446 THE JOURNAL OF GEOLOGY. 



The well known characteristic rocks of the Lower Huronian are i) con- 

 glomerates, quartzites, quartz-schists, and mica-schists, 2) limestones, 3) 

 various ferruginous schists, 4) basic and acid eruptives, which occur both as 

 deep seated and as effusive rocks. The order given, with the exception of 

 the eruptives, is the order of age from the base upward. In the Lower 

 Huronian are placed the Lower Vermilion, Lower Marquette, Lower Felch 

 Mountain, Lower Menominee, the cherty limestone formation of the Penokee 

 district, and also probably the Kaministiquia series of Ontario, and the Black 

 River Falls series of Wisconsin. 



The formations of the Upper Huronian are i) a basement slate and 

 quartzite, frequently bearing basal conglomerates, 2) an iron-bearing forma- 

 tion, consisting originally of lean cherty carbonate of iron, calcium and mag- 

 nesium, and 3) an upper slate. Associated with the sedimentaries in the 

 Michigamme, Crystal Falls, and other districts, are great volcanic series, com- 

 prising greenstones, agglomerates, greenstone conglomerates, volcanic ash, 

 and amygdaloids. Where these occur the orderly succession is destroyed. 

 Included in the Upper Huronian are the Penokee, Mesabi, Animikie, Upper 

 Marquette, Upper Menominee, and Upper Felch Mountain districts. 



The Keweenawan consists of interstratified lavas, sandstones and con- 

 glomerates. The lavas are prevalent at the lower part of the series ; inter- 

 stratifications of the two occur in the middle portions ; and the pure detntals 

 exclude the volcanics in the upper portion of the series. 



The Lower Huronian is largely crystalline, the Upper Huronian semi-crys- 

 talline, and the Keweenawan simply cemented. Locally along axes of intense 

 plication, both the Lower Huronion and Upper Huronian have been trans- 

 formed into completely crystalline schists. The Cambrian of Lake Superior 

 is a horizontal sandstone, and rests unconformably upon all the precedmg. 



Smyth' describes a contact between the lower quartzite of the Lower 

 Huronian and the underlying granite at Republic, Michigan. Below the 

 lowest exposures of magnetite-actinolite-schist are. exposures of the lower 

 quartzite, and below this, hanging upon the northern flank of the granite, is a 

 conglomerate containing very numerous well rounded bowlders of granite 

 and gneiss, identical with the rocks immediatiately below. It is concluded 

 that this conglomerate from its position can not possibly belong to the Upper 

 Huronian, and that it is a true basal conglomerate of the Lower Huronian. 



Winchell, N. H.,^ gives the following as the general consensus of opinions 



'A contact between the Lower Huronian and the Underlying Granite in the 

 Republic Trough, near Republic, Mich, by H. L. Smyth, Journ. of Geol., Vol. I., 

 No. 3, pp. 268-274. 



^The Crystalline Rocks, by N. H. Winchell. In 20th Annual Rep. Geol. & Nat. 

 Hist. Sur., Minn., 1891, pp. 1-28. 



