PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 821 



Quartz-porphyry.] 



Meg. Dark, coarse, the conspicuous hornblendes lying in a sparse, fine, pinkish 

 feldspathic matrix. 



Mic. The hornblende is so abundant as to interlock with itself and with the 

 microcline. It embraces grains of epidote and of sphene, and a small amount of 

 crumpled biotite. One section. 



Aye. Archean(?) (boulder). N. H. w. 



No. 2010. QUARTZ-PORPHYRY. (Esterellyte?) 



Small island, east side of sec. 20, T. 62-15, south side of Vermilion lake. 

 Ref. Annual Report, xxiv, page 12. 



Meg. Two pebbles (Nos. 2010 and 2011) in the conglomerate forming this island, 

 lying adjacent, have different outward appearance, this being finer than the other. 



Mic. In a fine groundmass lie large crystals of feldspar and a few of quartz. 

 The feldspar crystals are uniformly triclinic and conspicuously twinned onthealbite 

 and pencline plans, and on the Carlsbad (?), the last consisting of the connection of 

 one or two small crystals apparently on the plane 010 of a larger one, in a manner 

 similar to the twinning of some of the feldspars in the schist of Kekequabic lake. 

 These feldspars are all much and evenly decayed, and are thickly sown with particles 

 of calcite and of sericite. They frequently have their own crystalline forms, but there 

 are many parts of crystals of all sizes, running down to the matrix, and in the 

 matrix can be seen forms that show a gradual disappearance of some of the smaller 

 feldspars by the growth of a fine granular secondary substance identical with that 

 seen in the schists of Kekequabic lake, but usually somewhat less observable. This 

 secondary growth has slightly affected the borders of the larger feldspars, giving 

 them a differently extinguishing narrow fringe which is interlocked with the contig- 

 uous fine groundmass; and it is evident that the groundmass or finer cement consists 

 very largely, if not entirely, of this secondary generation of a granulitic matrix, as it 

 is intimately and universally interlocked, the small grains not being round altogether, 

 but sometimes elongated in a feldspathic manner. It contains very little if any 

 quartz; indeed, it is impossible to affirm that it contains any quartz. The larger 

 grains of quartz, comparable with the larger feldspars, are quite evident, but quite 

 few. One section. 



Age. Upper Keewatin (pebble in). N. H. w. 



No. 2011. QUARTZ-PORPHYRY. (Esterellyte?) 



Same place as the last. 



Ref. Annual Report, xxiv, page 12. 



Meg. Granular, coarser than No. 2010. 



Mic. This rock is coarser, has larger and more numerous quartzes, and larger 

 feldspars, and a finer cement, but in all other respects it is quite similar to rock No. 



