196 THE GLACIAL LAKE AGASSIZ. 



distinct stream erosion across the rim di^^dino• adjacent river basins, which 

 now in many instances send their waters respectively to the Gulf of Mex- 

 ico and to Hudson Bay or the Gulf of St. Lawrence. Obviously, water- 

 courses could exist in these positions only as the outlets of lakes which 

 were jjent up by some barrier that is now removed. Shore-lines traceable 

 northward from these deserted channels must therefore belong to a lake, 

 and can not l^e regarded as the record of any marine submergence. 



Closely associated with such channels crossing watersheds, and at the 

 same level, are the three following classes of proof cited, namely, eroded 

 cliffs, beach ridges, and deltas ; and below these shore records are the fine 

 lacustrine sediments. These are found in hydrographic basins which are 

 now drained by a continuous descent northward, presenting no indication 

 that any land barrier ever existed across their lower portions to form these 

 lakes, being afterward removed by erosion or by depression. The shore- 

 lines, as shown thus by wave-cut cliffs, wave-built beaches, and deltas 

 brought by inflowing rivers, extend far along both sides of the present 

 hydrographic basin, often rising slightly and regularly northward, instead 

 of sinking in that du-ection, as they would do if there had been a depres- 

 sion of the land at the north. When traced carefully with leveling, they 

 are found, sometimes after an extent of hundreds of miles, as on the glacial 

 Lake Agassiz and about the great lakes tributary to the St. Lawrence, to 

 terminate abruptly where the basin attains its greatest width. Hence it is 

 manifest that the barrier of these lakes could not have been land formerly 

 raised higher than now, but was the receding ice-sheet, against which the 

 land shores terminated. 



On slopes descending in parallelism with the retiring ice border, drain- 

 age from it in many places flowed in channels from which the streams 

 became turned into new and more northerly courses as the ice retreated. 

 Several glacial river courses of this kind I have observed between the 

 Coteau des Prairies and the Minnesota River. ^ Others have been noted 

 by G. M. Dawson,- McConnell, ^ and Tyrrell,* in various parts of Alberta 



' Geol. and Nat. Hist. Survey of Minnesota, Final Report, Vol. I, 1884, pp. 508, 509, 606. 

 -Report on the Geology and Resources of the Region in the Vicinity of the Forty-ninth Parallel, 

 1875, pp. 263-265; Geol. Survey of Canada, Report of Frogress, for 1882-83-84, p. 150 C. 



'Geol. Survey of Canada, Annual Report, new scries, Vol. I, for 1885, pp. 21 C and 74 C. 

 ' lliiil.. Anniiiil Report, new series. Vol. 11, for 1886, pp. 43 E, 45 E, and 145, 146 E. 



