52 THE CRYSTxVL FALLS IRON-BEAHmG DISTKIOT. 



and also lie between the grains. In one instance fragments of tlie original 

 feldspar were found in the midst of sucli an area. These quartz-sericite 

 areas are unquestionably of secondary origin, and the minerals have devel- 

 oped in connection with pressure. They were probably produced from 

 feldspar which existed in the original granite. 



Whether this schistose rock was formed from a weathered but not 

 transported granite, from an arkose or feldspathic sandstone, or from the solid 

 granite, it is impossible to say. A similar sericite-schist which developed 

 from recomposed granites has been described by Van Hise as occurring at 

 several localities in the Marquette district.^ In these cases at places the 

 fragmental characters are still sufficiently clear to admit of the statement 

 that the rocks are sedimentary. In the Crystal Falls rock mashing has 

 destroyed all original characters. The rock occupies an intermediate posi- 

 tion between a metamorphosed sedimentary and a metamoi-phosed eruptive, 

 and grades on the one hand into the sedimentary and on the other into 

 the eruptive. This makes it impossible to say whether it belongs exclusively 

 to the one or to the other, or in part to both. Similar relations in other 

 parts of Michigan were explained by Rominger^ as cases of progressive 

 metamorphisin of sediments, the granite being supposed to be the extreme 

 stage of alteration of the sedimentary rock. Later the finding of basal 

 conglomerates at or near these localities has shown conclusively that this 

 explanation is incorrect, and it has been abandoned by Rominger. 



The quartzite, which immediately overlies the rock of doubtful char- 

 acter, is composed of angular grains of quartz, between which are plates of 

 sericite which have an imperfect parallelism, thus giving a certain degree 

 of schistosity to the quartzite, possibly enough in places to warrant its 

 being called a quartz-schist. The rock shows no conclusive microscopical 

 evidence of a sedimentary origin, but difiPers from the cherts, with which it 

 might be confused, in the size of the grains and in the presence of sericite. 

 This rock was originally probably chiefly composed of quartz sand, with 

 some feldspathic material from the disintegrated granite.. Coincident with 

 the pressure which produced the striking schistosity in the underlying rock, 

 this sand was also mashed, resu.lting in the production of sericite and quartz 



' Mou. U. S, Geol. Survey Vol. XXVIII, 1897, p. 226. 



-The Marquette iron district, Ijy Carl Rominger: Geol. of Jlichisau, Vol. IV, Parti, 1878-1880, 

 pp. 15-.52. 



