THE GLACIAL LAKE AGASSIZ. 



By Warren Upham. 



CHAPTER I. 

 INTRODUCTION. 



BASTlSr OF THE RED RIVER OF THE I>^ORTH AND OF LAKE 

 WINNIPEG. 



The glacial lake which is the theme of this volume extended along the 

 Red River Valley and covered the lake country of Manitoba. Its situation 

 in the center of the continent, and its geographic relation to the drift- 

 covered area and to lakes Bonneville and Lahontan, are displayed in 

 Plate II. Lake Agassiz was the largest of the many Pleistocene lakes of 

 North America, some of which were formed by the barrier of the ice-sheet 

 during its recession, while others were produced by increased rainfall in the 

 great western arid region that has no drainage to the sea. 



Only a comparatively small fraction — about one-fifth — of the area of 

 Lake Agassiz lies within the United States, but this includes the greater 

 portion of its exactly explored shore-lines. A very large part of its area 

 in Canada, besides a considerable tract within its limits in northern Minne- 

 sota, is covered by forest, which makes it impracticable to trace there the 

 beach ridges and deltas, low escarpments of erosion, and other evidences of 

 this lake so continuously as has been done through the prairie region. 

 This great expanse of prairie, upon which the shore-lines have been accu- 

 rately and continuously mapped, comprises the Red River Valley and 

 adjoining higher land, and reaches north to the southern ends of lakes 

 Wimiipeg and Manitoba and of Riding Mountain. Farther nortli tracts of 

 prairie, divided by woodlands and thickets, continue interruptedly along 

 the eastern base of Riding and Duck mountains, permitting considerable 

 parts of the ancient shores to be traced in that district. 



MON XXV 1 



