PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 717 



Diabase. Granite. Greenwacke.] 



No. 1401. DIABASE. 



Small island in Kekequabic lake ; E. J N. E. J sec. 31, T. 65-6 W. 



Ref. Annual Report, xvi, pages 101, 124 ; see, also, Annual Report, xv, pages 153, 3G8. 



Meg. A rather fine-grained, fresh, dark-gray diabase. No section. 

 Age. Perhaps Keweenawan. u. s. G. 



No. 1402. GRANITE. 



On the west side of the dike in the southerly of the islands. 



Ref. Annual Report, xvi, pages 101, 124 ; Bulletin ii, pages 41, 422. 



Meg. Fine, gray, red-weathering. 



Mic. The section appears like the granite seen on the south side of the lake 

 further west, in larger amount, but rather finer. There is no augite, but in its place 

 is a congeries of biotite scales mingled with some actinolite. The old feldspars are 

 present, but smaller and apparently in fragmentary condition, and crowded with 

 minute crystalliths resulting from alteration; while, with the appearance of consid- 

 erable calcite, the micro-granulitic groundmass of quartz and feldspar has risen to the 

 aspect and proportions of a granitic structure. One section. 



Age. Archean (intrusive in Upper Keewatin). N. H. w. 



No. 1403. GRANITE. 



A little further west. 



Ref. Annual Report, xvi, pages 102, 124. 



Meg. Somewhat porphyritic. Compare Nos. 1044-1046. 



Mic. The rock shows the old zoned feldspars, but in the sparse matrix which 

 embraces them the grains are coarse, and, with their own fragments, constitute a 

 granitic rock. There is no augite, but in its place is actinolite, or at least some amphi- 

 bole, epidote and biotite. In this rock, in fine grains, are also magnetite, hematite and 

 sphene, and apparently a little garnet. One section. 



Age. Archean (intrusive in Upper Keewatin). N. H. w. 



No. 1404. GREENWACKE. (Conglomeratic.) 



From a ridge near the centre of the south side of sec. 31, T. 65-6, south shore of Kekequabic lake. 

 Ref. Annual Report, xvi, pages 102, 124. 



Meg. Hardened, graywacke-like greenstone. Compare Nos. 1051 and 1059. 



Mic. The green element in the rock is hornblende, which appears in the form 

 of ragged crystals and crystal fragments which sometimes appear to have slight 

 secondary enlargements and as fine debris throughout the slide. The next most 

 abundant ingredient is a micro-granulitic rock which is in rounded pebbles. Some- 

 times the micro-granulitic structure is sub-microscopic, and sometimes it is quite 

 coarse. Debris of the same kind is evidently dispersed widely and generally 

 throughout the rock, constituting the most of the finer matrix. Then comes quartz, 



