446 THE CRYSTAL FALLS IKON-BEARING- DISTRICT. 



undoubted presence of lavas in the series, shown by the sericite-schists, 

 amygdaloids, and greenstone conglomerates or agglomerates. Furthermore, 

 the minerals which compose the schists are those which would result from 

 the alteration, in connection with dynamic metamorphism, of igneous rocks 

 of basic or intermediate chemical composition. Finally, the grain and 

 character of the groundmass, and in some slides the presence therein of 

 plagioclase microlites disposed in flow lines, point directly to an igneous 

 origin and to consolidation at the surface. 



Mr. Clements has reached similar conclusions for the formation above 

 the Randville dolomite^ on the western side of the Archean dome. There 

 metamorphism seems to have progressed less far than in the Fence River 

 area, and among the more basic rocks he has recognized andesites and 

 basalts. 



I conceive, then, that the Hemlock rocks of the Fence River area are a 

 series of old lava flows, varying in composition from acid to basic, wdiicli 

 first underwent dynamic disturbance, which developed the secondary cleav- 

 ages, and afterwards, in a state of rest, the porphyritic minerals were 

 formed. It is an interesting fact, for which I can suggest no explanation, 

 that metamorphism is further advanced in the northern part of the area 

 than in the southern, and the schists luore distinctly crystalline. This is 

 also true of the underlying dolomite. 



SECTION VI. THE GROVELAND FORMATION.^ 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



The Groveland formation in this area, as in the Felch Mountain range, 

 consists mainly of siliceous iron-bearing rocks, which hold much fragmental 

 material, together with certain subordinate schists. While it is of wide 

 extent thi-oughout the area, its known outcrops are limited to three local- 

 ities, namely: The vicinity of Michigamme Mountain, in sees. 33, T. 44 N., 



1 Volcanics of the Miobigamme district of Michigan, by J. Morgan Clements: Jour. Geol., A^ol. 

 Ill, 1895, No. 7, p. 801. 



'-This formation was originally named by me the Michigamme Jasper (Am. Jour. Sci., March, 

 1894). The name Michigamme was subsequently used for one of the Upper Marquette formations, in 

 the Preliminary Report on the Marquette District, 15th Ann. Kept. U. S. Geol. Survey. I now aban- 

 don the old name, although it is entitled to stand by the rules of priority, in order to avoid the con- 

 fusion which would necessarily arise from its retention. 



