ALLUVIAL FORMATIONS. 293 



The marine formations are conjectured to have been 

 deposited from the waters of the ocean, but the fresh 

 water rocks from the waters of lakes. This hypothesis 

 supposes an alternate flux and reflux of the waters of the 

 ocean, and an appearance and disappearance of the wa- 

 ters of lakes. However amusing such an hypothesis may 

 be, we must confess that it is not consistent with the 

 usual course of nature in the mineral kingdom, and that 

 it is also contradicted by the geognostical relations of 

 the individual formations themselves. In describing a 

 formation, we cannot rest satisfied with the mere enume- 

 ration and description of the organic remains it contains ; 

 these alone will never enable us to characterize it as an 

 unity in the great series of rock formations : in order to 

 determine it with accuracy, we must state the characters 

 of each individual bed, describe the imbedded and veni- 

 genous minerals they contain, the relation of the beds 

 to each other, in regard to position, transition, intermix- 

 tures, &c., and lastly describe the fossil organic remains 

 enclosed in it. But this is not exactly the method follow- 

 ed by M. Cuvier and Brongniart; they seem to consider 

 the fossil organic remains as affording characters of supe- 

 rior importance to all the others; in short, that from them 

 'alone the principal and gole distinction amongst flpetz for- 

 mations are to be made. Thus the gypsum formation in its 

 lowest part, where it rests on the marine limestone, con- 

 tains fresh water organic remains ; hence it is said to be 

 a fresh water deposite ; the part of the same formation 

 immediately above this contains salt water petrifactions, 

 it is therefore formed from the waters of the ocean ; the 

 thick bed of gypsum in the middle and upper part of the 

 formation, from its containing remains of fresh water 

 shells and of quadrupeds, is another fresh water formation ; 

 ^nd the uppermost part of the formation, the marine marl, 

 from the nature of its organic remains, is maintained to 



