﻿256 R. D. Irving — Ferruginous Schists and 



observations have been confined to the Marquette region, where 

 the disturbances have been great, and where the difficulties are 

 consequently greater than in other regions. In support of an 

 igneous origin for these materials, which are supposed on such 

 theories to have been intruded as bosses, or to have formed 

 overflows at the time of the accumulation of the associated 

 strata, have been cited particularly: (1) an irregularity of contact 

 of the ore and jasper with the adjoining schists ; (2) the projec- 

 tion of stringers of ore and jasper into the adjoining schists ; 

 (3) the induration of the adjoining schists; (4) the curvature of 

 schistose cleavage by ore intrusions; and (5) the occurrence of 

 fragments of the ore and jasper in an immediately overlying 

 quartzite of the same series, this indicating their existence in 

 their present conditions of induration prior to the accumulation 

 of this quartzite.* On this theory the lamination of the ore and 

 jasper is taken to be probably a fluidal structure, and the inter- 

 bedding of ore and jasper with other schists to be the result of 

 a contemporaneous flowing of lava. Having carefully exam- 

 ined the localities cited by the last advocate of an eruption 

 theory as proving the above facts, I feel able to say that the 

 occurrences, save the last named (5) are mainly trivial matters 

 occurring within the space of a few inches, or feet at most, and 

 that all are more easily explicable — as irregularities in origi- 

 nal deposition, as irregularities due to the crumpled condition 

 of the strata, or, and this chiefly, as due to infiltrations of iron 

 oxide and silica into cracks in the rocks, and the replacement 

 of rock material by such substances—on theories of original 

 sedimentation of the iron beds than on those of an eruptive 

 origin. The last named point, viz : the occurrence of frag- 

 ments of the banded jasper in the immediately overlying 

 quartzite, deserves more consideration, since it certainly indi- 

 cates that, to some extent at least, these substances had 

 reached their present condition at an early day. But cooling 

 from a state of fusion is not the only way of reaching rapidly 

 the indurated condition, and a former fused condition seems to 

 be negatived at once by the nature of the material — quartz and 

 iron oxide. 



My own acquaintance with the ferruginous schists and iron 

 ores of the Lake Superior region began, fortunately for me I 

 think, in the Penokee country of northern Wisconsin, some 

 thirteen years since. I say fortunately, because from the un- 

 folded condition of the strata of the region most of the confus- 

 ing appearances which have baffled so many in the better 

 known Marquette district are eliminated here, while the forma- 

 tions and the ferruginous rocks are manifestly the same in both 

 regions. What I saw in the Penokee region during the succeeding 



* See M. E. Wadsworth in Bull. Mus. Comp. Zool., vol. vii, No. 1. 



