398 LOWEST RED SANDSTONE. 



faces, by a gradual intermixture of fragments of 

 calcareous matter, and of those which appertain 

 more properly to the sandstone. It is as yet 

 uncertain, whether the white sandstones which 

 are sometimes found similarly alternating with 

 the red, are to be considered as colourless portions 

 of the same deposit, or as alternating strata, like 

 the shales ; but, in truth, this seems rather to be 

 a doubt respecting the use of a term, than about 

 a geological fact ; as there are no means of de- 

 termining a real difference, under circumstances 

 of this nature, among rocks of mechanical com- 

 position deposited in the manner in which all the 

 arenaceous secondary strata appear to have been. 



It is almost unnecessary to repeat, that any one 

 of the secondary strata may follow the red sand- 

 stone in a continuous series, after it has disap- 

 peared, and that these are generally in parallel, 

 or conformable, order. 



The strata of red sandstone vary much in 

 thickness, individually, as the whole deposit itself 

 also varies in depth. As the latter sometimes 

 ranges from a thousand yards or more, to the 

 thickness of a few feet, so the strata may be found 



