Van Hise — Iron Ores of the Penokee- Gogebic Series. 47 



an eruptive rock ; but in the few cases of which we have defi- 

 nite knowledge, the manner in which the soapstones cut the 

 adjacent rocks is that of dykes. This is particularly well shown 

 at the large open pits at the Jackson Mine, ISTegaunee, Michigan, 

 and at the Champion Mine, Champion, Michigan. This same 

 dyke-like character of the peculiar schistose rock at one mine 

 in the Yermilion Lake series is described and figured by Pro- 

 fessor Alexander Winchell.* Mr. James R. Thompson, Min- 

 ing Engineer for the Iron Cliffs' Mining Company, of Negaunee, 

 Michigan, also finds in quite a number of mines in the Mar- 

 quette region, that the soapstones have a dyke-like character. 

 "With most of the soapstones of these regions, the only evidence 

 that they are of eruptive origin is their relations to the rocks 

 which they intersect. They have not been shown in many cases, 

 as in the Penokee- Gogebic region, to have the typical structure 

 of eruptive diabases ; but the transition phases between these 

 much altered rocks and the comparatively unaltered massive 

 eruptives have in some instances been found, and it is probable 

 that many of them are altered eruptives. At any rate, the 

 close association between the soapstones and the ores can hardly 

 be accidental, and, taken in connection with what has been 

 given in reference to the Penokee-Gogebic ores, it is very sug- 

 gestive that they, in some way, and perhaps in a way similar 

 to that in the Penokee-Gogebic region, have influenced the con- 

 centration of the iron in the ore-bodies at the places found. 

 To certainly determine the origin of all these " soapstones," 

 and their stratigraphical and other relations- to the ore-bodies 

 will require a detailed investigation. It would, however, be an 

 interesting illustration of the uniformity of nature's processes, if 

 such future investigation should show that the iron ores in the 

 otner regions of the Lake Superior country have an origin like 

 those of the Penokee-Gogebic series. 



Madison, Wisconsin, October, 1888. 



DESCRIPTION OF FIGURES. PLATE II. 



Figure 1. — Cross-section of the Penokee-Gogebic series at Penokee Gap, show- 

 ing: the relations of this series to the underlying Laurentian and the over- 

 lying Keweenaw series. The figure also shows the conformable succession 

 of the four members of the series itself. At this particular place, the quartz- 

 slate member, as compared with the iron-bearing member, is thicker than 

 usual. Scale 1" = 4000 / . 



Figure 2. — Elevation of First National mine, looking south. The eastern pitch 

 of the dyke is shown, and the resultant greater depth of the ore in passing 

 to the eastward. Scale 1" = 130'. 



.Figure 3. — Cross-section of same mine, looking east. Scale 1" = 130'. 



* Geol. and Nat. Hist, of Minn.; 15th annual report, pp. 24-25. 



