and Disturbed Stratification. 387 
sources, the great’ mass was gathered from the adjacent lime- 
stones 
TIL These hills were formed in the presence of an intermittent 
disturbing agency. It seems quite impossible to explain the 
curious relations of the disturbed and undisturbed portions of 
the mounds by postulating a single thrust, or even a succession 
of disconnected sudden impulses. It seems necessary to assume 
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V. I infer, therefore, that these hills could not have been 
vi. Their inherent characteristics, taken in connection with 
their association with morainic belts, supports the opinion that 
they were formed along the edge of the great ice sheet by 
numerous marginal streams. The disturbance of bedding and 
the intrusion of the till masses are attributable to the oscilla- 
tory action of the ice, while the partial assortment, feeble 
attrition of the gravel and the multiform phases of stratifica- 
tion, were accomplished by the issuing streams. e localiza- 
tion of these streams was of course determined by the special 
conditions of glacial drainage then existent, but now largely 
6 determination. The heaping of the gravels is thought to 
ave been aided by the ice which restrained both the stream 
and the dispersion of its products. The special phases of accu- 
-tMulative action were probably somewhat variable, being some- 
times purely marginal, the heaping being at the debouchure of 
the streamlets, sometimes within the walls of subglacial tun- 
nels * or small marginal ice cafions,t and sometimes, perhaps, 
* Hummel, loc. cit. Upham, loc. cit. 
