PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 679 



Basalt. Graywacke. Quartz-porphyry.] 



Age. Archean (Keewatin). 



Remark. This rock has a petrographic relationship with the porphyritic rock 

 at Kekequabic lake (Nos. 1061, 1094 and 1106), except that the augite, if it ever 

 existed in considerable quantity, has been destroyed by the exigencies through which 

 the rock has passed; and in that respect the relation seems to be nearer some of the 

 conglomeratic debris less metamorphosed, seen east from Kekequabic lake. N. H. w. 



No. 1280. BASALT. 



North shore of Gunflint lake, interetratified with the schists (Canada). 

 Ref. Annual Report, xvi, pages 67, 119. 



Meg. Having the appearance of a massive greenstone. 



Mir. In an originally glassy matrix lie microlitic feldspars and spicules of 

 magnetite of about cotemporary generation, the feldspars being generally a little 

 earlier, but occasionally cut by the magnetites. The zirkelyte is now devitrified. It 

 is filled with granular magnetite and pleochroic bwtite and apparently globular 

 augite. One section. 



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



No. 1281. GRAYWACKE (?) 



North shore of Gunflint lake (Canada). 

 Ref. Annual Report, xvi, pages 67, 69, 120. 



Meg. Gray, compact, weathering reddish, with sedimentary bands. 



Mtc. This is a rock similar to the fine-grained matrix of No. 1279, but finer and 

 less easily analyzed. There are fine mica scales everywhere in the rock, and these 

 scales are also gathered abundantly in spots, giving a spotted aspect to the slide 

 between crossed nicols. In some of the larger scales a pleochroism is visible. Hence 

 the mica is probably biotite. Some particles of sphene and groups of dark leucoxene 

 are identifiable. But the greater portion of the rock consists of fine angular 

 feldspars, which are fresh, and equally fine quartzes. One section. 



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



No. 1282. GRAYWACKE. (Sheared.) 



North side of Gunflint lake (Canada). 



Ref. Annual Report, xvi, pages 68, 120 ; Annual Report, xvii, pages 199, 202. 



Meg. Gray, gneissoid, slightly porphyritic. 



Mic. Like the last, excepting the presence of gneissoid structure and much 

 ml cite, with some quartz. One section. 



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



No. 1283. QUARTZ-PORPHYRY. ( Schistose debris. ) 



Bluff, north shore of Gunflint lake (Canada). 



Ref. Annual Report, xvi, pages 68, 120 ; Annual Report, xvii, pages 199, 202. 



