Report on the boundary between the Potsdam and Pre-Cambrian rocks north of the Adirondacks

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GEOLOGICAL SURVEY OF THE STATE OF NEW YORK.
| (GEOLOGICAL MAP.) | oo

- REPORT ON THE BOUNDARY BETWEEN THE POTSDAM <_

AND PRECAMBRIAN ROCKS NORTH OF THE
ADIRONDACKS. eA

JAMES HALL, | H.-P. CUSHING,

State Geologist. a Special Assistant.
1896.

[From 16th Annual Report of the State Geologist, 1898. |

ea

GEOLOGICAL SURVEY OF THE STATE OF NEW YORK.
(GEOLOGICAL MAP.)

REPORT ON THE BOUNDARY BETWEEN THE POTSDAM
AND PRE-CAMBRIAN ROCKS NORTH OF THE
ADIRONDACKS.

JAMES HALL, Hi. P. CUSHING,
State Geologist. ~ Special Assistant,

1896.

James Hatt, State Geologist.

Str :—The accompanying report is made in accordance with your instruc-
tions to map the northern boundary between the Potsdam sandstone and the
Pre-cambrian crystallines across Franklin county and as far into St. Lawrence
county as practicable; further, to determine what rocks younger than the
Potsdam come in on the north and their limits, and, in addition, to make
observations on the change in the character of the gneisses in going westward.

Respectfully yours,

H. P. CUSHING.
March, 1897. |

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GEOLOGICAL SURVEY OF THE STATE OF NEW YORK.
(GEOLOGICAL MAP.)

ed

REPORT ON THE BOUNDARY BETWEEN THE POTSDAM
AND PRE-CAMBRIAN ROCKS NORTH OF THE
ADIRONDACKS.

By H. P. Cusnine.

Contents. Introduction, p. 5; Topography, p. 6; Glacial Deposits, p. 7; Se-
quence of Geologic Events in the Adirondacks, p. 8; .Gneisses, p. 9; Grenville (Oswe-
gatchie) series, p. 10; Anorthosite intrusion, p.11; Later Gabbros, p. 11; Granite,
p. 12; Dynamic Metamorphism of the Region, p. 12; Precambrian Dikes, p. 12;
Palacozoic Rocks, p. 18; Post-Utica uplift, p. 13; Post-Utica Dikes, p. 14; Faults,
p. 14; Local Geology; Franklin county, p. 16; Bellmont, p. 16; Burke, p. 17;
Malone, p. 18; Bangor and Brandon, p.19; Dickinson, p. 20; St. Lawrence county,
p- 21; Hopkinton, p. 21; Parishville, p. 23 ; Pierrepont and Potsdam, p. 24; Calcit-
erous formation, p. 23; Dikes, p. 27.

Introduction.

The work of tracing this boundary was begun at the Clinton-Franklin
line, connecting with the writer’s work of the previous season. Thence the
boundary was mapped across Franklin county and into St. Lawrence
to afew miles west of Potsdam. It was not known to me until after my
return from the field that part of the area traversed in the latter county had
already been studied and reported upon by Professor Smyth. As the report
has not, at this writing, been published, what follows must unfortunately be
written without reference to 1t.

The country north of the Adirondacks is so heavily covered with drift
that outcrops of the Palaeozoic rocks are very infrequent and boundary map-
ping is rendered hazardous on that account. Over much of the distance the
best that could be done was to map the northerly limit of Pre-cambrian out-
crops. In Franklin county and as far west as Parishville in St. Lawrence
county. the mapping was a simple matter. The gneisses are so similar in

5

6 Repor’ oF: THE STATE GEOLOGIST.

character and in resistance to erosion that the boundary is not especially tor-
tuous, and though it is quite possible that isolated patches of the Potsdam
may occur within the gneissic area, as has been found to be the case in Essex
and Clinton counties, their discovery would require the mapping of a much
larger area,

Westward from Parishville, the Pre-cambrian rocks at the boundary con-
sist of an entirely different series of gneisses with belts of crystalline limestone.
These rocks resist erosion very unequally, and as a whole are less resistant
than those along the boundary to the eastward. The change in the topogra-
phy, which is there strongly marked, is here much less serviceable. Further-
more these rocks were profoundly and unequally eroded in pre-Potsdam time.
In the troughs thus formed the Potsdam sandstone was deposited and is yet
found in them far within the area occupied by the older rocks.* To fix
accurately the limits of the formations here will require areal mapping over an
extended territory.

No rock of younger age than the Calciferous was found in the district.
examined, the Pleistocene deposits of course excepted. Outcrops occur so
seldom that it is useless to attempt to show the limits of the formation
except in the most general way.

On the map accompanying this report these boundaries are indicated, and
the various outcrops seen are located. It must be borne in mind that the
small scale of the map makes the outcrops appear much more numerous than
is really the case. |

TopograPuy.

In a broad sense the topography of the district under consideration is
simple. The Pre-cambrian rocks come to the boundary in a succession of low
ridges and knobs which ordinarily do not protrude very greatly above the
general level, and which are separated by shallow, drift-filled depressions.
Thence northward the country is heavily mantled with drift, has little relief,
and slopes away to the north and north-west toward the St. Lawrence valley.
Only rarely does the underlying rock project above the drift, the small
streams do not cut through it, and in general the only outcrops to be seen are
those exposed in the larger streams where they are out of their pre-glacial
channels. |

The minor features of relief which characterize districts of morainic drift
(and much of it here is morainic) are here obliterated over much of the district,

more especially along the stream valleys, by the deposits of sand laid down

— oe.

* By way of illustration see Smyth’s map of the vicinity of Gouverneur. Rep. N. Y. State Geol., 1893, Vol. I, p. 493.

CusHING — PotspAM BOUNDARY. 4

upon it along the streams or the shores of the higher water levels which
accompanied and followed after the withdrawal of the ice-sheet from northern
New York.

The water-shed between the lake Champlain drainage and that direct
to the St. Lawrence, passes from north to south through Clinton county
close to the Franklin county line, till it veers to the south-westward into
Franklin county just south of Upper Chateaugay lake. On this watershed the
basal Potsdam reaches an altitude of about 1100’ A. T. Thence westward
along the boundary it decreases steadily until south of Potsdam city it
lies at an altitude of from 700’ to 800’ lower. This discrepancy must neces-
sarily be due to differential uplifting since its deposition.

The largest streams, like the Racquette, St. Regis, Salmon and Chateaugay
rivers flow in narrow valleys cut in the drift, and in still narrower rock gorges
where they are out of their old channels. They are all actively engaged in
deepening their channels and cutting back the rapids at the head of the gorges.
The gorge of the Chateaugay is, in impressiveness, second only to the Ausable
Chasm in the Adirondack region. The more westerly streams have less fall
and are not cutting so actively.

THe GruacraL Deposits.

Only general attention could be given to the drift deposits, so that the
hap-hazard observations made would not be commented on, were it not for the
fact that the deposits are of great interest and are but lttle known.

Over a wide area north of the Adirondacks the drift proper is submerged
beneath heavy sand deposits, the conditions being very similar to those pre-
vailing in Clinton county near lake Champlain. The sands are of course
mainly along the stream valleys but have considerable width on each side and
become confluent when the streams are not far apart. Moramic knobs and
ridges protrude through them here and there and cuts often show the under.
lying drift. The north and south roads in northern Franklm county and the
adjacent part of St. Lawrence county are commonly near enough to some
stream to make the roads excessively sandy, and driving over them 1s a most
irksome task. The cross roads pass over the divides between the streams and
are better. |

These sands are found abundantly at certainly three, and probably four
distinct levels and the descent from one level to another is sometimes quite
abrupt, the sand plains rising in terraces, one above another. This is well
shown just north of Malone, where the sand plain stretching north from the

8 REPORT OF THE STATE GEOLOGIST.

city terminates like a huge embankment, dropping nearly 100’ to a similar
sand plain below. The lower sands certainly represent delta deposits of the
streams in bodies of standing water. Whether that is true of the uppermost
is not so certain. What were apparently true beaches were noted at three or
four points, but no attempt to trace them could be made. These sand-covered
tracts are very level, and quite bare of vegetation, the sand often drifting
to a considerable extent.

Outside of the sand-covered areas the surface drift is largely morainic in
character. In many places heavy moraines lie in proximity to, or banked up
against the out-lying gneiss ridges. Surface boulders are numerous over most
of the district, and their extremely local character 1s worthy of remark and is
most strikingly shown along the line of contact between the Potsdam sand-
stone and the Calciferous.

In passing north from the outermost outcrops of gneiss in Bangor,
Brandon and Dickinson townships, Franklin county, one descends often into a
slight depression, then rises on to a morainic ridge with boulders mainly
of very large and sometimes of gigantic size, composed entirely of gneisses
precisely similar to those in place to the south. Practically no Potsdam
boulders are observable. The ridge is not entirely morainic, being composed
in part of modified drift. It has a variable width, reaching sometimes half a
mile. To the north of it, with an intervening depression is a much more
massive moraine whose boulders are of smaller size, and are mainly of Potsdam
sandstone, while the few gneissic boulders observable are of small size and,
when compared with the blocks on the other moraine are more worn and give
the impression of having traveled much further. The facts observed suggest
that the smaller moraine may have been formed by a local ice movement
outward from the Adirondack center after the withdrawal of the main ice
sheet. While they are far from being conclusive they certainly suggest an
interesting line of inquiry. Such a movement is perhaps @ przore to be
expected and Prof. C. I. Hitchcock has shown that a similar one took place
from the White mountains center after the withdrawal of the Laurentide
glacier.

SequENcE oF GroLocic Events in tHE ADIRONDACKS.*
1. The oldest rocks, and also the most widespread of the region, comprise a
series of gneisses of somewhat variable character and questionable origin.

Owing to profound metamorphism all trace of original structure is lost, their

*This summary of the geologic history of the region is intended merely to set forth the writer's present views
concerning that history, and is of course merely tentative, as work is really but fairly begun. These views, itis thought,
aro in substantial accord with those held by Profs. Kemp and Smyth, and the history is closely paralleled by that of the
Canadian area lying to the northward, as set forth by Prof. F. D. Adams.

PorspAm BounpDaRY. 9

CUSHING

present structure being predommantly cataclastic, though this structure is
often masked by a greater or less amount of subsequent re-crystallization.
They vary from well foliated rocks to those in which all trace of this structure
has well nigh disappeared. In texture they vary from very finely granular
rocks to very coarse varieties. They abound in quartz and pegmatite veins.
According to their mineralogic composition they may be roughly classified
in three groups.

(a2) Quite acid gneisses, poorly foliated, commonly of red color, mostly
poor in content of ferro-magnesian silicates, and with the mineralogy and com-
position of granites. They consist essentially of microperthitic orthoclase and
quartz, with magnetite always present, and with an acid plagioclase, microcline,
hornblende, biotite, apatite, zircon, and rarely garnet as accessory minerals.
A strongly absorptive green-brown hornblende is the usual dark silicate and
becomes a prominent constituent in portions of the gneiss. Biotite is an
exceptional mineral in these gneisses and even when present is always subord1-
nate to the hornblende, biotite gneisses being of extreme rarity in the rocks of
this group in the northern Adirondacks at least.

(4) Gmeisses whose main difference from those just described consists in
the predominance of microcline among the feldspars. In the field they are
often undistinguishable from the other gneisses. At other times owing to
their fineness of grain and their peculiar lilac grey or lilac brown shade on
fresh fracture, they appear quite distinct. They are so intimately associated
with, and pass so gradually into the other type that the wisdom of attempting
to distinguish them is by no means beyond question. ‘They commonly occur

in proximity to, and may belong with the Grenville series.

(c) Gneisses composed essentially of orthoclase, acid plagioclase and
augite, with accessory titanite, hornblende, apatite, magnetite and ilmenite,
quartz, garnet and biotite, in order of prominence. In composition they grade
from augite-syenites into gabbroic rocks, or from hornblende-syenites into
dioritie rocks according to the relative predominance of orthoclase or plagio-
clase. The more basic varieties, however, are more acid than the normal gabbros
of the region, their feldspars belonging to the oligoclase-andesine series, seldom
if ever becoming as basic as labradorite. The augites in these rocks are very
variable in character, ranging from a light-green, non-pleochroic diopside to
pleochroic varieties resembling aegerine-augite. The titanite is of a deep
orange color and is so constant and characteristic as to almost attain the dig-

nity of an essential constituent. Hornblende varies from complete absence to

LO Reporr or tre Stare GxEoLoGIst.

an amount considerably in excess of that of the pyroxene. Much of the
quartz present exists as inclusions in the feldspar and hornblende.

These gneisses are much more distinctly foliated than the other varieties,
due to the concentration of their dark silicates along the planes of foliation.
They pass into the others either by insensible gradation or by becoming finely
interbanded with them. They also seem to grade into the basic gabbros of
the region; at least these latter present phases practically not to be distin-
guished from them. The possible relationship between the two forms 1s one of
the most pressing and puzzling problems here presented for solution.

The gneiss series is thought to be of igneous origin and in part, at least,
of Archaean age, in the sense in which that term is used by the U.S.
Geological Survey. There are, however, certain difficulties in the way of this
view.

The magnetite deposits of the region are in this series, and, in large part
at least, in the augite-gneisses, the deposits at Mineville, Essex county,
according to Kemp, being in such rocks, as are also those of Lyon mountain
and of Arnold and Palmer hills in Clinton county.

Il. The Grenville (Oswegatchie) Series. The term “ Oswegatchie
series” was proposed by Smyth to include the coarsely crystalline limestones
and associated rocks as exposed in St. Lawrence, Lewis and Jefferson counties.”
In the writer’s opinion these rocks are so similar to those of the typical
Grenville series of Logan, and are separated from them by such a compara-
tively slight geographic distance that that term might with perfect propriety
be utilized for the New York rocks. |

This series is very heterogeneous in character. It comprises quartzose
eneisses and schists, darker colored quartzfeldspar-biotite gneisses, dioritic
and gabbroic gneisses, and occssional bands of coarsely crystalline limestone.
Graphite is an abundant mineral. Pyrite is another, aiding by its decomposi-
tion in the production of the rusty, decomposed aspect which some of the beds
present in outcrop. Sillimanite and tremolite are frequently present as is also
garnet. The rocks are cut by later gabbros and granites, and are accompanied
by belts of gneiss similar to the older gneiss, which seem at times to be inter-
stratified with the other rocks, but concerning whose real relationships we are
in doubt. | | |

For the most part the gneisses of this series differ widely in appearance
from the older gneisses, and may be distinguished from them in the field
almost ata glance. <A considerable portion seems to be unquestionably of

*C. H. Smyth, Jr., Rep. State Geologist, N. Y., 1898. Vol. I, p. 49¢.

Cusutnec -—— Potspam BounpDaARY. 11

sedimentary origin, yet has been so profoundly modified that practically all
trace of clastic structure has disappeared. The larger part of the rocks have
a very finely granulitic structure, having undergone nearly complete re-crystal-
lization. The dynamie metamorphism to which they have been subjected has
given them a foliation in common with the older gneisses, rendering the field
relations of the two exceedingly obscure.

From Parishville westward to Potsdam and beyond, the Grenville series
comes to the Potsdam boundary and may be seen to great advantage. Here,
on the western side of the Adirondacks, it differs somewhat in character from
the similar rocks to the eastward, being more widely distributed, less faulted,
less completely metamorphosed, hence with its original sedimentary character
less disguised. The distance from the great anorthosite intrusion, which has
so profoundly affected these rocks on the east, is a probable cause for these
differences.

That the eastern and western representatives are equivalent seems to be
beyond question. It is, however, quite desirable that. they should be connected

by tracing them across Franklin county.

Il. Lhe Anorthosite Intrusion. At some time after the deposition of
the rocks of the Grenville series, a great batholitic mass of the highly felds-
pathic variety of gabbro known as anorthosite was intruded into the existing
rocks. The structure of the gabbro indicates that it solidified at considerable
depth, hence the rocks with which it is now in contact must have been buried
beneath other rocks, since wholly removed by erosion. The anorthosite has
its largest development in Essex county. In Clinton county it 1s exposed
around Keeseville and on Catamount mountain and Rand’s hill. It occurs in
the eastern part of Franklin county but its extent is not known. Further

westward its presence 1s problematical.

IV. Later Gabbros. Dark colored rocks of the gabbro family, of greater
basicity than the anorthosites, occur wide-spread in the Adirondack region,
extending far beyond the limits of the anorthosites. They occur most
frequently in the form of dikes or sheets of no very great width, though
larger masses are not uncommon. In part they are certainly later than the
anorthosites, for they cut them. They may in part represent apophysae from
them, and basic peripheral portions of the intrusion, though this has not yet
been demonstrated. The gabbro at Port Henry has been described in detail
by Kemp,* and some occurrences from the western Adirondacks described by

a,

*J.¥. Kemp, Bull, G. 8. A., Vol. V., pp. 213-224.

12 Reporr or True STATE GEOLOGIST.

Smyth.* Similar gabbros have an extended distribution among the older rocks
to the south and west.

The wide mineralogic variations commonly exhibited by these rocks find
excellent illustration here, the typical gabbros grading into diorites on the one
hand, and into norites on the other. All are more or less fohated, the horn.
blendic varieties most markedly so.

Along with these rocks may well be included the narrow, dike-like bands of
hornblende-plagioclase gneiss found everywhere cutting the older gneisses of

the region, and which apparently represent ancient diabase or diorite dikes.

V. Granite. Granitic rocks are frequent in the Adirondacks. In part
they represent merely granitic phases of the basal gneisses, but in part they
are of later date. The writer has frequently found in the northern Adiron-
dacks, granites which cut across the gneisses, and Smyth has described an
occurrence from St. Lawrence county with irruptive contact against Grenville
limestone.+ Evidence of the time relation between the granite and the gabbros
is not at hand, though Smyth has described a contact where he believes the
latter to be the younger. {

The granite is commonly of red color, well jointed, unlike the gneisses,
and composed essentially of quartz, orthoclase, microcline and oligoclase, ferro-

magnesian silicates being absent, or at best only sparingly present.

VI. Dynamic Metamorphism of the Ieegion. After the time of these
various igneous intrusions the region was subjected to intense dynamic
metamorphism, whereby secondary structures were produced and the primary
ones destroyed ; the rocks were all rendered thoroughly crystalline and their
original relationships masked. That the rocks now exposed at the surface
were then deeply buried beneath other rocks, since removed by erosion, 1s
shown by the manner in which the rocks adjusted themselves to the forces
acting upon them, the adjustments being of the kind that can only oceur under

heavy load.

VIL. Precambrian Dikes. At some period subsequent to the meta-
morphism of the region, all the rocks so far described were fissured, and
through the fissures thus formed fused rock made its way toward the surface.
Along some of these fissures faulting took place. ‘That earth movements pro-
duced results of this character leads to the belief that the rocks were under

*C. H. Smyth, Jr., Bull. G. S. A., Vol. VI, pp. 268-274. Also, Am. Jour. Sci., Vol. XLVIII, pp. 54-65 and Vol. L,
pp. 273-281.

+C. H. Smyth, Jr. Bull. G.S. A., Vol. VI, p. 266.

+C. H. Smyth, Jr. Bull. G.S. A., Vol. VI, p. 270.

CuspHina — Porspam Bounpany. 13

less load than at the time of their great metamorphism, and thus a long inter-
vening erosion period is suggested.

The erupted rock may or may not have reached the surface. So far as
known it 1s found at the present day solely in dikes. These are exceedingly
abundant in the eastern Adirondacks. Though presenting considerable varia-
tion they may all be classed as diabases, and mostly as olivine diabases.

Accompanying these dikes, and having, so far as observed, the same area
distribution though far less abundant, are other dikes, ordinarily of red color,
of a much more acid rock. The writer has heretofore classed these with
the trachytes (bostonites), but they present constant differences when com-
pared with the lake Champlain bostonites, and evidence is accumulating that
they are distinct in age. They are quite numerous in Clinton county and in
the eastern part of Franklin, and have not been seen cutting any but the Pre-
cambrian rocks. While they may be nothing but representatives of the post-
Utica trachytes the writer is disposed provisionally to regard them as
distinct, and of Pre-cambrian age. They have the same general east and west
trend as the diabases, and neither has as yet been observed cutting the other.

VITt. Palaeozoic Locks. After this period of dike formation, erosion con-
tinued in progress for a considerable length of time. Then ensued a depres.
sion carrying all the peripheral portion of the Adirondack region below sea
level, where it remained during the deposition of the Potsdam sandstone and
the lower Silurian limestones, which were laid down on the deeply denuded but
uneven floor of the older rocks. |
‘The Potsdam sandstone north of the Adirondacks is of very considerable,
though unknown thickness. It is at least as much as 500’ however, and
probably considerably more. From the lack of fossils except in the upper por-
tion it 1s an extremely difficult formation to subdivide. The extreme basal
portion 1s a conglomerate, often very coarse, and also carries layers of coarse,
feldspathic and hematitic, easily rotting sandstone. Otherwise it is a quite
pure quartz sandstone, though occasionally some layers are dolomitic. The
basal one-fourth is prevailingly of red color, while the remainder is white,
yellow or brown. It grades into the Calciferous dolomites above through
passage beds, 30° to 50° thick, of alternating layers of sandstone and grey
dolomite. In its upper portion it carries an upper Cambrian fauna.

IX. Post- Utica Uplift. After the close of the lower Silurian the sub-
merged district was raised anew above sea level and was then affected by the
earth movements which caused the Green mountain uplift. But whereas the
rocks of Vermont were folded, faulted and metamorphosed by their action, the

14 Report OF THE STATE GEOLOGIST.

effect produced in New York was much less pronounced and mainly effective
in the production of faults, the rocks being only slightly folded and not
metamorphosed at all. The faults, however, are very numerous and often of
considerable magnitude. The present topography is largely due to their
presence and they have no doubt frequently served as lines of readjustment

since they were originally formed.

X. Post-Utica Dikes. During or subsequent to the time of the
dynamic movements just referred to, igneous rocks made their way toward the
surface through fissures. They are now found mainly as dikes and, as
shown by Kemp, are of two widely different types, both very basic rocks
(camptonites, monchiquites, fourchites) and quite acid rocks (trachvtes)
occurring. The basicity of the one type and the acidity of the other seem
somewhat more pronounced than in the case of the supposed Pre-cambrian
basic and acid dikes. As far as New York state is concerned, these dikes
seem confined to the vicinity of lake Champlain, not ranging westward as do

the earlier dikes.
Fautwts.

The true boundary, if its minutiae could be mapped on a large scale,
would necessarily be exceedingly irregular. The Potsdam was laid down on
an uneven floor, especially so when the Grenville series formed that floor, and
where it has been pared away by erosion down to its very base this irregu-
larity of floor must make a highly tortuous contact line. These minor details
are for the most part obscured by the drift covering. An interesting illustra-
tion is furnished by exposures two miles south of Nicholville, St. Lawrence
county, which will be described in their appropriate place.*

While some of the contacts are clearly those of deposition others are
unquestionably due to faulting. The much-faulted structure of the eastern
Adirondacks has been emphasized in previous reports by Professor Kemp and the
writer. In the district under consideration here, the evidence is less pro-
nounced, but that faults are present, and that numerously, is clear. The well
known outcrops of Potsdam sandstone along the Racquette river south of
Potsdam lie along the west side of a fault. The outlier of gneiss at Burke
village, Franklin county, seems brought up by a pair of faults. Two miles
northeast of Whippleville, Malone township, are Potsdam exposures whose
attitude is due to faulting.

—_——

*The areal results of the work are delineated, so far as may be, on the accompanying map. As outcrops of the
Potsdam sandstone are very infrequent much of the boundary as there shown can only be regarded as a reasonable
approximation, it being marked at the limits reached by the Pre-cambrian outcrops, with such aid as the topography
furnishes. Westward from Parishville its true position is quite uncertain, the conditions being much more complicated
than those prevailing to the eastward.

Cusuine — Potspam Bounpbary. 15

While the great scarcity of exposures of the Calciferous dolomites renders
hazardous any attempt to delineate the Potsdam-Calciferous boundary and to
generalize concerning structural relations, the prolongation of the north-
easterly strike invariably shown in outcrop would not connect the different
exposures, there is but little indication of folding, and a series of north-south

faults throwing to the east would furnish a satisfactory explanation of the
existing conditions.

Local Geology.

FRANKLIN COUNTY.
Belmont.

In the extreme north-western portion of ENenburgh township, Clin-
ton county, 1s a low ridge of gneiss whose edge reaches further north
than any other exposure of the New York Pre-cambrian rocks, the small out-
hier at Burke excepted. It is flanked on the north and west by most excellent
exposures of basal Potsdam, consisting mainly of massive arkose conglomer-
ates, which reach over the border into Franklin county. Thence westward
the level drops sharply into the Chateaugay valley, which is heavily drift-
filled on its eastern side, so that no rock shows, and the boundary here is
uncertain. Like so many of the Adirondack valleys, the river here seems to
occupy a fault line. On the west the river hugs the side of a ponderous
ridge of gneiss which extends northward to the town line. Somewhat more than
a mile further down stream commences the series of excellent Potsdam exposures
which culminate in the “Chasm” at Chateaugay village. Still further down
stream the overlying Calciferous shows near the mouth of Marble river. The
section here has been measured and described by Mr. Walcott.* It shows
the upper 250’ of the Potsdam, but gives no notion of the entire thickness of
the section along this line. |

Passing westward through Belmont the gneisses come up to the boundary
in a series of low ridges separated by shallow depressions filled with drift.
The gneisses consist here of the red, poorly foliated, microperthitic variety,
wlternating with dark grey plagioclase-pyroxene gneisses, in which the feldspar
is oligoclase or andesine and the pyroxene the aegerine-augite variety. The
former predominate toward the east and the latter to the west, but the two
occur interbanded in every section. There are also the usual dike-like bands
of gabbroic and dioritic gneiss. With the exception of the exposures in the
Chateaugay river but one outcrop of Potsdam sandstone was seen in the town-
ship in the vicinity of the gneisses. The exposure occurs in a depression
between two ridges of gneiss, and shows several layers of coarse, somewhat
pebbly rock, which is very quartzose and of light-brown color. Numerous
loose blocks occur wide-spread in the vicinity, some of which are of very

* Bull. U.S. G.S. No. 81, p. 343.

CusuinG — PotspamM BounDARY. 17

coarse conglomerate, though these also do not agree in color and composition
with the basal Potsdam as it usually appears. These loose blocks are mani-

festly not far removed from their parent ledge.

Burke.

In Burke township is a small and interesting Pre-cambrian outlier,
at a distance of over five miles from the main boundary. The rock is
well exposed in the Trout river at Mackenzie’s mill, half-a-mile north of Burke
post-ofiice, and thence may be traced westward for one-third of a mile, the out-
crops covering a wedge-shaped area with the apex at the mill, and the base to
the west. Both to the east and the west the rock passes beneath heavy drift,
concealing its extent in those directions, but Potsdam sandstone crops out near
at hand to the north and south. In the former direction and only 100 yards
down stream is a twenty-foot cliff of hard, yellowish sandstone, here abruptly
cut off. A half-mile to the south, at the village, similar sandstone appears in
the stream, dipping in the other direction. The accompanying section shows
the observed relations. The sandstone has the lithologic characters which
mark the middle and upper portions of the formation, and the writer sees no
way of accounting for the structural relations here exhibited except on the
assumption that the gneiss is brought up by a pair of faults.

The exposures here show a red, well-jointed, acid granitic rock composed
of quartz and microcline or microperthitic orthoclase and a little magnetite.
At the mill two large dikes constitute half the exposure. The southerly one
is of syenite porphyry and is 27’ wide with the south wall not showing.
Thirteen yards north of it is a 15’ dike of a diabasie rock which differs some-
what from the normal diabases of the region and is very coarse grained. A
few rods to the westward, in the woods, are two other dikes, both of normal
diabase, one of which is noteworthy in that it contains numerous inclusions
of the wall rock scattered through it, commonly of small size. Such

inclusions are not a common feature in the Adirondack diabases.

Iietre 1. Section north of Burke village

The occurrence of this Pre-cambrian outlier, probably brought up by
faulting, suggests interesting possibilities in the way of other occurrences of
hike nature, now concealed beneath the drift.

2

18 Report oF tHE STratTe GEOLOGIST.

Malone.

In this township the boundary pursues a_ west-south-west course
nearly to the western line of the town, when it bears away to the north along
the edge of Cornish hill, a massive ridge of gneiss which extends well up into
Bangor. As in Belmont, low ridges and spurs of gneiss protrude through the
drift along the boundary, separated from one another by shallow, drift-filled
depressions.

The gneisses are of the same general character as in Belmont. The two
extreme varieties are, on the one hand, red, acid gneisses, composed of quartz
and microperthitic orthoclase with magnetite and varying amounts of dark
green-brown hornblende, and on the other, grey, more basic gneisses, made up of
plagioclase, orthoclase, aegerine-augite and titanite, with or without hornblende
and quartz. Sometimes one or the other of these attains considerable thick-
ness, but ordinarily the two are interbanded, the bands not exceeding a few
inches in thickness, and the one rock grading into the other. The resulting
rock is therefore well banded, but neither in structure nor composition does it
give any hint of a sedimentary origin. The customary dike-like bands of
hornblendic gneiss occur in all exposures of any extent.

An interesting garnetiferous gneiss was found in the township outcropping
near the road one-half mile east of District School No. 6. It is a nearly black
gneiss and occurs interbanded with a reddish pyroxene gneiss of intermediate
composition. Garnets, which are so deeply colored as to be almost. black,
make up nearly half the rock. In thin section they become transparent in
deep yellowish-brown tones. The resemblance to colophonite is strong. A
careful qualitive test made by Prof. E. W. Morley shows the presence of
titanium in small amount, and the color is probably due to it. In addition to
the garnet the rock is mostly made up of microperthite, but holds also a little
aegerine-augite, oligoclase and quartz.

But two localities were found in Malone where the Potsdam was exposed
near the boundary. The first is along the Adirondack railroad about two
miles south of Malone, where 15’ of red, thin-bedded, feldspathic sandstone are
exposed at the south end of a cut within 100 yards of massive exposures of
red, microperthitic gneiss banded with pyroxene gneiss. The dip is in the
normal direction and is not high, 10° to N. 85° W.; the character of the
rock indicates the basal portion of the formation and there is no sign of
faulting.

The second locality is a mile and a half distant and one mile east of School
No. 6. Here ina field south of the road, lying in an embayment between

CusuHina — Potspam Bounpary. 19

two gneissic ridges and with gneiss within a quarter-mile on each side, is a
knoll of hard, well indurated, red and white banded sandstone which has been
somewhat quarried. The location of the exposure, the 25° dip and the fact
that the horizon in the Potsdam is somewhat above that of the previous ex-
posure, indicate that the presence of the sandstone here is owing to dislocation.

The higher portion of the formation is well shown in the river at Malone
and thence northward, it being quarried considerably about a mile north of
the city. Beyond, occasional outcrops are found along the river for a distance
of several miles before the Calciferous is reached near Westville. For about
half of this distance the inter-stratification of grey dolomite with the white
sandstone indicates the presence of the passage beds to the Calciferous, which
apparently occupy the centre of a shallow synclinal trough, as the north-
westerly dip beyond is replaced for some distance by one to the south-east.
The wide extent of surface underlaid by the Potsdam here is thus explained.
In the passage beds at this place are iron-grey sandy dolomites presenting a pecu-
liar appearance, and such are found to characterize this horizon throughout
northern New York. On the fresh fracture, glittering cleavage faces
are shown a half inch or more in length and dotted in a psuedo-peecilitic
fashion by numerous rounded quartz grains, giving a peculiar satiny lustre.
The thin section furnished the explanation. The rock 1s a fine mosaic of
dolonute crystals im which are streaks numerously set with somewhat
rounded grains of quartz. In the quartzose bands are frequent areas
in which the cement enclosing the grains has the same extinction throughout.
In these cases the matrix is found to be of calcite instead of dolomite. In the
sandy streaks then, rather coarsely crystalline secondary calcite has been
deposited around and including the quartz grains, its good cleavage manifesting
itself when the rock is broken.

Bangor and Brandon.

The only Pre-cambrian rocks exposed in Bangor are the gneisses of Cornish
hill which extend northward four miles beyond the average line of the bound-
ary. Following the west side of the ridge the boundary passes into northern
Brandon, then swerves to the westward and continues in that direction across
the township into Dickinson. |

The gneisses exposed are quite homogeneous and consist mainly of micro-
perthitic gneiss in the eastern, and microcline gneiss in the western half of the
township, the two having the same color and appearance and grading into one

another. Hornblende is present in variable amount in all the exposures, and

PA) REporRT OF THE STATE GEOLOGIST.

the rock is well foliated. The more strongly acid gneisses are well jointed, the
ordinary gneiss lacking this structure; the former may represent the later
eranites, decisive evidence on this point not having been found. ‘The pyroxene
gneisses, which are such a feature in Malone and Belmont, are mainly lacking
here, though they are present to some extent. Considerable gabbro-diorite
gneiss occurs together with the usual dikes of hornblende gneiss. Near the
west line of the township are widespread exposures of acid granitoid gneisses,
which alternate with masses of gabbro-diorite gneiss of considerable thickness.
The two blend into each other along their contacts.

The Potsdam sandstone makes but meagre showing in these townships,
the drift being very heavy. In the stream at South Bangor there are shght ex-
posures of a buff, hard, coarse sandstone. There is an old quarry on the
Bangor-Brandon line from which a slight amount of stone has been taken, the
rock here being white and not well indurated. One mile to the south-west the
red, hematitic arkose of the basal portion of the formation is poorly exposed
by the roadside only a few yards away from the gneisses. This was the only
outerop lying close to the boundary observed in the township.

Dickinson.

In this township the boundary trends to the south-west. In the
north-eastern corner the gneisses are well exposed at the end of a low
ridge with Potsdam sandstone close at hand to the north. The entire western
flank of the ridge is, however, so thoroughly drift-covered that no exposures
are to be found until those opened by the Deer river are reached, so that
the boundary here is uncertain though the topography indicates a position
approximately as shown on the map. <A\t Dickinson Centre and thence west-
ward to the county line and beyond, outcrops of gneiss are plentiful with, in
one case, the Potsdam in place only a few yards away. |

The gneisses in the north-eastern part of the township are for the most
part red, acid gneisses of microcline or microperthite and quartz, often coarse and
full of quartz and pegmatite veins, as is usual 1m these gneisses. With these
are narrow, sharply defined basic bands of hornblende gneiss which constitute
but an insignificant proportion of the whole.

Around Dickinson Centre and for a mile and a half eastward, the rock is
largely gabbro-diorite gneiss. This grades on the one hand into hornblende
gneiss (diorite gneiss) and on the other into a red orthoclase gneiss which
carries the same aegerine-augite and deep orange titanite which are found in

the gabbro-dioriie. This in turn gradually shades into the ordinary red

Cusnine — Potspam Bounpary. 91

granitoid gneiss of the region. These relations are well shown one-half mile
north-west, and again the same distance south of the Centre. At the latter
locality a hornblende gneiss at the base of the section grades upward into
gabbro-diorite and this in turn into red orthoclase-quartz gneiss. <A
considerable biotite content characterizes some of the gneisses here and is
worthy of note as it is not an important mineral in most of the basal gneisses.

The gradual passage of one kind of gneiss into another in this region is
not thought to possess the significance which would attach to it in an
unmetamorphosed district. It is so general, and the rocks concerned are often
so diverse that it would seem to have been produced during the metamorphism
of the region and therefore to be secondary, instead of representing an original
structure due to community of origin. North-west of Dickinson Centre quite
massive gabbro-diorite is seen passing over into red orthoclase gneiss, not
however by a gradual change but by the most minute kind of interbanding of
the black and red gneisses, both of which here have a composition inter.
mediate between that of the two extreme varieties.

One mile west from the Centre on Macomber’s farm, is aledge of Potsdam
sandstone outcropping one-fourth mile south of the road. It is red in
color and thin bedded, but hard and firm and has been quarried
somewhat for local use. It has the usual moderate dip to the north.
west. ‘lo the south it shows cut off edges, a marshy tract intervenes, then at
a distance of 75 yards appears a massive wall of red, acid, microcline-quartz
gneiss. This kind of topography prevails where the gneiss and the sand
stone are found near together and may perhaps be accounted for by the easily
erodable character cf most of the basal Potsdam. —

tuast and west of Dickinson Centre along the Deer river are heavy sand
deposits which cover considerable territory. They are on nearly the same
level as the upper sand at Malone, but probably represent deposits along
stream made by the river during its flooded condition following the retreat

of the ice sheet, while local glaciers may have still lingered in the Adirondacks.

ST. LAWRENCE COUNTY.
Hopkinton. |
The boundary pursues a nearly east and west course across this
township. It presents certain differences in character when compared with
the boundary in Franklin county, owing to the fact that the gneisses here strike
east and west so that the ridges run parallel to the boundary instead of coming
up to it, while depressions are less freyuent and cut across the strike. Out-

99 Report oF THE STATE GEOLOGIST.

crops of Potsdam sandstone are more numerous close to the boundary in this
township than in any other part of the district examined.

The gneisses along the boundary in Hopkinton are quite homogeneous
and quite similar to those already described, their main distinction being the
not infrequent occurrence of considerable biotite, this being especially true of
those in the western half of the town.* In the eastern half they are mainly
well foliated orthoclase or microcline gneisses with the usual variations in
structure and texture and in the amount of quartz present, containing also
varying amounts of plagioclase and hornblende and sometimes biotite. The
usual bands of diorite gneiss occur plentifully. In an exposure on the Meacham
farm, two miles south of Nicholville, 1s a dike-like band only 18 inches wide
cutting the gneiss, and this furnishes the best and least metamorphosed speci-
mens of the basic, ophitic gabbro which the writer has yet seen in the
Adirondack region.

The Potsdam, as exposed in the township, possesses considerable interest.
Near the roadside at the Meacham farm and near the gabbro just discussed
are the outcrops mentioned on a previous page, + a low knoll of very coarse,
rotten, acid gneiss crossing the road, followed to the south at a distance of 15
yards by exposures of a coarse, feldspathic conglomerate which disintegrates
with great readiness. The conglomerate is composed of debris from the
eneiss and occupies a depression in its surface, as gneisses appear again in
force a short distance further south.

One mile to the eastward, on a lane running south from the main road,
is an old quarry opening in a single ledge which protrudes through the drift.
The rock is a well laminated, coarse sandstone, in white and buff or brown
colors, and has the abnormal dip of 18° to 8. 20° . It seems to represent an
horizon well above the base of the formation and its attitude suggests disloca-
tion. It lies, however, in a wide depression with no other outcrops near
at hand.

One and one-half miles west of the Meacham farm exposures and less than
two miles south of Hopkinton village, a ledge of red, feldspathic sandstone, con-
taining also much magnetite sand, is well exposed by the roadside and for some
distance to the westward, with the normal low dip to the north-west. Only
ten yards south of it and parallel with it on the west, is a ridge of very coarse
acid gneiss. There is no evidence of faulting between the two. One mile to
the northward is Budd’s quarry where a firm, red stone, often prettily banded

* As Professor Smyth is engaged in a detailed study of the Pre-cambrian rocks of St. Lawrence county, they will be but

briefly referred to here.
t+ Page 14.

CusuHine — Porspam Bounpary. 23

with white 1s opened and has a considerable local use. White sandstone
is exposed by the river at Nicholville, and near Fort Jackson much quarrying
is done in white and buff sandstone. Westward from this line of outcrops no

Potsdam was seen in the township.

Parishville.

In this township the boundary at first bears to ‘the north to enclose
the massive but low ridge of gneiss lying to the northward of Parish-
ville village. The exposures are excellent and show a well foliated gneiss of
intermediate composition, for the most part with a considerable bi-silicate
content which is usually hornblende. This is sometimes replaced by a
pleochroic augite. Biotite is also a prominent ingredient and a little muscovite
shows in some of the shdes. The predominant feldspar 1s plagioclase, either
oligoclase or andesine, but orthoclase, microcline and quartz are present in
considerable amounts.

Just to the westward of Parishville village, the Grenville series comes to,
and forms the boundary. Rocks which unquestionably belong to that series
are separated by ridges of gneiss of uncertain relationship, but these excepted,
the Grenville series remains at the boundary as far as the work was carried.
The unequal resistance to erosion presented by the various members of this
series, coupled with the fact that the general altitude of the country 1s much
below that to the eastward so that erosion does not go forward so rapidly,
combine to render the boundary very uncertain, both because of the exceed-
ingly erratic distribution of the Potsdam and because it rarely shows in
outcrop. | :

‘hese rocks will be described by Professor Smyth. It may be said in gen-
eral that the gneisses in this’ series differ from the older gneisses in being for
the most part much more finely and evenly granular and in having, in many of
the beds, abundant biotite as the only ferro-magnesian mineral.

The Potsdam was found exposed in but two localities in the township,
both along the brook which empties into the river one mile west of Parishville.
The best exposures are about a mile up the brook and consist of coarse sand-
stone of medium induration, striped in white and flesh color, or white and buff.
The other outcrop is further north where the road from Parishville to
Parishville Centre crosses the brook, and the exposure is but meagre. These
rocks lie in a trough ereded in beds of very quartzose gneiss which oppose but
feeble resistance to degradation. Sufficient data were not obtainable to admit

of determining whether the Potsdam owes its present position to faulting or

24. REPORT OF THE STATE (GEOLOGIST.

to original deposition. It is quite possible that it reaches further south than
is indicated on the map.

To the southward, in Colton, crystalline limestone outcrops In association
with the gneisses which here appear. One mile south of the main Potsdam
exposure, the brook shows an excellent section of the quartzose gneisses on
each bank, along with some curious rocks of very uncertain origin, and in any
event profoundly changed from their original condition. The exposure 1s

mentioned here as it is of great interest, yet is an easy one to miss.

Pierrepont and Potsdam.

The boundary so far as traced in these towns 1s shown on the map
accompanying this report. More detailed areal work would probably
necessitate considerable changes as the relationships here are complicated,
and the drift very heavy. The rocks of the Grenville series are well shown
and possess great interest.

The Potsdam sandstone in the vicinity of Potsdam shows features of
importance, and the accompanying map (Figure 2) has been prepared to show
in detail the conditions along the river south of the city. Both east and west
of the city the Grenville gneisses reach as far, or nearly as far, north as the
city itself. They are even found in the city itself. But the river valley 1s so
heavily encumbered with sand deposits and other drift that the limits reached
by these rocks are completely hidden. Along the river, however, outcrops ot
Potsdam sandstone are found for a distance of six miles south of Potsdam,
and probably extend still further in the same direction. The structure
is sufficiently well shown to prove that it owes its position and attréude to
faulting. |

Northward from Potsdam, the upper beds of the sandstone are shown along
the river, with the customary low north-westerly dips, followed by the passage
beds, and, just below Norwood, by the Calciferous. These are all with the
same dip, and manifestly in a continuous and undisturbed section. At Pots-
dain, as shown by N. TH. Winchell, gneisses of the Grenville series outcrop in
the river and in the city itself.* The heavy drift covering east and west
prevents tracing this rock to any connection with Grenville exposures in those
directions, but it seems most probable to the writer that it is brought up here
by afault. The absence of allthe lower portion of the Potsdam formation in
the exposures to the northward, and the high dips and disturbed character of

* Geol. Surv. Minn. 21st Am. Rep. pp. 103-104.
These outcrops were not seen by the writer, but a letter just received from Professor Winchell verifies the statements
made in his report. The presence of this gneiss is the cause of the rapids in the river at Potsdam.

Cusning —- PorspAm BounpbDaARY. 95

the exposures of the same formation to the southward harmonize with this
view.
At Clarkson’s quarry, three miles south of Potsdam, the rock 1s a firm

red sandstone which is so cross-bedded and jointed that it 1s not easy to
make out the true dip, which is, however, somewhat to the south of west.

Crarkson's que

Merritt quarr

Nee

SS Sh
5 WRAY
Be BAS \
K 50° ” $0
N 20° WwW. Vv Yo °F

FigurE 2. Map of a portion of Potsdam and Pierrepont Townships.
The lithologic character of the rock suggests an horizon low in the for-
mation. A short distance further south, at Merritt and Tappan’s quarry,
the flesh-colored stone is banded with white and the structure is synclinal,

as shown by N. H. Winchell.* Nearly a mile further south are excellent

* Loc. cit. p. 101.

96 REporRT OF THE STATE GEOLOGIST.

exposures at Hanawa Falls, where the rock is prevailingly red and massive,
the dip to the south-west has been resumed, and the horizon seems
much the same as at Clarkson’s.* Still another mile to the south is Elliott’s
quarry where the rock is light colored, being merely tinged with red. The
dip is still to the south-west though here it is quite low.

One-fourth mile further south are most interesting exposures on both
sides of the stream, at the site of an old mill. The west bank is formed of
Potsdam sandstone, here of white color and with a south-west dip. It must
lie higher than the rock at Elhott’s quarry, and apparently is at a higher
horizon than any other seen south of Potsdam. The east bank of the stream,
which is here only a few rods wide, is composed of rotten pyritiferous, quartz-
ose gneisses, much stained by hematite in their upper portion, which belong
to the Grenville series. The river just here is clearly occupying a fault line,
to the presence of which the disturbed character of the Potsdam is due.
Drillings for hematite ore not far east of the river, show apparent Potsdam
conglomerate overlying the Grenville rocks, so that the throw of the fault is
probably not excessively great.

To the west of Potsdam is a great development of kame and drumlin-
like drift hills. he boundary indicated on the map merely connects the most
northerly Pre-cambrian outcrops seen, and in the absence of Potsdam outcrops
to the northward, must be regarded with considerable suspicion. The only
exposure seen was a meagre one at West Potsdam.

The Calciferous Formation.

No attempt to make a section of the Calciferous was undertaken. With
one exception all the outcrops seen were in close proximity to the Pots.
dam and merely represent the basal portion of the formation. The rock
exposed is a hard, iron-grey, often sandy dolomite, occasicnally with nodules
of coarsely crystalline calcite, and quite like the layers of dolomite in the
passage beds. |

In the Racquette river north of Norwood near the Norfolk-Potsdam
line, the rock exposed differs somewhat from the foregoing, being a quite
pure blue dolomite. One layer in particular is quite fossiliferous though the
fossils are not easily obtained in good condition. Quite a variety of forms are
present here, including species of Asaphus, Orthoceras, Nautilus, Pleurotomarta
and a httle Murchisonia which is identical with the species occurring in
the Ophileta beds at Beekmantown, Clinton county The locality is at the

* Ibid. p. 104.

Cusuine — Potrspam Bounpary. 27

bridge over the river on the town line. It seems further south than the one
mentioned by Winchell and from which his party obtained fossils.* The horizon
can not be far above the base of the formation, if undisturbed.

Dikes.

In following the boundary across Franklin county, eleven dikes were noted
cutting the Pre-cambrian rocks. These were all in the eastern half of the
county. In St. Lawrence not a single one was seen in the belt examined, and
Professor Smyth’s work shows them to be rare in most of that county. In the
eastern Adirondacks they are exceedingly abundant and the same is true
further westward at the Thousand Islands as described by Smyth, who has
demonstrated them to be there of Pre-cambrian age.+

Of the eleven dikes, ten were of diabase and one of syenite porphyry.
Nearly all the diabases contain olivine. One of them is noteworthy in that it
contains frequent large phenocrysts of a light green, almost non-pleochroic
orthorhombic pyroxene, probably enstatite, a mineral not of common occurence
in diabase. |

A more detailed description of the dikes will be printed elsewhere.

* Minn. Geol. Surv., 2ist Ann. Rep., p. 109.
i Trans. N. Y. Acad. Sci., Vol. XV, p. “«L.

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