150 OBiarKAL a^rticles. 



Europe and America. Witli regard to this question I have been led to 

 differ from these authors, and am confirmed in the view advanced by 

 Dr. Asa Gray* in reference to plants, and previously by Mr. Dax'winf 

 with regard to animals, that the migrations resulting in a community 

 of types in the tertiary beds of Europe and the present flora of the 

 Eastern states of the Nortli American continent, took place probably in 

 a comparatively high latitude to the north of the Pacific ocean. In 

 this short paper I propose to give the grounds upon which I think 

 this opinion may be based. I shall embody further, some observa- 

 tions bearing upon the general and mutual relations of the North 

 Temperate floras, with others of a critical character, which have 

 suggested themselves by the comparisons I have had occasion to 

 institute, referring to some of the determinations of fossil species in 

 Professor Heer's " Flora Tertiaria Helvetise." 



Had I felt myself on more secure ground in touching upon ques- 

 tions intimately bound up with geological problems, I might have 

 chosen to prefix the title of Professor Heer's work to tliis notice, and 

 to have aimed at a more complete review of it than, in my inability 

 to appreciate properly some of the more strictly geological features, 

 I can venture upon. 



The data upon which my enquiries are based, are chiefly these. 

 So far as the Tertiary Flora of Europe is concerned, I believe that the 

 general aspect of the questions touched upou is not sensibly atFected 

 by confining myself almost exclusively to the materials furnished from 

 Switzerland in the " Flora Tertiaria." The statistics of recent Floras 

 rest upon Njnnan's " Sylloge Flora3 Europcefe," Mr. Bentham's 

 "Hand-book of the British Flora," Mr. Black's Catalogue of 

 Japanese Plants appended to Hodgson's Japan, A. Grray's " Manual" 

 for the Northern, and Chapman's " Flora" for the Southern United 

 States, AYebb and Berthelot's " Hist. Nat. des iles Canaries," and minor 

 papers. The Hookerian collections have been of essential service in 

 the comparison of specimens and of recent with extinct forma. 



With regard to the basis upon which comparisons between recent 

 and fossil (tertiary) floras should rest, I appi-ehend that the principal 

 reliable results which are attainable in the present state of know- 

 ledge are, in the main, quite as Hkely to issue from comparisons of 

 genera as of species. It is true, that in some cases, fossil remains suflice 

 to enable the further step to be taken of tracing identical, analogous 

 or representative specific forms in past and present floras ; but these 

 are rather exceptional, and from the necessity of attaching a primary 

 importance to the character of the nervation, venation and form of 

 leaves, which must often render even ordinal determination ex- 

 ceedingly uncertain, from the very fragmentary character, frequently, 

 even of these imperfect data, and, farther, from our ignorance of 

 types which, it may be assumed, are now extinct, I believe that we 

 can best eliminate several sources of error by depending rather on 

 generic than specific identifications or parallels. It may be truly 



* Mem. Am. Acad. N.S., vol. vi. p. 377. fVoyage of Beagle. Ed. 1839, p. 151. 



