MUSEUM OF COMPARATIVE ZOuLOGY. 25 



223). The gi-eenstoncs of the Huronian were also said to be indigenous, 

 i. e. rocks formed in situ from sediments (/. c, p. 221). 



We next come to the report of Air, Charles E. Wright,* in which we 

 are informed that all the granites of the Upper Peninsula and Wisconsin 

 that have been examined by the writer are metamorphic. This view is 

 based upon microscopic characters, and we should object, in tuto, to the 

 premise. He also states : " Some objections were made last summer 

 (187G) by Dr. Ilomingcr as to the non-conformability of our so-called 

 Laurentian and Huronian series, on the ground that he had observed in 

 several instances ' a perfect couformability of these supposed distinct 

 series.' It seems perfectly natural to me that this should often occur; 

 and were I to find ninety-nine places where an apparent conformability 

 existed, and only one of decided non-conformability, the latter would, in 

 my estimation, outweigh all the former." (^. c, p. 11.) He states that 

 a perfect case of nonconformability exists at " Penoka Gap," Wisconsin, 

 to which we have before referred ; but if we remember correctly Mr. 

 Wright's personal statement to us, neither was the junction seen nor 

 the kind of junction known that the two made with each other. It is 

 too fast to assume, as has been done by Messrs. Brooks, Irving, and 

 Wright, that the strike and dip of a foliated rock is the strike and dip 

 of its stratification. This is especially the case when the view that they 

 were ever stratified is still a disputed point. 



Of the Huronian series the quartzite is said to show frequent ripple- 

 marks. The soft hematite is thought to have been formed as follows : 

 " In these mines it appears that the finely divided silica has been more 

 or less dissolved out by alkaline thermal water, leaving the iron oxide 

 and other bases behind." (/. c, p. 15.) The iron ore is regarded as 

 sedimentary, and Brooks's geological ideas are closely followed. 



He sustains Mr. Brooks's division of the gi-anites into Laurentian and 

 Huronian (Formation XX.), by the statement that he finds salt cubes 

 in the fluidal cavities of the latter, but not in the former. 



Lastly, we have Mr. W. 0. Crosby's paper, "On a Possible Origin of 

 Petrosiliceous Rocks,"t in which he thinks it probable that the jasper 

 and its associated iron ores are the ropi-esentatives of a deep-sea deposit, 

 like the " red clay " discovered by the Challenger expedition, below the 

 depth of 2500 fathoms. 



It may not be amiss to incidentally refer to the treatise of Mr. 



* First Annual Report of the Commissioner of Mineral Statistics for the State of 

 Michigan, 1879. 

 t Troc. Bost. Soc. Xat. Hist., 1S79, XX. 160-169. 



