630 ON THE RED SANDSfONE OF THE 



been the case with the ironstone. It is a frequent 

 mineral in several red sandstone districts. 



5. Trap--tuff. This remarkable rock occurs in 

 beds, often of a great thickness, in red sandstone. 

 It passes not only into claystone, but also into the 

 red sandstone. It is by no means an uncommon 

 rock in some of the red sandstone districts in the 

 tract of country we are now describing. 



6. Amygdaloid^, This rock contains many dif- 

 ferent minerals, either in its vesicular cavities, or 

 imbedded in it. These are calcareous- spar, stea- 

 tite, quartz, agate, zeolite, and felspar. It occurs 

 in beds, and also in veins : the beds vary in thick- 

 ness from a few feet to many fathoms. It is fre> 

 quently traversed by veins of sandstone ; and beds 

 of sandstone and also conglomerate, many hun- 

 dred feet in extent, and of considerable thickness, 

 occur in the cliffs of amygdaloid in different 

 parts of this district. Cotemporaneous masses 

 of amygdaloid occur imbedded in the sand- 

 stone. It passes into trap-tuff, and also into sand - 

 stone. 



7. Basalt, A. rock having several of the cha- 

 racters of basalt, occurs, in beds and veins, in tlie 

 red sandstone. 



