340 THE GEOLOGY OF MINNESOTA. 



[Quartz, calcite. Schist. 



No. 377. QUARTZ, CALCITE, ETC. ( Vein matter. ) 



Same locality as No. 376. 



Ref. Annual Report, ix, page 95. 



Meg. Coarsely crystallized quartz, with calcite, pyrite, green carbonate of 

 copper, evidently from the decay of some copper mineral and limonite. 



Mir. The section shows much fractured grains of quartz, which make up most 

 of the section, around and between which is a finely crystallized mass of sericite, 

 calcite, and evidently quartz and feldspar; in fact, this material is quite similar to the 

 groundmass of No. 375. Green, brown and red staining material has been deposited 

 in the cracks of the quartz in places. 



One section.. 



Age. Vein in Archean (Keewatin) rocks. u. s. G. 



No. 378. QUARTZ SCHIST. ( Sericitic. ) 



Mud creek; N. W. % S. E. J sec. 4, T. 62-14 W. 

 Ref. Annual Report, ix, page 96. 



Meg. Slaty, quartzose, fine-grained, rusty with the oxidation evidently of 

 carbonate of iron. 



Mic. The matrix of this rock appears much like that of No. 376, but the quartz 

 is more fragmental, and the matrix contains more calcite, while the pyrite of No. 376 

 is here replaced by siderite, whose conspicuous, partly oxidized idiomorphic rhombs 

 are everywhere present. 



One section. 



Age. Keewatin. 



Remark. This seems to be a condition of the rock Nos. 375 and 376, but more 

 sheared. The carbonate of iron was generated instead of the pyrite, and since there 

 is no evidence to show that one was derived from the other, it is reasonable to assign 

 them both to the date of the shearing. N. H. w. 



No. 379. CHLORITE SCHIST. 



Vermilion lake, at the mouth of Mud creek; near the centre of the south side of the S. W. J^ sec. 6, T. 62-14 

 W. "This rock is like that in a range of hills which continues all the way to Mud lake, along the north side of 

 this stream, apparently confining the stream on that side, the slates running west-southwest at Vermilion lake." 



Ref. Annual Report, ix, page 96. 



Meg. A soft, greenish-gray, very fine-grained schist. 



Mic. The section shows a very fine-grained rock composed of numerous 

 minute flakes of chlorite, calcite and feldspar. There are also gray areas, which, 

 under a high power, are seen to be, in part at least, composed of very minute grains 

 which are probably epidote. The section is more or less confused, the different 

 minerals, especially the feldspar, having indistinct outlines, probably due to over- 



