270 Count Gaston de Saporta on the Temperature 



which must not be passed over in silence. What must we con- 

 clude if the two series of genera to which I have just referred 

 combine, instead of mutually excluding each other ? The ex- 

 amination of this question, one of the most curious of those 

 suggested by the study of the European fossil floras, would be 

 best placed at the end of my notice, when I shall discuss the 

 legitimate consequences of the facts that I may have established; 

 however, as the objection has presented itself, I shall state my 

 opinion on this point, in order that, by at once getting rid of 

 what has a specious appearance, the course that we have to 

 follow may be cleared in advance of all obstacles. 



There are, in my eyes, some truths so clear that they cannot, 

 without paradox, be questioned. It follows incontestably, from 

 the totality of the facts known in geology, that the temperature 

 was higher formerly than at the present day in the zone of 

 which the continent of Europe forms a part. The phenomenon 

 of initial elevation of temperature is therefore not under dis- 

 cussion : what we have to seek are the successive degrees of this 

 temperature, the period and the mode of its decline. As regards 

 the fact of its definitive diminution, its results are before us. 

 There were formerly in Europe palm trees, screw-pines, arbores- 

 cent ferns, Laurinese, and other exotic forms, which have dis- 

 appeared to give place to the plants which we have before our 

 eyes, and of which we know the organization to be adapted to 

 the action and periodical return of cold seasons. Thus the fact 

 of the lowering of the ancient temperature evidently follows 

 from the elimination of these first types : therefore this elimina- 

 tion must be regarded as its true sign ; and whenever, in a fossil 

 flora, we observe a mixture of European with truly tropical 

 forms, the presence of the latter will be to us a sufficient indi- 

 cation of the maintenance of a high temperature. When the 

 European climate became decidedly too cold, these forms must 

 have disappeared from the middle portions of this continent, 

 and have left only faint traces of their former existence in its 

 southern parts : this, in my opinion, is a certain proof that their 

 coexistence with the forms which have continued indigenous 

 had been possible previously only by the aid of climatic com- 

 binations which did not exclude the maintenance of at least a 

 part of the ancient heat. 



Thus, to my eyes, the elimination of the tropical genera is the 

 great fact which reveals the moment when the temperature 

 decreased, and even the proportion of this decrement. To us, 

 therefore, the time when this elimination became complete will 

 be that in which, the latitudes being constituted nearly as at 

 the present day, the diff'erences observed no longer depend upon 

 any other than certain purely local causes. 



