286 Apparent objections to the Glacial Theory. 



till the termination of the tertiary epoch, so likewise has the cold ; 

 and if no lands have arisen from the waters since that time, the maxi- 

 mum decrease of temperature took place at that period. In order 

 therefore to raise the temperature again and dissolve the glaciers, 

 the northern lands should have decreased at the commencement of 

 the modern era ; yet this so far from being true, is actually dis- 

 proved by the fact, that land is still rising in the north, and has con- 

 tinued to do so, we are informed, since the commencement of the 

 tertiary period. The climates of the earth are therefore colder 

 now than they have been at any former period, and this the pheno- 

 mena of the strata confirm, and the theory of refrigeration demands ; 

 for it must be evident, that if the theory of internal heat be true, 

 such a result as this must be inevitable, for in by-gone ages when 

 the central heat was greater, and the crust of the external earth 

 less thick and solid, the surface temperature must have been kept 

 higher by the radiating heat ; whereas in our time it is proved, the 

 the surface is scarcely affected by the internal temperature of the 

 planet. 



" All the observations collected and discussed by the most learned 

 physiologists of our days, inform us, that the increase of temperature 

 in the strata lying immediately beneath the surface, is about a 

 degree in thirty metres, at a medium. In a globe of iron, a similar 

 increase would only give a quarter of a centesimal degree, for the 

 actual elevation of the temperature of the surface. As a conse- 

 quence of the influence of the central fire, this elevation is very 

 trifling, and almost imperceptible ; that, however, which the earth 

 experiences is much less still. In fact, the strata of the mineral 

 shell are not composed of iron, but of substances which offer much 

 less facility for the transmission of heat. Now, the heating of the 

 ground is (for the same level of temperature in the direction of the 

 depth) directly proportioned to this facility ; whence it follows 

 that if, as is very likely, the substances of which the upper envelope 

 of the earth is composed, conduct eight times less heat than iron, 

 the excess of heat communicated by the internal fire will only be the 

 32d part of a centesimal degree, a quantity quite insignificant. 

 When we examine attentively and according to known principles, 

 all the observations relative to the figure of the e arth, we cannot doubt. 



