GEOLOGICAL EXPLORATIONS AND LITERATURE— 1851. 31 



to the oe.eurreuce of beds of coug-loinerate, slntes, etc. On tlie Hue between 

 sees. 2-9 and 32, T. 47 N., R. 26 W., near where tlie viUage of Pahuer is 

 now situated, a large exi^osure of conglomerate was found whicli "is made 

 up of coarse blocks of various sorts Avhich belong to the ucighljoring 

 trappean and slaty beds, and are of very considerable dimensions. Anion"- 

 them we recognized not only fragments of the rock associated witli the 

 iron, but masses of the iron itself, and of the Ijanded and jasper)- varieties." 

 This is evidently the description of an exposure of Upper ]\Iarquette basal 

 conglomerate. The authors regard it, however, as a friction conglomerate, 

 whose origin is connected with the "eruption" of the adjacent granite, i. e., 

 the granite to the south. The ore deposits are older than the conglomerate, 

 because they yielded fragments to the latter. But, since these and other 

 fragments were cemented by ferruginous material, it w^as presuijaed that 

 "emanations of metallic matter must still have been issuing from beneath" 

 when the conglomerate was formed (p. 41). The relations existing between 

 the granite and the Azoic slates are thoi;ght to be those of an intrusive 

 rock to an intruded series. The hornblende-slates near the southeast corner 

 of sec. 25, T. 47 ISl., R. 27 W., for instance, are penetrated l:)y a wedge of 

 granite, "shooting out in ramifying branches." Such are, indeed, the 

 relations of the granite to these hornblende-slates. The authors did not 

 realize, however, that these hornblende-slates are older than many of the 

 other members of their Azoic series. 



From the quotations that have been given it is seen that Foster and 

 Whitney regarded as present in this region two series of sedimentary rocks, 

 the Potsdam representing the Silurian, and the Azoic a pre-Silurian series. 

 The former were shown to be much younger than the Azoic rocks, which 

 are mucli metamorphosed. The Azoic series alone is cut by dikes of green- 

 stone and by granite; hence both these rocks are younger than the Azoic, 

 but not so young as the Potsdam. In the Azoic occur the ore beds. 



These ore beds were found principally in a belt of crvstalline schists 

 and intercalated trappean rocks, bounded on each side bv a l:)elt of granite. 

 Many occurrences of the ore were located in the present Marquette district, 

 and a large number of the occurrences are described at some length. In 

 some of these exposures dark quartzites are associated with the ores, and the 



