376 COMPACT FELSPAR. 



there is much to reform, and where the various 

 effects which may flow from such changes can- 

 not be foreseen, it is at least prudent to go on as 

 long as possible with the established materials. 



The compact felspar in question, is only 

 found, as far as I know, situated in gneiss, in 

 which it commonly forms large flattened masses 

 or imperfect beds. These do not possess the 

 characters of veins, like the compact felspar of 

 the secondary class, but either resemble the 

 masses of limestone which occur in the same 

 situation, or else graduate into the surrounding 

 rock. In this case they are often, but not neces- 

 sarily, connected with that peculiar variety des- 

 cribed in the Synopsis of Gneiss, into which 

 compact felspar enters as an ingredient, 



Occasionally, this substance is also found in 

 smaller lumps in the same rock, or else in those 

 forms which are sometimes called by the ques- 

 tionable name of contemporaneous veins ; origi- 

 nating and terminating in the mass in which 

 they lie. It also occasionally forms single laminae 

 in that gneiss which possesses the granitic or schis- 

 tose character. More rarely, it occurs in a 

 larly limited manner in granite. 



