Geography of Ohio 217 



Lake Warren. This next lake level, which overflowed through 

 the Mohawk valley, is thus named. Its outline may be traced 

 entirely across Ohio. Lake Warren included the ponded waters in 

 the Saginaw Bay valley, waters in the Detroit region, waters 

 extending across the present basin of Lake Erie and continuously 

 through Cental New York. Warren thus had many times the 

 area of our Lake Erie. How long it existed we have no way of 

 telling. Judging from the pronounced beaches and other shore 

 phenomena which now mark its level in Ohio, it must have en- 

 dured a long period. Its existence was terminated when the ice 

 retreated sufficiently to disclose a still lower outlet. 



THE ORKilN OF LAKE ERIE 



Much has been written on the origin of our Great Lakes. In 

 genesis they are associated; therefore, it is difficult to discuss one 

 without going into the origin of all of them. 



Lakes in general. It is well to remember that lakes are always 

 short-lived. Frequently they are but broad portions of rivers; 

 as the river lowers its bed, these broader sections are drained to 

 normal channels. Other lakes occupy basins due to various causes, 

 but in time, the outlets of these basins will be cut down and the 

 lakes be drained ; the only insurance against such a termination of 

 a lake is found in basins below sea level, in a humid climate ; in this 

 case, with sufficient rainfall, the lake surface will rise till it reaches 

 an outlet; the erosion of this outlet, and the deposits of streams 

 in the basin wdll eventally bring the lake to an end. Along ocean 

 borders bodies of water are sometimes isolated, forming in a short 

 time brackish lakes and eventually bodies of freshwater; such 

 lakes are also temporary, because vegetation, generally with the 

 aid of sediment from streams, fills them. Of the several details 

 that make up the features of our land surfaces, few, if any, are 

 less enduring than lakes. 



It is an obvious fact that those parts of the continents which have 

 many inland bodies of w^ater have been recently glaciated. South 

 of the ice margin in North America and in Europe, very few lakes 

 exist. Our knowledge of the conditions that surround the lakes 

 of Africa is not sufficiently complete to assert their origin ; it has 

 been suggested that part of them, at least, occupy rift valleys, that 

 is, depressions due to the subsidence of a long block of the crust 



