CURRENT PRE-CAMBRIAN LITERATURE. 753 
recognizes the fact that the logical course is to confine the term Lau- 
rentian to the older rocks. ‘This usage of the term is a serious obsta- 
cle to the progress of structural geology in this region, for two entirely 
different series of rocks are confused. Plainly the rocks called Lau- 
rentian upon which the Huronian was deposited are pre-Huronian; it 
is equally certain that the granites called Laurentian which cut the 
Huronian are Huronian or post-Huronian in age. So long as these 
two classes of rocks are confused on the maps, no such thing asa 
structural map of the area northwest of Lake Superior is possible. 
Coke Lemar 
