346 



The location of the primary divide, if tlie preglaeial drainage lines 

 have been established correctly, can be followed in a general \A'ay by a 

 glance at the maps (Pis. IV, V). The portion of the divide, and the most 

 important portion, between the Wabash and Erie basins has not yet been 

 satisfactorily located. Upon its accurate determination depends most of 

 our knowledge of the outlet of the drainage of soutliern and southeastern 

 Ohio. Some general facts concerning it will appear in the following dis- 

 cussion. From near Mt. Vernon east and southeast to New Martinsville 

 the divide is well located, and the area northeast and north drained to the 

 northward. The present Ohio is seen to fall into two divisions on this 

 basis. 



The portion of the Ohio above New Martinsville reached some northern 

 outlet by three different streams (PL V). These are easily located, with a 

 few minor exceptions, for the preglacial cols are usually apparent. Carll 

 (17) called the attention to a narrowness of the Allegheny valley at 

 Thompson's gap and shows that the rock floor of the valley, now covered 

 w^ith drift, sloped northward from the divide, and he concluded that the 

 luadwaters of the Ohio once drained northward by this valley. He con- 

 cluded that the outlet was through the Cassadaga valley, but Chamberlin 

 and Leverett made later studies, found the Cattaraugus creek valley the 

 deeper and more direct route to Lake Erie and concluded that the outlet 

 was by that valley (6.5: 129-30; 21: 101: 159-60). 



Another prominent col just north of Parker separates another section 

 of the Allegheny which included the Allegheny to a little below Oil City. 

 French creek reversed to Meadville and an old vallej' continuing northward 

 to some preglacial valley in the Erie basin were the main stream in the 

 system, for here is an old, wide rambling valley in which Cussewaga creek 

 flows south to join French creek. Leverett accepts this outlet, showing that 

 the drainage could not have been up French creek above Martinsville, be- 

 cause of a col in French creek valley a few miles northeast of Meadville 

 (65: 134-8). 



The next lower section of the preglacial system, whose main stream 

 was the Beaver reversed, and the Grand, is variously known as the Spen- 

 cer (35), Old Lower Allegheny, Pittsl)urg (109) and CJrand river (21). It 

 has been well studied and most authors agree upon its course. The drift 

 is deep norlh of the source of the Beaver; but the old gradation plain 

 slopes north to Sharon and then upward farther north. A depression 



