53 S OGILVIE 



consists of a very friable, easily weathered, dark rock, which 

 usually forms a depression. It consists of blue "augen" an inch 

 or less in length in a ground-mass of brown mica and feldspar. 

 The augen are without orientation, and the mica plates also have 

 no uniform arrangement. In the border zones the rock is schis- 

 tose. The biotite and the augen are arranged with the long axes 

 in the same direction. The latter often being completely crushed 

 and represented by white bands between the mica plates. This 

 border rock resists weathering much better than the rock of the 

 core, hence it usually forms ridges. It is not among the 

 hardest rocks of the region, but it is sufficiently resistant to form 

 hills of moderate altitude. Fresh specimens of the border rock 

 can readily be found, while the core disintegrates so readily that 

 it might easily be overlooked altogether, and fresh specimens 

 are difficult to obtain. 



Microscopically the augen are found to be similar to the graphic 

 granite which forms one of the youngest intrusions of the region. 

 They consist of albite, microcline, microperthite and orthoclase, 

 in order of abundance, with sometimes a little quartz. A few 

 scales of mica are to be seen scattered through the augen, 

 especially in the sheared varieties. Zonal structure is common 

 in the feldspars. The augen are essentially similar in all var- 

 ieties of the rock, differing only in degree of metamorphism. In 

 some instances they are cracked, the cracks being filled with 

 either quartz or muscovite, the former containing dark in- 

 clusions. Other occurrences are granulated on a microscopic 

 scale, and still others are so completely crushed that they are 

 drawn out into bands and are white megascopically. 



The feldspars contain large numbers of inclusions. Quartz, 

 titanite, perofskite, magnetite and rutile could be identified, 

 the needles of the last-named being usually arranged in two 

 intersecting directions. In the following analysis, care was 

 taken to exclude as far as possible the scales of biotite which 

 are occasionally within the augen. The mica of the ground- 

 mass adheres most persistently to the augen, and particular care 

 was taken to break it away. Considering these precautions, 

 the amounts of iron, magnesia and titanium are very large; they 

 are undoubtedly to be accounted for in the inclusions, as is some 



