PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 841 



Dioryte.] 



There is a little secondary quartz which embraces and interlocks with the feld- 

 spars. and apparently lencoxene, which is nearly opaque, but in reflected light is white 

 and similar to the feldspars. One section. 



Age. Keewatin. 



Remark. This rock in its recrystalline condition is comparable with the 

 granites of Kekequabic and Snowbank lakes. N. H. w. 



No. 2120. DIORYTE. 



About 200 feet above Long lake, and from the very top of the hill west side of sec. 18, T. 63-12 W. 

 Ref. Annual Report, xxiv, page 43. 



Medium-grained, greenish gray. 



Mic. This rock exhibits an ophitic relation between the feldspars and the horn- 

 blendes, showing that its constituents crystallized from a magma, and that the feld- 

 spar formed first. These have suffered a complete transformation, being permeated 

 by fine, granular elements, such as serieite, zoisite, epidote, so that their optic char- 

 acters are wholly obliterated. Subsequently they have suffered a regeneration, and 

 have fresh, narrow veins of secondary feldspar, and inter-lamellar growths in an 

 imperfect micro-pegmatitic form. 



The hornblende has secondary fibrous enlargements in a manner similar to that 

 described in No. 2104, but far less marked. The slide also contains several small 

 areas of quartz which appears to be secondary. One section. 



Age. Keewatin. 



Remark. In all respects, except in having an ophitic structure, this rock resem- 

 bles that of No. 2104. N. H. w. 



No. 2125. DIORYTE. ( Probably fragmental. ) 



N. E. J^ S. E. 14 sec. 150, T. 63 13 W., west end of Long lake. From a ridge between the quartz vein and 

 the railroad. 



Ref. Annual Report, xxiv, page 43. 



Meg. A medium-grained rock of greenish-gray color, composed essentially of 

 feldspar and hornblende, the latter being conspicuous by its size. All the grain and 

 structure indicate a much pressed and perhaps sheared rock. 



Mic. The hornhlntde is in ragged, and often chloritized, grains. It has no 

 ophitic structure, or other relation to the feldspars that would show that it crystal- 

 lized from a molten magma. Its forms and sizes are consistent with the supposition 

 that the hornblende was a fragmental ingredient in the process of accumulation of 

 a green debris from older greenstones, and this origin is still more strongly probable 

 from the nature of the rest of the rock, which consists of fragments of hornblendes, 

 tending to become rods by separations along the cleavages, of secondary feldspars, 

 epidote, calcite (sometimes surrounding crystals of epidote), sericite, zoisite, and nearly 

 opaque leucoxene. One section. 



