40 THE MARQUETTE IROX-BEAEIXG DISTRICT. 



schists, slates, quartzites, and limestones, but also "the extraordinary and 

 extensive intermixture of the beds of greenstone and granite which defy 

 descri})tion and classification." 



1S6.5. 



Kimball, J. P. On the iron ores of Marquette, Michigan. Am. Jour. Sci. (2), 

 Vol. XXXIX. 18G5, pages 290-303. 



In the year 1865 Kimball published the most important article on the 

 iron district of ]\Iarquette that ajjpeared between the report of Foster and 

 "Whitney and that of Brooks. In it the author contradicts Whitney's 

 notion that the Azoic of the Marquette region is nondivisible. Following 

 Hunt, he divides the rocks underlying the Lake Superior sandstone into 

 two series, the Laurentian and the Huronian. He calls attention to the 

 fact that the granites are separated from the Azoic schists by Foster and 

 Whitnev on lithological rather than structural grounds, and therefore that 

 the relations of the schists t(i the granite have not been established upon 

 sufficient data. From his own observations made in the Huron Mountains 

 and elsewhere he concludes that the granites and the associated rocks are 

 metamorphic and indigenous (were formed in their present positions), and 

 are not exogenous (intrusive), as Foster and Whitney declared the granite 

 to be. It is true that Mr. S. W. Hill, working with Foster and Whitney, 

 discovered a granite dike intrusive in slates, and therefore younger than 

 the latter; but Kimball explains this as an independent dike, not in any 

 way connected with the greater masses of granite. On account of the 

 lithological similarity of this rock with the Laurentian granites of Canada, 

 and in accordaqpe with the author's notion as to its origin, the granites and 

 gneisses of the Marquette district are placed in the Laurentian series, which 

 is older than the Huronian. 



This conclusion is correct, but the granite is nevertheless intnisive, as 

 Foster and Whitney supposed. 



South of the granite and its associated gneisses lie the great greenstone- 

 schist areas of later authors. These are described by Kimball as dark- 

 coloi'ed hornblende-schists, which represent the "baseof the Azoic or Huro- 

 nian series." They are separated from the gneisses, so far as we can leani, 



