GRANITE. 227 



masonry. The angles of the prisms being fur- 

 ther subject to wear, as are the contiguous sur- 

 faces in a less degree, the result is an aggregate 

 of irregular spheroids often piled on each other 

 in a very fantastical manner. This consequence* 

 it is evident, can only take place when the fis- 

 sures are nearly horizontal and vertical. In 

 all others, the detached parts must fall away. A 

 few rare instances occur in nature where the 

 dimensions of the prisms are so considerable in 

 one direction, that, when grouped in erect po- 

 sitions, they present an irregular columnar ap- 

 pearance. 



Lastly, the great laminae, or beds of granite 

 are often vertical, as well as horizontal or in- 

 clined ; and it thus presents continuous smooth 

 precipices laterally, while, above, it terminates 

 in sharp peaks. 



A minute, but irregular prismatic structure, 

 independent of the former, is sometimes to be 

 seen in granite. It is also occasionally mir 

 nutely laminar, or exfoliates in crusts. These 

 crusts are sometimes concentric, respecting one, 

 or more, centres ; at others they are flat. In 



Q 2 



