338 RED PRIMARY SANDSTONE. 



whole series of strata ; a circumstance of very 

 rare occurrence in the secondary sandstones. 



The mineral composition of this rock is in 

 general far simpler than that of the correspond- 

 ing secondary sandstone ; a circumstance not 

 difficult, of explanation when its more antient 

 origin is considered. The prevailing strata con- 

 sist either of quartz alone, or of quartz mixed with 

 felspar; and the latter mineral is much more 

 commonly crystalline than reduced to the state of 

 clay. Argillaceous varieties are therefore com- 

 paratively rare, and mica is also very seldom 

 found in this sandstone. In the conglomerate 

 varieties, the prevailing fragments consist of 

 quartz and felspar. Red jasper is also not unfre- 

 quent; and, if the compound rocks, of which 

 the characters are still to be traced, I have rarely 

 observed any except gneiss and argillaceous schist. 

 Where this latter rock abounds in the fragments, 

 it often also forms a sort of joint cement for the 

 whole mass, and the specimens of this character 

 thus pass into a gray wacke or coarse argillaceous 

 schist. All these fragments may be either angu- 

 lar or rounded ; but the latter form is prevalent, 



