CURRENT PRE-CAMBRIAN LITERA TURE 5 1 9 



Lane 1 gives a detailed account of the geology and petrography of 

 Isle Royale, Lake Superior. The island trends north of east and the 

 edges of the strata outcrop in approximately this direction. The rocks 

 are interbedded conglomerates, sandstones, and traps of Keweenawan 

 age, dipping in a southerly direction at angles varying from 8-32 , 

 the higher dips in general to the north. Faults are shown to exist at 

 various places with directions approximately northeast-southwest and 

 northwest-southeast, and the probable existence of other more exten- 

 sive faults running entirely across the island is indicated. The detailed 

 sections with correlations with the Keweenawan of other parts of Lake 

 Superior are given in table on page 520. 



Hubbard 2 discusses the geology of Keweenaw Point with particular 

 reference to the felsites and their associated rocks. The term felsite 

 is used to include all the very fine-grained and highly acid igneous 

 rocks. These occur at a number of horizons below the Bohemian con- 

 glomerate, so-called from the fact that it skirts the northern side of 

 this range near the northeastern end of Keweenaw Point. The out- 

 crops of felsite studied occur in Sec. 30, T. 58, R. 27 (New England 

 or Keystone location); Sec. 25 (?), Sec. 35 (Fish Cove), Sees. 26 and 

 27 (Little Montreal River), all in T. 58, R. 28; Sees. 29 and 30, T. 

 58, R. 28 (Bare Hill and westward therefrom) Sees. 23 and 24, T. 58, 

 R 29 (Mt. Houghton) and both eastward and westward therefrom ; 

 Sec. 10, T. 57, R. 31 (Suffolk location, Praysville); Sec. 4, T. 56, R. 32 

 (Allouez Gap, east of the Kearsage and Wolverine mines); Sec. 30, T. 

 56, R. 32 (falls on branch of Trap Rock River); Sec. 36, T. 56, R. 33 

 (Douglass Houghton Falls), and Sec. 1, T. 55, R. 33 (Hecla and Torch 

 Lake R. R). 



The evidence concerning the source of the Keweenawan lavas is 

 considered and it is concluded that they may probably have come from 

 a higher level somewhat back from the edges of the present Kewee- 

 nawan basin. 



With this probability in mind, the following hypotheses are sug- 

 gested : 



1. The irregularities in the lower beds of the Keweenaw series in 

 the Portage Lake area, contrasted with the greater regularity of the 



1 Geological Report on Isle Royale, Michigan, by A. C. Lane : Geol. Surv. of 

 Mich., Vol. VI, 1898, Pt. 1, pp. 1-281. With geological map. 



2 Keweenaw Point with Particular Reference to the Felsites and their Associated 

 Rocks, by L. L. Hubbard : Geol. Surv. of Michigan, Vol. VI, 1893-1897, Pt. 2, pp. 

 184. With plates. 



