GEOLOGICAL EX^LOl;ATIO^^S AND LlTKL'ATUrfE— 1892. 133 



and were ;^t"tel•^\•ar(l slie;uv(l, and that tlie schistosity (if tlie ore at the con- 

 tact of the Upper aud Lower series, as well as that iuterl)anded with the 

 jaspers, is the result of this shearing. The magnetic ore in the contact 

 deposit is thought to have been directly deposited in that form, while tliat 

 in the actinolite-schists may have been formed by direct oxidation oi' an 

 original iron carbonate. 



The Upper Marquette ores have in general the same origin as the Lower 

 ones. The impervious strata here are often beds of black slate. Unaltered 

 carbonate is often found associated with the ores, and there is little difficulty 

 in recognizing all the stages of alteration between this and the oxide ores. 



Sometimes a single ore body may belong in part to the Lower Huro- 

 nian and in part to the Upper Huronian, the replaced ore of the former and 

 the mechanical ore of the latter, at the contact of the two formations, being 

 welded together by secondary intiltrations. 



Van Hise, C. R. The iron ores of the Lake Superior region. Trans. Wisconsin 

 Acad. Sci., Arts, and Letters, Vol. VIII, 1892, pages 219-228. 



The author treats the same subject in this article as in the last. The 

 discussion in the present paper, however, is more comprehensive and less 

 technical than that in the preceding one. 



Van Hise, C. R. Correlation papers — Archean and Algonliian. Bull. U. S. 

 Geol. Survey No. 86, Washington, 1882, pages 52-208, and Chapter VIII. With map, 

 page 48. 



This is the correlation essay to which reference has already been 

 made. In it the author reviews the literature on the Lake Superior region, 

 summarizes it, and interprets it with the aid of his own experience. The 

 conclusions as to the succession in the Marquette district are in accord with 

 the author's views as published in earlier papers. 



Some of the general conclusions reached in the study have a direct 

 bearing on the geology of the Marquette district, since this is one of the 

 areas that have yielded premises for the conclusions. 



It is showii that the schistose crystallines under the Huronian rocks in 

 this district are older than the latter, forming a basement on which the 

 fragmental rocks were deposited. 



