322 QUARTZ ROCK. 



flattened cylindrical bodies of considerable size, 

 very much resembling those found in the secon- 

 dary sandstones; but without the scaly surface, 

 and easily detached, even without the assistance 

 of the weather, from the surrounding mass. 



The varieties in the mineral character of 

 quartz rock are numerous ; but I shall limit this 

 enumeration to the most important and the best 

 marked, as a more full account of them will be 

 found in the Synopsis. 



It is occasionally, but rarely, found in a com- 

 pact state, and crystalline throughout ; little dif- 

 fering from quartz as it occurs in veins ; but even 

 in these cases showing a constant tendency to 

 divide in parallel beds. More generally, when 

 pure, it has an aspect obscurely granular, which 

 by degrees becomes somewhat lax and arenace- 

 ous ; the grains varying in size and in the inti- 

 macy of their union. In some of these examples, 

 it appears to be a granular crystallized mass ; in 

 others, it possesses a mixed mechanical and 

 chemical texture ; while, in a third, the rounded 

 aspect of the grains, and the small number of the 



