352 THE JOURNAL OF GEOLOGY. 



one the cementing material is vein -quartz; in the other the 

 sandstone has been feebly cemented by quartz enlargement. 



A movement later than the one which produced the cemented 

 fractured rocks and breccia has broken broad zones of the 

 massive beds of quartzite into lozenge -shaped blocks, the longer 

 axes of which are parallel to the bedding and movement. These 

 later -formed blocks have not been re-cemented by secondary 

 quartz, and the cracks are taken advantage of in quarrying, the 

 fragments being easily picked apart.- Thus the rock has been 

 affected by at least two dynamic movements, separated by a 

 considerable -interval of time. 



The shear -zones, often several feet in width, particularly 

 affect the more finely -laminated layers, which are lean in quartz, 

 while the relief in the more massive layers has resulted in com- 

 plex fracturing. In the first phase of production of the schist, 

 the irregular fractures pass into rather regular fractures, cutting the 

 beds nearly at right angles. As the action becomes more intense 

 in the more argillaceous beds, the angle of fracture, or cleavage, 

 as it may now fairly be called, becomes more acute, and in the 

 most intense phase this cleaved rock passes into a well -devel- 

 oped schist, the foliation of which is parallel to the bedding. 

 The phenomena of shearing are here therefore very similar to 

 those at Devil's Lake, except that the process has gone 

 farther. 



When studied in thin section, the massive beds of quartzite 

 show more decided effects of dynamic action than at Devil's 

 Lake. However, the major portions of the grains of quartz 

 have distinct cores which are often beautifully enlarged. In 

 some cases nearly every grain has thus grown, perfectly indurat- 

 ing the rock. But, also, nearly every grain of quartz has a wavy 

 extinction, and many of them have been fractured, as mentioned 

 of a few of the quartz grains of the quartzites of the south range. 

 In one case the pressure has been so great as to produce rather 

 numerous roughly parallel lines of fracture. It is thus seen that 

 the dynamic effects are not confined to the schist zones, but are 

 also prominent within the heavy beds of quartzite. This was to 



