386 



THE MARQUETTE IROX-BEARIXG DISTRICT. 



greenstone, the formation having been spread out, as it were, by the entering 

 material. As seen in cross-section, the greenstone occurs in dome-like forms 

 under the schists, or as masses cutting across or between the layers. In 

 some cases the dip of the schists is comparatively little affected by the intru- 

 sive greenstone (fig. 17, p. 330), but in other cases the schist to some extent 

 mantles over the greenstone, although the schistosity is cut across on one 



Fio. 24.— Section ahowiiij; relations of griinerito-magnetite-scUiat and intrusive iliorite 

 (111 Mount Humboldt. 



side, and the dips remain prevailingly to the north (fig. 24). As seen in 

 plan, the greenstone often appears as oval areas sun-ounded by the schists, 

 the latter curving about the intrusive areas, as if bent by it (fig. 25). 



The griineritic and magnetitic rocks of Mount Humboldt rest upon the 

 Ajibik quartzite below, and are overlain upon the north and west slopes of 

 the bluff hj a thin belt of jaspilite, connecting the row of mining pits which 



Fig. 25. — Plat sliowiag relations between griinerite-magnetite-schist and intrusive 

 diorite on Mount Humboldt. 



extend from the old Humboldt to the Barron mine. This jaspilite is in 

 most respects like that at IMichigamme, different places showing beautifully 

 the white and red siliceous bands and varieties intermediate between the 

 two. However, at Mount Humboldt the jasper is extremely plicated, often 

 brecciated, and the ferruginous bands are most brilliant, coarse-grained. 



