130 Van Hise — Attempt to harmonize some apparently 



the microscope at a glance. These series present thick beds of 

 fragniental rocks, the induation of which has been caused by 

 the same process which vitrified the quartzites of the Original 

 Huronian. The supposed absence of ferruginous rocks in these 

 districts has been used in the past as an argument against the 

 correlation of them with the Penokee and Animikie Series 

 below considered, but this absence has no particular weight 

 because such beds, as compared with the fragmental rocks, are 

 insignificant in amount ; and farther, it is quite possible that 

 such non-fragmental water-deposited formations may in the 

 future be found in several or all of these districts. The prob- 

 ability of this is rendered greater by the fact that explorations 

 for iron have very recently developed beds of this sort between 

 the two quartzite ranges of Baraboo and in the northward 

 extension of the St. Louis Slates. The rocks here found are 

 the exact parallel of the iron-bearing beds of the Penokee and 

 other iron-bearing districts. The percentage of iron is so great 

 in certain localities that the material is being mined for an ore. 

 The Penokee- Gogebic and Animikie Series. — In the Penokee- 

 Gogebic district of Michigan and Wisconsin we have the fol- 

 lowing succession : At the base is a gneiss-granite schist com- 

 plex. The schists are always completely crystalline, although 

 often finely laminated or foliated. The contact of the granites 

 and granite-gneisses with the crystalline schists is the irruptive 

 one so well described by Lawson as prevailing in Ontario. 

 Above this granite-gneiss-schist complex, and separated from 

 it by a great unconformity, is a Cherty Limestone Member 

 which in places is 300 feet thick. While it extends east and 

 west many miles, it is not longitudinally continuous. Above 

 this cherty limestone, separated by an erosion interval, is the 

 Penokee-Gogebic series proper, which consists of a Quartz- 

 Slate Member, the upper horizon of which is a vitreous quartz- 

 ite, an Iron-Bearing Member, and Upper Slate Member. Above 

 the Penokee series, separated by another very considerable 

 unconformity, is the Keweenawan Series. The parallelism 

 between this region and the Marquette already described is at 

 once manifest. The Penokee series proper is the equivalent of 

 the Original Huronian, Tapper Marquette and their equivalents : 

 The Cherty Limestone Member stands as a possible equivalent 

 of the Lower Marquette. But this correlation is of uncertain 

 value, and, if sound, in the Penokee-Gogebic district the upper 

 members of the equivalent of the Lower Marquette have been 

 removed by erosion. That this is not improbable is indicated 

 by the fact that the cherty limestone is of very considerable 

 thickness in some places and has entirely disappeared in others, 

 while numerous fragments of it are found in the basal member 

 of the Penokee series proper. 



