214 THE GLACIAL LAKE AGASSIZ. 



Agassiz (excepting only the unimportant stage recorded by the Milnor 

 beach) extended north along the Pembina Mountain into Manitoba and 

 northeast to the south side of Red Lake, being contemporaneous with the 

 accumulation of the Fergus Falls, Leaf Hills, Itasca, and Mesabi moraines, 

 so that the single lacustrine plane of the uppermost in the series of the 

 Herman beaches covered, at its final stage of greatest extent, all of the 

 lake area to the latest of these moraines, wliich is the most northern one 

 that has been definitely traced and mapped across this area. 



Yet again, and doubtless many times again, the ice-sheet was com- 

 pelled to retreat across spaces of varying widths, sturdily resisting the 

 encroachments of the warmer climate and of its product, the glacially 

 dammed lake, pausing here and there long enough to heap up moraines, 

 then shrinking and dissolving away fi'om new tracts strewn with its diift 

 deposits. When future researches shall enroll the numbers and delineate 

 the com-ses of the probably many morainic belts lying still farther north, 

 it will be possible to show the later stages of the gradual extension of this 

 lake along the gTeat Cretaceous escarpment and over the great lakes of 

 Manitoba, across Rainy Lake, the Lake of the Woods, and the Winnipeg 

 River, over a large region east of Lake Winnipeg, and to some now 

 unknown distance down the Nelson River. 



Step by step, as fast as the ice-sheet waned. Lake Agassiz grew. The 

 whole lacustrine area, as mapped provisionally for its northern and north- 

 eastern boundaries on PI. Ill, was about 110,000 square miles or more, 

 considerably exceeding the combined areas of the great Laureutian lakes. 

 Although it was not entirely occupied by Lake Agassiz at any one stage 

 of its existence, the beaches and terminal moraines indicate that the lake, 

 during both its earlier and later stages, covered the greater part, probably 

 three-fourths, of this area. 



The chief cAadence of such great extension of the lake during the first 

 half of its history is tlie observed extent of the higher and earlier Herman 

 and Norcross beaches, which have been mapped from near Red Lake, Min- 

 nesota, southward to Lake Traverse, and thence northward tlu-ough North 

 Dakota to Riding and Duck mountains in Manitoba, a distance of about 



