402 LOWEST RED SANDSTONE. 



finer sandstones are produced ; when larger, the 

 results are coarser grit-stones, and conglomerates, 

 or breccias. The term sandstone, is however 

 applied equally to the whole ; although, rather 

 in a geological, than in a mineralogical sense. 



In the finer sandstones, the adhesion of the 

 parts is sometimes slight ; and the rock is there- 

 fore of a feeble texture, while its mechanical 

 structure is also in this case most evident. In 

 others., the adhesion is very firm, although it is 

 impossible to trace any particular cementing me- 

 dium by which the union of the parts is effected. 



But, in some varieties, it is very apparent, 

 that the harder parts are united by the interven- 

 tion of a general cementing medium or paste ; 

 commonly consisting of that ferruginous clay to 

 which the colour of the rock is, in most cases, 

 owing. In a few instances, this medium appears 

 to be carbonat of lime ; or else, by a mixture of 

 the two, there is formed a sort of general basis, 

 in which the harder parts are imbedded. 



It was formerly shown, that, in the primary 

 sandstone, the grains of quartz, of which it is 

 principally composed, were often firmly com- 



