PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 849 



Greenstone. Porpkyrel.] 



Remark. This rock is allied to the greenstones of clastic origin, of which it 

 furnishes a novel phase. It occurs within the genei-al greenstone belt, and it 

 probably fades out into that rock. Compare No. 869. N. H. w. 



No. 2164. GREENSTONE. 



Northwest corner S. W. ^ sec. 26, T. 64-10, Pine lake. 

 Ref, Annual Report, xxiv, page 53. 



Meg. Speckled with light and dark, a kind of "pepper-and-salt" rock, appar- 

 ently a phase of a massive greenstone. 



Mic. This rock perhaps had originally an ophitic structure, and some of the 

 feldspars still show a " radial " arrangement, but the pyroxene is altered to hornblende, 

 which is probably the " pepper " of the megascopic aspect, while the " salt " is repre- 

 sented by feldspar and epidote, and by calcite. Feldspar is present in ragged remnants, 

 and in altered crystals. The finer epidotes are sometimes idiomorphic within an 

 isotropic chlorite. The rock also contains a liberal amount of coarse leucoxene. One 

 section. 



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



No. 2170. PORPHYREL. ( " Porphyrit'ic" conglomerate. J 



N. E. } N. E. } sec. 32, T. 64-9, near Moose lake. 

 Ref. Annual Report, xxiv, page 55. 



Meg. Apparently a porphyry. 



Mic. This rock is peculiar in having large feldspars, which speck the surface 

 as in a porphyry, some of them with sharp idiomorphic outlines, and yet in being 

 clastic in all its other characters. There are occasionally quite well rounded feld- 

 spars which have the shapes of water- worn pebbles. There are fragments also of 

 all sizes, but in general there is a sharp and remarkable contrast between the feld- 

 spars and the matrix in which they are embraced. They are completely permeated, 

 uniformly, by the products of alteration, principally by sericite, and their twinning 

 characters are very milch obscured, although it is plain that they are twinned quite 

 conspicuously and coarsely. In this character they are like those of Kekequabic 

 lake. Quartz in large grains also is seen in this slide, again resembling the conglom- 

 erate of Kekequabic lake. The matrix is fine and has much scattered calcite. It 

 also contains much fine feldspar. These are interlocked in a characteristic mosaic 

 or micro-granulitic structure with quartz. It is also evident that this groundmass 

 consists in part of a finer micro-granulitic structure which comes and goes in a 

 manner indicating that some of the smaller original feldspar grains have given place 

 entirely to the groundmass structure, as in the Ogishke conglomerate, or that there 

 were originally in the rock pebbles of different structure. 



55 



