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218 NOTICES OF BOOKS. 



I 



PalEeontology, or on the mode of creation of sgecies, the number ori- 

 ginally created, and their primitive distribution. Botanical Geography 

 can indicate certain probabilities, certain theories, but the principal 

 facts in distribution depend upon more recent and less obscure causes. 

 It suffices to understand and to allow certain facts and tlieories, which 

 appear probable, namely, that groups of organized beings, under different 

 hereditary forms (Classes, Orders, Genera, Species, andKaces), have ap- 

 peared at different places and at different times, the more simple perhaps 

 first, the more complicated afterwards ; that each of these groups has 

 had a primitive centre of creation of greater or less extent ; that they 

 have, during the period of their existence, been able to become more 

 rare or common, to spread more or less widely, according to the nature 

 of the plants composing them, the means of propagation and diffusion 

 they are possessed of, the absence or presence of animals noxious to 

 them, the form and extent of the area they inhabit, the nature of the 

 successive climates of each country, and the means of transport that 

 the relative positions of land and sea may afford ; that many of these 

 groups have become extinct, whilst others have increased, at least as 

 far as can be judged from comparing existing epochs with preceding 

 ones; and lastly, that the latest geological epoch, the Quaternary (that 

 which preceded the existence of man in Europe, and which followed 

 the latest elevation of the Alps), has lasted many thousand years, during 

 which important geographical and physical changes have affected Eu- 

 rope and some neighbouring countries, whilst other regions of the globe 

 have suffered no change, or have been exposed to a different series of 

 changes. 



" Thus the principal facts of Geology and PalEeontology, reduced to 

 the most general and incontestable, suffice to explain the facts of Bo- 

 tanical Geography, or at least to indicate the nature of the explanation, 

 which it requires the progress of many sciences to complete. 



" The most numerous, the most important, and often the most ano- 

 malous facts in the existing distribution of plants, are explained by 

 the operation of causes anterior to those now in operation, or by the 

 joint operation of these and of still more ancient causes, sometimes of 

 such as are primitive (connected with the earliest condition of the 

 plant). The geographical and physical operations of our own epoch 

 play but a secondaiy part. I have shown that in starting from an 

 original fact, which it is impossible to und erstand, of tlje creation of a 



