386 NATURE AND CHARACTERS 



from the abundance and nature of the organic 

 remains which they contain, are subjects for the 

 especial consideration of geological treatises, or 

 theories, and can find no place in this work. 



As a class, the secondary strata still require 

 a few observations before proceeding to enume- 

 rate the individual rocks ranked in it. 



In comparing the catalogues of the primary 

 and the secondary strata, it will be seen that many 

 very distinct species are contained in the former, 

 but that the species in the latter are nearly con- 

 fined to sandstone, limestone, and shale. Notwith- 

 standing this limited number of leading distinc- 

 tions, they present much variety in the details ; 

 even independently of the organic remains con- 

 tained in them, by which other differences of a 

 very important nature are also frequently produced. 

 These distinctions, however, are of such a nature 

 that they can claim but little notice in a catalogue 

 of rocks. They appertain, for the most part, 

 either to that branch of geology which is of a 

 geographical nature, or to that which treats of the 

 order of succession, and of the characters, of 

 those interesting strata which indicate the succes- 



