146 



ARRANGEMENT OF DEPOSITS. 



Occasionally the columnar and massive structure of basalt 

 are exhibited in conjunction, as in fig. 76. 



FIG. 76. 



ARRANGEMENT OF DEPOSITS. We have described the 

 unstratified rocks, especially granite, as constituting the 

 foundation and the framework of the whole superstructure 

 of our globe. The accompanying figure exhibits the varied 

 situations of the granite, as forming the basement-rock 

 on which all the others repose, and the nucleus of the 

 mountain, which, having been forced through the superin- 

 cumbent rocks, has borne them upwards in its ascent ; the 

 strata in the vicinity of the mountain, a, being raised at 

 an acute angle at b, and sinking to nearly a level position in 

 the plains at c. 



FIG. 77. 



The form and succession of the rocks above described 

 prevail, with some local exceptions and modifications, over 

 the whole earth ; so that its entire surface may, be con- 

 sidered to form a series of basins, of which the largest, 

 deepest, and thickest lie at the bottom, and are filled up by 

 others, which become smaller, shaUower, and thinner as they 

 approach the top, the deposits being uplifted and raised 

 towards the edges of these basins, and becoming level, or 

 nearly so, towards the centre. 



