PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 697 



Quartzyte. Gabbro.] 



No. 1340. QUARTZYTE (with diallage ). 



One-eighth of a mile west of the ore pits (No. 1336) at Chub lake. 



Ref. Annual Report, xvi, pages 85, 122 ; Annual Report, xvii, pages 199, 203 ; Annual Report, xviii, page 

 62; Annual Report, xix, pages 198, 199, 201, 203. 



Meg. Purplish-gray, vitreous, with magnetite. 



Mic. The magnetite is in the main at the borders of the quartz grains, which are 

 rounded, closely compacted and adjusted at their margins, but not interlocked, yet 

 embraces frequently small, round magnetites. A few grains of diallage, with enstatite 

 in the parting planes parallel to 100, are in like manner crowded amongst the quartzes, 

 generally giving place to the forms of the quartz, but sometimes independent of the 

 quartz. In the former are small globular inclusions of pyroxene and of magnetite. 

 It is only the generally rounded shapes of the quartz grains and their uniformity of 

 size that can be considered perhaps an indication of their earlier clastic origin, for 

 at present the original outlines are lost, if they ever had any others. The three 

 principal minerals quartz, magnetite and diallage mutually enclose small globular 

 individuals of the others. One section. 



Age. Pewabic (modified jaspilyte o'f the Keewatin). N. H. w. 



No. 1341. GABBRO. ( Muscovadyte. ) 



Near the top of the quartzyte ridge visible on the north side, a sill, one-fourth of a mile west of the ore 

 pits (No. 1336), Chub lake. 



Ref. Annual Report, xvi, pages 85, 122 ; Annual Report, xix, pages 198, 201, 203. 



Meg. Granular, gray, magnetited. 



Mic. Prof. W. S. Bayley's description of this rock is as follows: 



"The gabbro interbedded with the crystallized quartzyte is in an intermediate 

 phase between the coarse grained normal olivine gabbros and the granulitic varieties, 

 in which the pyroxene occurs in small rounded grains. The olivine is in the ordinary 

 form. The plagioclase is in irregular grains, with a tendency to the lath-shaped 

 forms of diabasic feldspar. Its gabbroitic character is evinced in the abundance of 

 dust-like particles scattered through it, and especially by their thick accumulation 

 toward the centres of all grains. The pyroxene is a light colored augite, thickly 

 crowded with magnetite grains, small masses of limonite and tiny plates of brown 

 biotite. Some of the augite is in ophitic plates between the feldspars, but most of it 

 is in little rounded grains. The magnetite, nearly all of which is secondary, is thickly 

 strewn through the section in long irregular grains in and between the other constit- 

 uents, especially the augite and olivine, and in tiny rounded grains in the augite and 

 the plagioclase." 



In the light of previous descriptions and interpretations, this rock is a secondary 

 one. The above description would apply to many muscovadytes or regenerated 

 greenstones. The bed from which the rock came is hence to be regarded as originally 



