PETROGRAPHIO GEOLOGY AND DESCRIPTIONS. 851 



Andesyte. Greenstone.] 



Remark. The hornblendes were derived from augite in the same manner as 

 those of the Kekequabic Lake region, and they show also the same zoned and parti- 

 coloration between the nicols, the darker, and generally central, areas indicating the 

 forms of the original augite grains the latest of the hornblende to be formed. 

 Compare Nos. 1051, 1060, 1409-1413. N. H. w. 



No. 2176. ANDESYTE (?) 



From a dike cutting the conglomerate ; near the same place as No. 2175. 

 Ref. Annual Report, xxiv, page 56. 



Meg. A light-brown rock, fine-grained and compact. One of the specimens is 

 roughly schistose, the other is not. The rock seems to be composed of feldspar, 

 possibly quartz, and dark minerals, probably hornblende and chlorite, in fine grains. 



Mic. The section was made from the non-schistose specimen. The rock is 

 porphyritic with small feldspars which, in part at least, appear to be near andesine- 

 oligoclase. These phenocrysts are set in a fine-grained groundmass in which feldspar 

 seems to be the only original mineral remaining. It is in part plagioclase. Through- 

 out the section and in the porphyritic feldspars much Muscovite and calcite have 

 been developed; also some chlorite. M aynetite and a little pyrite are seen also. There 

 are some grains of quartz which are larger than the grains composing the ground- 

 mass, but these quartzes do not appear to be phenocrysts. They sometimes occur 

 in connection with collections of chlorite scales, this mineral and the chlorite appar- 

 ently occupying the place of an original ferromagnesian mineral. The quartz, in 

 large part at least, thus seems to be secondary. One section. 



Age. Dike in Archean (Keewatin). u. s. G. 



No. 2177. GREENSTONE. 



Near the "contact" between the foregoing tuff and graywacke and a greenstone, but on the greenstone 

 side. The conglomerate all along dips south about 85, i. e., toward this greenstone, which is a wide belt extend- 

 ing, in general terms, to the Kawishiwi river. 



Ref. Annual Report, xxiv, page 56. 



Meg. Apparently massive, at least not showing distinctly any stratification, 

 and thus in marked contrast with the tuff and conglomerate. Weathered surfaces 

 show a protruding siliceous mesh, a character that sometimes distinguishes a clastic 

 greenstone from an igneous one. 



Mic. This consists of hornblende, feldspar, quartz, epidote, sphene, calcite. The 

 feldspars have been much eaten into by a secondary micro-granulitic generation, 

 which also serves to form a part of the finer matrix or groundmass for the rock in 

 general, constituting the siliceous roughness of the weathered surfaces, but in nearly 

 all cases there is still quite evident a remnant of the original feldspathic constituent. 

 One section. 



Age. Archean (Keewatin). 



