GEOLOGICAL EXPLORATIONS AND LITERATURE— ISTd. 63 



region, the aiithoi- writt's, tlieso cruptivos "have pushed up thr()U<rh tlie 

 Huronian beds, cuttini;;' tlieiu and the Potsthim at tlie same time," but 

 he does not give jiarticuhn-s. llie oi'es of the Marquette area and their 

 associated rocks are beheved to belong in the Huronian svsteiu, wliicli in 

 Michigan and in Canada possess a remarkable similarit\'. Incidentally the 

 author gives a sketch of the relations between the trap and sandstone at 

 Presque Isle. The former is re])resented as penetrating the sandstone and 

 producing on the contact a friction conglomerate. 



1S76. 



Bkooks, T. B. On the youngest Huronian rocks south of Lake Superior, and 

 the age of tlie copper-bearing series. Am. Jour. Sci. (3). Vol. XI, 187(5, pages 

 20C-211. 



In his ^lichigan re})ort on the iron-l)earing series Brooks places the 

 granites with the gneisses of the Upper Peninsula, and regards them all as 

 belonging- with the Laurentian, unconformably beneath the Huronian l)eds. 



In 1S76, however, in an article dealing more particularly with the 

 Menominee iron district, the same author notes the discovery of granites 

 cutting micaceous and hornblendic schists similar to those in Formation 

 XIX of the Manpiette series. If this formation is the toiimost portion of 

 the series, as is suj)posed, the granite must be Huronian. ^lorcover, the 

 Huronian series is so different lithologically from the copper-bearing series, 

 and the movements that have been undergone by the two series are so dif- 

 ferent in amount, that it is necessary to conclude that the copper-bearing 

 series is much younger than the Huronian. "We are therefore justiiied, 

 I think, in regarding the copper-bearing rocks of Lake Superior as a dis- 

 tinct and independent sei'ies, marking a definite geological period which 

 separates the Silurian from the Huronian ages." For this series the author 

 proposes the name "Keweenawian," unaware that Hunt' two years earlier 

 had reached the same conclusion and had proposed as thc^ name of the 

 series "Keweenian." 



This article, though dealing almost exclusively with a region outside 

 the Marquette area, is of interest, since it contains the first definite statement 



'Trans. Am. Inst. Miu. Eng., Vol. I pp. 339-341. 



