336 RED PRIMARY ^SANDSTONE. 



secondary sandstones, and which so much re- 

 sembles the marks left by the retiring sea on a 

 shore of sand. 



The texture of this rock is various. It is some- 

 times fine and granular, resembling the more 

 ordinary varieties of the red sandstone of the 

 secondary class. But it is much more common 

 to find the granular intermixed with a continu- 

 ous crystalline texture ; or the grains, which oc- 

 casionally adhere by mere agglutination, are 

 united into a continuous mass by a cement of 

 crystalline quartz. That compactness is some- 

 times so perfect, that the marks of a granular 

 imbedded structure, nearly, or entirely* disap- 

 pear ; and the sandstone then resembles those va- 

 rieties of quartz rock which are scarcely distin- 

 guishable from common venous quartz. Under 

 such circumstances also, and under particular 

 modes of composition, it sometimes presents a 

 minute splintery fracture. It is in this circuit- 

 stance of frequent and crystalline compactness, 

 that this sandstone is principally distinguishable, 

 in hand specimens, from those of the^secondary 



