In selecting specimens of serpentine, care should be taken to procure that which is the most translucent, and that holding miniature veins of asbestos.  These are not so plentiful as those of the pure serpentine alone, but occur in the southern end of the main quarry.  The width of these veins of asbestos is seldom over an inch, but those of even much less are highly prized as specimens.  These veins of asbestos are, in places, several inches in length, but are generally much broken in removing them, as their fibrous structure, at right angles to their length, makes them very fragile, and pure specimens of asbestos can seldom be found.  However, they make much finer specimens when with the serpentine.  Frequently these specimens may be obtained with a layer of gurhofite above them, and separated by the serpentine; this assortment is very interesting, revealing to us the manner in which they were formed, which was by a process termed segregation.

This gurhofite, called bone by the quarrymen, occurs in white, dense looking masses, intermingled with the serpentine, especially in the upper end of the quarry, where veins six and eight inches in thickness are abundant, and from which specimens may be readily obtained showing the fibrous structure of the gurhofite and the association with the serpentine, to which it is found attached; it is quite different from the limestone in appearance, and need not be mistaken for it.

Phlozopite.—­In a vein near the lower end of the quarry, near the asbestos locality, occurs large plates 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.