504 OVERLYING ROCKS. 



der which head they have already been enume- 

 rated. 



b. The felspar predominant. 



This also forms one of the prevailing varie- 

 ties of syenite, and occurs under the same cir- 

 cumstances as var. A, b, of this division. The 

 same remarks respecting variations of structure 

 and connections, are applicable to it. Its aspect 

 is more decidedly granitic than that of the variety 

 which contains compact felspar. When the fel- 

 spar is of a dark grey, as sometimes happens, it is 

 also included, but improperly, under the general 

 term greenstone. In some cases, compact and 

 common, or common and glassy felspar, occur 

 together, and chiefly in var. a ; but these varia- 

 tions do not seem to require separate places. 

 C. Compact felspar and quartz. 



This occurs in conjunction with the syenites 

 and the simple rocks, of which it is an occasional 

 modification ; nor does it appear to form exten- 

 sive distinct masses. Quartz is found, in the 

 same way, united with the simple substances D, 

 E, Division First ; but it is unnecessary to mul- 

 tiply these distinctions. 



