26 FOSSIL MAMMALIA. 



Strata just enumerated, and appears the most ancient of the 

 Parisian depositions, is itself supported by the chalk. This 

 formation, of immense thickness and extent, appears in coun- 

 tries as remote from us as Pomerania and Poland. But in 

 the neighbourhood of Paris, in Berri, in Champagne, in Pi- 

 cardy, and a considerable part of England, it predominates 

 uninterruptedly, and forms a most extensive circle, or basin, 

 in which all the strata we have mentioned are contained, and 

 its edges are barely covered by them in these places where the 

 superstrata are least elevated. 



Such superstrata are not confined to the countries just in- 

 stanced, or to the basin in question. Depositions, more or less 

 similar, and containing organic remains, are found in other 

 regions, wherever the surface of the chalk affords similar 

 cavities for their reception. They are found even where no 

 chalk formation exists, and where the most ancient strata con- 

 stitute their only support. The two distinct formations with 

 fresh-water shells have been found in England, Spain, and 

 even on the confines of Poland ; the marine beds interposed 

 between them exist along the entire range of the Apennines. 

 Some of the quadrupeds of the Parisian plaster- stones have 

 been found elsewhere, as, for instance, in the gypseous strata 

 of Valai, and in the molasse quarries in the South of France. 



Thus it appears, that the partial revolutions which took 

 place between the era of the chalk-formation, and that of the 

 last great inundation, and which consisted in the alternate 

 inversion and retreat of the sea, occurred in many countries. 

 This globe has undergone a long series of agitations and 

 changes, which appear to have been rapid in their operation, 

 from the comparative slightness of the depositions they have 

 left behind. The chalk has evidently been the production of 

 a more tranquil and extensive sea. It contains marine pro- 

 ductions alone, but among them the most remarkable remains 

 of vertebrated animals, all of the fish or reptile class — tortoises 

 and lizards of colossal size and extinguished genera. 



