tener Adams. Several specimens.

Florida to Gulf of St. Lawrence; low water to 12 fathoms.

Cumingia tellinoides Conrad. Common.

Florida to Cape Cod; 3 to 12 fathoms.. In the post-Pliocene and Miocene of South 

Carolina, etc.

Petricola pholadiformis Lamarck. Kare.

Gulf of Mexico to Massachusetts Bay; local in Gas co Bay and southern part of the 

Gulf of St. Lawrence; low water to 4 fathoms. In the post-Pliocene and Pliocene 

from Florida to Virginia.

Venus mercenaria Liune".' The variety abundant; a nearly typical form not uncommon.

Florida to Massachusetts Bay; local on the southwestern coast of Maine and southern shores of the Gulf of St. Lawrence and Bay of Chaleur ; low water to 8 fathoms. 

In the post-Pliocene of Point Shirley, Gardiner I., Virginia., Florida; Miocene from 

Maryland to South Carolina.

V. mercenaria, var. antiqua Verrill. By this name I propose to designate the unusually 

massive and strongly sculptured variety to which most of the fossil shells belong, and 

which has been discussed on a previous page.

The shell is rather obtusely rounded posteriorly, and is thickly covered with prominent concentric lamelliform ridges, which mostly extend entirely across the shell, 

but are often reflexed, appressed, and more or less confluent over the middle region, 

where the ordinary variety is nearly smooth (except when young). The violet color 

can still be traced in some specimens entirely around the inner marginj as in many 

recent Nantucket examples.

Tottenia gemma Perkins. Few specimens obtained.

South Carolina to Labrador; low water to 4 fathoms.

Gouldia mactracea Gould. One specimen.

Florida to Cape Cod ; 3 to 15 fathoms.

Scapliarca transversa Adams. Very abundant and large.

Florida to Cape Cod; low water to 15 fathoms. In the post-Pliocene of Cape Cod, 

Gardiner I., Virginia, South Carolina; Miocene of Virginia and North Carolina.

Mytilus ed'iilis Linne". Common.

Circumpolar; Arctic Ocean to North Carolina; littoral to 50 fathoms. In the postPliocene from Florida to Greenland and northern Europe.

Modiola liamatus Verrill. Common.

Gulf of Mexico to Long Island Sound and Narragansett Bay; littoral.

Crenella gldndula Adams. Few specimens obtained.

(633)
36 GEOLOGY OF NANTUCKET. [BULL.53.

Labrador to Long Island; 5 to 60 fathoms. In the post-Pliocene of Montreal.

Anomia glalra Verrill.

Florida to Cape Cod; and locally farther north to Nova Scotia; littoral to 20 fathoms. In the post-Pliocene and Pliocene of South Carolina.

Ostrea Virginiana Lister. Abundant and well-grown.

Gulf of Mexico to Cape Cod, and locally farther north, at Damariscotta, Me., and 

in the southern part of the Gulf of St. Lawrence; low water to 5 fathoms. In the 

post-Pliocene of Point Shirley, Gardiner I., South Carolina, etc. Both the short, 

rounded specimens and the much-elongated and narrow forms occur, as well as all 

the intermediate states, just as in many modern oyster-beds, showing that in postPliocene times the same kind of individual variations prevailed that have perplexed 

many modern systematists, but they have not yet become specific, nor even definite 

.varietal characters.

BRYOZOA.

HippothoavariaUlisV. (Escharella variaUlis Verrill, in Report on Invert.) Common 

 on Serpula, etc.

Florida to Massachusetts Bay ; low water to 20 fathoms. ' 

Biflustra tennis V. (Membranipora tennis (Desor); Verrill, in Report on Invert.) 

Common on shells.

Delaware to Massachusetts Bay; low water to 15 fathoms. 

Hembranlpora catenularia Smitt. Common on shells; 

Arctic Ocean to Long Island Sound; low water to 50 fathoms. Northern Europe.

CRUSTACEA; ANNELIDA; PORIFERA.

Panopeus sp. Several claws were found.

Eupayurus pollicaris Stimpson. A claw, probably from this bed, is recorded by 

Desor.

Florida to Massachusetts; 2 to 15 fathoms. 

Balanus eburneus Gould. Common.

"West Indies to Massachusetts Bay ; littoral to 3 fathoms. 

.Balanm crenatus Bruguie're. Common. 

West Indies to the Arctic Ocean; 3 to 15 fathoms. 

JSerpula dianthus Verrill. Very abundant.

North Carolina to Cape Cod; low water to 15 fathoms.

Cliona siilplmrea Verrill. The excavations are abundant in oyster-shells. 

Florida to Massachusetts Bay; 1 to 15 fathoms.

List of species, found only in the upper shell-bed. 1

MOLLUSCA.

Buccinum undatum Liune". Common.

Arctic Ocean to New Jersey ; northern coasts of Europe; low water to 100 fathoms. 

In the post-Pliocene, Maine to Labrador and northern Europe.

Neptunea curta Verrill. Several specimens ; one of large size.

Labrador to Massachusetts Bay, and in deep water farther south to Long Island.

Lunatia heros Adams. Common, but badly broken.

Georgia to Gulf of St. Lawrence ; low water to 40 fathoms. Post-Pliocene, Canada, 

South Carolina; Pliocene, South Carolina ; Miocene, Maryland to South Carolina.

L. heros, var. triseriata. One specimen occurred.

Neverita duplicata Stimpson. One broken specimen.

'A valve of Saxicava Norvegica was found after this list was put in type. Arctic 

Ocean to Massachusetts Bay. -Foot-note in Am. Jour. Sci.

(634)
BHALKB.I FOSSILIFEEOUS DEPOSITS OF SANKATY HEAD. 37

Yucatan to Massachusetts Bay; low water to 10 fathoms. Post-Pliocene, Virginia 

to Florida; Pliocene, South Carolina ; Miocene, Maryland to South Carolina.

Crucibulum striatum Adams. One large specimen.

New Jersey to Bay of Fundy ; low water to 40 fathoms.

Scalaria Groenlandica Perry. Recorded by Desor, and doubtless from this bed.

Arctic Ocean to Block Island; 10 to 109 fathoms; northern Europe. Fossil in postPliocene of northern Europe.

Diodora Noachina Gray. Two good specimens.

Arctic Ocean to Cape Cod; 8 to 70 fathoms. Northern Europe.

Mya truncata Linne". Several large specimens.

Arctic Ocean to Nantucket Shoals; low water to 10 fathoms. Northern Europe. 

In the post-Pliocene, Maine to Labrador.

Thracia truncata Mighels and Adams. A few valves, special bed not indicated.

Greenland to Long Island; 10 to 60 fathoms.

Clidiophora trilineata Carpenter. One valve.

Florida to Gulf of St. Lawrence; low water to 30 fathoms.

Macoma fragilis Adams, var. fusca (Say). A few valves.

Greenland to Georgia; littoral to 6 fathoms. In post-Pliocene from South Carolina

to Greenland.

Ceronia arctata Adams. Abundant and large.

Gulf of St. Lawrence to Long Island.

Mactra solidissima Chemnitz. Common, fragmentary.

Florida to Labrador; low water to 12 fathoms. Post-Pliocene of Point Shirley, 

Mass.

Cyclocardia lorealis Conrad. Common.

Labrador to New Jersey; 3 to 80 fathoms. In the post-Pliocene of Gardiner I, 

Point Shirley, Labrador.

Cyclocardia Novanglios Morse. A few valves.

Gulf of St. Lawrence to Long Island Sound; 3 to 40 fathoms.

Astarte undata Gould. One worn valve.

Long Island Sound to Northumberland Straits in Gulf of St. Lawrence; low water 

to 100 fathoms. In the post-Pliocene of Gardiuer I. and Point Shirley.

Astarte castanea Say. Abundant.

New Jersey to Nova Scotia ; 5 to 40 fathoms. In the post-Pliocene at Point Shirley.

Modiola modiolus Turton. Many worn valves.

Circumpolar; Greenland to New Jersey; low water to 80 fathoms. In the postPliocene of Point Shirley, Canada, and northern Europe.

Anomia aculeata Gmelin. Common.

Arctic Ocean to Long Island Sound; low water to 100 fathoms.

BP.YOZOA.

Eschara verrucosa Esper. On shells of Ceronia.

Arctic Ocean to Nantucket Shoals; 3 to 45 fathoms. Northern Europe. In the fossil 

examples the surface of the cells is covered with radiating ridges, often rising into 

an eminence in the middle, and is perforated with numerous pores in the grooves. 

Orifice somewhat semicircular, with a median avicularium in front of the proximal 

edge. '

Celleporaria incrassata Smitt ? . Several.

Off Martha's Vineyard to Spitzbergen ; 10 to 160 fathoms. The specimens are thick, 

irregular masses. The apertures are small, rounded, oblong, constricted on the sides 

by small points projecting inward near the middle, and sometimes with a small proximal spine.

(635)
38 GEOLOGY OF NANTUCKET. [BULL. 53.

CRUSTACEA AND ECHIXODERMATA.

Balanmportatus. Very abundant and large, but broken. 

Arctic Ocean to Long Island Sound ; 2 to 90 fathoms. 

Strongyloceytrotus Drobachiensis A. Agassiz. Spines only.

Arctic Ocean to New Jersey; circumpolar; low water to 430 fathoms. Post-Pliocene of Maine and northward.

List of species found in both shell-beds.

Species.

TritiaTrivittata... ...............................

Lower bed.

Few..............................

......do...........................

......do...........................

Few ..............................

......do ...........................

Few..............................

......do...........................

Upper bed.

One.

T7rtTir

do.

do.

do.

do.

Few.

' do.

Professor Verrill is of the opinion that 

The fossils of the lower bed indicate, for the water, a summer temperature of 70° 

to 75° Fahr., while those of the upper bed correspond to a temperature of 55° to 60°, 

thus showing plainly the influence of the Arctic current along the coast. All the 

species still inhabit the waters of southern New England, except Diodora Noachina, 

found in the upper bed, but this occurs in Massachusetts Bay, and will probably be 

found hereafter in the deeper channels among the Nantucket Shoals.

All the species found in this section appeared to Professor Verrill 

identical with those now found along the shores of this region except 

the quahog ( Venus mercenaria). In these shells he notes certain slight 

but apparently unimportant peculiarities. It does not seem possible 

to conclude from the difference in the character of the shells in the upper and lower parts of the section that any general climatal change 

in the temperature either of water or of air took place at the time when 

these two portions of the section were formed. The result may have 

been due altogether to changes in the direction of the ocean current, 

changes dependent on geographical modifications, which may have occurred at considerable distances from this point.

A diagrammatic section of the cliff, as far as it is determinable in the 

present condition, is given in Fig. 11. It will be seen that, as shown 

at present, the fossils occur at various levels in the bed, some of the 

species occurring as much as fifty feet above the surface of the water. 

The deposit is, throughout, composed of alternating layers of sand and 

pebbles. Save in the upper fifteen or twenty feet of the section, the peb-

(636)
FOSSILIFEROUS DEPOSITS OF SANKATY HEAD. 39

bles are rather small, few exceeding three inches in diameter; near 

the top they are coarser and more angular, resembling the matter of a 

frontal moraine which h.as been stratified. In this uppermost section 

the fossils are wanting.

Contact/ <z£.cLJb.:no£&eens.

FIG. 11. Diagrammatic section of beds at Sankaty Head, 

a, peat beds; 6, tops of glacial drift.

The distribution of the fossils in the part of the section where they 

are found is extremely curious; they occur as small isolated patches, 

lying generally at a considerable angle, clipping in most cases to the 

southwestward. The specimens are usually in a fragmentary condition 

and are packed together as if by the action of waves or by motion of 

swift currents. It is evident that a larger part of these remains were 

not formed just where they lie, but were swept into their position after 

having been comminuted by the waves. As will be seen from the list 

of fossils given above, the species are all those which belong to shallow 

water in the parts of the shore-which are open to the wide sea. This 

leads me to the belief that the fossiliferous deposits now exhibited at 

Sankaty Head were formed along an old beach line. The considerable 

thickness of the section in which they occur, which is 50 feet or more 

in depth, makes it necessary to suppose that the shore line remained 

nea.v this place for a considerable time.

The upper part of this section for ten to twenty feet is pretty sharply 

divided from the lower fossiliferous portion, not only by the absence of 

fossils in its strata but by the disposition of its materials. The bed- 

. ding from the base to the height of about fifty feet is, wherever observable, of the irregular, stratified type characteristic of the shore. Above 

that point, where the fossils cease to appear, the bedding becomes more 

horizontal, in this resembling our ordinary terrace drift, such as is found 

on the main-laud and is exhibited in the terraces on the southern part 

of the island. Here, as everywhere else, so far as observed, these reg-

(637)
40 GEOLOGY OF NANTUCKET. [BULL. 53.

ular stratified terrace deposits are devoid of organic remains. Above 

this last-named deposit lies a mass of apparently unstratified coarse 

pebbles, which, though wanting the clay element so generally found in 

the till, probably is of that nature. This is capped by a layer of blown 

sand of very recent origin.

At a point about five hundred yards south of Sankaty Head lighthouse there is a section exposed which differs in an interesting way 

from that on the higher and more northern section of the cliff. The escarpment has a height of about thirty feet. The general nature of the 

ore deposits, which are fairly well disclosed) is indicated in Fig. 12. It 

will be observed that besides the variation arising from the presence 

of peat deposits and layers of bog iron ore, which may be fairly considered unimportant, the section departs in essential regards from that figured in the section given by Messrs. Desor and Cabot and that which 

represents the present condition of the higher cliffs. The till like deposit near the top of the main section has apparently become in a southward extension of a few hundred yards a stratified clayey sand with angular pebbles. The sands next lower in the sections are apparently 

alike in thickness and character. But the fossiliferous sand is entirely 

wanting, unless it be represented by some small fragments of shells 

found on the talus at the point indicated in Fig. 12. The lower greenish gray clay appears to be identical with the deposit which I have considered as till in other parts of the island, where its character is much 

more distinct than at this point. e I am disposed to believe that this 

blue clay may be the equivalent of the deposit which Messrs. Desor and 

Cabot considered of Tertiary age. In color and character it closely resembles the clay which overlies undoubted till at other points on the 

island. The contact between this stratum of clay and the overlying 

sands has not been seen, but from the imperfect indications I am 

inclined to believe that it is probably irregular, i. e,, that the surface Of 

the Clay was, to a certain extent, eroded by the action of water or of 

ice before the sands were laid down. (See PI. VIII.)

This sudden change in the character of the section is possibly due to 

the fact that within the interval which separates it from that at Sankaty Head we pass from the southernmost limit which the ice0 sheet attained in its last advance to the region where the sea-floor received the 

deposits of sand and gravel which came from the subglacial streams. 

It is likely that during the second stage of the last Glacial Period, the 

ice for a time extended beyond the southern shores of Nantucket. This 

is indicated by the rounded character of the mass of till which lies between the two arms of Hummock Pond, as well as by the extensive deposits of apparently rnorainal matter which exist in the ridges of Nantucket Shoals. But in its retreat the glacier made a considerable pause, 

in which the ice-front lay near the line of the center ridge of this island. 

The southernmost point occupied by the ice-front during this division 

of the period was near the portion occupied by the sections shown in

(638)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. VIM

^^ *.^^-;i^*P^^v^;. ^llfi^:^r;.^^^ :^ £i

VIEW OF COAST ESCARPMENT, 500 YARDS NORTH OF SANKATY LIGHT.
SHALER.] FOSSIL1FEROUS DEPOSITS OF SANKATY HEAD. 41

Figs. 10 and 11. The section shown in Fig. 12 lies about four hundred yards south of the inorainal accumulations.

Brorrn, samZ. 2ft

Srorm, Sand, -Sin*. 

, G to Sin.

a--pe6b~le»

liog irmaret 4fC.

liYliftidu tlaycysanc^mOifery 

anguhvpeSbteSt fifl/,

'law sand, niSfuml clay or 

8ft.

Contact "not ob$&TefL+

FIG. 12. Section south of beds at Sankaty Head.

In my opinion the history of this Sankaty Head section is as follows: 

After the first advance of the ice and its subsequent retreat, a movement 

which left the underlying till of the island in its present position, there 

was a considerable period in which this part of the shore was occupied 

by the sea. During this time the Sankaty beds were deposited, the sea 

shore probably sinking as they were formed; when, with the readvance 

of the ice, the organic life was expelled from these waters and the terrace deposits were formed above the level of the fossil-bearing bed§. 

The passage from the obliquely stratified to the horizontal drift is so 

sudden that it must be taken to indicate a rapid change in the conditions which prevailed on the sea-shore at this point. This horizontal

(639)
42 N GEOLOGY OF NANTUCKET. [BULL. 53.

stratified drift, which contains no fossils, is capped on the top by irregular patches of bowlder material, which seem to me to be essentially 

till-like and to indicate that after the period of the fossil-bearing sands 

the glaciers again eroded this surface. It is, however, likely that only 

the extreme and thin edge of the ice attained to this point in its readvance. This description of the section at Sankaty Head applies to 

the higher part of the cliff alone; a little to the southward the section 

changes greatly, as is shown in Fig. 12.

SUCCESSION OF GEOLOGIC EVENTS.

We are now in a position to consider the general history of this island 

during the Glacial Period, the only chapter of the geologic record which 

 we can trace in its structure. First in this history is the series of events 

which led to the formation of the blue, pebbly clay or till, which, as 

before shown, appears to underlie the island, though it occasionally 

rises above the level of the sea. This deposit apparently must have 

been formed during the stage of the Glacial Period when the ice sheet 

was over this section. The unstratified nature of the mass compels us 

to believe that it was formed as ground moraine beneath the surface of 

the ice sheet, or immediately in its front. There is no evidence that 

this deposition continues to any distance south of the present shore of 

the island, but the occurrence of the mass on the ridge between the 

branches of Hummock Pond makes it clear that it extends about as 

far south as the southern shore. It does not appear possible to determine whether this region was above or below the level of the sea when 

this deposit was formed.

After the deposition of this mass the ice sheet retreated from the 

district and the climatal conditions became such as admitted the return 

of the marine life to the shore line, which must have been near its present position. This was certainly the case if the broken shells and 

coarse bedded sands at Sankaty Head be properly taken as evidence 

of sea-shore action. The level of this shore at one time must have been 

at least fifty feet below the present high tide mark. This condition in 

which the region was reoccupied by a marine life must have continued 

for a considerable period. After the fossiliferous beds were formed the 

ice again advanced until its southern front came at least to the middle 

of the island. The first result of this readvahce of the ice was to erode 

the surface of the till and of the stratified deposits which had been 

formed above it. At certain points, probably over the greater part of 

the district, the beds were eroded all the way down to the till, as for 

instance at Pocomo and at some points in the center of Nantucket 

village. At other points, as on the north shore near the water-works, 

the stratified clays, which rest directly upon the till and which were 

probably deposited while the retreating ice front was still near the 

island, were not altogether removed by the later incursion of the ice.

(640)
SHALER.] SUCCESSION OF GEOLOGIC EVENTS. 43

At Sankaty Head, where the ice appears to have acted with much less 

energy than on the north shore, the fossiliferous beds, which doubtless 

lie at a considerable height above the surface of the till, and the stratified clays and sands, which normally covered it, were not removed, 

though they doubtless lost a portion of their thickness. As a result of 

this erosion by the second advance of the ice the beds containing the 

fossils, which possibly at one time covered the whole of the island, 

were left as separated patches.

During this readvance, or, perhaps, in several successive readvances, 

were accumulated the existing heaps of stratified and amorphous sand, 

gravel, and bowlders as well as the southern sand plains which constitute the principal features of the island. The conditions of their 

accumulation are, as far as determinable from the evidence, as follows, 

viz:

(1) The surface was below the present level of the sea. This is shown

by the fact that there are no, drainage channels leading out of the many 

valleys between the sand hills, such as would have been formed if the 

masses had been accumulated above the level of the sea, as are moraines at the front of a land glacier, as well as by the numerous bowlders apparently dropped from icebergs.

(2) The drift materials were partly shoved forward by the glacier and 

partly deposited by the streams which escaped from beneath the ice. 

This is shown by the intermingling of confused or amorphous drift with 

large bowlders and with stratified deposits of fine sands.

(3) The existence of considerable streams rising from the ice front 

and extending to the south is shown by the numerous deep channels 

which are excavated in the southern terrace or sand plains. These 

valleys originate in the hills and extend southwardly as distinct channels. They are comparable to the channels which are cut through sand 

deposits below the level of the water at the mouth of estuaries where 

considerable streams escape into the sea. It should be observed that 

all these valleys do not clearly head up against the base of the sand 

hills, though all of them trend in that direction. It appears likely, from 

what we know of the tendency of subglacial streams to change their 

position, that all of these streams may not have been flowing at the 

same time; indeed, they may have been made in succession by the 

changing direction of a few of these rivers which emerged from beneath 

the ice. The irregular accumulation of de"bris near their points of escape from beneath the ice sheet would of itself have a tendency to direct 

these streams to new channels. Clearly, we can not suppose that these 

channels were formed after the ice left this region, for there is no form 

of water action disconnected with glaciation which can be imagined to 

have produced them.1

(4) The sand plains on the southern part of the island, which exist 

nowhere else upon its surface, were deposited during the time when the

Geology of Martha's Vineyard: Seveatli Auu. Kept. U. S. Geol. Survey.

(641)
44 GEOLOGY OF NANTUCKET. fBi'LL.53.

detrital hills of the northern section were being accumulated. This is 

shown by the fact that they at some points pass by gradual changes of 

form into these hills. The fact that they are intersected by the ancient 

valle'ys which originate in the morainal hills is evidence that the plains 

were here before the glacial sheets formed the hills or that they were 

formed at the same time as th'ose elevations. The shape of the valleys, 

as is shown in the section (Fig. 7) and on the map, is best reconcilable 

with the hypothesis that they were formed as the sands of the plains 

were deposited. The whole of this work of deposition appears to have 

taken place beneath the surface of the sea, for, as before remarked, the 

whole character of the topography is inconsistent with subaerial action.

(5) After the foregoing stages of the re-advancing ice the glacier appears to have again retreated to the northward for the last time. During or after the process of retreat the surface must have been suddenly 

elevated above the level of the sea. Probably this process of reelevation was extremely rapid, for unless we suppose that there was at that 

time some barrier on the south to protect the coast from the waves of 

the Atlantic, a barrier which has since been swept away, these delicate 

hills of sand and gravel would have been subjected to swift destruction 

by the action of the sea. The supposition that such a barrier ever existed finds no support from the facts.

This sudden uplift of the moraines and kaines of this coast after the 

ice sheet went away is the most puzzling feature of its history. The 

evidence of this uplift seems to me ample; it does not rest upon the 

evidence presented on this island alone, but on the proof of the same 

nature afforded by the coast line from north of Boston to New York 

City. Everywhere along this part of the coast we have the same series 

of delicately molded kames that occurs on this island. We are compelled, therefore, to believe that they were formed below the surface of

the sea and uplifted above its surface after the last retreat of the ice, I

can not here discuss the whole array of evidence on which this assertion 

rests; that evidence will be considered in a special report on this subject, but one consideration in addition to those already adduced in this 

memoir will serve to show most essential grounds for this opinion. On 

the mainland, where there are extensive terraces of stratified drift deposits clearly formed beneath the surface of the sea, we often find 

these terraces passing gradually into sand hills or kames, the tops of 

these hills being on the same level as the upper part of the terrace. 

Now, these terraces were certainly formed below the level of the sea. 

The kames lying upon and inclosed within them must have been formed 

at the same time; for, if formed before, they would have been effaced 

in the construction of the terraces. They could not have been formed 

afterward for they are often completely inclosed in the terrace deposits.

Accepting, then, the hypothesis that these drift hills of Nantucket 

were accumulated below the level of the sea and afterward lifted above

(642)
SHALEH.J SUCCESSION OF GEOLOGIC EVENTS. 45

its surface, it is evidently very important to determine whether there was any action of the 

waves on their surface during the 

process of uplift. We may be sure 

that if they were exposed even for 

a few days to the action of the Atlantic surf and tides they would 

bear the unmistakable marks of 

water action. If we could plant 

these hills in the open sea on Nantucket Shoals, for instance, they 

would in one month have benches 

cut in their sides and a detrital 

apron formed on their front which 

would endure even longer than the 

delicate curves which now characterize their forms.

On the south side of the kanie 

ridges between Nautucket village 

and the east end of the island where 

the hills are highest there is a faintly indicated shelf which possibly 

marks the action of the sea during 

 a very brief period. (See PI. VI.) 

This scarf is only a steeper slope of 

the hills and a faint terrace of sands 

with an inclined surface at its base. 

Although this may possibly indicate 

a temporary pause in the process of 

uprising which brought this surface 

from the bottom of the sea to above 

its level, it does not relieve us from 

the need of supposing that the elevation was really paroxysmal in its 

suddenness; for the fact that the 

summits of the sharp sand hills have 

not been planed down to the level 

is still before us. At one stage in 

the inquiry it seemed to me possible that these kames might have 

been worn down on their tops and 

become again pointed by the* action 

of the rain; but a careful examination of the circular valleys between 

these ridges shows this not to have 

been the case, for these depressions 

(643)

i-.'i- i

9 JWl3%.; 

. »v:;^.:tf>,''i
46 GEO'LOGY OF NANTUCKET. [HULL. 53.

do not contain any such mass of de"bris as would have been swept into 

them by this process. It is true that the bottoms of the depressions 

often contain a small amount of sand, such as could be washed into 

them by torrential rains. These deposits are not disposed in the form 

of a flat-surfaced mass of stratified sand and gravel, as would have been 

the case if they had been formed by ocean waves, but they are made of 

fine sand which slopes gently toward the center of the pit. (See Fig. 14.)

In a word, we can not believe that ridges of sand and gravel, with the 

accompanying sand plains, having the delicacy of outline which marks 

the contours of these great morainal accumulations could have been 

formed except,beneath the sea. We are also forced to the conclusion 

that these deposits escaped from the water through the surf by a very 

sudden movement. In a report on the geology of Mount Desert, Maine, 1 

I show that we have other evidence leading to the conclusion that 

the recovery of this shore from the deep subsidence that attended the 

Glacial Period was extremely sudden.

At this point we may discuss the peculiar compass course of the 

Nantucket moraines. So far as we can determine the matter the front 

of the ice during the formation of the Nan tucket moraine lay in a nearly 

east and west direction. The exact alignment is not determinable from 

the direction of the separate mounds of drift, which are too isolated and 

irregular to afford any indication of the movement of the glacier. But 

considering these morainal masses as a topographic whole it is clear 

that their extension is within 5° of an east and west direction. This 

course is a wide departure from that of the other similar moraines 

of this district. The Elizabeth Islands frontal moraine has a nearly 

northeast and southwest trend, both in the islands whose name I have 

given to»it and in its obscurer extension on the mainland of Cape Cod. 

It preserves this northeast and southwest course for a distance of over

40 miles without showing at any point a departure of more than 8° from

the average direction of the line. The older moraine on the northern 

shore of Martha's Vineyard, although much shorter, evidently has the 

same direction. So far as I have observed, the moraines on Cape Cod, 

which, ifc is true, are very fragmentary, have the same general alignment.

On the other hand, the moraines of Long Island, New York, have a 

general course which is intermediate between those just noted and that 

of Nantucket. Their course is about N. 70° E. and S. 70° W. It is

 Q

thus evident that there is a considerable range in the direction of these 

frontal moraines within 200 miles of distance on the southern shore of 

New England.

The wide difference between the direction of the ice front on Martha's 

Vineyard and that on this neighboring island of Nantucket may be due 

either to the existence of a great loop in the ice front at this point or to 

the fact that this Nantucket moraine, being the outermost of the frontal

1 Eighth Annual Eeport U. S. Geol. Survey. 

(644)
BULLETIN NO. 53 PL. IX

ASPECT OF NORTH SHORE FROM NEAR UPPER END OF LONG POND, LOOKING EAST.
BHALBR.J SUCCESSION OF GEOLOGIC EVENTS. 47

deposits on this part of the continent, had a direction different from the 

later formed moraines on Martha's Vineyard and Elizabeth Islands.

The existence of such great loops in the frontal moraines has been 

made clearly evident by the labors of Professor Chamberlin and his 

assistants in the northern part of the Mississippi Valley. They maybe therefore reckoned upon as possible accidents on all parts of the ice 

front. So far, however, I have not been able to reconcile the facts presented by the Nan tucket moraine with the hypothesis that it is a part 

of a loop in a frontal moraine of normal direction. There is no trace of 

curve in its considerable length and it is not possible to connect it with 

any of the existing moraines by any hypothesis of form which. I have 

been able to apply to it. Moreover, there is the important fact to be 

considered that we have as yet no evidence of any loops in the moraines 

in this part of the continent. In favor of the view that it is the frag, 

inent of a moraine older than any other occurring along this part of the

coast, we have the important fact that the pebbles are much more decayed than they are in any of the morainal accumulations which He to 

the northwest of it. It may reasonably be asserted that this difference 

in the measure of decay amounts to as much as one-half of the total 

oxidizing action which has been applied to this drift material.

The difference in orientation of this and other moraines may possibly 

be explained by the supposition that in the time when the glacier had 

its furthest extension, the movement of the ice was along the north and 

south line; while when the ice began to retreat the direction of the 

flow was gradually changed, the movement in the end being from the 

northwest. There is a good deal of evidence to support this view which 

can only be suggested in this memoir. The most important part of this 

evidence is found in the direction of the troughs excavated by the ice 

during the glacial period. These troughs probably owe their formation 

in the main to the force exerted in that part of the glacial epoch when 

the ice was deepest. The general trend of these troughs is from north 

to south. Although the cutting action which formed this valley has 

been in part guided by the positions of the rocks, that is, by their strikes 

and dips, it is clear that it was more generally determined by the direction of the ice movement. I therefore think it possible that the ice 

during the period of its greatest extension moved in a more meridional 

direction than during the period of its decline.1

POST-GLACIAL CHANGES OP NANTUCKET.

We shall now consider the changes which have taken place in this 

district since the last retreat of the glacial ice. These changes may be

1 1 venture iu passing to call attention to the fact that this change in direction may 

he due to the very great extent to which the ice overlapped the shcre during the time 

when it was thickest, when it probably had its front far one on the relatively level 

surface of the continental submarine shelf. It probably moved southward rather than 

toward the deeper sea on the east. As it shrunk, the eastern movement became more 

evident. 

(645)
48 GEOLOGY OF NANTUCKET. [BULL. 53.

grouped under three heads, viz, changes of level, changes due to the 

alteration of the surface, and changes due to the wearing action of the 

sea.

The principal change of level vras that which brought the sand and 

gravel hills and the fringe of lower land on the south above the surface 

of the sea. The amount of this elevation can not be accurately determined, at least from the evidence afforded by this island; still we may 

fix the minimum amount of the change in a rough way. .Assuming 

that the sand hills were formed on the sea-floor at the front of the ice, 

we must suppose that they were originally at a depth which protected 

them from the action of the ocean waves. This requires us to suppose 

a submergence of their summits to a depth of at least 200 feet below the 

level of the sea, and even at that depth it is difficult to see how their 

easily moved sands remained undisturbed by the waves of great storms, 

which at the depth of two or three hundred feet produce a considerable 

motion in the water. As the highest of these sand hills now lies about 

90 feet above the level of the sea, it is evident from our premises that 

the post-glacial uplift was not less than 300 feet and may have been 

much greater. This estimate, it may be remarked, is quite consonant 

with the evidence which is afforded by the other parts of the shore in 

this district.

After the first elevation there came at least one other movement of 

this shore, this time in a downward direction, which brought the freshwater peat deposits beneath the sea-level. This last movement, possibly did not change the level of the land to more than ten feet of altitude, though the alteration may have exceeded this amount.

There is another feature in the structure of the island which seems to 

afford some evidence of the recent subsidence of the shore. It will be 

seen from the map that the portion of the northern shore of the island 

which lies inside of Coatue Beach has a very indented shore-line, while

the coast to the west of the harbor has a shore which has the outline 

proper to all coasts where soft materials have been subjected to the 

long continued action of the waves. The interpretation of this peculiarity seems to me to be as follows, viz: This shore after the post-glacial 

elevation must have been much farther to the northward than it is at 

present; then came the subsidence indicated by the submerged peats, 

as before .described, which brought the land to about its present level. 

The beach of Coatue was rapidly formed in front of a portion of the 

north shore, and has since served as a protecting barrier against the assaults of the vigorous waves which form in Nautucket Sound. If this 

part of the shore had long been exposed to the action of the open water 

it would certainly have a different contour from that it now exhibits. 

The failure to form a similar barrier along the shore to the west of the 

harbor is probably due to the originally deeper water on that part of 

the coast, or to the absence of the supply of detrital material necessary 

for the formation of a barrier beach.-

(646)
SHALEB.J POST-GLACIAL CHANGES. 49

It must remain an open question whether these last described elevations and subsidences were local or general in their nature, or, in 

other words, whether they are in consequence of a general continental 

movement or were due to forces affecting only the district in which the 

island lies. Still further we are left in doubt whether these changes in 

level were of equal amount in all parts of the island. A comparison 

of the evidence attainable in this area with that which may be found 

on other parts of the neighboring land must be made before these points 

can be decided. So far as I have been able to compare the facts with 

those which are evident on the shores of Martha's Vineyard, the following results only have been found: On that island, as set forth in my 

memoir in the Eighth Annual Report of the U. S. Geological Survey, 

conclusive evidence of extensive subsidence is wanting. The conditions 

there are unfavorable for the preservation of such evidence. Still, 

we note the fact that on both these islands there is a remarkable correspondence in the height of the southern glacial plaiu above the level 

of the sea; in both islands the altitude of the southern escarpment 

along the Atlantic shore is essentially the same, and the channels which 

extend from the frontal portion of the moraine to the sea are about the 

same height above the tide-level. If there be any difference it is that 

these channels on Nantucket are at a slightly lower level than those on 

Martha's Vineyard. On the assumption that these frontal aprons were 

originally formed at the same height, the island of Nantucket has 

not been lowered more than 10 feet below the level to which the southern shore of Martha's Vineyard has attained since the close of the Glacial Period. It is not positively certain that these frontal aprons were 

originally formed at the same depth beneath the sea, yet the equal elevation of these two fragments of the coast is, considering the small distance which separates the two islands, a fair basis for believing that 

they were formed at aboutrthe same depth beneath the sea, and that 

they have since retained their positions relative to each other during 

the process of elevation which brought them to their present altitudes.

KECENT CHANGES ON THE COAST OF NAN TUCKET.

The recent changes on the coast of Nantucket have a special interest, 

for the reason that they include some very curious horizontal modifications. (See PI. IX.) While the larger part of the coast of Martha's 

Vineyard is now wearing away with considerable speed, rather more 

than the half of the periphery of Kantucket is at the present time not 

only exempt from wear, but exhibits a gradual accretion (Fig. 15). The 

gain of land on the sea is at present most conspicuous on the southeast 

section of the shore from Tom Never's Head to Siasconset. Along this 

portion of the border of the island the sea no longer attains the bluffs at 

any point, being shut out from them by a strip of sand which forms the 

crescent-shaped apron extending, at its widest part, about one-third of a 

mile from the shore. These sands have apparently been derived in part 

Bull. 53 4 (047)
50 GEOLOGY OF NANTUCKET. . [BULL. 53.

from the erosion of bluffs to the north and west of the site where they are 

accumulated, but perhaps in larger measure they may have been washed 

in from the floor of the sea. The formation of this extensive deposit appears to indicate a recent change in the regimen of the currents along 

this part of the coast; for it is evident that the coast-line was rapidly 

working inland until this apron began to form. It has evidently been 

but a short time since the sea beat against the cliffs inside of this protecting accumulation. These cliffs retain in good part the original shape 

given them by the erosive action of the waves. I have not been able to 

obtain any satisfactory information as to the growth of this apron 

within the historic period, but I am inclined to believe that it has been 

largely, if not altogether, formed since the settlement of the island by 

European population.

Fig. 15. Section of shore east of Surf Side.

I have also been unable to determine the nature of the alteration 

which led to the construction of this apron. The currents of these waters 

depend upon so many conflicting conditions that it does not seem possible at present to say to what this change is due. It appears, however, to have been connected with an alteration which seems to be now 

going on in the channels immediately to the eastward of Siasconset. It 

is a common opinion among seafarers of Nantucket that this channel is 

now less obstructed by sands than formerly ; at present, ships venture 

through this passage, where of old. on account of its shoals, they did not

dare to sail. If we may assume that such changes in this channel have

really occurred we might suppose that the greater scour of the tidal 

currents in this water has removed from the bottom of the channel a 

quantity of sands and accumulated them in this shelf, which would afford not unnatural lodgment for them. It is evident that this.apron of 

sand is extending its extremities to both the north and west. Jn the 

former direction it is affording some protection to the steep bluffs at 

Sankaty Head; although yet not a complete barrier/to the action of the 

sea, it has diminished the wear on the shore bluffs in a noticeable way. 

Within a few years this escarpment has become in part grassed over. 

To the westward this apron is extending with considerable rapidity, as 

is indicated by the fact that the bluff still retains the marks of sea 

action at points where it is now completely defended by the protecting 

apron.

Another region of extensive accumulation in very modern times is 

that part of Great Head which extends from the apex of the triangle in 

which lies Croscaty Pond and forms a remarkable promontory (Fig. 16).

(648)
U. S. GEOLOGICAL SURVEY BULLETIN NO. 53 PL. X

SPLIT PEBBLES, RESEMBLING STONE IMPLEMENTS.
8HALER.J RECENT CHANGES ON THE COAST. 51

s?1

This accession is evidently of less recent origin than the Siasconset 

ttpron. It consists of extensive sand dunes and beaches, the sand of 

the dunes having been borne to them by the winds. Although these 

dunes are frequently much wasted by the action of the 

same force which brought them to their present position, 

they are still very remarkable examples of wind blown 

sands. The extremity of this cape is now separated by a 

channel having about four fathoms of water at mean low 

tide from the point of the rip shoal, on parts of which there 

are not over four feet of water at low tide. Within the last 

century the extremity of this cape has fallen back southward for the distance of 1,400 feet, as noted by Prof. Henry 

Mitchell. This recession of Great Point has probably been 

a consequence arising from the rapid extension of the 

promontory of Monomoy, which, according to his determinations, has extended southward two miles during the past 

century. 1 It is possible that a portion of the material 

wasted from this point has been contributed to the Siasconset apron.

The most extensive of these modern contributions to the 

shore of Nantucket is found in the mass of Coatue Beach, 

which contains a larger body of recently drifted sands than 

all the other similar deposits found along the shores of this 

island. If we consider the submarine portion of this peninsula as well as the emerged part we find it to contain a 

mass about equivalent to a layer a hundred and fifty feet 

deep occupying a square mile of area. A part of this material appears to have been derived from the bottom of 

Natitucket Bay by the action of the waves; a portion of it 

may have come from the recession of Great Head.

About one-third of the coast-line of Nantucket appears 

now to be undergoing erosion. At the eastern extremity 

of the island the erosive action appears at present to be 

limited to the section from the southern end of the Sankaty 

bluffs to a point just beyond Haulover Beach at the head of 

Coatue Bay. In 1873 Prof. Henry L. Whiting found by a 

resurvey of this portion of the shore that the eastern or 

sea side of the coast at the Haulover had receded by an 

average of about one hundred feet since 1846. Between 

Sachacha Pond and the Haulover, especially at Squam 

Head, the wasting is evidently at this day quite rapid, 

probably amounting to at least a foot a year.2 The southern 

coast westward from Tom Never's Head, especially the section west of

1 Monomoy and its shoals: Annual Report of the Harbor and Land Commissioners 

of Massachusetts, Boston, 1887, p. 42.

2 Report of Harbor Commissioners of Massachusetts, 1873, p. 109.

(649)
. 52 GEOLOGY OF NANTUCKET. |BULL. 53.

Weedweeder Shoal, is also the seat of a considerable, though apparently 

inconstant, wear. A remarkable but probably temporary change has 

recently taken place in the long spit which forms the western extremity 

of the island as it is delineated on the Coast Survey maps. Twenty 

years ago this spit at low tide constituted an almost complete bridge 

extending from Nantucket to Tuckernuck Island. Of recent years this 

point has in good part been washed away almost down to its base near 

Further Creek. It seems possible that the existing separation of Tuckernuck from Nantucket may have been brought about by the action of 

marine currents within a relatively short time.

VEGETATION OF NANTUCKET.

The present condition of the flora of this island deserves some notice 

in this memoir, for the reason that it throws light upon its geological 

history.. At present this is the most treeless area on the eastern coast 

of the United States. There are no traces of original forest upon its 

surface. About. the borders of the smaller ponds, especially where 

these pools are well sheltered by the kame hills, there are a few stunted 

oaks and other forms of our ordinary New England trees, but in no 

case do they give the conditions of a forest. None of the specimens 

of this natural growth exceed 20 feet in height. Ou certain parts of 

the central region of the island artificial plantations of pines exist, but 

the trees, though in some cases nearly half a century old, have never 

attained a height of more than 20 feet and survive with difficulty, in the 

existing conditions of the climate and soil. Although the greater part 

of the surface of the island has remained entirely wild there is no trace 

of a tendency to return to the condition of forest.

There is a tradition, not, so far as I have been able to find, supported 

by any trustworthy records, that this island when first occupied by the

European settlers was generally forest-clad, and that the trees of oak

and pine were sufficiently large to afford ship-timber as well as material for edifices. Those who have had occasion to examine traditions 

as to the nature of forest-covering of a region now deprived of trees, 

know how untrustworthy such reports frequently are. At a number 

of points along the eastern shore of the United States where the poverty of the soil is very great and the timber extremely stunted we hear 

the same vague account'of vanished woods. Nevertheless, though such 

traditions are open to suspicion, I am inclined to believe that when this 

island was first settled the greater part of its surface, at least that portion of the area north of the southern plains, was covered with a forest 

growth which afforded some architectural timber. As soon as this covering was removed, as it was before the middle of the last century, 

without any effort to restore its forest coating, the soil came to its present treeless state.

The failure of these woods to recover possession of the earth demands an explanation. This explanation we may find in either of two

(650)
BHALER.] VEGETATION. 53'

ways. We may suppose that there has been in modern times a change 

in the climatal conditions affecting this portion of the continent which 

makes it impossible for forests to be reestablished. Or we may account 

for the nudity by supposing that in the earlier day the island was very 

much more extensive than it is at present and that the climate was so 

far locally modified by the greater land area that the timber was enabled to gain a foot-hold. This latter supposition appears to be the 

most consonant with the known facts. It seems to me tolerably clear, 

from the topography of Nantucket as well as that of the. sea-bottom 

north and south of it, that the island has not lost much of its surface 

for a considerable time in the past; but if we go back to the time when 

the last subsidence of this shore took place the subsidence which 

lowered the peat deposits before mentioned belowthe level of the sea 

we may be able to assume a reduction in the area of the land resulting 

from that down-sinking sufficient to account for the required change of

the climatal conditions.

That there has been a general change of climate on this part of the 

continent sufficient to ac'count for the failure of these woods, to repossess the surface of the island appears to me an unreasonable assumption, because on the mainland we find no evidence of such a modification of climatal conditions. I am, therefore, disposed to believe that 

the forest-covering of Nan tucket was established at a time before the 

last subsidence of the shore, and that this subsidence so far reduced 

the area of the laud that the well-known influence of the sea air penetrating to the central portions of the island served to prevent the restoration of the timber after it had been removed.

The present flora of Nantucket, though it wants the larger trees, is 

extremely rich and varied. The absence of a forest-covering has enabled a host of low-growing plants to establish themselves upon its 

surface and to develop with a luxuriance which they do' not attain on 

the mainland. The interaction of these plants in their unwonted freedom of development affords many problems of interest to the botanist 

which deserve more attention than they have yet received. It would 

be particularly interesting to consider the differences in the vegetation 

determined by the peculiarities of the soil in the various parts of 

the island, were it not that these problems lie beyond the scope of 

this report. I venture, however, to note for further inquiry on the part 

of those who may take up the question, that the differences between 

plants growing on the sand hills on the southern plains and in scanty 

areas of clay soil which exist on the surface of Nantucket are very 

great; and, furthermore, that very large areas of the southern plains, 

where the soil is composed in the main of quartzose sand, are occupied 

almost exclusively by mosses and lichens.

A peculiar feature in the botany of the island is found in the presence 

of cacti in the region north of Coatue Sound. Along Coatue Beach 

and in the district about Croskaty Pond, as well as on Great Head, one

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54 GEOLOGY OF NANTUCKET.

or two species of Opuntia are 'extremely abundant. This is certainly 

the easternmost and possibly the northernmost station in the region 

east of the Appalachians attained by any part of this interesting group 

of American plants. I have been unable to ascertain when this form 

appeared upon the island, whether it has been introduced by human 

agency or has come to its position in a natural way. It seems clear 

that it has been upon the island for a long time. If it be true that 

there are two distinct species present on this shore, then it is most 

likely that the introduction took place in the natural way. The field 

now occupied by these cacti has a length of about four miles. and a 

width near Croskaty Pond of about a mile. It is a singular fact that, 

although within this area the plants abound and apparently find the 

circumstances well suited to their needs, the species has not extended 

to the southern portions of the island. Apparently the great beach 

apron at Siasconset affords a site equally well suited to these plants, 

but a careful search of this field, made in 1875, failed to show a single 

specimen of the genus upon it. Within the field occupied by these cacti 

they never depart from the areas of blown sand. The hummocks of 

karne drift which rise within this field do not seem, to afford conditions for their development.

(652)
INDEX.

A. Page.

Abbott, C. C., cited on stone implements... 24 

B.

Bowlders, abundance of.................... 18

Decay of............................... 21-23

C.

Cabot, Edwnrd C. (See Desor E.)

Cacti abundant north of Coatue Bay....... 53,54

Chamberlin, T.C.,citedonmorainalloops.. 47 

Coast line of Nantncket ................... 11-15

Coatue Bay,peculiar configuration!of...... 12

Coatue Beach, peculiar topography of...... 14,48

Croskaty Fond..................'........... 14

D.

Desor, E., and Edward C. Cabot, ou geology

of Nantucket......................31,32,40

Detrital materials, origin of................ 26

Drift hills, conditions of accumulation of... 43,44

F. 

Flora of Nantucket............. ....... 52-54

Fossils of Sankaty Head, list of............ 34-38

G.

Glacial period on Nan tucket............... 42-47

Great Head, peculiar topography of ....... 14

H.

Hummock Pond. 19

I.

Implement-like stones, mode of formation of 23-26

K. 

Kames................................l8,19, 44, 45

L. 

Long Pond................................. 19,20

M.

Moraines ..........................18,19,44,46,47

Mitchell, Henry, cited on recession of shore. 12, 51 

On fossiliferous beds................... 30

N. Page.

Nantucket, general form of................ 11-15

Surface of.............................. 12

Coastline.............................. 12,15

Topographic peculiarities.............. 12

Fresh-water system of................. 14

Nantucket Village, geologic features

near ...............................16,17,45

P.

Peat....................................... 28-30

Pebbles resembling paleolithic implements 23-26 

PolpisHarbor.............................. 19

Ponds....................................14,19,20

Porphyry on. Nantucket, sources of....... 26,27

S.

Sachacha Pond ............................ 19

Sands, conditions of the accumulation of... 43,44 

Sankaty Head, chipped pebbles at.......... 25,26

Fossiliferous deposits of............... 30-42

Scudder, S. H,, on geol ogy of Sankaty Head 32,33 

Shore-line of Nantucket.................... 11-15

Siasconset, peat near....................... 28

Plants at............................... 54

Squara Head............................... 10

Subsidence indicated,recent............... 29,30

Streams, no well-defined................... 14

Swamps,submerged ........................ 28-30

T.

Timber of Nantuc'ket*..................... 52,53

Trenton, IT. J., chipped pebbles near....... 24,25

Tuckernuck and Uantucket, relations of... 20,52

TJ.

Uplift, post-glacial. 48

V.

Verrill, A. E., on Nantucket fossils ......32,34-3J

'W.

Whiting, Henry L., cited on recession of

certain coast line .................... 51

55