21.3 



CHAP. XXXIV. 



Lowest, or Old Red, Sandstone. 



IT is difficult to discover the exact natures of the red 

 sandstones described by authors, and consequently, to 

 adopt their observations, so as to illustrate the history 

 of this rock as it occurs in our own country. The 

 two distinctions relied on for discriminating it, are its 

 colour, and its position towards the primary ; being 

 the first of the secondary strata, and immediately in 

 contact with these. Hence it has been called the old 

 red sandstone. But as I have shown that there is a 

 primary red sandstone, the descriptions of authors 

 have possibly been sometimes derived from it instead 

 of from this rock. And as the red marl has been 

 actually confounded with the present, the sources of 

 confusion respecting its characters and connexions are 

 obvious. 



The mere fact of contact with the primary strata, is 

 not an infallible criterion by which to distinguish the 

 lowest secondary one, as I have formerly shown. 

 Therefore, although the red marl occupies a position 

 distant from this in the order of succession, it may 

 come into contact with these, and thus be confounded 

 with the present deposit, as it has been by Werner 

 and his followers. Nor is the red colour an invariable 

 characteristic of this rock ; since it is occasionally grey, 

 and also white, even in one bed ; proving, that this 

 does not form a geological distinction. Hence the 

 geologist must not conclude that every red sandstone 

 in contact with the primary rocks, belongs to this one; 

 while, as the different strata in nature are rather ana- 

 logous than identical, serious differences may exist in 

 the constitution of this deposit in different countries, 



