644 GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



streams, uniting in the bottom of the drained lake, completed the erosion of 

 the present sinuous course of Fort River, across the drift area south of the 

 college, apparently to a level somewhat lower than the present bed of 

 the river, without striking rock, for the stream now flows over a muddy 

 bottom, and there is no trace of the sheet of bowlders which it must have 

 concentrated out of the till. It has, however, sufficient slope for a water 

 power, and the ponding back may have caused it to cover this up, as below 

 the dam it flows over a bottom of coarse bowlders. 



THE HIGH TERRACE OR BENCH ALONG THE WEST SIDE OF AMHERST KIDGE. 



So long as the water passage from the main basin into the north end 

 of the East Street basin was open, and the sands of Cushmans Brook (or 

 Mill River) were carried down along the flank of the Pelham Hills, the 

 work of the lake waters along the west side of the Mount Pleasant block 

 of hills, and along the west side of College Hill, and its prolongation north- 

 ward to the head of Prospect street, and of Mount Doma farther south, 

 consisted mainly in the concentration of a coarse, well-washed and well- 

 rounded beach gravel out of the till, of which all these hills are composed. 



Because of the narrowing of the channel by the hills named above, 

 and by Mount Warner, farther west in mid-channel, the current was here 

 somewhat accelerated, and, aided also by the prevailing west winds, wore 

 with exceptional force into the hillsides along the line we are now trac- 

 ing, cutting deep into the till along the 300-foot contour, or a little lower, 

 as the eff'ective erosion level was often somewhat below the highest water 

 stand, and forming thus a broad horizontal or outwardly sloping bench in 

 the till, over which sheets of the concentration gravel spread in bars and 

 low ridges. 



The exceptionally steep slope above the 300-foot contour, often, indeed, 

 slightly concave, which I have called the horizontal fluting, is best devel- 

 oped along the west flank of Mount Pleasant and its continuation north 

 past the Plant House and through the chestnut woods farther north. All 

 the plain south of the Plant House has been formed thus by erosion, and the 

 hill formerly extended here as far west as the new road to North Amherst 

 aci'oss the College farm. 



The gravel spread over this plain in great sheets has been largely used 

 for sidewalks, taken mostly from the pits just south of the Plant House. 



