1808.] 149 [Hyatt. 



we may, without any great difficulty, account for tliis local deficiency 

 in the evidence of glacial erosion. 



Concerning the absence of transported materials in these regions, 

 there is no explanation required if we suppose there was little motion 

 to the mass. But as there must have been some outlet if there was 

 any accumulation going forward, we may find a better explanation in 

 the fact that it is only where a considerable portion of the surface 

 of a country remains uncovered by the ice sheet, that any large 

 quantity of erratic material can be tbrmed. The surface covered by 

 moving ice cannot yield much material for transportation in the shape 

 of large erratics. Most of the material removed is borne away in the 

 condition of mud and sand. The few considerable masses which are 

 torn up from the glaciers' bed are continually grinding against the 

 rock, and are soon reduced to powder. In the Alpine glaciers com- 

 paratively few fragments emerge at the extremity of the stream, and 

 those generally of small size, by far the greater part having been 

 ground to mud. Of twentj^ tons of fragments which find their way 

 to the base of the glacier, probably not one ton emerges at the termi- 

 nal moraine. It is chiefly the masses which have been carried on the 

 surface of the stream Avhich build up the terminal moraine. And of 

 the fragments constituting such accumulations, probably not the fiftieth 

 part has been torn from the bed over which the stream grinds its way. 

 The material eroded at the base of the glacier passes away in the 

 almost impalpable mud which whitens the stream that bursts through 

 the terminal moraine of every glacier. 



The fiord zone, one of the most unquestiojiable evidences of glacial 

 erosion, is as clearly indicated, at least on the southern part of 

 Alaska, as upon any portion of the eastern coast of North America. 

 To make the case still clearer, the heads of these fiords are at some 

 points still occupied by the remains of those glaciers which excavated 

 their channels. 



Is it to be believed that the glacial sheet of the last geological 

 period descended to the Pacific between the parallels of fifty and 

 sixty of north latitude, while the region beneath the next ten degrees 

 to the northward, was not glaciated at all ? Is it not more reasonable 

 to regard the want of evidence as explicable on the hypothesis above 

 presented ? 



Mr. A. Hyatt remarked that the absence of drift material and of 

 glacial scratches or grooves in the territory under consideration, 

 especially for thirteen hundred miles in the great valley of the Yukon, 



