﻿268 H. D. Irving — Ferruginous Schists and 



sures, rising in considerable measure into bold hills, of two 

 principal kinds of ferruginous rocks, viz: a black to dark 

 gray ferruginous schist, and a bright red, banded jaspery schist. 

 These two kinds occur in part in distinct exposures, but 

 also occur most intimately mingled. In fact, between the 

 two there are such intimate associations and such minute 

 gradations, that a general community of origin is entirely 

 manifest. In this connection it should be said, however, in 

 order to avoid possible misunderstanding that there are here 

 also, interbanded with the ore belts, light-colored schists of a 

 totally different character from those now referred to. Between 

 these light colored schists and the ferruginous materials no gra- 

 dation is observable. The dark-colored schists are carbona- 

 ceous, at times so highly so as to present a graphitic appear- 

 ance. They are very commonly banded with a light colored 

 to perfectly white, cherty silica, which is minutely crystalline 

 or even chalcedonic, and which even to the naked eye is 

 most manifestly a result of the secondary process of silicifi- 

 cation; for, while commonly occurring in bands parallel to 

 bedding of the rock, this cherty material will frequently break 

 across the lamination, forming a system of interlacing veinlets 

 between which are patches of the white-and-black-banded ma- 

 terial. Equally evident is it in the field that the jaspery silica 

 here is identical in origin with the whiter more chalcedonic 

 form ; for not only do we find all stages of passage between 

 the two forms of the silica, but often in the most completely 

 jaspery forms the minute but strongly marked sedimentation 

 films of the original slaty rock are repeated in lighter and 

 darker colored bands in the jasper itself. Indeed the transition 

 from this laminated jasper to the dark-colored slate may be 

 seen to occur within the distance of a few feet at most. Equally 

 with the white form of the silica do the most jaspery forms 

 occur in traversing bands #r veins. The ores, which are, so 

 far as now known, wholly specular, are found associated with 

 the jasper schists often in large bodies, but in the most irregu- 

 lar forms, at times grading into the banded jasper-schist, and 

 again traversing it in sharply defined tongues, or bodies of 

 most irregular outline. It is rarely that the relation of the 

 richer ore to the leaner jaspery material can be so well realized 

 as at this place; for here we have the unusual case of great 

 smoothed and glaciated surfaces upon which the contrasts be- 

 tween the steely ore and the bright red jasper are most strik- 

 ingly displayed, and the relations of the two thus made far 

 more evident than is generally the case in the openiugs made 

 in mining. 



The phenomena which have been appealed to to prove 

 an eruptive origin for the ore and jasper of the Marquette 



