208 M. de Beaumont ow the Temperature of the 



near the poles; and M. Elie de Beaumont is of opinion, that 

 this normal maximum of terrestrial temperatures, cannot have 

 varied considerably since the earth was covered with vegetables* 

 For if the temperatures of the winters, and those of the warmest 

 periods of the year, were, in the basin of Paris, at the epoch of 

 the deposition of the calcaire grossier, the same as those of the 

 present day at Cairo, the mean temperature must also have been 

 the same, that is 22° cent. (72° F.) 



M. Deshayes founds his higher calculation on the great num- 

 ber of fossil shells collected in the basin of Paris. This number 

 amounts to 1200, while in the seas of Senegal and of Guinea 

 not more than 900 are known ; but it must be remarked, says 

 M. Elie de Beaumont, that the 1 200 species of fossil shells found 

 in the basin of Paris, did not live simultaneously ; they are ob- 

 tained from several layers formed successively, and of which the 

 richest would be very far from affording so large a number ; 

 and probably also, he adds, we are better acquainted with the 

 fossil shells of the environs of Paris, than with the living shells, 

 of equatorial seas, 



M. Elie de Beaumont then enters into some details on the 

 manner in which he conceives the diminishing temperatures of 

 successive geological periods may have resulted from the gra- 

 dual cooling of the internal mass of the earth. We know that 

 a constant relation exists between the excess of temperature pre- 

 sented by the surface of the earth, above that which the sun and 

 the atmosphere tend to communicate to it, and the gradual aug- 

 mentation of the temperature of deep places. At the present 

 day, when we descend into the interior of the earth, we find that 

 the temperature augments about l-30th of a degree cent, for 

 every yard, and the excess of temperature of the surface is 

 about l-32d of a degree. At the epoch of the coal formation, 

 the augmentation of temperature may, without doubt, have been 

 about l-3d of a degree for every yard ; but important geologi- 

 cal considerations are opposed to the supposition that it was more 

 considerable. The excess of temperature of the surface, then, 

 could not be higher than l-3d of a degree cent., a quantity too 

 small to account directly for the difference of the climates of the 

 present day. The explanation of this difference, so well ascer- 

 tained by geologists, can be found only in the accessory effects; 



