414 SUPERIOR SANDSTONES. 



panying rocks, which, in those tracts at least, are 

 constant ; although the same order and the same 

 associations, are not found in remoter tracts and 

 in other countries. Mineralogical differences, in 

 other respects trifling, thus become of great con- 

 sequence in geological investigations and descripr 

 tions ; more particularly in the local or geogra- 

 phical department of geology. But the interest 

 of these strata chiefly depend on their geological 

 associations and characters ; sometimes on the 

 nature of the organic remains which are con- 

 tained in them or in the accompanying lime- 

 stones. They rarely, if ever, are founded solely 

 on mineral characters ; nor is it possible, by such 

 characters alone, except in some peculiar in- 

 stances, to distinguish them from each other, so 

 as to recognize them when separated from their 

 connections. Even in those few cases where 

 they may be distinguishable by an eye practised 

 in their peculiar niceties of aspect, the distinctive 

 characters can seldom be conveyed by words. 



If the mineral resemblance of these sand- 

 stones, is such, that distinctions can be rarely 

 made among them, sufficient to justify the placing 



