PETROGEAPHIC GEOLOGY AND DESCRIPTIONS. 769 



Quartzyte. Gneiss.] 



times rise in bold exposures 125 feet above the lake, becoming a characteristic coarse 

 conglomerate, undistinguishable from the Ogishke conglomerate, hard, semi-granit- 

 ized, generally green but weathering with a red tint. At points a little further east 

 granitic dikes cut it and replace it, changing it to a micaceous condition (No. 1728). 



Mic. The rock has a coarse schistosity, expressed in the uniform direction of 

 the longer axes of the minerals. Quartz is the most conspicuous and the most coarse 

 of the elements of the rock. It is of secondary origin, interlocking with the finer 

 grains of the matrix in which it lies. These quartzes are isolated, having an oval or 

 sub-oval general outline (with but few exceptions) and but seldom coming into 

 contact with each other. There are also finer quartzes, pertaining to the matrix, 

 equally of secondary date, and on careful examination it can be seen that a few grains 

 occur intermediate between the coarse and the fine, thus causing a gradation from 

 one to the other, but the contrast between the large quartzes and the groundmass is 

 not destroyed by this gradation. The most conspicuous part of the groundmass 

 consists of hornblende in small irregular and ragged bits. The larger pieces are 

 about one-half or one-third the size of the larger quartzes, but there are many much 

 smaller and quite irregular, not actinolitic. The groundmass, so called, also embraces 

 isolated grains that are of diopside( ?) of sphene, and considerable epidotc. Still, the 

 finer substance which embraces the coarser parts is apparently composed of altered 

 old feldspar crystals and crystal fragments whose integrity is almost destroyed by 

 inclusions, but which still can be discerned by an occasional feeble trace of albite 

 twinning, and also by a general simultaneous extinction over certain areas. The 

 minute inclusions in these feldspars are chiefly of sericite, globular minute feldspars 

 whose orientations are various and thus obscure the general extinction, and other 

 indeterminable grains, some of which are apparently of zoisite. There is also an 

 occasional grain of iron ore which may be large enough to rank with the larger 

 quartzes. One section. 



Age. Archean (Keewatin). 



Hi- mark. Structurally and petrographically this rock is referable to the conglom- 

 erate, but it has been largely reconstructed in the generation of secondary minerals. 

 Even the old, "much altered " feldspars appear in high powers to consist, so far as 

 they are of feldspar, of a fresh feldspar material, generated in the same spaces as 

 originally were filled by an older species. N. H. w. 



No. 1725. GNEISS. 



The country rock, a short distance east of No. 1724, S. W. % sec. 26, T. 64-9, shore of Snowbank lake. 

 Ref. Annual Report, xxi, page 156. 



Meg. Fine, granitic, a portion of the same mass as No. 1 724. 



50 



