276 ON THE PARTICULAR ORDER OF 



invariably associated with particular rocks and in % 

 particular order. 



Limiting ourselves now to Europe and to our 

 present knowledge, there appear to be three leading 

 deposits, in this upper part of the great secondary 

 series, of sufficiently constant character and place, to 

 which all the others can be referred. These are, the 

 red marl, last named, the oolithe limestone, and the 

 chalk. The others are the Magnesian limestone, the 

 Muschelkalkstein, the C)uadersandstein, the Lias, the 

 Ferruginous sand, and the Green sand ; the two first 

 of which are not thought to exist in England, and of 

 which the ferruginous sand is either not sufficiently 

 distinguished from the last, or else is conspicuous 

 chiefly in our own country. 



', But the details of these deposits, if examined, con- 

 vey a far different impression from the terms them- 

 selves, which are, in a certain sense, conventional 

 associations. Under almost every one of these terms, 

 which, in an exact and mineral sense, are classes 

 rather than single deposits, we find the same sub- 

 stances, sandstone, limestone, shale, clay, and marl, in 

 perpetual alternations, and in such perfect disorder, 

 that, even in immediate, connexion, no two parts of 

 the deposit are like each other. Of these beds also? 

 if some are, in one country, considered as subsidiary 

 or subordinate, in others they have received greater 

 notice ; as happens with ourselves respecting the 

 Weald clay. Nevertheless we must, for the present, 

 take these divisions as we find them arranged ; only 

 cautioning the student against supposing that any one 

 of these terms, Lias, or green sand, means literally 

 what it appears to do, or is a definite substance, or 

 even a definite association of strata. 



