516 THE GLACIAL LAKE AGASSIZ. 



depressed fully 15(-) feet, which would currespoud to au average of about 

 3,600 feet of ice ou the glaciated areas of North America and Europe. 



For the secoud factor in causing such changes, ]\Ir. Woodward's compu- 

 tations before cited indicate that gra^atatiou toward the ice would further 

 depress the ocean ])robaldy 25 to 75 feet within the ti'opics and in the 

 southern hemisphere, while it Avould raise the level enough near the borders 

 of the ice-sheets to counterbalance approximately the depression due to the 

 diminution of the ocean's volume, and would lift portions of the North 

 Atlantic and of the Arctic Sea perhaps 200 or 300 feet higher than now. 

 Sti'eam erosion while the sea was lowered to supph' the ice of the Glacial 

 period may explain the indentations of the southeastern coast of the United 

 States, as Pamlico and Albemarle sounds, besides similar inlets in many 

 other parts of the world; but the excavation of Chesajieake and Delaware 

 bays seems more probably referable, at least in part, to the time of pre- 

 glacial elevation, with the chamieling of the now submerged Hudson fjord. 



PROBABIiE REIiATIOXSHIP OF EPBIROGENIC MOVEMENTS THROUGH- 

 OUT THE ^VORT.D TO GliACIATION. 



In ^new of the extensive Pleistocene oscillations of laud and sea both 

 in glaciated and uuglaciated regions, it seems a reasonable conclusion that, 

 while some of these movements, as those aftecting the beaches of Lake 

 Agassiz, have resulted directly from the accunudation and dissolution of 

 ice-sheets, more generally, when the whole area of the earth is considered, 

 they have been independent of glaciation. May not such movements of 

 the earth's crust, then, have elevated large portions of continents, as the 

 northern half of North America and the northwestern part of Europe, either 

 together or in alternation, to heights like those of the present snow-lines on 

 mountain ranges, imtil these plateaus became deeply channeled by fjords 

 and afterward covered by ice-sheets? For the recentness of the Ice age, 

 believed to have ended in the region of Lake Agassiz and the Laurentian 

 lakes not more than 10,000 to 6,000 years ago,^ forbids our referring the 

 glacial climate to conditions brought about by a period of increased eccen- 

 tricity of the earth's orbit from 240,000 to 80,000 years ago, which has been 



' See Chapter V, pp. 238-240. 



