THE 



JOURNAL OF GEOLOGY 



FEBRUARY- MARCH, 1893. 



AN HISTORICAL SKETCH OF THE LAKE SUPERIOR 

 REGION TO CAMBRIAN TIME.^ 



(with plate I.) 



The ancient formations south of Lake Superior may be 

 grouped into five great divisions : the Basement Complex, the 

 Lower Huronian, the Upper Huronian, the Keweenawan, and 

 the Lake Superior Sandstone. These five divisions are separated 

 by unconformities of great magnitude, two of them at least 

 being of the first order. According to the classification adopted 

 by the United States Geological Survey, the Basement Complex 

 is Archean ; the Lower Huronian, Upper Huronian and Kewee- 

 nawan constitute the Algonkian for this region ; and the Lake 

 Superior Sandstone is Cambrian. 



The Basement Complex. — -The characteristic rocks of the 

 Basement Complex are ( i ) light colored granites and 

 gneissoid granites, and ( 2 ) dark colored finely foliated or 

 banded gneisses or schists. These are cut by various basic and 

 acid intrusives, many of which are not different from eruptives 



'In this very general article no attempt will be made to give references to the 

 many authors from whom facts are taken. To give full credit for all information 

 used would require citations from scores of papers. The writer gives a summary 

 of the literature of the Lake Superior Region in Bulletin 86 of the U. S. Geol. 

 Survey. 



Many of the problems considered have no definite answers as yet. The aim of 

 the article is to give a summary of the very limited knowledge available on a sub- 

 ject that has not before been considered, because the data were not at hand upon 

 which to base an\- reliable conclusions. 

 Vol. I. — No. 2. 



