139 



CAVERNOUS. 



The cancellated structure, arising from the 

 intersections of numerous laminae, passes into 

 a decided disposition of a cavernous nature ; 

 the intervals by which the cells are separated, 

 no longer bearing the appearance of veins. 

 The small cavernous is distinct from this 

 particular structure, and generally accompanies 

 the amygdaloidal. 



The large cavernous, or cancellated struc- 

 ture, like the veined, is scarcely to be dis- 

 covered but after the weathering of a rock, and 

 it then becomes apparent on the surface. The 

 cells vary much in size, in form, and in aggre- 

 gation ; and hence a variety of appearances, 

 examples of which are afforded in sandstones 

 and limestones ; as the merely veined is chiefly 

 prevalent in the traps and in granite. 



The small cavernous structure actually exists 

 in the rock so as to be always visible ; and it is 

 more or less perfect ; as the cells are sometimes 

 partly filled with some foreign substance. They 

 vary in number within a given space; being 

 sometimes sparingly dispersed, at others crowded, 



