^68 Count Gaston dc Sapoita on the Tcinperaiure 



Nor did they consider that, in making the vegetable combi- 

 nations peculiar to this epoch dependent on the existence of a 

 very elevated temperature, the important fact was left out of 

 consideration, that the other categories of plants not having yet 

 appeared, their absence was a negative phenomenon which de- 

 prived the exclusive predominance of Cryptogamic groups of a 

 great part of its significance. 



In reality nothing was evident except the existence of a more 

 genial and more uniform temperature than at present — the only 

 rigorous deduction from the facts observed. 



But, by assuming for the Carboniferous period a very high 

 degree of heat, a starting-point was established in harmony with 

 the supposed progress of vegetation, since this appeared to have 

 been gradually modified in proportion as the temperature was 

 continually lowered by an insensible gradation. 



To sum up. A great initial heat combined with a great cli- 

 matic uniformity ; a diminution at first not very marked, but 

 becoming very sensible towards the commencement of the Ter- 

 tiary period, still more marked towards its middle, and com- 

 pletely established towards the end of this period ; a progress 

 starting from a state very different from our own, and approach- 

 ing the latter gradually from epoch to epoch : such, it appears 

 to me, is a faithful representation of the most rational induc- 

 tions that science had formulated. We must now see whether 

 this view is in accordance with the most recent observations. 



II. 



The domain of fossil botany has been enormously enlarged of 

 late Years. One of the most interestins; results of this recent 

 progress is, that we can trace the course of a considerable num- 

 ber of genera through several successive stages ; and where the 

 species belonging to these genera, as is almost always the case, 

 show a close affinity to those which correspond with them in the 

 present state of things, we are justified in assuming that the 

 fossil species lived under the rule of the same conditions 

 as its living homologue, or at least under very similar condi- 

 tions. 



Thus the existing genera the ancient existence of which it is 

 possible to prove must assist us in the investigation of the 

 temperature proper to the times and places which they seem to 

 characterize ; whilst the extinct genera can only furnish us with 

 such information in a very indirect fashion, according to the 

 more or less distant relationship which they bear to those of our 

 own day. On the other hand, when we have to do with a spe- 

 cies which closely resembles a living congeneric species, the 



