SECONDARY LIMESTONES. 245 



lower beds, which sometimes also pass into a compact 

 limestone. Though white when pure, it is sometimes 

 yellow, grey, and reddish, and occasionally contains 

 magnesia, or clay, and more generally, sand. 



The organic remains are numerous, and, like those 

 of the inferior strata, belong to species, at least, which 

 are supposed to be no longer existing. Some traces 

 of fishes and of lacerlse have been found in it; but the 

 most remarkable circumstance consists in the great 

 quantity and variety of echini tes which it contains. 

 It is also noted for its sponges and alcyonia; con- 

 taining moreover, encrinites, corals, and many genera 

 of shells, for which I may refer to the same catalogues. 

 Including the green sand with it, the vegetable fossils 

 exceed fifty; of which, with some fuci, six are said to 

 be coniferous, and two liliaceous plants, in addition to 

 the genera usual in the coal strata. But when it is 

 inferred that coniferous or liliaceous plants had never 

 existed in former conditions of the earth, that new 

 aeras of creation are thus marked, and that the cha- 

 racters of the plants in former strata prove differences 

 of temperature in the Earth at those periods, this is 

 the ignorant and rash reasoning from negative evidence 

 which I hope I have sufficiently exposed OR former 

 occasions. 



Such are the leading divisions of the secondary 

 limestones ; and there is nothing here to add respect- 

 ing those which occur in the coal series or elsewhere ; 

 while, for the minute descriptions of these, and of 

 those which are found in the tertiary deposits, I must 

 refer to the authors who have described them. But I 

 must proceed to add what applies equally to this and 

 to the preceding chapter, and which I therefore re- 

 served to this place. 



The remark is general ; I have often made it already. 



