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LETTER XXXII. 



TOSSILS CONSIDERED IN CONNECTION WITH THE STRATA IN WHICH 



THEY ARE CONTAINED. 



1 HAVE now arrived at the termination of my proposed attempt, having 

 placed before you as correct a sketch as I was able of the fossil remains 

 of those organized beings, which existed on this planet previous to its 

 possessing its present form. 



Your attention has been hitherto called, chiefly, to the original modes 

 of existence of those beings, and to the nature of the changes which 

 they have undergone. You have seen, that some of these remains have 

 belonged to beings whose living analogues may still be found ; whilst 

 others have belonged to beings differing essentially from any which are 

 now known to exist, and in those particular characters which are em- 

 ployed by naturalists as marking generic difference. 



You have also seen, that the fossil remains of both vegetables and ani- 

 mals have undergone the most extraordinary changes. I have endea- 

 voured to prove to you that most vegetable fossils had undergone a pro- 

 cess of bituminization, by which their conservation was secured, previ- 

 ously to their impregnation with earthy or metallic salts. I have also 

 suggested the probability of a correspondent preparatory change, in 

 many animal substances, previous to their mineralization*. 



* In addition to the instances which have been already adduced in proof of the petrifac- 

 tion of vegetables having been in general affected by the impregnation of previously bitu- 

 minized vegetable matter, with earthy or metallic solutions, and not by substitution, I have 

 met with one striking fact. I two years since obtained from the shore at Walton, wood 

 changed into marble, capable of receiving a beautiful polish, and which, on being deprived 

 of its carbonate of lime by the action of muriatic acid, left the light, inflammable, bitumi- 

 nous wood, possessing a volume very little less than that of the marble in which it had been 

 contained. 



