PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 711 



Green wacke. Aruillyte. Dioryte.] 



No. 1383. GREENWACKE. 



Prom the centre of the same section, south of Prog Rock lake. 

 Ref. Annual Report, xvi, pages 98, 123. 



Mey. Greenstone. 



Mic. With the elements mentioned in Nos. 1381 and 1382, in this rock are 

 also angular grains of quartz, and a large increase of calcite. One section. 



Age. Ai-chean (Keewatin). N. H. w. 



No. 1384. GREENWACKE. 



Associated with the last, interbanded with it, and finer grained. 

 Ref. Annual Report, xvi, pages 98, 123. 



Mey. Finer grained than the last. 



Mic. Similar to the last. Here, however, the areas of the larger crystals are 

 occupied sometimes entirely by calcite in a finely granular state. One section. 



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



No. 1385. ARGILLYTE. 



West end of Ogishke Muncie lake at the southern portage to Dike lake. Near the centre of the west side 

 of the S. W. % sec. 27, T. 65-6 W. 



Ref. Annual Report, xvi, pages 78, 99, 124. 



Mey. Almost black, fissile argillyte, showing markings qn the surface like 

 minute ripple marks, but which may be due to movements since the solidification 

 df the rock. No section. 



Aye. Archean (Keewatin). u. s. o. 



No. 1386. DIORYTE. (Greenstone.} 



Summit of East Twin mountain. 



Kef. Annual Report, xvi, pages 99, 124. 



Meg. A coarse greenstone. 



Mic. The original ophitic structure is very evident, although the pyroxene is 

 now wholly altered to itralite. The feldspar is well preserved, considering the age of 

 the rock and the position of great exposure, showing its twinning lamellae distinctly, 

 both albite and pericline. There is one large crystal which shows a pegmatitic inter- 

 growth of quartz and feldspar, and isolated angular areas of quartz appear elsewhere. 

 The uralitic product takes the form, also, of numerous needles, which, by reason of 

 their higher double refraction and their form, appear to be of actinolite. A little 

 mlfiti' is sheltered in some of the interstices of the larger crystals. One section. 



Age. Archean (Keewatin). 



Remark. This was plainly an original basic igneous rock of the diabase order, 

 and owing to its known age it illustrates the preservation of the mineral composition 

 in the oldest known rocks having a Known igneous origin, and, by comparison, it 



