THE DATE OF THE GLACIAL PERIOD. 



599 



about half-way up the bank, which is about two feet thick, 

 and contains pebbles several inches in diameter. Not much 



Fio. 153.-Sectk>n in till near Darrtown, Butler County, Ohio, sixty-five feet high. 

 Coarse line of stratification near the middle. Fresh cedar logs at the bottom. (See 

 text.) (United States Geological Survey.) (Wright.) 



wood is found above this line, yet there is some, and the 

 structure above seems identical with that below. All this 

 would seem to indicate that there was a temporary retreat of 



