INTERGLACIAL SAXDS. 557 



greater portion of these beds, evi;u inovini^' and partiully molding- into tlu' 

 till beneath it great sheets of the sand, as in tlie I'usu of the bed (4) just 

 described, more commonly destroying its identity entirely. Nevertheless, 

 I think one would be strongly inclined, from a study of the cellar section 

 alone, to assume a second retreat of the ice for- tlie formation of the second 

 sand bed, and a third and final advance, during which the third layer of tlic 

 till was deposited. 



Or, finally, one has an alternative; namely, to explain all these .sand 

 beds intercalated in the till as deposited 1)\' suliglacial streams during 

 the progi'ess of a single glaciation of the country. The fact of a i-etreat 

 and second advance of the ice seems abundantly proved for western 

 Europe, and many observations in this country point in the same direction, 

 especially those made toward the borders of the ice sheet, since traces of 

 a double glaciation wMnxld naturally be more abundantly preserved there 

 than farther north, where the ice a second time occupied the country in 

 such force as to obhterate most traces of the incoherent deposits made 

 in the interim. Again, the compact, uusorted, and clayey character of the 

 till above and below the sands shows that for the most part there was here 

 no free circulation of the waters below the ice, and Ave should expect the 

 waters to have escaped along the bottom of the valley and not along its side 

 300 feet above the bottom. On the other hand, the sand beds occupy just 

 the same position fringing the valley and have just the same structure as 

 the flood beds which attended the final disappearance of the ice, and seem 

 to me to bear the same relation to tlie retreating ice of the earlier epoch.' 



In 1881 the deep railroad cutting south of College Hill exposed the 

 same sand beds at a distance of 1,463 feet south of the first locaHty cited 

 above on the Northampton road, displaying the following section: 

 Section in railroad cutting south of CoUcfie Hill. 



Stratified gravel *> (•*<"' 'J 



Laminated clays *' 



Gravel ^ * 



Till, olive-green to brown 6 6*°^ 



Sand 



Till, blue 



3 6 



lto3 4 

 1 to 3 4 



Sand 



Till, bine; bottom not exposed. 



1 I prefer to leave this section as it was written in 1879, although now the case in favor of a 

 second Glacial epoch seems to me less strong than then. 



