96 THE PENOKEE IRON-BEAEIXG SERIES. 



pits, is almost iiivarialily lollowi'il by a (Iccliiic in tlic iron foiitent.s. Altliongh the 

 ore from a few mines is almost too liigli in pliospliorns, the aveiage product of the 

 district is of Bessemer .yrade. The ore carries about 1.'5 per cent ol' moisture in the 

 winter, sometimes runniiifi' as hij;li as lo per cent, while iu ttie suuuuer it is from 4 to 

 5 i)er cent less, avera.i;iii,u- 7 lo 10 per cent (pj). 1S4-1.S7). . 



lRVlN(i (K. D.). On the Olassiticatiou of Mic Early ("anibriaii and pre-Cambrian 

 rormatious: A Brief Discussion of riincii)les. Illustrated by P^xamjiles Drawn 

 jMaiidy from the Lake Superior Region. U. S. Geological vSurvey, J. AV. Powell, 

 Direct(U'. Seveuth Annual Report, pp. 365-45-1. 



Til this paper Prof. Irving' o-ives a lull aci-oiiut of the "Uncouloriiiities 

 of the Penokee-Go^^ebic region of northern Wisconsin and Michigan." 

 The following is tlie first ])aragrapli of the discussion: 



No other so striking exami)le of iinconforniity between a series of liighly tilted 

 but unfolded strata above the break, and a deeply folded series below, as that afforded 

 by the Penokee region is known to the writer. Indeed, there are in this legion two 

 notable stratigrapliical Ineaks: <me between the iron-bearing series and the folded 

 gueissic formation to the south of it; auother between the unfolded but inclined 

 iron-bearing series and the e(|ually highly inclined Keweenaw series to the north. 

 These breaks and the terranes which they separate are the counterparts of tliose just 

 described as obtaining north of lake Superior (p. l'2o). 



The proof of tlie positions here taken are not oi\en, as the whole 

 question is gone over in a subsequent chapter of this monograph. 



WiNCHELL (N. H.). The Gogebic Iron Region. In the Geological and Natural 

 History Survey of Minnesota. Sixteenth Annual Report, for the year 1887. St. Paul, 

 1888, pp. 54-60. 



A cursory examination was made of some of the mines in the Gogebic iron 

 region, in order to be able to compare the features of the rocks and the manner of 

 occiu'rence of the ore with the iron-bearing rocks of the Vermilion iron range, and 

 some rock-samples were collected for future microscopic comparisons (p. 54^. 



At the Colby mine . . . there is ajjparent no hanging wall or footwall cxcejit 

 the rock of the country, and that is a thin-bedded siliceous rock which itself is almost 

 ore in some places, l)ecause of the high degree of ferrugiuization. This siliceous 

 material is jasperoidal and distinctly bedded exactly like the bedding of sedimenta* ' 

 tion. The base of it all is api)arently a line "chalcedonic" silica, tlic same as that of 

 the jaspilitc, though in sonic, or majiy, of the beds it is a softer material, which nuiy 

 be earthy. . . . The south wall of the .south Colby miuc consists of a crumbliug, 



