GEOLOGICJAL EXPLORATIONS AND LITERATUEE— 1881. 91 



quartz, 1)arite, and inulular masses of a soft aluminous silicate are associated 

 with tliese ores. Where the ore beds are in contact with the diorites there 

 is usually an unconformity between them. 



All the tire l)eds of Negaunee are placed together. The luu-d-ore for- 

 mation is not separated from the lower soft-ore series, the latter ores being 

 regarded as local phases of the former. East of Negaunee the lower 

 portion of the iron series is found. 



The absence of tlie upper ore-bearing, red jasper-banded rock series, with 

 inclosed seams of liaid specular ore, and of the quartzites incumbent on it, from 

 the exposures of the lower part of this group on the east side of Negaunee, is 

 remarkable, because younger strata, which elsewhere have their place above these 

 eliminated beds, directly succeed the others. These younger rock beds cover most 

 of the .surface east of this place for many square miles, and no more of the iron 

 formation can be discovered in that direction. (P. 80.) 



After his description of the mines the author declares that "every one 

 of these localities difters somewhat from the other in the character of its 

 layers, but the unity of all these deposits as coordinate mendjers of one 

 formation is plainly obvious" (\). 87). At Teal Lake the entire series is 

 oyerturned with the quartzite under the ore formation. 



The actinolitic schists of the western portion of the iron range are 

 placed in the iron formation. ■ 



At the Republic mine the diorite beds that were reported by Brooks 

 as interbedded with the sedimentary formations are found b}- Rominger to 

 be "intrusive belts of short local extension" (p. 101). At the Spurr and 

 Michigamme mines, however, diorite forms the base of the series and this 

 rock, which is often chloritic, exhibits sometimes obscure traces of former 

 stratification. 



The formation lying above the quartzite is termed the "arenaceous slate 

 group," because so many of its members are "sandy, siliceous layers," alter- 

 nating with "slaty argillitic l)eds." The character of the strata differs in 

 different places, but on the wdiole the nature of the series is as indicated. 

 The rocks comprising this series are found sometimes lying upon the 

 quartzites, sometimes upon the iron formation, and often directly upon the 

 diorite sei-ies. The most easterly exposures of them are near the center 



