LOWEST RED SANDSTONE. 407 



supposed to have been derived, in some cases, 

 from granite, among the varieties of which, as for- 

 merly remarked, such substances are often found . 

 With respect to the component parts of this 

 rock, it must lastly be observed, that fragments 

 of previous sandstones are sometimes found im- 

 bedded in it. Whether these are portions of 

 unknown rocks that have disappeared from the 

 surface, is an object for geological inquiry ; but 

 as it has been already shown that there is a red 

 sandstone among the primary strata, it is to this, 

 in all probability, that we must look for their 

 origin. 



Few imbedded minerals are found among the 

 secondary rocks. In this, sulphat of barytes some- 

 times occurs in veins, as does gypsum. Iron 

 stone is not unfrequent, and pyrites also is some- 

 times present : oxidulous iron is rare. In no case, 

 however, do any of these interfere with the tex- 

 ture, or modify the general character of the rock. 



Few organic substances occur in the red 

 sandstone, nor have the species which do occur, 

 been fully investigated. At any rate, they are 

 not within the limits of the present inquiry. 



