conflicting Views of Lake Superior Stratigraphy. 119 



N. H. Winchell,* to whom it appeared so great that the 

 rocks above it were provisionally referred to the Potsdam. 

 It has later been more broadly recognized by Prof. Alexander 

 Winchell, who maintains two systems have been " confounded 

 in the Huronian."f 



Our recent studies have shown the break to be universal in 

 the Marquette district. In order to understand fully its 

 nature it is necessary that the facts shall be given in some 

 detail. The greater part of the ore taken from the more prom- 

 inent mines occurs associated with hematitic, magnetitic and 

 actinolitic schists and jaspers. This jasper is curiously banded 

 and contorted, is often of a beautiful blood-red color, and is 

 commonly interlaminated with iron ores. Of prominent mines 

 among many which fall in this horizon may be mentioned the 

 Republic and Lake Superior. Below the iron- bearing mem- 

 ber is the lower quartzite of Brooks, which locally becomes a 

 marble or novaculite. Above the iron-bearing member is 

 Brooks' upper quartzite.^ This is in many places a pure thick 

 quartzite which immediately overlies the ore. This quartzite, 

 even when fine-grained, is of the variety in which the enlarge- 

 ment process has changed it from a sandstone to a vitreous 

 quartzite. It shows nowhere any evidence of having been 

 subjected to powerful dynamic action. It is at the base of 

 this quartzite that, the physical break referred to occurs. 



At the Goodrich Mine, just south of a large open pit, is the 

 banded ore and jasper formation which contained small bodies 

 of rich ore. The formation is exceedingly contorted, the 

 ribboning of the jasper now running in one direction, now in 

 another. The foot-wall of the large pit just mentioned is 

 this jaspery formation. Locally the banding of the jasper 

 abuts perpendicularly against the foot- wall. This foot-wall 

 strikes nearly in an east and west direction and dips at an 

 angle of 60° or 70° toward the north. The rock resting upon 

 the banded jasper, including that which has been mined for 

 ore, is a conglomerate, the fragments of which are chiefly from 

 the immediately underlying rock. These fragments vary from 

 those which are minute, to bowlders ten 'inches or a foot in 

 diameter. They are all thoroughly well rounded, so that there 

 is no question of their water- worn character. As indicated, 

 they are most abundantly of the jasper and ore immediately 

 below, and the ore, upon account of its softer character, is 

 predominant in the matrix. Mingled with the fragments 

 mentioned are numerous ones of white quartz, which are 



*Geol. and Nat. Hist. Survey of Minnesota, 16th Annual Report, 1887, pp. 

 43-47. 



f "Two Systems confounded in the Huronian," Am. Geol., vol. iii, pp. 212-214. 



\ Iron-Bearing Rocks of the Upper Peninsula of Michigan, T. B. Brooks: Mich. 

 Geol. Survey, 1873, vol. 2. p. 149. 



