138 GLACIAL FOKMATIONS OF EEIE AND OHIO BASINS. 



connected with the Conneaut outlet along the line of the old Beaver canal. 

 In apparent support of this view, there is found to be a very low divide 

 on this line composed of drift. But within a short distance back from the 

 canal on either side rock appears above the canal level, a feature which 

 suggests that the drift here covers a low rock ridge instead of an old chan- 

 nel. It seems probable, therefore, that the middle Allegheny received very 

 little of the present Shenango drainage. 



OLD DRAINAGE BETWEEN THE UPPER AND MIDDLE ALLEGHENY DRAINAGE SYSTEMS. 



The greater part of Brokenstraw, Little Brokenstraw, Oil, and French 

 Creek drainage basins appear to have been largely independent of either 

 the Upper or Middle Allegheny. Instead of discharging, as now, in a 

 southeastward direction to the Allegheny, they appear to have taken a 

 northwestward course to the Lake Erie Basin. Only a small part of the 

 ancient drainage can be readily traced, owing to the deep filling of drift, 

 which completely conceals many of the low divides and renders it difficult, 

 if not impracticable, to locate them. The borings, also, are not sufficiently 

 numerous to afford a satisfactory knowledge of the slope of the rock floors, 

 except in a few localities especially favored by oil-well borings. The 

 present discussion can therefore set forth only a few of the points which 

 bear upon the ancient courses of di-ainage. 



The enlargement of Oil Creek, a small northern tributary of the Mid- 

 dle Allegheny, was brought to notice by Carll.' He called attention to the 

 old divide just south of Titusville, and to the fact that in the part of tlie 

 present creek above this divide the rock floor slopes toward the Lake Erie 

 Basin. 



The region now drained by French Creek seems to have suffered 

 greater changes than that drained by Oil Creek. Indeed, the present 

 stream appears to unite several areas which were drained by distinct lines. 

 The lower course, as already indicated, formed the old line of discharge for 

 the Middle Allegheny, while a small section in the middle of the present 

 valley was occupied by the stream which drained the headwater part of the 

 present Oil Creek Basin, and which may be called Muddy Creek, from the 

 stream which now connects it with the Allegheny. Between these two 

 lines of drainage there was a smaller line which crossed the present French 



' Op. cit, pp. 356-360. 



