104 THE MARQUETTE IROX-BRARING DISTRICT. 



jaspery and chert rocks, aud limestones. As stated above, the chloritic and horn- 

 blendic schists I regard as in part the products of the alteration of basic eruptives-, 

 and the hydroinica-schists of acid eruptives. The chert and jasper rocks I am 

 inclined to look upon as of some sort of original chemical origin ; certainly they are 

 not the results of a metamorphism of sedimentai-y material. The limestones do not, 

 as far as I know them, appear in any essential i-espect different from many met with in 

 the unaltered formations of later date. There remain the mica-schists and slates, and 

 some of the hydromicaschists and chlorite-schist. That these latter often contain 

 much of the original fragmental material we have satisfied ourselves, but how far 

 those of their constituents which are plainly of original crystallization were so 

 crystallized when the rooks were in the state of mud, or have been produced by 

 purely pseudomorphic change upon fragmental material, or how far, finally, they 

 may be the result of a genuine recrystallization or metamorphism, are questions for 

 •which I have no answer. However they may be answered, it seems to me that it will 

 remain true that the various formations here classed as Huronian, including the 

 origiual type Huronian, are in the main not properly strongly metamorphic formations, 

 as, for instance, the older gneisses must be, if of sedimentary origin. (Pp. 241-242.) 



The g-eneral map of the Lake Superior region pubhshed with this 

 report, so far as it reUites to the Marquette district, does not differ essen- 

 tiallv from that aecompauyinii- tlie earher paper on the eoj)i)er-])earin<>- 

 rocks. 



At the close of the paper is an abstract of the buHetin l)y Irving 

 and Van Hise on the enlargement of quartz and other grains in fi-agmental 

 rocks. 



Irving, E. D. Divisibility of the Archeau in the Northwest. Am. Jour. Sci. (3), 

 Vol. XXIX, 1885, pages 237-249. 



In the paper just quoted Irving referred to the gneisses and schists 

 as older than the Huronian series. In another paper published in the same 

 year he gives his reasons for regarding them as much older than the latter 

 rocks. In the Peuokee-Gogebic district he finds six reasons for conchiding 

 that the succession of formations is as follows: Gneiss-granite-green-schist 

 formation; great unconformity; iron-bearing- slate formation; unconformity; 

 Keweenawan series. In the ^Marquette district the iron-bearing rocks are 

 in a highly folded condition, and there is thus this difference between the 

 Marquette and the Penokee districts. The author agrees with Rominger 



