METAMORPHOSED QUARTZITES. 869 



grains may be but slightly fractured. In passing to more mashed varieties 

 regular lines of fracture occasionally appear at right angles to each other. 

 As the mashing becomes more advanced, granulation begins. This first 

 affects the exteriors of the grains, but as the process continues the grains 

 may be granulated throughout. (PI. IX, D.) Generally, however, before 

 granulation is far advanced recrystallization begins. As a result of this, in 

 the interstices new quartz and mica develop (the latter from the impurities) 

 and the recrystallization of the old grains of quartz occurs, as described on 

 page 865. Recrystallization checks, and finally reverses, the tendency of 

 granulation to produce finer and finer particles. Where recrystallization 

 becomes important, and especially where it becomes dominant, the mineral 

 particles may grow to a relatively large size. In proportion as a mass is 

 deep seated and the mashing is extreme there is a marked tendency to a 

 parallel dimensional arrangement of the newly, crystallized particles (see 

 pp. 688-689, 760), and the final process is a schist-quartzite or quartzite- 

 schist which shows no sign of fragmental origin. In many instances the 

 coarser quartzite-schists have particles averaging- 7 mm. in length and 

 4 mm. in breadth. The common ratio between minor and major diameters, 

 as ascertained by Leith, varies from 20:100 to 100:100, with an average of 

 perhaps 50: 100. a 



The schist-quartzites and quartzite-schists which are largely readjusted 

 by recrystallization beautifully illustrate the principle that this process 

 lags behind mechanical deformation. (See Chapter VIII, pp. 696-698.) 

 Residual strain effects, as shown by strain shadows, are very general. 

 Occasionally, however, the entire rock has largely recrystallized under 

 static conditions after mashing ceased, and there has been produced an 

 interlocking granular quartz rock in which the quartz particles have no 

 similar dimensional orientation and in which there is little residual strain 

 effect. This peculiar variety is beautifully illustrated by the quartz rocks 

 of Rib and Mosinee hills, near Wausau, Wis. (PI. IX, C.) After complete 

 recrystallization has taken place, producing a granular quartz rock, when 

 the rock is again deformed granulation may occur. This further change 

 has locally taken place at Rib Hill. (See PL IX, D.) 



In proportion as the sands, sandstones, and quartzites are impure the 

 schist-quartzites and quartzite-schists forming from them will be impure. 



« Leith, C. K., Rock cleavage. 



