PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 913 



Camptonyte. Diabase. Gabbro.] 



and others of pyrite, and groups and scattered grains of epidote; but the general 

 aspect is that of a much altered diabase rock of originally massive nature, there 

 being a structure which is like the ophitic structure of diabase. One section. 



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



No. 139W. CAMPTONYTE (?) 



N. W. M S. W. M sec. 18, T. 63-11, Fall lake. 

 Ref. Annual Report, xv, page 66. 



Meg. Coarse, green, schistose, with distinct hornblende crystals. 



Mic. In a fine groundmass of indistinct feldspar and fibres of hornblende are 

 numerous idiomorphic crystals of hornblende usually twinned on 100, and frequently 

 showing a narrow peripheral zone which extinguishes with the central area, but 

 exhibits slightly different polarization tints, and in some instances the original 

 augitic form is well preserved by this difference of polarization. The rock is not 

 much decayed. One section. 



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



No. 177 W. DIABASE. (Altered.) 



N. E. y N. E. % sec. 30, T. 04-10, Urn lake. 

 Ref. Annual Report, xv, page 95. 



Meg. Doleritic. 



Mic. With much calcite and magnetite and some chlorite, a little hornblende and 

 leucoxene this rock still shows, in the position of the feldspars, that it was originally 

 a diabase with ophitic structure. One section. 



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



No. 770W. GABBKO. 



T. 64-5 E. (unsurveyed), Pigeon river. 

 Ref. Annual Report, xvi, page 289. 



Meg. Compact, hard, gabbroid. 



Mic. This rock seems to have been an olivine gabbro, but nothing now remains 

 to attest the former presence of olivine except a yellowish, serpentinous substance 

 in which apparently antiyorite takes part. The augite was nearly cotemporary with 

 the feldspar and is in small grains. The feldspar is evidently labradorite. 



Age. Cabotian. N. H. w. 



5'J 



