130 
GEOLOGY OF THE FOURTH DISTRICT. 
Above the village of Fredon this rock is seen in all its varieties for half a mile on Mud 
creek ; and along the line from Manchester to that village it approaches the surface and could 
easily be obtained in any required quantity. Thence it extends west to the quarries in Men- 
don, though the surface of the intervening distance is mostly covered with deep alluvium. 
At Mendon the strata of this division are exposed in the bed of the stream below the falls. 
There is also a quarry a few rods below the village, where the stone is wrought for build¬ 
ings, step-stones, and other purposes. At Tinker’s, near the west line of the town, this rock 
crops out on the side of a hill, and it has been extensively quarried. This point offers a good 
exposure of the rock ; the strata are from half an inch to eighteen inches thick, generally 
from four to eight. The higher layers for about five feet are thin and argillaceous, of a light 
grey color. Eight feet below the surface is a bed which is very soft and porous, crumbling 
rapidly on exposure to the air. The greatest depth penetrated is twenty-five feet; the lower 
layers are the hardest, some of them having parallel seams of siliceous matter like agate, ex¬ 
tending through them ; and all of them are more or less of this character. 
The vertical striated surfaces, supposed to be caused by the crystallization of sulphate of 
magnesia, (the lignilites of Prof. Eaton,*) occur both in this quarry and at the village of 
West-Mendon. These vary from a scarcely perceptible seam or suture in the rock to a 
columnar mass several inches in length. Jn some instances these columns are curved as if 
the action whatever it may have been, operated more powerfully on one side than the other- 
The following woodcut illustrates an example of this kind, where a single fascicle is curved, 
while the others in the same specimen are straight. 
52. 
These striated surfaces in this part of the salt group differ from those in the Niagara linve- 
Canal Rocks, page 134.. 
