Ch. XXXIIL] 



GENERAL ASPECT OF GRANITE, 



561 



The surface of tlie rock is for the most part in a crumbling state, and 



he hills are often surmounted by piles of stones like the remains of a 



stratified mass, as in the annexed figure, and sometimes like heaps of 



boulders, for which they have been mistaken. The exterior of these 



Fig. 681. 



Mass of granite near the Sharp Tor, Cornwall. 



stones, originally quadrangular, acquires a rounded form by the action 

 of air and water, for the edges and angles waste away more rapidly than 

 the sides. A similar spherical structure has already been described as 

 characteristic of basalt and other volcanic formations, and it must be 

 referred to analogous causes, as yet but imperfectly understood. 



Although it is the general peculiarity of granite to assume no definite 

 shapes, it is nevertheless occasionally subdivided by fissures, so as to 

 assume a cuboidal, and even a columnar structure. Examples of these 

 appearances may be seen near the Land's End, in Cornwall. (See 

 figure 682.) 



Fig. 6S2. 



Granite having a cuhoidal and rude columnar structure, Land's End, Corawall. 



The plutonic foroaations also agree with the volcanic, in having veins 

 )r ramifications proceeding from central inasses into the adjoining rocks, 



36 



