3. _Quartz._ Though quartz is scattered through all the preceding rock in masses of different sizes, it is found in great quantity on the northeast part of Saddle Mountain, 300 or 400 feet above the college, and thence to the Hoosack along the side of the hill (L.) It is granular, often white and translucent, and often coloured with oxyd of iron. It forms _Stone Hill_, (N) a mile southwest of the college, on the vertex of which is argillaceous slate. This hill slopes to West Brook, where quartz often forms perpendicular banks from 50 to 100 feet high. Here also argillaceous slate rests on the quartz, as well as on the vertex, and on the east side of Stone Hill. Quartz appears again on the opposite side of West Brook, but further north, on a hill connected with the Taconick range. On these two hills, it lies in large strata, inclining, like the mica slate, to the east and northeast, often divided by veins into rhomboidal masses. On the east side of Stone Hill, it is more granular, and may perhaps be called _arenaceous quartz_, containing a larger proportion of iron. Near the base of Hoosack Mountain, similar quartz is found, which extends round the north side of the Hoosack to Oak Hill, (D) which is wholly composed of it. It lies in rounded fragments, called _hardheads_, through the northern part of the valley, and on the sides of Oak Hill in huge rocks, presenting nearly perpendicular fronts from 20 to 50 feet in height, and many rods in length. The strata are in some places horizontal, and in others nearly perpendicular. In one place it forms plates, from 2 to 5 feet on a side, and from half an inch to several inches in thickness, which are nearly perfect rhomboids, the edges never being perpendicular to the sides. Most of the quartz, except the white, yields a small portion of lime, and has been called _calcareous quartz_. _Greasy quartz_, _rose quartz_, hornstone, and _rock crystal_, are occasionally found; the last in considerable quantity south of Stone Hill. On the stream which issues from the _Hopper_, is arenaceous quartz of a slaty structure, which is an excellent stone for sharpening the _chisels_ used by _stonecutters_.