Mctamoyphisin of Glacial Deposits 



13 



bed of the stream where it forms a riffle. These locaHties are just 

 within the margin of the Wisconsin drift, where the ice was at- 

 tenuated as well as short-lived. It is certain that in these two cases 

 time has been the important factor in the alteration ; no great mass 

 of ice ever stood here for even a short period. If this hard bluish 

 till was deposited by Wisconsin ice, its color is genetic; but on this 

 hypothesis it is difficult to understand why the superjacent drift is 

 yellowish, and the line of division is so sharp. 



But there can be no Cjuestion that the old valley of Rocky 

 River, west of Cleveland, was buried by a pre-Wisconsin ice- 

 invasion, presumably the Illinoian. The bluish till in this buried 

 stream-course is apparently identical with the dense drift referred 

 to in central Ohio and New York. 



Fig. 7. — Faulted glacial gravels. Yellow till has been removed from the top. 



These facts suggest the following conclusions : 

 I. Glacial deposits, regardless of their constituents, when 

 buried for a long time appear to become compact, and bluish in 

 color. This assumption does not disregard the possibility that 

 some deposits have always been bluish. The dozens of exposures 

 studied in both states show a great variety of rock-constituents, as 

 well as wide variation in the general texture of the drift ; this color 

 is constantly noted in drift ranging from the fine silt to an ex- 



