294 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



the surface, whereas in the Wisconsin drift the leaching has seldom been 

 carried to so great a depth as 6 feet. It seems clear from the position and 

 relations of this old land surface that the leaching took place before it was 

 buried under the silt. In view of these facts, this may safely be considered 

 one of the main intervals of deglaciation. 



The erosion of the Illinoian drift in the Sangamon interglacial stage 

 was not so conspicuous a feature as the weathering. This is true not only 

 in the region under discussion, but also in the region to the west, covered 

 by the Illinois glacial lobe. The channeling seems to have been shallow 

 and broad wherever new lines were opened, while the old lines, being already 

 largely open, suffered but little excavation. These features indicate that 

 drainage conditions were less favorable than now, but they should not be 

 cited against the evidence of a long interval derived from the leaching and 

 weathering of the surface. The conditions for erosion seem to have become 

 worse rather than better toward the close of the Sangamon interglacial 

 stage, and in the stage which followed, as indicated below, erosion was either 

 suspended or became so feeble as to allow silt to accumulate on the surface. 



