192 LIFE OF THE PLEISTOCENE 



of tall cliffs. The early lakes were probably of short duration and of fluctuating 

 size, but the later ones, especially the larger lakes in the Huron-Erie-Ontario 

 and Michigan basins, existed for a long period of time. 



Of the Nipissing beach Taylor says, 225 "It is altogether the most remarkable 

 littoral feature of the Great Lake region. It is a shore line well advanced to- 

 ward old age. All other beaches are youthful in comparison. . . . Instead 

 of the slender spits and barrier bars of the Algonquin and the other beaches, the 

 Nipissing has what may be called barrier plains, made up of many, sometimes 

 forty or fifty, massive beach ridges laid one against the other. Many bays 

 were entirely filled with these beach plains and others were cut off, so as to 

 form small littoral lakes. Some of these plains are a mile and a half wide. 

 In some instances the old deltas of other beaches are large and conspicuous, 

 but the constructive products of wave action have no comparison to those of 

 the Nipissing beaches. " 



2. REPOPULATION OF THE GLACIATED AREA 



It may be stated without fear of contradiction that the Wisconsin ice cap 

 absolutely exterminated all life within the area covered by this huge glacier. 228 

 The area covered by this drift sheet is shown in Plate LVI. In the Great 

 Lakes region the return of the fresh water life could be made only by way of 

 the larger streams forming outlets from the glacial lakes, such as shown in 

 Plates L and LI. From the Mississippi Valley the biota reached Lake Erie 

 via the Fort Wayne outlet; Lake Michigan by the Chicago outlet; Lake Superior 

 by the St. Croix outlet; and Lake Agassiz by the Lake Traverse outlet. An 

 outlet from Green Bay, via the Wisconsin and Fox rivers is also believed to have 

 afforded means for reaching this portion of Lake Michigan. 



The data considered in the previous pages show conclusively that the 

 Chicago outlet was used by the fresh water biota to reach the Lake Michigan 

 basin, and that the Lake Huron basin was reached via the Grand River outlet. 

 No direct data has been seen relative to fossiliferous deposits in the Fort 

 Wayne outlet, but such deposits undoubtedly exist and will some day be 

 brought to light. It is believed by some biologists, including the writer, that 

 this outlet was used in restocking the waters of Lake Erie. 227 



The present distribution of the naiad fauna of the Great Lakes, as well as 

 the distribution of the fossil fauna, points conclusively to a postglacial 



225 Amer. Geol. XVII, pp. 398. 



228 Scharff, in his work "Distribution and Origin of Life in America" states his belief that 

 there was an unglaciated region in central North America, where a part of the fauna found 

 refuge during this cold period. He believes that the peculiar naiad fauna of Lake Erie is a 

 relict. Studies in the geology, as well as the present distribution of the naiad fauna, fail to 

 provide data for this theory. 



227 See Walker, The Nautilus, XXVII, Numbers 2, 3, 4, 5, 1903. 



