SoLLAs — On the Structure and Origin of Qitartzife Rochs. 183 



exactly due north and south. Professor Blake remarks that since 

 this makes a very large angle with the direction of the ridge itself 

 we must assume, on the hypothesis that they indicate bedding, a 

 very extensive faulting on all sides of the quartz mass. This, to 

 my mind, is by no means an objection, but harmonizes very well 

 with what one would expect in the case of an isolated mass, which 

 can be best explained, like the mass of Howth, as a " horst," 

 which remains standing above the sea-level, while the rest of the 

 country has been gradually let down to " the depths." 



Although I first noticed these bands in Carrickgologan (and 

 specimens preserved in the Geological Museum of Trinity College 

 show that they must have been observed before, probably by Pro- 

 fessor Haughton), they are equally well or perhaps better displayed 



Fig. 6. — Magnified section througli quartzite of Loughereen Hill: d.b. direction of 

 dirt band ; c.c' direction of incipient cleavage within the dirt hand. 



by some of the quartzite masses of Howth, e. g. in Loughereen Hill, 

 from which I obtained specimens for slicing. Under the micro- 

 scope the difference in the corflposition of the bands which was 

 naturally to be expected is very clearly revealed ; the bands are 

 distinguished by the presence of a larger quantity of sericite and 

 opaque earthy and ferruginous matter than the intervening rock. 



