OVERLYING ROCKS. 501 



the constituent parts and the size of the particles, 

 no less than from their various colours. Rocks 

 not distinguishable from the dark varieties, occur 

 together with granite, as noticed under that head ; 

 nor do they, in this case, present any distinction 

 but that of their geological connections. 



The felspar is sometimes accumulated in spots 

 in the general mixture ; presenting a porphy- 

 ritic appearance and forming pseudo-porphyries. 



When the felspar is red, this rock has often 

 the general aspect of some varieties of granite. 



b. The compact felspar predominant. Sye- 

 nite. 



This rock is also important, from its fre- 

 quency, and the extent which it occupies ; oc- 

 curring principally in mountain masses, much 

 more rarely in veins. It is sometimes found par- 

 tially laminar, like former varieties of this family, 

 and it is also occasionally columnar ; a circum- 

 stance, of which Ailsa presents a striking example. 



As in other instances in this family, this 

 rock is not always consistent in its composition 

 throughout a large space ; so that the determi- 

 nation of the character of a specimen does not 



