143 



may also rank under this title, but it includes 

 other appearances distinct from aggregation. 



In the granular structure, one, or more 

 minerals may be engaged ; and the latter variety 

 includes the compound rocks, in which the 

 several minerals are distinguishable, and which 

 are not noticed under other titles. 



The granular structure may, from its mi- 

 nuteness, be united with many of the preceding 

 without destroying their characters ; and hence 

 a rock may be granular, and at the same time 

 foliated, or columnar, or spheroidal. 



In the strictly granular structure, grains of the 

 same, or of different minerals, are closely aggre- 

 gated, as if by a simultaneous and confused crys- 

 tallization ; and hence they influence or destroy 

 each others regular forms. The magnitude of 

 the parts is various, but generally limited ; rang- 

 ing most commonly from the twentieth to the 

 half of an inch. 



It is often difficult, in practice, to distinguish 

 between an aggregate and a granular structure; 

 and, in these cases, the nature of the structure is 

 presumed from that of the rock ; the true charac- 



