QUARTZ ROCK. 329 



SUBDIVISION. Of quartz and blue 

 schistose clay. 



A. A laminar alternation of pure quartz and clay 

 slate. 



B. Quartz, arenaceous and minutely interlami- 

 nated with black or blueish clay ; resembling* some of 

 the sandstones that accompany coal. 



C. Quartz sand intimately mixed with blueish 

 clay. 



This passes into the fine graywacke schist 

 which alternates with some examples, of quartz 

 rork. 



THIRD DIVISION. 



Containing more than two- ingredients^ or of a 

 conglomerated structure. 



A. Quartz sand alone, or sand and gravel of quartz 

 and felspar, with imbedded pebbles or fragments of 

 quartz. 



B. The same, with fragments of argillaceous 

 schist. 



C. The same, with fragments of micaceous schist, 

 or with both. 



These latter varieties pass into coarse gray- 

 wacke schist, and gray wacke conglomerate, a* the 



