SOME DYNAMIC PHENOMENA. 353 



be expected ; for while the major part of the accommodation 

 necessary to bend the rock mass as a whole took place along" 

 the shear zones, the accommodation required to bend each 

 of the rigid heavy beds of quartzite must have taken place 

 within each layer. To the consequent intense pressure and the 

 rubbing of the grains over one another, are wholly attributed 

 their wavy extinction and fractures. 



In the schists of the shear zones, as at the south range, 

 the thin sections show that the original quartz grains were 

 small ; interstitial material was present, and mica has developed 

 more largely than in the quartzite. However, in the most 

 crystalline phases, the fragmental cores of the quartz grains 

 and their frequent enlargements are plainly seen. Thus the 

 shearing has not been sufficient to produce a completely 

 crystalline schist, although this would not be macroscopically 

 discovered, unless it were suspected because the rock is not 

 thinly foliated. 



As the dip of the quartzite is so steep at this locality, it 

 is difficult to say how far the shifting of the beds over one 

 another lessens the apparent thickness. The shear zones as well 

 as the friction conglomerates appear to be parallel to the bed- 

 ding. If they are exactly so, this shearing action would neces- 

 sitate an estimate of the original thickness greater than now 

 shown, since the shear zones probably have less width at the 

 present time than the beds from which they were originally pro- 

 duced. 



Cutting the bedding are heavy joints inclined to the north at 

 an angle of 20° to 30"". If slipping had occurred along these in 

 the right direction, this might cause a small thickness of beds to 

 have a great apparent thickness. However, the schists above 

 described weather out on the face of the cliffs, and are therefore 

 marked by recessions in the walls. If slipping parallel to the 

 jointing had occurred since the schists were formed, these de- 

 pressions ought not to match on opposite sides of the joints ; 

 but, on the contrary, they continue unbroken from foot to top, 

 and probably the joints were formed simultaneously with or later 



