PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 879 



Granite.] 



No. 2265. GRANITE. 



On the portage from Moose lake to Flask lake, sec. 28, T. 64-9 W. At several places a rock of this kind 

 appears in lenticular bosses and dike-like intrusions in the coarse fragmentals. 

 Kef. Annual Report, xxiv, page 81. 



Mey. Except for a tendency to a reddish color this rock is quite similar to the 

 last two mentioned, but approaches nearer to No. 2263. 



Mic. The old. feldspars are crowded with Muscovite flakes, and these are some- 

 times interleaved with chlorite. Calcite is not so abundant as in No. 2263, nor pyrite 

 so abundant as in No. 2264. One section. 



Age. Intrusive in the Upper Keewatin. 



Remark. This rock is holocrystalline. The present feldspars, a regeneration 

 from the old clastic feldspars, like those of Nos. 2263 and 2264, while generally fine, 

 and for that reason hardly susceptible of specific determination, are occasionally larger, 

 presenting a vanishing, irregular and interlocking periphery, set in close order with the 

 finer feldspar grains that surround them. The present feldspar is probably more 

 basic than the original, some of the potassa having gone into the production of the 

 muscovite scales. The rock contains very little quartz. N. H. w. 



No. 2266. GRANITE. (Porphyritic.) 



On the same portage trail as the last, near the same place. 

 Ref. Annual Report, xxiv, page 81. 



Mey. A reddish rock, porphyritic with feldspar, sprinkled with pyrite, and with 

 an abundant finely disseminated, ferruginous oxide that appears to be the result of 

 alteration of a carbonate. Considerably coarser grained than Nos. 2263-2265, con- 

 taining pebbly forms, especially of greenstone. 



Mic. The ferruginous oxide surrounds more or less completely cores of a gray or 

 reddish-gray, highly doubly refracting, negative, uniaxial mineral, evidently that from 

 which the oxide is derived, and it is necessary to infer that the rock originally con- 

 tained a notable amount of siderite. It also contains now a large amount of pyrite, 

 which sometimes is also peripherally oxidized in the same way. The feldspars are 

 like those of the last described rocks (Nos. 2263-2265), except that some are larger 

 and present a distinctly porphyritic appearance. They are also accompanied by 

 original quartzes which are in part evidently bipyramidal. Some of the angular frag- 

 mental quartzes are enlarged by secondary rims which extend into and embrace the 

 surrounding matrix, causing a narrow simultaneous darkening with the regular 

 extinctions of the quartz. The feldspars are conspicuously twinned like those of the 

 porphyrel of Zeta lake, and like those of the porphyry and granite of Kekequabic lake. 



The matrix is non-homogeneous, but varies in spots in a manner suggestive of 

 the assimilation and reconstruction of pebbles under the action of profound meta- 

 morphism. For instance: (1) Siderite is very abundant or is wanting; (2) There 



