MUSEUM OF COMPARATIVE ZOOLOGY. 



25 



series. 



223). The greenstones of the Huronian were also said to be indigenous, 

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



Wc next come to the report of Mr. Charles E. Wright,* in wliich we 

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

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

 based upon microscopic cliaraeters, and wo should object, in toto, to tho 

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

 (1870) by Dr. Kominger as to the non-conformabiiity of our so-called 

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

 several instances ^ a j^erfcct conformability of these supposed distinct 



It seems perfectly natural to me that this should often occ\ir; 

 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 tho 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 granites into Laurentian and 

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

 in tho fiuidal cavities of the latter, but not in the former. 



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

 Petrosiliceous B,ocks,"t in which he thinks it probable that the Jasper 

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

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

 depth of 2500 fathoms. 



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



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

 Micliigan, 1879. 



t rroc. Bust. Soc. Nat. Hist., 1879, XX. 160-1G9. 



