PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 915 



Graywacke. Greenstone.] 



Mic. The quartz in this slide appears as a pneumatolitic product, and net as 

 original grains; along with feldspar in form of old (even porphyritic) crystals, is also a 

 considerable amount of hornblende, and, later, a large amount of epidote. The ground- 

 mass in general is coarser, and more varied, and the hornblendes are evidently the 

 result of uralitization, the old form of the augite scarcely remaining in the dark 

 central areas. One section. 



Age. Archean (Keewatin). 



Remark. This rock shows well the partial formation of granite from a clastic 

 rock, affording some of the same phenomena as described at Kekequabic lake. 



N. H. w. 

 No. 7H. GRAYWACKE. 



From the point, S. E. J4 sec. 8, T. 62-16, Vermilion lake. 

 Ref. Annual Report, xv, pages 282, 414. 



Meg. Gray, fine, slaty or coarsely schistose. 



Mic. A fine debris of feldspar and quartz, with a little hornblende; mica, epidote, 

 calcite, chlorite, as later products, having a schistose structure. One section. 



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



No. 8H. GRAYWACKE (?) (Sericitic.) 



Same locality as the last. 



Ref. Annual Report, xv, page 414. 



Finely conglomeratic; color varies from reddish to greenish; essentially 

 an acid rock, now sericitic. 



Mic. Coarse feldspars, large quartz grains and probably some augite composed 

 this rock originally. It is now so changed that the finer grains and much of the 

 feldspar have been recrystallized, forming an interlocking, finegroundmass; the feld- 

 spars are affected by the generation of multitudes of sericite scales and calcite, and 

 furnished with a new interlocking border, and the rare hypothetical augite is now 

 in the form of hornblende and chlorite. Cotemporary with this transformation has 

 been produced a considerable amount of epidote. A small sphene is preserved in one 

 of the old feldspars. One section. 



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



No. 9H. GREENSTONE 



N. E. 14 sec. 9, T. 62-16, Black Duck point, Vermilion lake. 

 Ref. Annual Report, xv, pages 282, 283, 299, 414. 



Meg. Acts somewhat like a dike, but has an indistinct sedimentary structure; 

 gray, schistose. 



Mic. This rock is similar to the last, except that it contains more chlorite and 

 hornblende, and the feldspars are almost entirely lost in the granulitization of the 



