MUSEUM OF COMPAFvATIVE ZOOLOGY. 



49 



These garnet-bearing, actinolite, intrusive rocks we cannot at present 

 definitely place in that position which sccnss to ns proper. In order to 

 do that, it is necessary to have part at least of the original structure or 

 constituents preserved; this we did not iind. So far as we can judge, 

 tliey are probably altered basalts or andcsites, most probably the former ; 

 this conclusion is, however, liable to be overthrown by new evidence 

 at any time. The reason for this decision is in the main their rehx- 

 tion in minerals, position, antl structure to the other highly altered 

 *' dioritcs," especially at Republic Mountain. The actinolite schists 

 wore in all probability formed from detritus of the same composition 

 as the dikes, and therefore under like conditions are mineralogically 

 about the same. 



In the Lake Superior mine, a banded greenish quartz rock resembling 

 prase was observed. In the thin section it is seen to be composed of 

 quartz containing magnetite and innumerable little scales of greenish 

 mica. The green color is due to the latter. Some fluidal inclusions 

 were observed. The quartz shows the granular aggregate polarization 

 observed in connection with the devitrification or alteration quartz in 

 rhyolites and fclsites. The relation of this rock to the ore and jasper 

 was that of an intruding, fracturing, uplifting mass, breaking across the 

 lamination but not reaching the surface. Above, and adjacent to it in 

 the disturbed jasper and ore ''soft hematite" was found. This rock, wo 

 think, would make a very pretty object when polished. 



■ ■■ 



The " Soft Hematites," 



One of the best localities that we have seen to study the formation of 



■t 



the *'soft hematite" is at the Salisbury mine, Ishpeming, just south of 

 the Lake Angeline mine. A "diorite" hill lies between the two mines, 

 wdiich, when erupted, we believe upheaved the jasjior and hematite lyitig 

 on both sides of it. ■ At the west end, on the north side of the hill, the 

 Lake Angeline mine is situated, and it is still an open question whether 

 the ore formation does or does not extend eastward along the flanks of 

 the hill. On the southern side, towards the northern end of the hill, 

 the Salisbury mine is located. This is a "soft hematite," which is held 

 by Mr. Brooks to belong to a different formation, in general, from tlie 

 hematite. We regard it as the same formation as the jasper and its 

 associated ore, but which has been acted upon by thermal waters. All 

 the writers on the "soft hematites" of this district have regarded 

 them as formed from the decomposition of ferruginous schists by thermal 



VOL. VII. — NO. 1. 4 



