80 GEOLOGY OF OHIO. 



removing ice-dams, may have produced the great changes in our drainage 

 system of which the evidence is so unmistakable. The accompanying 

 map, which is compiled from data furnished by Dawson, Logan, Whit- 

 tlesey, and my own observations, will probably aid in making the views 

 advanced on the preceding pages a little more intelligible than they 

 would otherwise be. 



