PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 589 



Sericite schist. Schist.] 



No. 883. SERICITE SCHIST. 



N. E. J sec. 5, T. 62-15 W., Vermilion lake. 



Ref. Annual Report, xv, pages 303, 388. Compare No. 397. 



Meg. A soft, greenish-gray, fine-grained, schistose, rather fissile rock. 



Mic. The sections- show a very fine-grained rock, composed of quartz, feldspar, 

 chlorite, and micaceous scales which are probably both muscovite and kaolinite. 

 Scattered through the rock are small, sharply outlined rhombs of a carbonate which 

 from its absorption and its yellow color in places, appearing as if altering to limonite, 

 is thought to be largely siderite. Part of this carbonate may be calcite. Some 

 opaque, dust-like material is scattered through the slide, and there is some magnetite. 

 There are a few grains of quartz of larger size than the average and these interlock 

 around their borders with the smaller grains. 



Two sections. 



Age. Keewatin. u. s. G. 



No. 884. SCHIST. (Earthy.) 



Breitung mine, Soudan, near the west end of the North ridge. 



Ref. Annual Report, xv, pages 249, 250, 270, 388. Compare No. 384. 



Meg. A soft, earthy, buff or nearly white, very fine-grained schist. 



Mic. The section is too thick for careful study. The rock is markedly schistose 

 and of fine grain and greenish color in section. The minerals appear to be mostly 

 chlorite and a micaceous mineral. There are a few grains of quartz of considerable 

 size and one shows an embayment similar to some of the quartzes of the quartz- 

 porphyries. Magnetite is common in minute particles and there are many minute 

 prisms which look like rutile, but they are nearly opaque and have no effect, as far 

 as can be determined in this thick section, on polarized light. With these supposed 

 rutile prisms are some heart-shaped twins which also look like rutile. 



One section. 



Age. Keewatin. 



Remarks. The original nature of this rock is uncertain. It may perhaps have 

 been a quartz-porphyry, but, if such, it has been very highly altered. u. s. G. 



Remark. This rock, on re-examinatian, appears to be a fragmental one, com- 

 posed of very fine (jaspilitic) quartz mingled with some clastic quartzes from some 

 quartz-porphyry and a considerable amount of much altered fine debris from some 

 basic source, probably from the pre-existing ridges of the Lower Keewatin in the 

 near vicinity, and to be therefore a part of the Upper Keewatin. It appears that 

 the irregular loose masses of jaspilyte which characterized the Breitung and the West 

 Breitung mines are comparable to the large masses seen at the south side of the 

 South ridge, near Tower, and that, like them, they are not of the original ore deposit 

 of the North ridge, but belong in the base of the Upper Keewatin. N. H. w. 



