PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 631 



Jaspily te. Greemvacke. Greenstone . ] 



Mic. The forms of sections of microlitic feldspars are common in the section, 

 but these are dimmed by alteration products, appearing greenish and grayish in 

 natural light. Between them is a confused gray matrix, somewhat coarser grained 

 and so pierced by the feldspars, which lie in all directions, as to allow the suggestion 

 that the rock was once a fine-grained, ophitic diabase, but this matrix has no trace of 

 pyroxene, consisting rather of calcite, probably some leucoxene and irregular forms of 

 what is apparently a secondary feldspar. The green coloring matter is apparently 

 chloritic. Probably a clastic rock. One section. 



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



No. 1016. JASPILYTE (with magnetite). 



Centre of sec. 30, T. 63-11. 



Ref. Annual Report, xv, pages 325, 368, 394. Compare Nos. 2111, 2112. 



Meg. The usual banded iron ore of the Keewatin. 



Mic. The section is black in reflected light, like magnetite. The quartz, which 

 occupies angular openings in the magnetite, is crossed by intersecting fine bands of 

 black powder which is doubtless magnetite. One section. 



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



No. 1017. GREENWACKE. 



X. W. J4 sec. 28, T. 63-11, Garden lake. 

 Ref. Annual Report, xv, pages 327, 328, 394. 



Meg. Green schist, with megascopic crystals of white calcite and some granular 

 quartz like that of the jaspilyte. 



Mic. The slide shows none of the white masses and only a small amount of fine, 

 granular quartz, calcite and chloritic debris. The rock is evidently from a debris of 

 eruptive material. One poor section. 



Age. Archean (Lower Keewatin). N. n. w. 



No. 1018. GREENSTONE. 



N. W. 14 sec. 28, T. 63-16; same rock surface as the last. 

 Ref. Annual Report, xv, pages 327, 328, 394. 



Mey. Similar green schist as the last, but without evident calcite. 



Mic. Many microlitic feldspars, much decayed, originally twinned in twos, are 

 promiscuously disseminated in this rock. Much calcite is seen, not only within the 

 areas of the feldspars, but also in isolated grouped masses. There are clusters of 

 minute grains of a yellowish-gray, nearly opaque mineral, which in its thinnest edges 

 and projecting points is seen to be highly doubly refracting when highly magnified, 

 and is probably a form of leucoxene more dark than is usual. The distribution of the 

 feldspars in the mass hardly suggests a possible original diabase. There are a few 

 grains of pi/rite. The green coloring mineral is the same as seen in most of these 



