Iron Ore Ranges of Minnesota. 61 



be considered simply a phase of the iron ore, there are but two 

 rocks in the entire series of the Mesabi section, viz: quartzyte and 

 slate. By instituting minute distinctions certain varietes of these 

 two might be called different rocks. For instance, the quartzyte, 

 which is at the bottom, is sometimes a conglomerate, and the slate 

 which is usually dark colored or even black, is sometimes purplish, 

 or even red, and so soft as to be more correctly called a red shale, 

 or paint rock. 



The significance of this red shale has but lately been under- 

 stood, and even its existence was overlooked. It was first seen by 

 the writer at the west end of the Mesabi range where it was pen- 

 etrated to the depth of eight fe%t and was found lying on ore- 

 bearing rock, the latter resting on the well-known basal quartzyte. 

 This was in 1888, and the diagram published at the time, in his 

 seventeenth report, is seen in the following slide. 



(19) Section at the Diamond mine at the west end of the Me- 

 sabi range, showing red shale lying above the ore. 



A similar red shale can be seen at the east end of the Mahon- 

 ing mine, at Hibbing, where it lies at a stratigraphic horizon which 

 furnished a large amount of ore at a short distance further west, 

 in the pit of the great mine. This red shale cannot be distinguished 

 from the red shale of the Keweenawan seen at many places along 

 the shore of lake Superior, and in the lower valley of the St. 

 Louis river near Fond du Lac. 



10. The Pecularities of the Mesabi Ore. 



Without dwelling on the significance of this led shale, at this 

 time, we will now briefly notice the Mesabi ore itself. After what 

 has been stated as to the easy mining methods, it is hardly neces- 

 sary to say that it is a soft granular ore. If we inspect it closer 

 we find that the granules sometimes are made of concentric con- 

 cretionary shells. Some of them are roundish, and some are parts 

 of spheres that have been broken. Sometimes these spheres are 

 much increased in size, and are then not concretionary. The; 

 shaped like pebbles, evidently water worn, and they are in such 

 numbers that they form thick beds of conglomerate. As they still 

 consist entirely of hematite such conglomerate beds have been ex- 

 tensively mined by the use of the steam shovel. This is partic- 

 ularly true at the Mountain Iron mine, where the bed of conglom- 

 erate is at least a hundred feet thick. It is to be inferred from 

 this gradation that the fine and the coarse were from the same 

 source, and have suffered a similar history — in other words, thai 

 they have both resulted from an identical change to hematite from 

 some earlier condition of the parent rock. 



It is not warrantable here to rehearse the steps of the l< 

 research through which this Investigation has been carried— haying 

 for its end the proper answer to the question— What was the nature 

 of the original rock the alteration of which produced the Mesabi 

 iron ore? In other words, what was the origin of the Ifesabl ore? 



