CHAMPLAIX STAGE 533 



admirably shown, and is Pleistocene in age, probably corresponding 

 to one of the Glacial stages, though by some it is regarded as 

 Pliocene. 



In the Great Basin the Pleistocene was a time of far less arid 

 climate than at present. In the eastern part of the Basin was 

 established the great Lake Bonneville (see p. 146), which had an 

 outlet to the north into the Snake River. The deposits of this 

 lake show that it had two periods of expansion, separated by one 

 of almost complete desiccation. Lake Lahontan, on the western 

 side of the Great Basin, which had no outlet, had similar episodes 

 of rise and fall. The two relatively moist periods when these 

 lakes were high may correspond in time to the two stages of 

 greatest advance of the ice-sheets, the Kansan and Wisconsin, but 

 this is only conjectural. 



In the Glacial epoch a subsidence had begun which continued 

 until it became a very marked feature of the times. The depres- 

 sion was greatest toward the north and especially in the valley of 

 the St. Lawrence ; at the mouth of the Hudson, for example, the 

 land stood about 70 feet below its present level, on the coast of 

 Maine 150 to 300 feet, and in the St. Lawrence valley 500 to 600 

 feet below. The consequence of the depression was that an arm 

 of the sea extended up the St. Lawrence nearly to Lake Ontario, 

 which was little, if at all, above sea-level. Two long and narrow 

 gulfs reached out from this sea, one up the valley of the Ottawa 

 River and the other over Lake Champlain. The lines of raised 

 beaches, the sands and gravels filled with marine shells, and the 

 bones of whales and walruses, are the present evidences of this 

 submergence (the Champlain stage). These beds, so named 

 from their typical exposure of the shores of Lake Champlain, were 

 formed probably after the St. Lawrence valley had been freed 

 from the ice-sheet, but it is uncertain whether they were contem- 

 poraneous with, earlier, or later than the Columbian formation. 



On the Pacific coast also we find evidences of submergence. 

 The Chaix Hills in Alaska are made up of stratified moraine ma- 

 terial 4000 to 5000 feet thick (see Fig. 61, p. 157), and at cor- 

 responding levels Champlain species of marine shells are found. 



