of this mineral, which is a
variety of mica, and has all of the characteristics of a pure silvery
white color, and from one by three inches in area to less. It is easily
separable in folia, and cannot be confounded with any of the other
minerals. A huge mass of the veinstone holding abundance of this mineral
is exposed, whence it may be plentifully obtained in excellent crystals.

_Pyrites_.--White and yellow iron pyrites are abundant in the gneissic
rock adjoining the limestone, and frequently very fine, perfect crystals
may be found handsomely dressed upon the rock. There is no particular
portion of the quarries in which they abound.

_Biotite_.--This is a variety of mica in small crystals, of a dark brown
color, and quite plentiful in the gneiss inclosing the veins of
limestone. Up in the older quarries it is more abundant; on the north
wall of the vein it is often in very fine specimens, and there even in
large number, in a locality, generally a pocket in the gneiss.

_Tremolite_ is quite abundant on a large mass of limestone in the
extreme upper quarry, which is a short distance east of the main one,
over a small hill. The tremolite occurs in white crystals, about a
quarter inch in width and from a half to three inches in length. The
crystals are opaque, but very smooth and glistening, lining cavities in
this mass of limestone. It is a variety of hornblende, composed of
silica, lime, and magnesia, with a little alumina. It probably occurs in
places in the vicinity of this block, and in finer specimens, as these
are frequently, when near the surface, much weathered and worn. This is
a characteristic granular limestone mineral, and a very interesting one.
We will again meet it when examining the New York city localities.

_Aragonite_ occurs in very small masses, of a light yellow color and
fibrous structure, between layers of serpentine. When they are separated
by a small interspace, as it frequently is, the fibers are very large,
coarse, and brittle, and thus do not resemble asbestos, although in some
instances they might be mistaken for picolite, but, distinguished from
it by effervescing on contact with a drop of acid, as it is a carbonate
of lime, and also containing a trace of iron. I have never seen any fine
specimens of it from this locality, but deeper down in the rock it may
occur in greater profusion.

Dolomite occurs to a limited extent as such; most of it, being in the
form of gurhofite crystals, may