330 QUARTZ ROCK. 



former do into fine. They present great varie- 

 ties of compactness, and are either distinctly 

 schistose or not. They may be equally ranked 

 with the graywackes under the head of argilla- 

 ceous schist. 



Quartz rock, when in the vicinity of granite, 

 is sometimes broken and re-united, forming pe- 

 culiar local conglomerates ; and, in these cases, 

 the cavities which sometimes occur, contain 

 quartz crystals. 



I have observed no minerals imbedded in 

 quartz rock, except garnet, hornblende, oxydu- 

 lous iron, and titanite ; and even these are rare. 



