640 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



THICKNESS OF THE DRIFT. 



The thickness of the drift varies greatly along the line of the Cleve- 

 land morainic belt, possibly more than in any of the moraines yet described. 

 The moraine crosses tributaries of the Lake Erie Basin, which have received 

 a filling of several hundred feet, while on the high ridges between these 

 valleys there is usually a very thin coating of drift. Well sections in 

 Cleveland along the old line of the Cuyahoga show drift extending about 

 600 feet below the level of Lake Erie, while the drift filling near the south 

 border of the city reaches a level more than 200 feet above the lake. 

 There is thus possibly more than 700 feet of drift in places where the 

 deepest part of the old channel lies beneath uneroded parts of the valley 

 filling, and probably an even greater amount in the Conewango Valley, 

 which constituted the old northward line of discharge for the upper Alle- 

 gheny. This valley is filled to a level about 700 feet above the surface 

 of Lake Erie, yet its floor at the place where the moraine crosses was 

 probably but little, if any, above the lake level. The borings are not, 

 however, sufficiently deep to test this matter. The borings in Cattaraugus 

 Valle}", about 5 miles north of Maples, show a rock floor more than 700 

 feet below the level of the South Cattaraugus Creek bottom at the place 

 occupied by this moraine. Aside from the valleys just noted, a diift filling 

 of 300 to 500 feet or more may be expected in the valleys of Chagrin 

 River, Grand River, Pymatuning Creek, Pymatuniug Swamp, Conneaut 

 Creek, Cussewago Creek, French Creek, Lake Chautauqua, Cassadaga 

 Creek, and Genesee River. 



Of this large amount of drift in the valleys the greater part was 

 deposited at an earlier date than the Cleveland morainic belt. The amount 

 deposited in connection with the moraine probably exceeds by only a small 

 amount the relief of the moraine above the portions of the valleys outside. 

 Where outwash occurred in notable amount there may have been consider- 

 able filling in the part of the valley outside the moraine. But in general, 

 it may be stated that the morainic filling in the valleys does not exceed 

 100 feet, and is, therefore, but a small fraction of the total filling. 



The amount of drift deposited on the uplands in connection with this 

 moraine maj^ usually be estimated from the relief of the moraine, and this, 

 as indicated above, ranges from 10 feet or less up to about 50 feet. 



