74 



gical and the mineral characters. This term will 

 thus comprise, in the subsequent catalogue, a di- 

 vision much more comprehensive than any other ; 

 under which many rocks strikingly distinct in 

 character, will appear rather in the light of vari- 

 eties than in that of distinct species. If such a 

 blemish could have been avoided it would have 

 been desirable ; but as all these rocks are united 

 by a common geological position, as the natural 

 history of the whole is the same, and as they are 

 connected by indeterminate transitions, there ap- 

 peared to be no choice. 



In chusing the term overlying, a word in 

 many respects objectionable, regard has been had 

 to established habits, to the difficulty which exists 

 in framing new terms, and to the objections 

 against this practice ; but it will afterwards be seen 

 that these rocks are also occasionally inferior to 

 the strata which they accompany, and that they 

 are further connected with these in a variety of 

 modes. 



No remarks are here necessary on the divi- 

 sion of the stratified rocks in the secondary class ; 



