290 THE MAEQUETTE lEON-BEARING DISTRICT. 



biotitic aud sericitic slates and graywackes which are m every respect 

 similar to those described (pp. 265-269) under the Wewe formation. 



In the jjurest and least mashed phase of quartzite the rocks are com- 

 posed almost wholly of rounded grains of quartz of somewhat uniform size, 

 which ai-e beautifully enlarged, the enlargements filling the entire inter- 

 spaces. But even in this quartzite the grains unifomily show undulatory 

 extinction, aud some of them are distinctly fractured. Where the dynamic 

 effects are somewhat stronger, between and in connection with the enlai-ge- 

 ments of the quartz grains there is a fine mosaic of independent interstitial 

 quartz, aud with this there is a beginning of the arrangement of the grains 

 with their longer axes in a common direction. Very frequently the fractures 

 of the grains jjass directly across the cores and the enlargements, showing 

 that the fracturing occurred after the second growth of the quartz grains. 

 Occasionally with the simple quartz grains there are finely complex grains 

 of quartz, which appear to be derived from chert. In a phase intermediate 

 between the quartzites and the graywackes there is present with the quartz 

 a greater or less amount of kaolin, sericite, and chlorite. In some cases 

 these become rather abundant, so that the rocks are chloritic or sericitic 

 quartzites. Not infrequently the quartzites are feldspathic, and in some 

 cases this mineral has undei'gone to a greater or less degree the usual 

 decomposition into mica and quartz, or into chlorite and quartz. Where 

 the decomposition is complete, in place of the round grains of feldspar we 

 have an interlocking mass of sericite and quartz, biotite and quartz, or 

 chlorite and (juartz, as the case may be. At one place the feldspar grains 

 are as distinctly enlarged as tlie quartz grains. The quartzites usually con- 

 tain a small amount of iron oxide, which marks the cores of the original 

 quartz grains aud is intermingled with the new quartz. 



In the quartzites where the dynamic forces were still stronger the indi- 

 vidual grains of quartz are broken apart, or the rock is fractured through 

 and through, or even changed into a reibungsbreccia. In the larger crev- 

 ices and cracks is vein quartz or iron oxide — in some one alone, in others the 

 two together, although the quartz is more abundant. These veins in some 

 cases are coarsely crj-stalline quartz; in others they are finely crystalline, 

 cherty, or jaspery quartz, aud with either of these are iron oxides. These 



