732 EEPOET — 1881. 



and boreal plants on all their mountains, and of these fossilised on their low lands ;. 

 discoveries which led to the recognition of the glacial period and glacial ocean. 



The first and boldest attempt to press the results of geological and climatal 

 changes into the service of botanical and zoological geography, was that of the 

 late Edward Forbes, a naturalist of genius, who, like Tournefort, chose the Levant 

 as the field for his early labours. In the year 1845, Forbes communicated a paper 

 to the Natural History section of this Association, on the distribution of endemic 

 plants, especially those of the British Islands, considered with regard to geological 

 changes.^ In this paper the British flora is considered to consist of assemblages 

 of plants from five distinct sources, which, with the exception of one, immigrated 

 during periods when the British Isles were united to the continent of Europe, 

 and have remained more or less localised in England, in Scotland, or in 

 Ireland. Of these he considered the Pyrenean assemblage, which is confined to 

 the west of Ireland, to be the oldest, and to have immigrated after the eocene 

 period, along a chain of now submerged mountains, that extended across the 

 Atlantic from Spain to Ireland, and indeed formed the eastern boundary of an 

 imaginary continent of pliocene age, which extended to the Azores Islands, and 

 beyond them. This, the ' Atlantis ' of speculative geologists, has long since been 

 abandoned. The second assemblage is of plants characteristic of the South-West 

 of France, which now prevail in Devon, Cornwall, and the Channel Islands ; 

 their immigration he assigns to a pliocene date, probably corresponding to the 

 red crag. The third assemblage is of plants of the North-East ot France, which 

 abound in the chalk districts of the South-Eastern counties of England ; their 

 immigration is referred to the era of the mammaliferous crag. The fourth is of 

 Alpine plants now found on the mountains of Scotland, Wales, and England ; 

 these were introduced mainly by floating ice from Scandinavia during the glacial 

 period, when the greater part of the British Isles were submerged, its mountain 

 tops forming part of a chain of islands in the glacial sea that extended to the coast 

 of Norway ; this was during the newer pliocene period. Lastly, the Germanic plants 

 were introduced during the upheaval of the British Islands from the glacial ocean, 

 and as the temperature was gradually increasing ; these are spread over the whole 

 islands, though more abundant on the eastern side. At the commencement of this 

 immigration England was supposed to be continuous with the Germanic plains, from 

 which it was subsequently severed by the formation of the English Channel. Also,. 

 at the commencement of this immigration Ireland was assumed to be con- 

 tinuous with England, to be early severed by the formation of the Irish Sea ;. 

 which severance, by interrupting the migration of Germanic types, accounts for the 

 absence of so many British animals in the sister island. 



I have thus briefly related Forbes' views, to show how profoundly he was im- 

 pressed with the belief that geographical and climatal conditions were the all- 

 powerful controllers of the migrations of animals and plants. Forbes was the re- 

 former of the science of geographical distribution.^ 



' British Association Reporis, 1845, pt. 11. p. 67, and Annals and Magazine of 

 Natural History, vol. xvi. p. 126. This the author followed by a much fuller expo- 

 sition of the subject, which appeared in the Memoirs of the Geological Survey of the 

 United Kinydom, vol. i. p. 336 (1816), entitled ' On the Connection between the dis- 

 tribution of the existing flora and fauna of the British Isles, and the geological 

 changes which have afliected their area, especially during tlie epoch of the northern 

 drift.' After many years' interval I have re-read this Memoir with increased pleasure 

 and profit. The stores of exact information which he collected concerning the 

 plants, the animals, and the geology of Europe and North America, appear to me to 

 be no less remarkable than the skill with wliicli he correlated them and educed from 

 the whole so many very original and in great part incontrovertible conclusions. 



^ I cannot dismiss the subject of the geograpliy of the British flora without an 

 allusion to the labours of Hewett Cottrell Watson, wlio, after a life devoted to the 

 topograph}- of Britisli plants, was laid m the grave only a month ago. Watson was 

 the first botanist who measured the altitudinal range of each species, and, by 

 a rigidly statistical metliod, traced their distribution in every county, and grouped 

 them according to their continental aflinities, as well as by the physical conditions. 

 of their habitats. 



