1 i> Estimate of Temperature during the Tertiary Period, 



of ages, for accumulated generations to have formed of their 

 remains a soil of vast extent and considerable thickness. 



If, as I firmly believe, the basin of the Gironde has been 

 deposited under an equatorial temperature, a glance at the 

 map will suffice to convince us, that the influence of this 

 temperature must have been felt as far as Poland and the 

 south of Russia in Europe. 



To determine the temperature of my second tertiary period, 

 I have proved the analogy of nearly two hundred species of the 

 torrid zone with the fossil species distributed more particu- 

 larly at Bordeaux and at Dax, but found in all the other 

 basins belonging to this second period. 



An equally conclusive mode is, unfortunately, wanting to 

 determine the temperature of the first stage of tertiary strata. 

 This first group, represented particularly by the Paris basin, 

 occupies, also, that of London and that of Valognes, almost 

 all Belgium and Holland, many points of the Alps, Castel 

 Gonbereo, the Val de Ronca, some small basins of Hungary 

 and Moldavia, the lower part of the basin of the Gironde 

 (Blaye, &c), and, finally, but with some uncertainties, all the 

 lower tertiary strata of North America. 



Among more than 14-00 known species in the Parisian 

 strata, 38 only are analogous to recent ones. It is true, that 

 the greater part of these 38 species live solely in the equa- 

 torial zone ; nevertheless, there are some found among them 

 which are not only distributed through this zone, and found 

 also in our temperate seas, but even are seen to have passed 

 into the North Sea. 



We must abandon, then, in calculating the temperature of 

 the most important tertiary period, the means that I have 

 employed for the two preceding ones. I can, however, supply 

 its place by many other means, though of less value than that 

 which fails me in this instance. 



In the Icy Seas, there exist only a very small number of 

 Mollusca ; but other species are added to these in proportion 

 as we advance towards warmer regions ; and thus we see 

 them augment from 8 or 10 which subsist near the 80th 

 degree, to nearly 900, which live in the tropical region of 

 Senegal and Guinea. This increase of species with an in- 

 crease of temperature points out, also, the influence which 

 is exercised by an agent so powerful as heat upon the creation 

 of living beings. But these phenomena do not show them- 

 selves only in that part of the terrestrial globe which I have 

 chosen for an example ; they are produced, also, from the Sea 

 of Behring to the Isles of Sunda, on each side of North 



