founded upon the Study of Fossil Shells. \5 



America, and, in an inverse manner, on each side of South 

 America. 



An important fact has just given a new point d'appui to 

 the estimate of the temperature of the two latest tertiary 

 periods : it is the agreement in the number of fossil and re- 

 cent species. Thus, in the north, there are few recent species, 

 few in a fossil state ; in the region of the Mediterranean, 

 about 700 fossil species, nearly 600 recent. We must call to 

 our recollection, that this difference arises from the circum- 

 stance, that among the fossil species, there are a certain num- 

 ber belonmnsr to races now extinct. In fine, the high 

 temperature of my second period will be placed beyond 

 dispute, when, to the thousand fossil species of this epoch 

 are opposed the nine hundred recent ones in the African seas 

 lying between the tropics. 



Since the number of species increases with the tempera- 

 ture, since on a fixed point of the torrid region we find 

 900 species, it appears to me that, by a natural induction, 

 we may attribute to my first tertiary period a temper- 

 ature at least equatorial; for we recognise there, as we have 

 already said, 1400 species, of which above 1200 were accu- 

 mulated within the limits of the Paris basin; that is to say, in 

 an extent of 40 leagues in diameter one way, and 55 the other. 

 There no longer exists, in any of our seas, any single point 

 exhibiting an equal number of species in as small a space. 



If we now examine these species, we shall find them par- 

 ticularly large and numerous in the families and genera 

 whose species multiply in the warmest regions of the earth, 

 forty species of Cerithia, a great number of Pleurotomae, of 

 Fusi, of Mitrae, of Volutae, of Murices, of Veneres, of Cardia, 

 of A'rcae, &c, found, in a fossil state, in the environs of Paris; 

 the absence in this basin of the forms peculiar to the North 

 Seas ; all these facts relative to the number and nature of the 

 species, unite to attest strongly that the great Parisian period 

 took place under an equatorial temperature, probably higher 

 than that of the equator at present. 



In borrowing from other parts of Parisian palaeontology 

 documents comparable to those which conchology furnishes, 

 I find in the great number of Pachydermata, and their some- 

 times gigantic size, another proof of the high temperature of 

 the Paris basin. Where do we find, in the present day, 

 animals analogous to these, if it be not in the equatorial parts 

 of the old and new continents, in the Isles of Sunda, and in 

 the Asiatic islands ? By adding to these considerations those 

 furnished by a small number of fossil vegetables, particularly 



