PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 839 



Greenstone. Conglomerate. Porphyrel.] 



No. 2099. GREENSTONE. ( Matrix of conglomerate. ) 



Small island in Long lake near the west side of S. W. J4 sec. 29, T. 63-12 W. 

 Ref. Annual Report, xxiv, page 41. 



Meg. Bather light green, schistose, fine grained and rather soft. Some small 

 hornblendes are scattered through the rock. 



Mic. The most conspicuous and also the largest of the ingredients is feldspar. 

 It appears to have been enlarged by secondary growths, as it interlocks with the 

 grains adjacent, and its original (central) portions are altered, containing many 

 sericite scales and calcite, which are wanting in the peripheral portions. Quartz is 

 also secondary, forming some areas as large as the feldspars. Shreds of hornblende 

 give a green cast to the rock. These are but slightly pleochroic. Running across 

 the slide is a microscopic vein of fresh minerals. These are quartz and striated 

 feldspar. These minerals interlock in the adjoining rock mass. There is much calcite 

 and sericite in the adjoining rock, but none (or almost none) in the vein. One section. 



Age. Upper Keewatin, probably of the age of the Stuntz conglomerate. 



Remark-. This is a wholly crystalline rock, even in its interlocking structure, 

 and would pass for an " altered diabase," were it not for the field relations, which 

 demonstrate beyond question that it was at first fragmental. N. H. w. 



No. 2101. CONGLOMERATE. 



West shore of Long lake ; S. E. J sec. 30, T. 63-12 W. 

 Ref. Annual Report, xxiv, page 42. 



Meg. The three specimens collected vary from rock resembling No. 2099 to a 

 flue, almost flinty greenstone. These specimens evidently represent the matrix of 

 the conglomerate. No section. 



Age. Upper Keewatin. u. s. G. 



No. 2102. PORPHYREL. (Sheared. ) 



Same place as No. 2101 and rising in the midst of No. 2101. 

 Ref. Annual Report, xxiv, page 42. 



Meg. Gray, feldspathic and evidently siliceous. Crushed and deformed, medium 

 grained, appearing suddenly in the midst of No. 2101 in the manner of an isolated 

 mass or intrusive, but not determinable as to its extent. Holds some pyrite and was 

 originally interspersed with large feldspars, as if porphyritic. 



Mic. The large feldspars, which are polysynthetically twinned, seem to be 

 alhite, as they have n, in the acute angle of the optic axes and an extinction angle of 

 76 in a section nearly perpendicular to p , and 15^ on a section nearly perpendicular 

 to n,. They show much fracturing and alteration, being filled with fine grains of 

 calcite and sericite, the latter sometimes taking the form of semi-rosettes. They 

 grade downward through fragmentary grains to small sizes. There is a com- 



