and Birth of Lake Huron. 21 



the last, at the level of the Nipissing outlet, only by a river flow- 

 ing into the valley of the Ottawa.* 



As we ascend to the elevation of the higher beaches, the 

 question of glacial dams becomes more difficult, for we must 

 assume them to have been hundreds of miles long and at 

 enormous altitude, damming up bodies of water which had the 

 proportions of inland seas. Such, I do not here propose to 

 construct or dissipate, but I am compelled to assume the ini- 

 tial plain of the Algonquin Beach at sea-level, irrespective of 

 glaciers which may then have been moving into the St. Law- 

 rence valley, and obstructing open communication with the 

 sea, but not damming the waters at high levels. . There is as 

 much evidence of submergence in these deserted beaches as 

 there is in Professor Shaler's beaches f up to 1500 feet, on Mt. 

 Desert Island, without the intervention of dams, or of Mr. 

 McG-ee's Columbian formation:); which I have seen in Alabama, 

 at altitudes of about TOO feet without the support of dams. 

 Indeed, there is additional evidence, for crustaceans of marine 

 species have so adapted themselves as to still live in the depths 

 of Lake Superior,§ as also maritime plants upon its shores. || 



As Algonquin water received so much fresh water, the marine 

 conditions, indicated above, were modified, so that almost 

 immediately after, if not during the formation of the Algon- 

 quin Beach, the waters became sweet, as is shown by shells 

 referred to above. With the continued emergence and north- 

 eastward warping of the continent, a rocky barrier across the 

 Nipissing outlet was raised which eventually caused the waters 

 of Georgian, Huron, and Michigan Lakes to unite and over- 

 flow the southern extension of the lower beaches. Finally, 

 this warping, as before pointed out,T so tilted the basins of 

 the lakes that the waters overflowed the southern rim of the 

 Huron basin, and established the modern drainage of the 

 upper Lakes by way of Lake Erie. Not until this event did 

 the lakes assume their present form. 



*See History of the Niagara River, by G. K. Gilbert. 



f Geology of Mount Desert, by N. S. Shaler. Eighth Annual Report of IT. S. 

 Geological Survey, 1888. 



% By W. J. McGee. Bull. Geo). Soc. Am., vol. i, 1889. 



§ " On the Deep- Water Fauna of Lake Michigan." (Stimpsou) Am. Nat., vol. 

 iv, p. 403, 1870 ; also " The Crustacea of the Fresh Waters of the United States." 

 (Sidney I. Smith). Rep. Fish Commissioner, 1872-3, p. 643. 



I " The Distribution of Maritime Plants in North America." (C. H. Hitch- 

 cock). Proc. A. A. A. S, 1870. 



% Notes upon the Origin and History of the Great Lakes of North America, 

 Proc. A. A. A. S., vol. xxxvii, p. 197, 1888. 



