PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 481 



Granite. Diabase.] 



Meg. A dark reddish-brown, fine-grained, compact rock with a few small red 

 porphyritic feldspars and sub-porphyritic areas of a dark mineral. The weathered 

 surface is pitted by the more rapid decay of the dark mineral. 



Mic. The section is composed of the usual reddened feldspar, quartz, augite, 



'HHiijnetite, hematite, hornblende, chlorite and confused greenish and yellowish alteration 





 products. The quartz and feldspar are most frequently intergrown to form beautiful 



micropegmatyte, and commonly this takes a radiating structure around the feldspar 

 grains. This is evidently a coarse form of the granophyric texture. This feature of 

 the specimen is well represented in Mon. v, U. S. Geol. Survey, plate 14, figures 1 and 2. 



The augite is in grains of considerable size and frequently shows a decidedly 

 idiomorphic tendency. This mineral is of earlier date than the feldspar and quartz, 

 some of the longer individuals extending through one or more feldspar grains in a 

 manner similar to the diopside in rock No. 132A. The augite is almost colorless to 

 green and usually shows no pleochroism. It has altered in places to an almost 

 opaque yellowish material. A few small dark-green pleochroic grains appear to be 

 hornblende, perhaps original, and there is also some secondary hornblende and 

 chlorite. 



One section examined. 



Age. Cabotian. u. s. G. 



No. 668. GRANITE (with augite). 



"About one-third way across the portage from Owl lake to Little Pine lake." Probably a short distance 

 north of the centre of sec. 1, T. 62-1 W. 



Ref. Annual Report, x, pages 73, 74, 140; American Association for the Advancement of Science, vol. xxx, 

 page 1G5. 



Meg. A compact rock of red color, rather fine grained and granitoid texture. 

 The minerals are red feldspar, sometimes sub-porphyritic, quartz and a dark greenish- 

 yellow mineral. The weathered surface of the specimen is pitted, due to the 

 weathering out of the last mineral. 



Mic. The section shows one of the characteristic red rocks of rather coarse 

 grain, /. e., coarse for these rocks. The important point of difference between this 

 section and most of the other red-rock sections is the presence of green augite, which 

 is more or less altered. 



One section examined. 



Age. Cabotian. u. s. G. 



No. 669. DIABASE. (Lustre-mottled.) 



"Is from what appears to be a dike, about half way between Owl lake and Little Pine lake, though the 

 exposure is not sufficient to show whether a dike or not." Probably in N. E. tf N. W. J sec. 1, T. 62-1 W. 

 lief. Annual Report, x, page 73. 



Mi-g. A dark -gray rock of fine grain and showing lustre-mottling. It weathers 

 to a much lighter gray. 



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