858 



GEOLOGY 



as to the direction of ice movement, even though stri:r arc not 

 preserved. 



Summary. The characteristics of the drift, as set forth in the 

 preceding paragraphs, leave little room for random speculation 



Fig. 571. The radiation of stria) in the area of the Green Bay glacial lnl><'. 

 and in the west part of the Lake Michigan lobe, during the last glacial 

 epoch. 



concerning its origin. From its variable thickness we know that t he 

 force or forces which produced it must have been such as could leave 

 the drift now in thick bodies and now in thin, over either limited or 



