THE PLEISTOCENE OR GLACIAL PERIOD 849 



vironment, the Cordilleran ice-sheet seems to have conformed to 

 the habit of the Labradorean and Keewatin sheets in expanding 

 chiefly to windward. The plains of Alaska seem to have been 

 largely free from glaciation even when the waters of the Ohio and 

 the Missouri, 2,000 miles farther south, were being turned from 

 their courses by the ice-sheets. The localization of the glaciation 

 is one of its most significant features. 



South of the more or less continuous Cordilleran glaciation of 

 Canada, local glaciers were widely distributed in the western moun- 

 tains, even down to New Mexico, Arizona, and southern California. 

 They were larger at the north and smaller at the south. Of glaci- 

 ation in the mountains of Mexico little is known. 



Greenland was glaciated somewhat more extensively than now, 

 but its glaciers appear never to have extended to the continent, 

 as was formerly conjectured. Newfoundland seems to have had 

 its own ice-sheet, and the same was probably true of Nova Scotia, 

 and perhaps of the peninsula between the Bay of Fundy and the 

 lower St. Lawrence. 



Other continents. South of the ice-sheets of Europe, great 

 glaciers descended from the Alps to the lowlands in all directions, 

 and lesser ones among the lower mountains. Iceland was buried 

 in ice, and even Corsica had glaciers. In Asia glaciers larger than 

 those of to-day affected all the higher mountains, and ice-sheets 

 existed in some of the more northern lands. The southern hemi- 

 sphere was affected to a lesser degree, but the higher mountains 

 generally bore glaciers, and Antarctica is assumed to have been 

 buried beneath ice as now. In tropical regions, there were glaciers 

 in mountains where none exist now, and in mountains where there 

 are glaciers, the ice descended then to levels 5,000 feet or more 

 below its present limits. 



The Criteria of Glaciation 



The area of North America which was overspread by ice is 

 covered by a mantle of clay, sand, and bowlders, which taken to- 

 gether, constitute the drift. The various lines of evidence which 

 have led to the general acceptance of the glacial theory, have to 

 do with (1) the drift, (2) the surface of the rock which underlies 



