FOSSIL INVERTEBRATED ANIMALS. 451 



The state in which they are found would prove, on the con- 

 trary^ that those veins have not broken or traversed them. 



The chalk contains nineteen genera of polyparia, two of 

 stellerides, or rather debris, which may belong to four genera 

 estabHshed in this family, eight genera of echinodse^ two of 

 Crustacea, one of annelides, three of serpulse, twenty-five of 

 bivalve shells ; the genus 'planospirites, little known ; twelve 

 genera of partitioned, or comparted shells, two of lish, two 

 of reptiles, one of vegetables, and (which is remarkable for the 

 smallness of the number) four genera of univalve shells. 



It would seem that the chalk strata have not been placed in 

 circumstances proper for the production of marbles, for it does 

 not appear that any have been recognized in them. 



Silex is found abundantly in the chalk, and in the more 

 recent strata, but it is more rare in the ancient strata. The 

 wood which is found in the latter is not so generally siliceous 

 as that which is found in more recent depositions. It is very 

 rarely met with in a calcareous state. 



Some varieties of that species of silex called petrosilex mo- 

 larisy (vulgo, millstones,) contain shells, while others do not ; 

 but there is reason to believe that all those, which are in cir- 

 cumstances analogous to those of this silex which contains 

 the shells, did formerly contain some, which have disappeared. 

 Some of the shelly strata, posterior to the chalk, as that of 

 Grignon, in France, are not petrified, and their compactness is 

 comparatively trifling. In others, as at Dane, a department 

 of the Marne and Loire, and at Saillencourt, a department of 

 the Seine and Oise, the shells, polyparia, and the debris of 

 other marine bodies, are deposited lightly one over the other, 

 and connected by their point of contact with a crystallization 

 almost imperceptible, so that the mass is porous and incapable 

 of retaining the waters. At Sainteny, a department of La 

 Manche, a similar stratum exhibits all the marine fossil bodies, 

 and their debris, invested with a slight brownish-coloured crust. 

 In the strata of coarse, or, as we term it, crag-limestone, in 



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