164 LIFE OF THE PLEISTOCENE 



Alaska, but these may have lived in this region during the expansion of the ice, 

 portions of this region not having been covered by the continental glacier. 



5. Glacial Lake Agassiz 



As the Iowa and Dakota ice lobes retreated northward (Plate XL VI) a 

 ponding of the waters took place in North Dakota, Minnesota, and Canada, 

 which at first found an outlet thru the Minnesota River and Lake Traverse 

 into the Mississippi River. This outlet is called the Lake Traverse outlet. 

 This lake grew to the northward until it became the largest of all the Glacial 

 lakes, later finding an outlet to the north, and finally, after the ice had com- 

 pletely withdrawn from the Hudson Bay region, becoming extinct. Lake 

 Winnipeg is in a sense a successor of this huge lake. Several important beaches 

 mark the limits of the different stages of Lake Agassiz, in some of which evi- 

 dences of life have been found. This lake is believed to be correlative with the 

 Warren and Algonquin stages of the Great Lakes. 



The biota which had been driven south by the Wisconsin invasion again 

 advanced into the englaciated territory as soon as conditions were favorable. 

 The aquatic life emigrated into the Lake Agassiz basin in much the same man- 

 ner as did the biota which took possession of Lake Michigan thru the Chicago 

 outlet, but at a later period. The route was via the Lake Traverse outlet. 

 Life has not been found as abundantly in the Lake Agassiz deposits as in those 

 of the Lake Michigan basin, probably because exposures in protected spots have 

 not been observed. The Gladstone beach, one-half mile northeast of Glad- 

 stone, Manitoba, has yielded several species of mollusks. This beach is 875 

 feet above the sea and 165 feet above Lake Winnipeg. Four species are re- 

 corded. 159 



Lampsilis luteola Sphaerium sulcatum (= simile) 



Sphaerium strialinum Planorbis parvus 



From stratified clay deposits of Rainy River, Ontario, Coleman reports: 

 Eurynia recta? Sphaerium, 2 species 



Fresh water shells have been reported from old lake deposits north of Lake 

 Superior, by Coleman, Bell, and others. Six miles southwest of Campbell 

 Minnesota, in the Campbell beach, which is here 985 feet above the sea, Up- 

 ham 160 found Unio (Obovaria) ellipsis. In the reports of the Geological and 

 Natural History Survey of Minnesota, especially in the Final Reports, reference 

 is made to a number of locations where evidences of life have been found in the 

 bed or outlet of this ancient lake. These are briefly noted below: 



163 Upham, Rep. Prog., Can. Geol. Surv., p. 49 E, 1900; Lake Agassiz, p. 237; Coleman, 

 Trans. Can. Inst., VI, p. 40. 



160 Amer. Geol., VII, pp. 222-223. 





