26 BULLETIX OF THE 



D. C. Davies on Metalliferous Minerals and Mining.* It would be 

 difficult to imagine a description or a section so at variance ^Yith 

 the facts as the ones that he gives on pages 274 and 275. We 

 feel that all geologists who have been in this region will be sur- 

 prised to be informed that " lingulse are abundant in the overlying 

 sandstone." On page 149 he has represented the copper-bearing rocks 

 and sandstone (Potsdam) as resting directly upon, and at a steep angle 

 dipping away in both directions from, the iron-bearing rocks ; also, the 

 ■western copper rocks as dipping east, and resting upon a similar set of 

 iron rocks. It is to be hoped that the rest of his book is not so errone- 

 ous as this. 



Historical Summary. 



In general, then, in looking over the views advocated by past ob- 

 servers, we find, in brief, the following opinions held. 



The rocksf of this district were all taken as azoic by Foster and 

 Whitney, and not considered to be capable of subdivision into geologi- 

 cal periods. We must also notice that Prof. H. D. Rogers regarded 

 them as of primal or Potsdam age. On the other hand, we find that 

 this formation is divided by Murray, Hunt, Kimball, Winchell, Credner, 

 Brooks, and Wright into the Huronian and Laurentian. This division 

 is based upon lithological characters, and an unconformabilitj^ said to 

 exist between the two. Rivot considered the Avhole as Potsdam. 



The granite is regarded as an eruptive rock by Foster and Whitney, 

 Bigsby, and Whittlesey ; and as of sedimentary origin by Rivot, Kimball, 

 Bi'ooks, Hunt, and Wright. These latter, with Credner, take it as being 

 older than the schistose rocks associated with the iron ores, and, except- 

 ing Rivot, with its accompanying gneissoid rocks composing the Lauren- 

 tian formation. Foster and Whitney and S. W. Hill regarded the gran- 

 ite as younger than, and eruptive in, the schists. 



The gneisses and schists were taken by all the observers as being of 

 sedimentary origin, except possibly Whittlesey, whose language is as 

 obscure as the formations about which he writes. 



The metamorphism of the schists is supposed by Hubbard, Rivot, 

 Kimball, Hunt, Brooks, and Wright to be occasioned by chemical agen- 

 cies accompanied, as part tliought, by galvanism. Foster and Whitney 

 and Bigsby considered that the metamorphism was brought about by 



* London : Crosby, Lock\vood,& Co., 1880. 



t Excepting the sandstone, which will be s^wkeu of in our remarks on the Copper 

 district. 



