200 



MAN AND THE GLACIAL PERIOD. 



That Lake Erie is really nothing but a " glacial mill- 

 pond " is proved also by much direct evidence, especially 

 that derived from the depth of the bnried channels of the 

 streams flowing into it from the south. Of these, the 

 Cuyahoga River, which enters the lake at Cleveland, has 

 been most fully investigated. In searching for oil, some 

 years ago, borings were made at many places for twenty- 

 five miles above the mouth of the river. As a result, it 

 appeared that for the whole distance the rocky bottom of 

 the gorge was about two hundred feet below the present 

 bottom of the river, while the river itself is two or three 

 hundred feet below the general level of the country, occu- 

 pying a trough about half a mile in width, with steep, 

 rockv sides. These facts indicate that at one time the 



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Fig. 5.2. —Section across the valley of the Cuyahoga River, twenty miles ahove 

 its mouth (Claypole). 



river must have found opportunity to discharge its con- 

 tents at a level two hundred feet below that of the present 

 lake, while an examination of the material filling up the 

 bottom of the gorge to its present level shows it to be 

 glacial debris, thus proving that the silting up was accom- 

 plished during the Glacial period. 



As the water of Lake Erie is for the most part less 

 than one hundred feet in depth, and is nowhere much 

 more than two hundred feet deep, it is clear that the pre- 

 glacial outlet which drained it down to the level of the 

 rocky bottom of the Cuyahoga River must have destroyed 

 the lake altogether. Hence Ave may be certain that, before 

 the Glacial period, the area now covered by the lake was 



