Transverse Section of Rock Strata from Hoosack Mountain to Eleven Miles East of Connecticut River.
Williams' College is situated in a valley, having on the west the hills of the Taconick[48] range; on the east, Saddle Mountain, which separates it for the most part from Adams; and on the north, and northeast, two hills which belong to the southwestern part of the range of the Green Mountains. Hoosack River, rising several miles at the southeast, and passing through the northeastern part of Williamstown, winds its course northwest, to the Hudson. It is an inconsiderable stream, about six rods in width, and its current is rapid. From the south, runs Green River, a smaller stream, and enters the Hoosack one mile northeast of the college. The green colour of this stream, appears to be caused by a magnesian clay, which is washed from its banks at the south part of the town. At the west is Westbrook, rising in Williamstown, and entering the Hoosack one mile and a half northwest of the college. The soil in this whole tract is generally clayey, rather light for such a soil, and very rich. A gravelly soil appears in a few places, especially at the northern part. The interval on the Hoosack extends only a small distance from its banks, rarely exceeding, and often much less, than half a mile, and presents the common appearances of alluvial land. Rising from ten to twenty feet above this interval, the soil is in various places filled with rolled stones of quartz and limestone, as if the Hoosack had once been much above the banks which confine it at present. It is not improbable that its waters were formerly intercepted by the hills in Pownal, five miles at the northwest, forming a small lake in this valley.
The hills of the Taconick range, (A[49]) on which passes the line between Massachusetts and New-York, have generally an elevation from twelve hundred to fourteen hundred feet; Pownal Mountain (B) on the north, about fourteen hundred; and Oak hill (D) on the northeast, twelve hundred feet above the east college (C.) Saddle Mountain (EF) is an insulated mass, separated from the Taconick range by the valley of Williamstown, and from Hoosack Mountain, by the valley in Adams. It lies about south southwest, and is nearly eight miles in length, and two in breadth. It is composed of two ranges, the eastern and highest (FG) being in Adams. The mountain has its name from two of its peaks, which present at a distance the appearance of the two elevations of a saddle. The west range (E) is divided into two parts quite to its base, which with the slope of the east range encloses, on three sides, an irregular hollow, called the Hopper.(H) The northern part (E) of the west range is nearly two miles in length, and rises to the height of eighteen hundred feet; the southern (I) rises abruptly into a peak of the elevation of seventeen hundred feet. The height of the valley between the two ranges is about fourteen hundred feet. You enter the Hopper from the west, passing along a branch of Green River, and a romantic, wild, and sublime prospect opens before you. Nearly east of the entrance into the Hopper, lies the highest point of the Saddle, familiarly called Gray Lock, (F) being about twenty-eight hundred feet above the college, and probably four thousand feet above the tide-water of the Hudson at Troy. This is the highest land in Massachusetts. About two miles north northeast, is the northern peak (G) elevated twenty-three hundred feet. The valley in Adams is bounded on the east by Hoosack mountain, (K) elevated from fourteen hundred to eighteen hundred feet, and extending several miles west of south: it forms a part of the range which commences at West Rock in Connecticut.
The country included in this sketch is principally primitive; lying on the west of the summit of the primitive range, which passes southerly into Connecticut. The rocks and minerals will be mentioned in the following order.
1. Granite. A few pieces have been found at the foot of Oak hill, one mile northeast of the college. It consists principally of feldspar. Four miles east, are large masses of granite on both sides of the Hoosack, and on ascending Hoosack mountain they become more numerous. The principal part of this is quartz, often of a purple colour; the mica black, and the rocks exceedingly hard. I have never noticed any minerals imbedded in it. The vortex of Pownal mountain is also granitic.
2. Gneiss and Mica Slate. I connect these two, because they are not often distinct, and appear to pass into each other. They are found in large strata on Hoosack Mountain, on a hill (L) connected with Saddle Mountain, and on the east side of Saddle Mountain. The highest and the west ridge of Saddle Mountain are mica slate. The Hopper shows the inclination of the strata quite to the base of the mountain. The inclination is to the east and northeast, from ten to forty degrees. On the southwest mountain of Saddle, the strata are bare to the summit for a considerable distance, and are very fine grained mica slate, having somewhat the appearance of a soapstone slate. By this name they are called in Mr. Eaton's Index to Geology. Some of the rocks appear to be talcose. I have been able, however, to detect but a very minute quantity of magnesia in any specimens I have tried, though I obtained a considerable proportion of alumine. The higher hills of the Taconick range are composed principally of a similar slate, lying in the same direction, and with similar inclination; but it appears to have passed still farther from mica slate. At the northwest corner of the state, which is near the foot of the ridge in this place, the rock is very similar to some of that on the southwest mountain mentioned above. About a mile northwest of this corner, the rocks are cleft in several places, and in one, to such a depth, that the snow and ice remain here through the year. The Snow Hole (M) is about thirty feet long, and nearly as deep at the east end, ascends to the west, or towards the summit of the ridge, and is from ten to twenty feet wide. When I visited it in June, the snow was six feet deep on ice of unknown depth. The rock is here passing into argillaceous slate; and in many places it becomes argillaceous and chlorite slate. For the other rock, you have, I believe, proposed the name talcose slate.
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.
4. Granular Limestone is abundant at the Cave or Falls, in Adams, and on both sides of the Hoosack. The Cave or Falls, (O) is a singular chasm between limestone rocks. A small stream, which appears once to have run on the surface of the hollow between two small elevations, has now worn a passage many feet in depth through the limestone. The chasm is narrow, winding in its course several rods long, and its opposite sides were connected, till four years ago, by a natural bridge of limestone. From the bridge to the water is 70 feet. There is a dark cavern of several feet diameter, and some passages into the rocks. The white marble walls, the foaming of the water below, the piles and irregularity of the rocks, and the thick overhanging trees, make the scene very wild and interesting. The limestone rests on mica slate. On the west bank of the Hoosack, and east base of the hill, (L) the same coarse-grained and white limestone is found, resting on the mica slate at the west of it.
At the north and west base of Saddle Mountain, (E) and at a less elevation than the quartz, are extensive strata of limestone, inclining the same way as the mica slate of the mountain. It is less distinctly granular, and less white than the other, but belongs to the same rock. It forms tolerably good marble. Between the strata are crystals of carbonate of lime, rhomboidal, and tending to the lenticular form. Some of these strata appear to be composed of blended crystals of this kind. In one place are strata of several rods in length and breadth, which are inclined to the southwest, and thus lie against the mica slate of the mountain. The inclination is about forty-five degrees. Unless this limestone be connected with that on the east of Saddle Mountain, (and no connexion has yet been traced,) it must be considered as lying on both sides of the mica slate, or alternating with it.