GEOLOGICAL EXPLOEATIOXS AND LITERATUBE— 185G. 37 



thickness, aud passing- gradually iuto specular iron, wliicli frequently forms bands 

 of nearly pure ore, alternating with bands of quartz more or less mixed with the 

 same substance. * * * Deposits of this character are usually very distinctly 

 bedded. * * * These deposits seem to have been of sedimentary origin, having 

 been originally strata of siliceous sand, which has since been metamorphosed. 

 The iron ore may have been introduced either by the sublimation of metalliferous 

 vapors from below during the dei)osition of the siliceous particles or by precipi- 

 tation from a ferriferous solution, in which the stratified rocks were in process of 

 formation. 



RiVOT, L. E. Voyage an Lac, Superieur. Ann. des Mines, Ser. V, Tome VII, 

 1855, ])agcs 173-328; Tome X, 1850, pages 365-474. 



Rivot, of the iScole des Mines, Paris, made two visits to the Lake 

 Superior region in the years 1854 and 1855, respectively, with the purpose 

 of studying the geology of the copper rocks, more particularly on Kewee- 

 naw Point. In connection with his study he made a general survey of the 

 granitic and the iron-bearing rocks. According to this author, granites 

 associated with gneiss and various schists, quartzite, limestones, slates, aud 

 trap form a belt stretching from a point on the lake north of Marquette as 

 far west as the State of Wisconsin. They constitute a metamorphic series, 

 and in them are great beds of iron ore, associated with amphibole-schists. 

 At the Jackson mine the ores are accompanied by trap and by talc-schists 

 and amphibole-schists, in which the "primitive stratification" can still be 

 detected. To the north and south the iron-bearing beds are limited by 

 conglomerates composed of portions of all the rocks noticed in the region, 

 cemented by a ferruginous matrix. The traps associated with the ores 

 are said to be similar to those in the Keweenawau region. They pass into 

 the amphibole-schists, and like these latter are believed to be metamorphic 

 and "not igneous rocks" (p. 413). 



All the "metamorphic" rocks are believed to have been sediments 

 which have since their deposition been metamorphosed into crystalline 

 schists and granites, the latter of which in their present position are younger 

 than the traps and sandstone lying upon them. In other words, the granite 

 was apparently regarded as the fused basal portion of a sedimentary series, 

 which, after fusion, intritded the upper beds of the series (p. 231). The 

 granites, schists, traps, and sandstones are, seemingly, all believed to be of 



