the Earth at different Epochs, ^c. 359 



The numerical equality of the vascular cryptogamic plants, 

 the gymnospermous phanerogamic plants, represented by the 

 Coniferae, and the Monocotyledones, together with the less de- 

 velopment of the vegetables of the first of these classes, appear 

 to be the essential characters of the second period. 



The third period is peculiarly distinguished by the predomi* 

 nance of the gymnospermous phanerogamic plants, and espe* 

 cially of the Cycadeae. The vascular cryptogamic plants hold 

 the next rank, and after them come some Monocotyledones in 

 very small number. 



Lastly, the fourth period presents vegetables of all the classes 

 at present existing, among which, as at the present epoch, the 

 Dicotyledones are by much the most numerous. Then come the 

 Monocotyledones, the Gymnospermous Phanerogamic plants; 

 and, lastly, the Cryptogamic and Agamic. 



We therefore see that the terrestrial vegetation has always 

 been rendered more and more varied ; that, from being at first 

 limited to two principal classes, it presents three at a later pe- 

 riod, and at length five, and that in the vegetable kingdom as in 

 the animal kingdom, the beings which every thing leads us to 

 consider as the most simple, were the first formed, and the 

 classes of more complicated beings, which, for that reason, we 

 call more perfect, have been gradually added to these first 

 classes of more simple original beings. 



Such are the positive results, independent of all hypothesis 

 and all preconceived theory, to which the comparative examina- 

 tion of fossil vegetables conducts us. '>;■<) i»'. ^ - 



But, as by putting into the hands of' a botanist a herbarium 

 formed in a distant region of the earth, he would easily deter- 

 mine the nature of the climate under whose influence these ve- 

 getables grew, might we not, from the nature of the floras of 

 these diff'erent periods of formation of the terrestrial surface, be 

 enabled to determine some of the circumstances which presided 

 at the development of these vegetables .'' 



I am of opinion that, by attentively comparing the nature of the 

 vegetables of these diff'erent epochs with those which at present 

 grow in the different regions of the globe, we may arrive at re- 

 sults, if not certaio^ at least very. probable, in respect to this 

 subject, 'f'vnn ofji c'.^ > ' ' i 



