The Abandoned Shorelines of the Oberlin Quadrangle, Ohio 115 



which was partly filled with drift. Its irregular course still preserves 

 the meanderings of the consequeni: stream which flowed into lake 

 Maumee. Its tributaries are quite numerous relative to the small 

 areas which each controls; and the width of its valley corresponds 

 to the long period of erosion. 



The Whittlesey base-level. — Lake ^Nlaumee was lowered about 

 40 feet in establishing this level; the drop was not accomplished at 

 once, as is evidenced by the lower Maumee beach. Furthermore, 

 the multiplicity of barrier beaches, belonging to the Alaumee level, 

 indicates a halt in the change. 



The two branches of the Black river converge more when 

 brought under the control of the Whittlesey base-level, a fact due 

 to the shape of the preglacial basin which occasioned the local bay 

 in Lake Maumee. The 40 feet of fall added to the stream slope 

 did not have much effect on their erosive powers in the Maumee 

 part of their courses. This 40 feet is in the Berea sandstone, which 

 is quite resistant, and in all post-glacial times has not been cut 

 down so as to materially increase the gradient upstream. 



Laterally from the depression in which Elyria lies the streams 

 connected with die \\ hittlesev base-level were few and of slie'ht de- 

 velopment. Beaver creek, on the west side of the sheet, has made 

 more of a valley than either jjranch of Black river; this is due to 

 a steeper initial slope, and to the shorter distance through which it 

 had to channel the Berea sandstone. 



The U'ane}i base-lez'el. — The dift'erence in altitude between this 

 and the Whittlesey level is about 60 feet; the drop appears to have 

 been accomplished quickly. The accession of drainage territory was 

 not great because west of Black ri\er the Whittlesey and W arren 

 shorelines are close together. 



In this change of level. Black river was lengthened by about 

 four miles; the slope of this added length originally could not have 

 been over 60 feet. The stream therefore took a somewhat irregular 

 course, which it still preserves. Its channel lay across a slight 

 depth of glacial drift beneath which the rock is an easily eroded 

 shale; consequently this four-mile section was not long in reaching 

 the new base level. During the existence of Lake Warren, the 

 stream appears to have added about a mile to its length lakeward. 

 gaining through the off-shore development of barriers which eventu- 

 ally became the shoreline proper ; the river deposits account for this 

 prograding shoreline. These earlier formed ridges exercised an 



