REVIEWS 449 



iron bearing formations, this assumption is perfectly justified and 

 the conclusion follows as to the Upper Huronian age of the typical 

 conglomerates mentioned. 



But, lately evidence has been accumulated pointing to a conclusion 

 of a rather radical nature. This evidence has been such that Van 

 Hise' in a general article on the iron bearing formations of the Lake 

 Superior country just published, describes three iron bearing forma- 

 tions, the Upper Huronian, Lower Huronian, and Archeaii. The 

 most important of the Archean iron bearing formations are the Ver- 

 milion and the Michipicoten. 



Van Hise himself in his published articles on the pre-Cambrian 

 has persistently maintained the essentially non-clastic nature of the 

 Archean, and the post-Archean age of all the iron bearing formations 

 of the Lake Superior country. But new evidence on the subject, 

 secured principally during the past year, has been so decisive that he 

 has not hesitated lo announce as proven the existence of an Archean 

 or Basement Complex iron-bearing formation. 



If there is' an Archean iron formation, to which the IVIichipicoten 

 and Vermilion iron formations belong, then Dr. Coleman's argument 

 as to the Upper Huronian age of conglomerates containing iron for- 

 mation fragments is rendered ineffective, and the conclusions indicated 

 by the structural evidence that the great conglomerates and accom- 

 panying rocks above described are Lower Huronian must stand, until 

 decisive evidence to the contrary is found. 



Grant ^ describes and maps the Upper and Lower Keweenawan 

 copper-bearing rocks of Douglas county, Wisconsin. The Lower 

 Keweenawan appears in a broad belt running from northeast to south- 

 west across the county, widening toward the southwest, and in a small 

 belt cutting through the southeastern corner of the county. It con- 

 sists mainly of basic lava flows, associated with which, in the area in 

 the southeast corner of the county, are a few beds of conglomerate 

 composed of debris of the closely adjacent underlying rocks. The 

 Upper Keweenawan appears in a broad belt in the southeastern part 

 of the county between the two belts of Lower Keweenawan rocks. It 



'The iron-ore deposits of the Lake Superior region, by C. R. Van Hise: 

 Twenty-first Ann. Rept. U. S. Geol. Surv., Pt. Ill, igor, p. 322. 



* Preliminary Report on Copper Bearing Rocks in Douglas county, Wisconsin, by 

 U. S. Grant : Wisconsin Geological and Natural History Survey, Vol. VI, 1900, pp. 

 55- 



