PART I. CHAPTER IX. 



119 



General Aspect of Granite. 



culiar rounded form, usually clad with a scanty vegetation. The 

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

 the 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 ex- 

 terior of these stones, originally quadrangular, acquires a round- 

 ed 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 analo- 

 gous 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 fis- 

 sures, so as to assume a cuboidal, and even a columnar, struc- 

 ture. Examples of these appearances may be seen near the 

 Land's End, in Cornwall, (see figure.) 



Fig. 106. 



Granite having a cuboidal and rude columnar structure. 

 Land's End, Cornwall. 



The plutonic formations also agree with the volcanic, in hav- 

 ing veins or ramifications proceeding from central masses into 

 the adjoining rocks, and causing alterations in these last, which 

 will be presently described. They also resemble trap in con- 

 taining no organic remains ; but they differ in being more uni- 



