PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 339 



Schist. Quartz-porphyry.] 



No. 374. CLAY SLATE. 



Same locality as No. 373. 



Ref. Annual Report, ix, page 95. 



Meg. Resembles No. 373, but is greener and more siliceous, almost cherty. 



No section. 



Age. Archean (Keewatin). 



Remark. Later, a section of this rock was made by Marchand. It shows- a com- 

 position essentially like those already described, viz.: Nos. 170 and 171, but much 

 finer. N. H. w. 



No. 375. SERICITE SCHIST. ( Sheared quartz-porphyry?} 



South side of Mud lake; S. W. \i N. E. % sec. 3, T. 62-14 W. 

 Ref. Annual Report, ix, pages 05, 102. 



Meg. A light greenish-gray, roughly schistose, aphanitic rock, with large quartz 

 . grains and highly altered feldspars, a sheared quartz-porphyry (?) 



Mif. The section shows a groundmass of fine grain holding large crystals of 

 feldspar and quartz. This groundmass is composed of calcite, sericite and an indistinct 

 very fine-grained mass, apparently of actinolite quartz and feldspar. A little pyrite is 

 present. A noticeable part of the section is a fissured quartz grain, the fissures being 

 filled with calcite. The feldspar phenocrysts are very highly altered, so much so that 

 their species cannot be determined. They are in places hardly distinguishable from 

 the groundmass and are apparently decaying into an aggregate closely similar to this* 

 groundmass. 



One section. 



Age. Keewatin. 



Remark. The section was evidently cut about parallel to the schistose structure. 

 This rock perhaps represents a quartz-porphyry which has not only been sheared, 

 but is also highly decayed. u. s. G. 



No. 376. QUARTZ-PORPHYRY (?) (Sheared.) 



West end of Mud lake, at an old mining location; S. W. %N.W.% sec. 3, T. 62-14 W. 

 Ref. Annual Report, ix, page 95. 



Meg. Similar to No. 375, but perhaps more compact. A gray rock coarsely 

 schistose, with quartz, and mottlings of green, the greenish parts being apparently 

 amorphous, with hardness about 4. 



Mic. Very fine-grained matrix, embraces large quartzes, evidently the latter 

 the form of quartz that characterizes a quartz-porphyry. In the matrix are mica- 

 pennine, calcite and feldspar; the last in much decayed large crystals, with some 

 conspicuous deposits of pyrite. The chlorite polarizes in blue, like pennine. 



One section. 



Age. Archean (Keewatin). N. H. w. 



