METAMORPHIC ROCKS. 
483 
lage and hornblende rocks. The limestone is extremely impure from contained minerals, so 
that it would scarcely be recognized as limestone from its external aspect, when weathered, 
by one not familiar with all the protean forms of this rock ; the calcareous matter being re¬ 
moved to some depth, and the imbedded mineral substances remaining to form a crust of 
some lines or even inches in thickness exterior to the sound unaltered rock. Granite occurs 
in the cliff a few yards to the east, which contains imperfect crystals of black tourmaline.* 
6. An outheaved mass, as it is supposed, of this range of limestone, occurs about a mile 
north of the last locality, near the Beverly dock (the point from which the notorious and 
treacherous Arnold made his escape). This bed of limestone, which is small, lies transverse 
to the general direction, viz. northwest and southeast. The limestone is colored with serpen¬ 
tine, and contains plumbago ; but some of it is of a pure snow white, strongly translucent, 
and varies in texture from coarse crystalline to compact, like the finest alabaster. The white 
is much intermixed with augite and quartz, so that specimens for the cabinet can be obtained 
showing the characters indicated, but not large masses. The associated rocks are mica¬ 
ceous pyritous gneiss, and grey augite containing hexagonal plates of plumbago. A vein of 
pyrophyllite, six inches to a foot wide, traverses the grey augite rock. 
7. Some distance below the Cotton rock, perhaps one quarter to half a mile, the limestone 
bed that we have been tracing, forms the shore for some rods. The same minerals are found 
here as at many other parts of the bed, viz. magnetic oxide of irori, serpentine, and augite 
and hornblende in the vicinity, associated with granite and gneissoid rocks. A little farther 
south the limestone has an old mine hole in it, a little southeast of a small bay of the river 
shore, where the rock contains much magnetic oxide of iron. 
8. From this place, the limestone ranges south-southwest towards Anthony’s Nose point. 
This part of the range is perhaps of more interest to the geologist than any other portion, 
and particularly the tract of land between the “ old silver mine,” as it is called, and the Hud¬ 
son river, about a quarter of a mile in width. The limestone and all the associated rocks 
here, have been subjected to metamorphic agency in a high degree. 
The limestone lies at the base of the hill, adjacent to a granitic rock. It is white, highly 
crystalline, contains much mica, plumbago and various mineral substances. The plumbago 
is generally diffused in minute particles, but in some places is so abundant as to give a bluish 
tinge in streaks through the rock. The resemblance of this mineral thus diffused to the sul- 
phuret of silver in minute particles, its softness and lustre, led to the idea that silver ore was 
abundant at this place. 
This mine was opened in ancient times, for what purpose is not.known. Stalactites are 
found in the adit level, which is two hundred yards long, and old tools with the handles rotted 
* The Cotton rock is a noted place in the Highlands. It is on the shore of the Hudson, in Phillipstown, between high and low 
water mark, about three and a half miles below West-Point. The rocks here are impure verd antique (composed of limestone 
and serpentine, with brucite and other minerals imbedded), serpentine with diallage and veins of asbestus and delicate silky 
amianthus, diallage rock, augite rock and granite. The amianthus which comes from the veins in the serpentine, has the appear¬ 
ance of cotton or of raw silk, and has given rise to the name “ Cotton rock.” 
61 * 
