MUSEUM OF COMPARATIVE ZOOLOGY. 15 



with the axes of the folds which constitute a regular system of flexures 

 coextensive with the distribution of the Huronian scries in the vicinity 

 of Marquette, are, in reality, indigenous greenstone, and a portion of the 

 development of the diorite upon which repose the upper members of the 

 series, and which, as will hereafter be shown, is uncovered along most of the 

 ridges of the region." (L c, p. 2 'J 6.) " The position of the beds of specu- 

 lar iron ore has already been stated to be at the top of the Huronian series, 

 .... interstratificd with talcose and argillaceous schists. Sharing the 

 plications of the entire series, these specular schists, as they may prop- 

 erly be called, are accordingly folded into synclinal basins and anticlinal 

 crests." (/. c, p. 299.) " It has been shown that the iron ores of the Hu- 

 ronian series in Michigan are essentially schists and heavy-bedded strata, 

 in which none of the phenomena of aqueous deposits formed by precipita- 

 tion from water on the one hand, or by detrital accumulation on the 

 other, are wanting. They exhibit not only stratification, anticlinal and 

 synclinal folds, but ai'e invariably traversed by systems of joints, and at 

 many points exhibit a perfect slaty cleavage. The intimate connection 

 between the greenstones, hornblende rocks, and aluminous and mague- 

 sian silicated schists of the ferriferous series, has already been indicated 

 in general terms, these rocks not only alternating with, but passing into 

 each other." (/. c, p. 302.) "Chemical reactions in crystalline sedi- 

 ments resulting from the disintegration of crystalline silicated rocks, and 

 operated upon by carbonated waters, are amply capable to have pro- 

 duced the lithological conditions of augitic rocks, clay-slates, schalstone, 

 and other schists, together with the oxidized ores of iron intercalated 

 with greenstone among the ancient crystalline rocks of Xorth America 



as well as of Europe From a stratigraphical point of view, while 



evidence is elsewhere often obscure, the Huronian greenstone, schists, 

 and iron ores of Northern Michigan, in the absence of close attention to 

 their special chemical conditions, exhibit sedimentary and metamorphic 

 phenomena adequate to render quite untenable, it is believed, the theory 

 of the exotic character of any portion of them." (/. c, p. 303.) The 

 granite is also regarded as indigenous by Dr. Kimball. 



Mr. J. W. Foster, in 18G.5,* states: "The Iron Region consists 

 of an assemblage of rocks of various kinds, such as argillite, talcose, 

 chlorite, and hornblende schists, quartzites, and occasionally dolomites, 

 all of which are supposed to be of metamorphic origin, intermingled 

 with rocks whose igneous origin can hardly be doubted, consisting of the 



* Geology and Metallurgy of the Iron Ores of Lake Superior, hy J. W. Foster 

 and J. P. Kimball, New York. 



