520 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



It would be tedious to detail all the observations upon wiiicli this descrip- 

 tion of the present surface of the rocky substratum of the valley is based. 

 One may trace on the map the crystalline rocks emerging from below the 

 sandstones of Mount Toby and appearing at the surface in scattered out- 

 crops southward to South Amherst, and the same thing may be seen, 

 though less clearly, south of Mount Warner. At East street a well 50 

 feet below the lowest ground there failed to reach the ledge, and at the 

 Northampton bridge piles were driven in the clays 110 feet below low 

 water of the river without reaching bottom. 



The most remarkable eflfect upon the present contour of the basin of 

 this general erosion of the ice was in excavating hollows so deep and capa- 

 cious that — especially where they lay aside from the direct line of the cur- 

 rents of the floods in the subsequent period — they have remained only 

 partially filled to the present time, notably in the case of the East street val- 

 ley and the southern part of the middle de))ression, wliich lies west of the 

 village of South Amherst. 



South of the Holyoke range the protecting influence of the ridge is as 

 plainly seen as its agency in reenforcing the power of the ice on its nortli 

 and west, and the sandstones stand much higher and appear abundantly 

 above the surface of the later deposits and doubtless make a continuous 

 substratum for the latter, while north and west, I imagine, the erosion 

 over much of the deeply covered area must have cut down through the 

 sandstones to the crystalline rocks below. 



The low rock-floored valley bottom, everywhere nearly at and often 

 much below the present river level, stretching across from the Pelham Hills 

 to the western line of Noi'thampton and broken only by the Amherst ridge 

 and Mount Warner, not only sent a lobe southwardly through Easthampton, 

 but another of exceptional depth up through the Deerfield Valley to the 

 north line of that town, which was continued still farther north in a strange, 

 narrow depression running up the west side of Greenfield and ending 

 abruptly at its north line — a depression which was left unfilled in Cham- 

 plain time. 



North of Mount Toby the Montague basin would be also largely 

 increased toward the north by the removal of the drift. The immense 

 sand desert between Millers Falls and Turners Falls and all the hills 

 except one that rise above it would be removed, leaving a great depression, 



