PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 627 



Iron ore. Greenstone.] 



No. 1001. IRON ORE. 



Harvey test pits, S. E. ^ sec. 27, T. 63-12. 



Ref. Annual Report, xv, page 393. 



Mey. Compact, fine-grained magnetite. 



Mlc. This iron ore is crossed by veins of microscopic size of secondary quartz, 

 but in general the section is opaque. One section. 



Aye. Lower Keewatin. N. H. w. 



No. 1002. GREENSTONE. (Tuff?) 



South shore of Long lake; sec. 28, T. 63-12. 



Ref. Annual Report, xv, pages 325, 326, 393; Annual Report, xxiii, pages 204, 213. 



Mey. Fine-grained, gray, siliceous, almost aphanitic. 



Mlc. The large amount of calcih' in this rock is the most striking peculiarity. 

 The masses are not large, but scattered widely, and frequently. The rock has a 

 rather firm frame-work, apparently of secondary i/nartz and feldspar, the latter 

 clouded principally by chlorite and zoisite. The rock darkens sometimes over small 

 areas in which are embraced numerous crowded grains of all the other substances, 

 most of which are undeterminable, but in the main it is finely granular. There are 

 evident feldspars, some being twinned on the albite plan. Fine grains of leucoxene 

 were probably derived from ilmenite. 



In general, the rock is a congeries of secondary minerals that have arisen from 

 the decay of evidently eruptive matter, but, from this specimen alone, it is impossible 

 to say whether originally massive or fragmental. Its structural relations, however, 

 and its complete alteration indicate that it is one of the basic tuffs of Keewatiu 

 so common in the vicinity. 



Aye. Lower Keewatin. N. H. w. 



No. 1003. GREENSTONE. (Tuff?) 



Prom about half way from the shore of Long lake to Patterson's trenches; sec. 28, T. 63-12. 

 Ref. Annual Report, xv, pages 325, 326, 393. 







Men. Slaty or schistose, more green than the last, fine grained. 



Mic. With an equal amount of chlorite and calcite, and less quartz, this rock 

 differs from the last also in having a large amount of green hornblende. It also 

 shows the outlines of the old feldspars which are crowded with chlorite, calcite and 

 minute hornblendes. In some parts of the slide are many tabular microlitic feldspars 

 which extinguish nearly or quite parallel with their longer sections, although the 

 included calcite does not allow perfect extinction. These may indicate an original 

 diabasic nature for the whole rock, or they may appertain to fragments of diabase 

 included in the debris. One section. 



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



