PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 781 



Graywacke. Gneiss. Conglomerate.] 



Mir. This rock is like the last, but somewhat more decayed, showing areas of 

 rn/rifc, and some of the feldspar grains are affected by a micro-granulitic alteration. 

 Such alteration of feldspar grains is not uncommon in the Ogishke conglomerate, as 

 already noted. One section. 



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



No. 1772. GRAYWACKE. (Tuff?) 



N. W. J4 S. W. )4 sec. 31, T. (!5 5, north shore of Gabemichigama lake. 

 Ref. Annual Report, xxi, page 159. 



Meg. Pebbly, no strike or dip visible, though there is a dim appearance of 

 strike northeast. 



Mic. Angular (jintrlzes are sparsely distributed with fragmental fdi/sjHirx and 

 honibh'iuli'H through this rock. At the same time there are many areas of micro- 

 granulitic structure which were formerly occupied by feldspars, a feature which is 

 recognizable in much of the Ogishke conglomerate. This slide has more the struc- 

 ture of a tine agglomerate or tuff than of conglomerate. One section. 



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



No. 1773. GKAYWACKE. (Tuff?) 



One hundred yards north of the last, on a low, sloping surface. 

 Ref. Annual Report, xxi, page 159. 



Mr;/, lias no evident dip or structure. 



Mic. Similar to the last, but with more abundant micro-granulitic structure. 

 The larger (and fresher) feldspars and the quartzes lie in a general matrix of micro- 

 granulitic structure in which it is not possible to distinguish the forms of older 

 grains, but which still must be supposed to have originated in the same way, but 

 from finer original material. One section. 



A//r. Archean (Upper Keewatin). N. H. w. 



No. 1775. GNEISS. (Bio/tibia.) 



Prom the older formation, near the gabbro, on the east side of the northeastward bay, Gabetnichigama 

 lake; S. W. % sec. 29, T. 65-5 W. 



Ref. Annual Report, xxi, page 159. 



Meg. Fine grained. 



Mic. Feldspar and biotite make up the most of this rock, but small globular 

 diopsides( ?) are also common, with a little magnetite and pi/rite. It has no schistose 

 structure, but was produced by a regeneration of a fine fragmental rock, probably 

 some part of the Ogishke conglomerate. One section. 



Age. Archean (Upper Kewatin). N. H. w. 



No. 177(i. CONGLOMERATE. (Finer i>rHn .) 



N. E. J4 S. E. J4 sec. 30, T. 65 5, Gabcmichigaiua lake. From a hill rising 150 feet. 

 Ref. Annual Report, xxi, page 159. 



