332 W. UPHAM — PKEGLACIAL AND TOSTGLACIAL VALLEYS. 



tain that the delta deposition failed to extend so far until some time after 

 the ice had retreated. 



POSTGLACIAL EROSION. 



Since the continuance of the glacial recession withdrew the northeast 

 barrier of lake Warren, permitting that lake to be succeeded by lakes 

 Algonquin and Lundy, the latter in a little time sinking to the small 

 Champlain representative of lake Erie, which occupied only the north- 

 eastern part of the present lake basin, the Cu3^ahoga river, outflowing 

 across many miles that are now the lake bed, to the early diminutive 

 Erie, channeled quickly through the shallow delta and deepl}'' into the 

 till. The resulting crooked valley or trough has a width of one-third of 

 a mile to one mile through the city of Cleveland, and is bounded by 

 steep bluffs on each side which rise 100 to 150 feet (from north to south) 

 above the river and its bottomland, the latter being 5 to 15 feet above 

 the river and partly overflowed by its spring floods. 



The river meanders along the flat bottomland, which is alluvium de- 

 posited by the stream during its slow U[)lift while the differential eleva- 

 tion of the land northeastward has caused the lake to extend southwest- 

 ward and to rise gradually on all its southern shores. The alluvium 

 earlier carried away by the river during its postglacial erosion was 

 deposited in the central part of the present lake area, being there a delta 

 of the smaller lake Erie, and the ensuing work of the river has been the 

 partial refilling of the deep postglacial channel. In this process horse- 

 shoe-shaped moats have been left, cut off from the former winding course 

 of the stream ; and within apparently only a few centuries the river has 

 rei)eatedly changed its lower course and its mouths, which became suc- 

 cessivel}^ closed by the bars of the drifting beach sliingle and sand. An 

 old river channel, having such history, reaches a mile west from near 

 the present mouth, and is now utilized with wharves on its sides for lad- 

 ing and unlading ships. 



Valleys of the Rocky River. 



relation and character of the t^vo valleys. 



The next important tributary of lake Erie west of the Cuyahoga is the 

 Rocky river, in Rockport township, which adjoins Cleveland. This 

 stream entirely lost its valley by its being filled with drift and obliterated 

 during the Ice age. We have, therefore, in this case two valleys, the 

 preglacial one, w4th its very interesting drift section on the lake shore, 

 and the postglacial wide and deep gorge, cut in the Erie shales. 



