G. F. Wright — Continuity of the Glacial Period. 185 



Glacial radiation was in the vicinity of James Bay. A land 

 elevation of three or four thousand feet would perhaps have 

 been sufficient to produce the Glacial conditions ; but the accu- 

 mulation of Glacial ice would eventually raise the surface 

 several thousand feet higher. 



4th. Before the climax of the Glacial period, and perhaps in 

 consequence of its burden of ice, the glaciated area began to 

 sink until the land was, north of the Great Lakes at any rate, 

 several hundred feet, at least, lower than it now is. But for 

 some time after the beginning of the subsidence of the land the 

 rate of accumulation of ice would be greater than that of the 

 subsidence ; so that the general level of the glacier continued to 

 rise. Thus the maximum extension of the ice-held was actually 

 reached but a short time before the decline of the period set in. 



5th. As suggested to me by Mr. Upham, " The frontal slope 

 of the ice-surface was then less steep than when the warmer 

 climate, bringing the end of the Glacial period, had begun to 

 melt away the southern border. At the maximum of extent 

 the slope may be thus represented : — terminating in a very 





Fig. 7. 









s - 



Land Surface 







N 



■ - >•»»• 



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W^S5S5^\\NV>^\>*$^^ 



gentle declivity, allowing some transportation of bowlders to 

 'the boundary, but not generally so steep as to produce there 

 any well-defined moraine. In the Glacial recession the warm 

 sunshine and rains were especially efficient, on a belt a few 

 miles or a few tens of miles wide adjoining the boundary, so 

 that when any temporary colder series of years caused a halt or 

 slight re-advance a moraine would be formed. " 



Lack of personal familiarity with glaciers of the first class 

 has, I am persuaded, led Professor Chamberlin to misinterpret 

 many of the facts connected with what he calls the moraine- 

 headed terraces of the later Glacial epoch. As good an ex- 

 ample as any is furnished on the Conewango Creek at Ack- 

 ley, Pa.,* a region which I had repeatedly visited, both before 

 and after my study of the Muir Glacier. Professor Chamberlin 

 has much to say about the signs of vigorous ice-action in con- 

 nection with the moraine of the second Glacial epoch, and of 

 the moraine-headed terraces. The indications of this vigorous 



* See map, Fig. 3. 



