CHAPTER V 



PREGLACIAL CONDITIONS AND LIFE 



It is believed that the area covered by the great ice sheets had been sub- 

 jected to subaerial conditions since the close of the Paleozoic Era. During 

 this vast period of time there occurred changes of level, resulting in deepening 

 or otherwise modifying the valleys cut by erosion and subjected to atmospheric 

 agencies. Previous to the Pleistocene Period, the country embraced in the 

 northern and northeastern portion of the United States, as well as in British 

 America, had been reduced to a condition of great maturity, or, in other words, 

 base leveled, producing a grandly rolling surface, covered with a deep residual 

 soil and subsoil. 



1. Ancient Drainages 



a. the basins of the great lakes and the buried river valleys 



For many years the belief was held by the majority of geologists that the 

 basins of the Great Lakes — Superior, Michigan, Huron, Ontario, Erie — had 

 been scooped out by the great continental glacier. Data supplied by lake 

 soundings and well borings have clearly indicated that this theory can no longer 

 be held, and that these lake basins represent ancient river valleys, occupied 

 by a great river system comparable to that of the Mississippi in magnitude. 

 These valleys and their connections and tributaries have been carefully worked 

 out by Prof. J. W. Spencer, and others, and are graphically shown on the 

 accompanying map. 1 (Plate LTV) . 



1 J. W. Spencer, The Falls of Niagara. Can. Geol. Surv., 1907, pp. 391-412. 

 Discovery of the Preglacial Outlet of the Basin of Lake Erie. 



Proc. Amer. Phil. Soc, XIX, pp. 300-337; Second Geol. Surv. Penn., 

 Rept. Progress, 1879, QQQQ, pp. 357-406, 1881. 

 High Continental Elevation preceding the Pleistocene Period. 



Bull. Geol. Soc. Amer., VI, pp. 141-166, 1895. 

 Relationship of the Great Lake Basins to the Niagara Limestone. 

 Bull. Geol. Soc. Amer., XXIV, pp. 229-232, 1913. 

 Newberry, On the Origin and Drainage Features of the Basins of the Great Lakes. Proc. 

 Amer. Phil. Soc, XX, pp. 91-95, 1883. 



