ORE DEPOSITS OP UPPEE HUEONIAN. 183 



spondiiig to the pitches of the axes of the synchnes in which they occur. 

 The pitches of these folds in turn correspond to the westward pitch of the 

 Crystal Falls synclinorium, of which the secondary sj^ncliues containing 

 the ore bodies are a part. A typical example of the occurrence is shown in 

 the Armenia mine ore body, which is found, according to Van Hise, "at the 

 bottom and on the sides of a synclinal trough, pitching* at an angle of about 

 45°"' The trend of the axis is to the south and west. 



The dip of the ore bodies is always steep, and generally to the south, 

 but varies in places to a few degrees north. 



The fact that the important mines in the district are located in a 

 synclinal basin and that they all possess an impervious footwall of black 

 slate gives very clearly the reason for their existence and indicates their 

 mode of origin. They are concentrates in synclinal troughs. 



In the j\Iarquette and Penokee-Gogebic districts the ore bodies are 

 frequently found associated with dikes of dolerite (diabase), which have 

 been altered to ''diorite "-schists, and so-called soapstone or paint rock.^ 

 Only one such association is known for the Crystal Falls district. Wads- 

 worth mentions having seen a dike in the Paint River mine.^ 



In the field notes of the Lake Superior survey for 1891, I find the 

 statement made that "the strata of the ore formation, which here strikes 

 nearly east and west, is cut by an eruptive dike which runs about north- 

 west and southeast. This dike hades to the west, and forms with the 

 hanging slates of the ore formation a trough pitching to the west at a very 

 steep angle. In this trough is situated the ore body upon which the Paint 

 River and the Monitor * mines are working." This ore body is stated to be 

 about 100 feet wide, 300 feet long, and of unknown depth. When I was 

 in the district, the mines were closed, or only shipping from stock piles, so 

 that I had no opportunity of verifying this observation. From this state- 

 ment it appears that in this particular case the ore is due to the j^resence of 



Iron ores of the Marquette district of Michigan, by C. R. Van Hise: Am. Jour. Sci., 3d series, 

 Vol. XLIII, 1892, pp. 130. 



-Merriam also mentions in his notes a dolerite dike found cutting the ferruginous rocks at the 

 Glidden exploration. In this case it does not appear that an ore body was formed. 



Sketch of the geology of the iron, gold, and copper districts of Michigan, by M. E. Wads- 

 worth ; Rept. State Board of Geol. Survey for 1891-92, 1893, p. 108. 

 <Now known as Lamont mine. 



