426 SUPERIOR SANDSTONES. 



lity of the quartz from which they are formed. 

 When highly indurated, they cannot be distin- 

 guished from some of the varieties of quartz 

 rock, except by their position. They are occa- 

 sionally indurated to the state of common quartz 

 in the vicinity of trap. 



SECOND DIVISION. 



Compound : of two or more ingredients. 



A. Quartz sand and carbonat of lime. 



a. Large grained ; gravelly. 



b. Fine ; arenaceous. 



These varieties are generally white. 



B. Quartz sand with clay. 



a. Large grained ; gravelly. 



b. Fine; arenaceous. 



The colours of these are various. They are 

 either white, or ochre yellow of different hues, 

 or red, or grey of different degrees of intensity, 

 or greenish, or black. They are also occasionally 

 mottled and striped of various colours. The red 

 varieties, more particularly, but many of the 

 grey and white also, are not distinguishable from 

 some of the lowest (or old red) sandstone, ex- 

 cept by their geological positions. As sufficient 



