558 GEOLOGY OF OLD HAMPSHIRE COUNTY MASS. 



The lower sand l^ed inaintaiued a constant thickness for 450 feet east 

 and west, going below the surface at the east end of its exposure and dis- 

 appearing at the end of the cutting (opposite the northeast corner of Col- 

 lege Grove) with the same thickness. It agreed in all particulars with the 

 lower sand in the cellar section above. 



The upper layer of sand was exposed for 325 feet east and west, 

 measured back from the end of the cutting. It is greatly contorted and 

 twisted in every conceivable way into the upper layer of till, and in one 

 place it is wholly interrupted for 65 feet and appears in long patches and 

 filaments of sand, one above the other, in the mass of the upper layer of till. 



At one place also a third layer of sand is intercalated in the mass of 

 the till halfway between the two more extended layers of sand, with a thick- 

 ness of 3^ feet and a length of 80 feet, and ending abruptly. This seems 

 also to have been a great slab of frozen sand from the lower bed, while the 

 extent of the upper bed here makes it possible that there were two inde- 

 pendent sand beds deposited, which it did not seem necessary to assume 

 from the former sections. 



THE UPPER TILL. 



I have called the stratum below the interglacial sands the first till, as 

 the product of the first glaciation, and that above the second till, it having 

 been formed during the second advance of the ice, reserving the name upper 

 till for a deposit to which Prof C. H. Hitchcock has called special attention 

 and to which he has given this name. It is conceived by him to have been 

 derived from the material taken up into the mass of the ice itself, and to have 

 sunk down, when the ice melted, in a coarse, uncompacted, and unstratified 

 sheet upon the lower till, which had been compacted beneath the ice. 

 While the lower till is compact, with few small bowlders, well scratched and 

 not far-traveled, and is bluish in color, having been protected from the air by 

 the thick ice, the upper till is loose, contains many large bowlders, angular 

 and far-traveled, and is reddish from oxidation. I have been able to recog- 

 nize this distinction only partially in the valley. The immediate deposi- 

 tion of the Champlain clays upon the surface of the lower till proper at 

 several places in the valley shows that tlie upper till was not uniformly 

 spread upon the latter, and where, as along the northern jDart of High street 

 in Amherst, an upper loose buff layer from 1 to 6 feet, thick covers the blue 

 compact till, I do not find the bowlders to be more angular or far-traveled 

 than below, and am inclined to explain the peculiarities of the surface layer 



