WAEREN UPHAM, ESQ., ON CAUSES OP THE ICE AGE. 203 



Vancouver island. It extended beyond the Ohio river only 

 for sliort distances in the vicinity of Cincinnati; but the 

 Missouii river lies mainly within the glaciated area. On the 

 Mississippi. 300 to 450 miles north of the boundary of the 

 ice-sheet, where it reached farthest south, a large driftless 

 Jirea, including south-western Wisconsin and parts of adjoin- 

 ing states, escaped glaciation. In the Rocky mountains, the 

 Cascade range, and the Sierra Nevada, ice-fields of great 

 extent were accumulated along distances of 700 to 800 miles 

 south from the border of the continental ice-sheet to latitude 

 37° S. ; but no evidences of such local glaciation south 

 of the ice-sheet are found in the Appalachian mountains. 



Upon British America the directions of the glacial striae 

 and transportation of the drift show that there were two 

 areas of glacial outflow, one reaching from Newfoundland 

 and Labrador to the Rocky mountains and the Arctic ocean, 

 having its greatest thickness of ice, probably about two 

 miles, over the Lam-entide highlands and James Bay, with 

 outflow thence to the east, south, west, and north ; and 

 the other west of the Rocky mountains, covering British 

 Cc)lumbia, where the ice-sheet attained a maximum thickness 

 of about one mile, outflowing south into the United States, 

 west into the Pacific ocean, and nortliward to the upper part 

 of the Yukon basin. The portions of the ice-sheet pouring 

 outward respectively from these two areas have been named 

 by Dr. George M. Dawson the Laurentide and Corcilleran 

 glaciers. Toward the south, west, and north-west, the Cor- 

 dilleran outflow extended to the boundaries of our glaciated 

 area ; but eastward, pouring through passes of the Rocky 

 mountains, and in the Peace river region probably over- 

 topping the highest summits, which there are only about 

 6,000 feet above the sea, the Cordilleran ice pushed across a 

 narrow belt adjoining the mountains, to a maximum distance 

 of nearly 100 miles, and there (on land about 2,500 feet 

 above the sea) became confluent with the Laurentide ice, the 

 two united currents thence passing in part to the soutli and 

 in part to the north from the interior tract where the con- 

 fluent ice was thickest. At the time of maximum extent of 

 the North American ice-sheet, it was continuous from the 

 Atlantic to the Pacific, covering approximately 4,000,000 

 square miles of this continent. 



5 Nearly half as large an area was ice-covered in Europe, 

 with the basins of the Irish, North, Baltic, and White seas, 

 the principal centre of outflow being the plateau and mouu- 



