72 THE PENOKEE IRON BEARING SERIES. 



these, they have yet furnished to another portion an abundance of frag- 

 mental material. 



The remarks quoted below are in no part a reply to these considera- 

 tions. It will be seen that Dr. Roming-er, while retaining his position in 

 the main, has yet modified it so far as to accept an older granite in addition 

 to the areas which he regards as newer than the schists adjacent to them. 



In a previous report,' which couiiiiences witli a description of tlie jreologiciiil 

 structure of tlie environs of Marquette, I have spoken of the occurrence of laige 

 areas of granite some distance nortli and south of the city and of the intermediate 

 space from 4 to 5 miles in width as being occmpied by a large l)ody of massive and 

 schistose <lioritic rocks. These in turn are succeeded upward by argillitic, chloritic, 

 and hydromlcaceous schistose layers, inclosing lenticular seams of hematitic iron ore, 

 which on their part are overlain by a large (piartzite formation and by still higher 

 beds of siliceous limestones iiiterstratifte<l with argillitic or hydromlcaceous schists of 

 various color, sinne of them intensely impregnated with hematitic iron oxide. 



All these strata I described as being steeply njjheaved in a constant axial direc- 

 tion from east to west, and as excessively folded and corrugated, suggesting as the 

 principal cause of these disturbances the uprising of the granite into a synclinal 

 trough compressing the incumbent sedimentary layers. 



I further stated, that particularly the lower dioritic portioii of the rock beds 

 inclosed within this trough was found intermingled with belts of granit<% partly 

 parallel to the stratification, partly transverse to it, from which ciix-umstance I inferred 

 the intrusive nature <>f these belts, and suggested that this intrusion occurred con- 

 temporaneously with the upheaval of the granite into a trough, and that part of it at 

 least must have been then in li(iuid or plastic condition. 



Generally, a solid <',rust of granite probably served as a substratum on whi(rh the 

 Huronian sediments were laid down, but occasion is not often offered to see the rocks 

 in contiguity well enough exposed to allow a. discrimination as to wiiether such con 

 tact is an original primary one or resulted from subsecpient dislocation. 



The existence of granite as a surface rock at the time the Huronian sediments- 

 formed is proved by the occurrence of belts of granite conglomerate and breccia in 

 different horizons of the series. 



A large belt of conglomerate formed of rounded, water-worn granite pebbles and 

 schistose rock fragments, cemented by a matrix of similar schisto.se material is .seen in 

 contact with a granite ])elt in the .south half of Sec. 2, T. 48, R. 26, but this instance 

 is not a satisfactory exami)le of the depositicm of sediments inclosing debris of the 

 underlying rock, as the granite i)ebbles in the conglomerate are totally different from 



I Geol. Survey of Mich., vol. IV, ISSl, pj.. lH-19, 22-39. 



