FOSSIL INVERTEBRATED ANIMALS. 435 



respecting that in which organic remains are found, and which 

 evidently appears to have been operated in that liquid medium. 

 On this hypothesis, if it do not deserve a better name, it is 

 probable that the waters, which contain the elements of those 

 crystallizations, contain little or nothing of them any longer at 

 the present day, since we do not find that genuine petrifactions 

 are formed now, as formerly. Nevertheless it appears, as we 

 shall show hereafter, that certain crystallizations, which have 

 taken place after a preceding one had engaged the bodies which 

 we find in a fossil state, must have been operated subsequently 

 to the retreat of the waters. 



We may believe that certain strata, such as those of the 

 phyllades and of the chalk, have been deposited in fluids which 

 had the property of destroying or dissolving certain calcareous 

 substances which existed in these strata, but where no further 

 traces of them are to be found at the present day. 



If we have nothing but analogy to lead us to such a conclusion 

 respecting the phyllades, it is not so with the chalk, which 

 exhibits phenomena, conferring a character of certitude upon 

 our inferences to this effect. 



In the strata of phyllades, we find, in general, only trilobites, 

 and other turbinated bodies, such as ammonites, and the shell 

 of which exists no longer ; but these strata must have contained 

 a much greater number of marine bodies which have been 

 destroyed. What leads us to this belief is, that, in the time 

 when those trilobites existed, there also existed a very great 

 number of other marine animals. The proof of this is to be 

 found in many localities ; and, among others, at Dudley in this 

 country, and Chimay in the Netherlands. 



Since, then, it is clear that, at the period when the trilobites 

 existed at Dudley and Chimay, there also existed, in the same 

 places, a great quantity of marine animals, why should we not 

 extend the same conclusion to the formations of phyllades and 

 transition limestone, and believe that, with the trilobites of these 

 latter strata, there existed an equal quantity which have disap- 



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