484 
GEOLOGY OF THE FIRST DISTRICT. 
out have been found in it. It was reopened some years ago, with the hope of getting silver ; 
the man who worked it having been told that the scales of plumbago in the rock were sulphu- 
ret of silver. He is said to have spent all his property, and to have died in a mad-house. 
Sphene and zircon are occasionally seen in the augitic and calcareous rocks at this place, 
but they are not common. 
The most interesting mineral substance in a geological point of view, found at this old mine, 
is quartz. It is strongly translucent, almost transparent like hyalite, in irregularly round 
masses from the size of filberts to that of an egg. They seem to have been melted to as¬ 
sume their present form. The first public notice of such facts, so far .as I know, was by 
Prof. Emmons, in the Second Annual Geological Report of New-York, 1839, p. 202. I had 
observed the rounded, apparently fused quartz at the opening next the marsh, near the south 
end of the adit level of the “ Old silver mine,” in 1825 ; but did not consider it of any spe¬ 
cial importance as connected with the age of these rocks, until the subject was brought before 
the public by Prof. Emmons. The spinelles of some localities in Orange county have their 
angles rounded, and contain spheric.^! cavities, apparently produced by the same cause ; and 
the crystals of phosphate of lime, sent me by Dr. Crawe and Prof. Gray, from St. Lawrence 
county, have their angles rounded, and contain cavities which seem to be referable to the 
same agency that has caused the crystallization of the limestone, and the formation and crys¬ 
tallization of the plumbago, and various minerals in these rocks. 
The rocks at this locality of the “ Old silver mine,” are well worth studying. The rock 
next the limestone on the west of the adit, is composed of augite and manganesian garnet; 
sometimes one, sometimes the other predominating. Both are crystalline, and sometimes exhi¬ 
bit perfect crystals. The garnet and augite frequently assume the granular form of colophonite 
and coccolite ; red for the first, and green, brown, and purple for the latter. The rock is very 
heavy, and very similar to some of the beds at Rogers’s rock on Lake George. 
The rock farther west, is a gneissoid silico-felspathic rock, containing in many places mag¬ 
netic oxide of iron in grains, and in small strings and veins parallel to the strike of the rock ; 
also schorl in masses of quartz, and sometimes crystals of allanite like those near Fort Mont¬ 
gomery. 
Still farther west is a range of limestone, very similar to that at Cotton rock, but purer. 
It contains an abundance of imperfectly characterized brucite. Gneissoid rocks intervene 
between this bed and another of limestone seen still farther west, which has the general cha¬ 
racters of verd-antique, being composed principally of limestone and serpentine ; but it con¬ 
tains other minerals that are hard, and would prevent its being sawed easily. This rock is 
seen at the south point (called Marble point), and a few rods south of the north point of this 
neck of land. Granite is frequently seen interlaminated among the strata described, which 
are about vertical. The gneiss along the shore between the two last masses of limestone, 
and west of the last mass described, along the shore, contains pyrites, and by its decomposi¬ 
tion gives a reddish tinge to the rocks. The same character, and arising from the same cause, 
is seen in the slaty and micaceous gneiss along the shore, most of the distance from this place, 
north-northeast to Gouverneur’s landing opposite to West-Point. 
