224 OBSERVATIONS ON THE MEAN TEMPERATURE 



was much colder in ancient than in modern times. When we 

 learn that the Tyber was often frozen ; — that snow lay at 

 Rome for forty days ; — that grapes would not ripen to the 

 north of the Cevennes ; — that the Euxine Sea was frozen over 

 every winter in the time of Ovid ; — and that the ice of the 

 Rhine and the Rhone sustained loaded waggons ; — we cannot 

 ascribe the amelioration of such climates to the influence of 

 agricultural operations. 



The cold Meridian which now passes through Canada and 

 Siberia, may then have passed through Italy ; and if we trans- 

 fer the present mean temperatures of these cold regions, to the 

 corresponding parallels in Europe, we shall obtain a climate 

 agreeing in a singular manner with that which is described in 

 ancient authors. 



It is not, however, in the altered condition of our atmo- 

 sphere merely, that we are to seek for proofs of a periodical 

 rotation of climate. The impressions of the plants of warm 

 countries, and the fossil remains of land and sea animals, 

 which could exist only under the genial influence of the Tem- 

 perate Zone, are found dispersed over the frozen regions of 

 Eastern Asia ; and there is scarcely a spot on the solid cover- 

 ing of the Globe, that does not contain indications of a revo- 

 lution in its animal and vegetable productions. 



This interchange of the productions of opposite climates, 

 has been ascribed to some sudden alteration in the obliquity 

 of the Ecliptic, and even to a violent displacement of the 

 Earth's axis ; but Astronomy rejects such explanations, as ir- 

 reconcileable with the present condition of the system, and as 

 incompatible with the stability of the laws by which it is go- 

 verned. 



Having 



