128 THE JOURNAL OF GEOLOGY. 



than the level of Lake Superior, but it has since been almost 

 completely removed, so that it occurs only in patches within the 

 depressions of the older rocks. 



Since Cambrian time no important orographic movements 

 nor outbursts of volcanic material have occurred in the Lake 

 Superior region, consequently the rocks have received little sub- 

 sequent alteration. To these facts is due the possibility of out- 

 lining the pre-Cambrian history of this area with greater fullness 

 than has been done in areas in which later disturbances have 

 obscured the early history. 



C. R. Van Hise. 



