218 Frank Carney 



between adjacent portions that remained stationary; the valley 

 of the Jordan and Dead Sea is of this origin. Since, therefore, 

 most of our lakes occur within the glaciated portions of the con- 

 tinent, and since Pleistocene glaciation is so recent, it is easy to 

 accept the conclusion that lakes are geologically temporary. 



The St. Laivrence drainage hasin in preglacial times. Our Great 

 Lakes are virtually but parts of the St. Lawrence River. The 

 St. Lawrence River then is very peculiar. Normallj^, a river 

 and its tributaries form a symmetrical outline, and among these 

 tributaries there is an orderly arrangement. It is commonly 

 thought that the Great Lakes occupy preglacial stream courses. 

 The St. Lawrence and the lakes within its basin do not conform to 

 a normal drainage pattern. Lakes Superior and Michigan unite 

 in a manner that is not out of harmony wdth the confluence of 

 stream tributaries; but, when considered in connection with Geor- 

 gian Bay and Lake Huron, they together present an unusual 

 alignment for drainage courses. It is very evident that the St. 

 Lawrence drainage is abnormal. 



Whatever may have been the pre-glacial topography of this 

 area, the present Great Lakes are not parts of a former continuous 

 river system. Before the ice sheet spread over the region, valleys 

 must have existed. The perplexing question is as to the direction 

 of flow of these valleys. Many conjectures have been offered on 

 this point. Most of these suggestions are based upon the estab- 

 lished presence of buried channels, contiguous to many of these 

 lake basins. It is thought that if a buried channel, entering Lake 

 Erie, shows rock removed to a depth of 470 feet below the lake 

 level, ^ some stream to which the channel was tributary, must have 

 occupied its basin preglacially ; and if this tributary has such a 

 deep channel, the major must have been still deeper. About the 

 margins of some of the other lake basins are found buried channels, 

 the rock beds of which are even below sea level. Along the 

 continental shelf, soundings have revealed canyon-like depres- 

 sions, continuous with rivers now entering the Atlantic ; thus we 

 speak of the drowned canyons of the Hudson and St. Lawrence 

 rivers. The submerged courses of these streams over the conti- 

 nental platform, and the existence of deep buried valleys about the 

 Great Lakes of to-day, have led to the suggestion that pregla- 



* Warren Uph am, Bulletin Geological Society t)f America, vol. viii. (1S97), p. 8. 



