ANNIVERSARY ADDRESS OF THE PRESIDENT. XXXlll 



the Distribution of the existing Fauna and Flora of the British Isles, 

 and the Geological changes which have affected their area." '* In 

 this work," to use words already printed, " the happy combination 

 of great botanical and zoological knowledge is made to bear on some 

 of the most intricate inquiries with regard to the age and relationship 

 of the rocks of Great Britain." 



Mr. Horner, when President of this Society, has borne his ready 

 testimony to the merits of this work, when he says in his Anniversary 

 Address in 1847, that this Essay "is an admirable example of the 

 light to be derived from other branches of natural history in the 

 prosecution of geological inquiries ; of the application of animal and 

 vegetable physiology, and a knowledge of the habits and distribution 

 of animals and plants to the elucidation of very difficult problems in 

 geology." Mr. Horner, in the Address from which I have quoted 

 these words, has given an admirable account of this interesting and 

 attractive memoir, so suggestive as it is of great and enlightened views. 

 I will therefore here only observe, that the principal theory which 

 it is the object of this Essay to establish, is based on the assumption 

 of the existence of specific centres^ that is, of certain geographical 

 points from which the individuals of each species have been diffused, 

 involving their consequent descent from a single progenitor, or from 

 two, according as the sexes might be united or distinct. Prof. Forbes 

 further declares, as his opinion, that the " abandonment of this doc- 

 trine would place in a very dubious position all evidence the pala3on- 

 tologist could offer to the geologist, towards the comparison and 

 identification of strata, and the determination of the epoch of their 

 formation." Having assumed the truth of the doctrine of specific 

 centres, the problem which he proposes to solve is the origin of the 

 assemblages of the animals and plants now inhabiting the British 

 Islands. Within this limited area he considers that the united labours 

 of British naturalists have shown that there are a great number of 

 animals and plants which are not universally dispersed, but are con- 

 gregated in such a way as to form distinct regions or provinces. The 

 vegetation, for instance, presents five well-marked Floras, four of 

 which are restricted to definite provinces, whilst the fifth, besides 

 exclusively claiming a part of the area, overspreads and commingles 

 with all the others. 



Prof. Forbes considers that, of the three given modes by which an 

 isolated area may become peopled by animals and plants, "immigra- 

 tion before isolation" of the area was the mode by which the British 

 Isles have chiefly acquired their existing flora and fauna, terrestrial 

 as well as marine, and that it took place subsequently to the Miocene 

 epoch. It follows from this argument, that previous to the isolation 

 of this area, it must have been in direct union with those portions of 

 the European continent the floras of which are shown to be identical 

 with one or other of the five floras of the British isles. I will briefly 

 mention the five distinct floras which he has noticed, and the districts 

 with which he considers they prove our former connexion. 



1 . The West Irish Flora. — The high lands in the north of Spain 

 present the nearest point where a vegetation occurs identical with 



