458 THE MAEQUETTE lEON BEARING DISTRICT. 



many cases much feldspar occurs with tlie quartz, so that technically the 

 rocks are mica-gneisses. As the rock becomes more foliated the mus- 

 covite is relatively more important, and occasionally it is predominant. 

 Oxide of iron, and especially magnetite, is found as minute specks and 

 as crystals included within all of the foregoing minerals. The amount 

 varies greatly; some slides are comparatively free from iron oxide; in others 

 all of the minerals have a blotched apjiearance throughout, due to the 

 inclusion of innumerable minute flecks of iron oxide, and perhaps also of 

 carbonaceous or graphitic material. Between the two extremes there are 

 all gradations. 



In the coarse-grained micaceous gi-aywackes adjacent to the border of 

 the lake, where metamorphism is partial, the processes of development of the 

 mica-schists are best made out. Here the decomposition of the coarse frag- 

 mental feldspar into interlocking secondary chlorite, biotite, muscovite, and 

 quartz may be beautifully seen. Also the original roundish fragmental 

 grains of quartz are recognizable. They show undulatory extinction, and 

 oftentimes fracturing into two or more individuals, whereas the secondary 

 quartz is in small granules which do not show pressure effects. In a coarse 

 variety of the ordinary biotite-schist, not of the completely crystalline type, 

 two classes of quartz are still recognizable. There are coarser grains, which 

 have a distinct roundish appearance, averaging from 0.15 to 0.20 mm. in 

 diameter. Some of these have their longer axes transverse to the schis- 

 tosity. These larger particles are taken to be clastic. They are associated 

 with much more abundant, finer-grained quartz, averaging from 0.04 to 

 0.05 mm. in diameter. Much of this quartz is plainly a secondary devel- 

 opment, but also a part of it may be original fragmental material. In both 

 the micaceous graywackes and the fine-grained biotite-slates the mica 

 has in general a parallel airangement, is in small flakes, and is of secondary 

 origin. 



In passing to the completely crystalline biotite-schists the recognizable 

 coarser grains of quartz gradually disappear by granulation, and we have 

 a background of quartz grains of approximately the same size, generally 

 arranged with their longer axes in a common direction. The mica also 

 becomes more coarsely crystalline and has a greater uniformity in its 



