8 INTRODUCTION. 



ancient or modern, which has not been more or less modified 

 by the influences described, even to the extent, in many cases, 

 of owing its origin to them. The work will be incomplete so 

 long as any portion of the State remains uncharted. And it 

 must extend still further before a complete history of the Ohio 

 river can be written. As yet, we know nothing of the pre- 

 glacial conditions below Louisville, or of the tributary streams 

 in southern Indiana and western Kentucky. 



It may not be out of place to call attention here to a matter 

 which seems to have escaped notice heretofore. 



The oldest land in Ohio is that along the Cincinnati axis, 

 in the western part of the State. From here, through three 

 geological eras, the Upper Silurian, Devonian, and Sub-Car- 

 boniferous, the slope was toward the southeast; consequently 

 the surface flow must have been in the same general direction. 

 It is quite possible that to this epoch are to be assigned the older 

 erosion planes mentioned by Professor Tight in his present 

 paper. Not only in Ohio, but in the neighboring States as well, 

 are to be observed these old levels at an average elevation of 

 about two hundred feet above the present streams. The sugges- 

 tion is ventured that these represent drainage lines as they ex- 

 isted prior to the Appalachian uplift. Such valleys rriust have 

 formed in the immense length of time during which surface 

 waters sought the constantly receding ocean that bordered the 

 swamps of the coal measure period. When these were up- 

 lifted into mountain ranges, the elevation must have been gen- 

 eral enough to produce a considerable effect upon the region 

 to the westward. Otherwise a trough would have resulted be- 

 tween the land just emerging from the sea and that which had 

 so long stood above the waves. Had this been the case, it would 

 seem that the ancient rivers must have turned toward either 

 the north or the south, and flowed around the island on which 

 they had their birth. Instead of this, however, we find the 

 entire drainage of the newly risen country flowing back di- 

 rectly across the formations whose waste had assisted in building 

 it up. It is a plausible supposition that the high level valleys 

 pertain to a pre-Carboniferous drainage toward the southeast; 

 while some at least, of the narrow and deep valleys cut through 



