CRUISE OF STEAMEB CORWIN IN THE ARCTIC OCEAN. 147 



heavily abraded. It appeals, therefore, that the thickness of the ice-sheet throughout a consid- 

 erable portion of its history was not less than 2,500 feet and probably more, over the northern 

 portion of the region now covered by Bering Sea and part of the Arctic Ocean. 



Now, in view of this colossal ice-flood grinding on throughout the hundreds of thousands of 

 years of the Glacial period, the excavation of the shallow basins of Bering Sea and Strait and Arctic 

 Ocean must be taken as only a small part of the erosion effected; for so shallow are these waters, 

 were the tallest sequoias planted on the bottom where soundings have been made, their tops 

 would rise in most places 100 f et or more above the surface. The, Plover Bay glacier, as we have 

 shown, eroded the granite in the formal ion of its channel to a depth of not less than 2,000 feet, 

 and the amount of erosion effected by the ice-sheet was probably much greater. 



We might go on multiplying evidence, but enough, we think, has been already presented to 

 show — 



(1) That the regions under discussion were covered with a mantle of ice, which pursued a 

 general southerly direction, and discharged into (he Pacific Ocean south of the Aleutian Islands. 



(1!) That after the close of the period of universal glaciation, the mountains along the coasts 

 of Bering Sea and the Arctic Ocean were loaded with distinct glaciers, many of which have but 

 recently vanished. 



(•'') That the sculpture of the region in general, with all its main distinguishing features, if 

 due to Glacial action. 



(4) That the basins of Bering Sea and Strait and of the adjacent portion of the Arctic Op Ijan 

 are simply those portions of the bed of the ice sheet which were eroded to a moderate depth 

 beneath the level Of the sea, and over which the ocean waters were gradually extended as the ice- 

 sheet was withdrawn, thus separating the continents of Asia and America, at the close, of the 

 Glacial period. 



