574 HISTORY OF GEOLOGY. 



place it among the known causes of change which in this chapter we 

 are considering. The bare conviction that a creation of species has 

 taken place, whether once or many times, so long as it is unconnected 

 with our organical sciences, is a tenet of Natural Theology rather than 

 of Physical Philosophy. 



[2nd Ed.] [Mr. Lyell has explained his theory 13 by supposing man 

 to people a great desert, introducing into it living plants and animals ; 

 and he has traced, in a very interesting manner, the results of such a 

 hypothesis on the distribution of vegetable and animal species. But 

 he supposes the agents who do this, before they import species into 

 particular localities, to study attentively the climate and other physical 

 conditions of each spot, and to use various precautions. It is on 

 account of the notion of design thus introduced that I have, above, 

 described this opinion as rather a tenet of Natural Theology than of 

 Physical Philosophy. 



Mr. Edward Forbes has published some highly interesting specula- 

 tions on the distribution of existing species of animals and plants. It 

 appears that the manner in which animal and vegetable forms are now 

 diffused requires us to assume centres from which the diffusion took 

 place by no means limited by the present divisions of continents and 

 islands. The changes of land and water which have thus occurred 

 since the existing species were placed on. the earth must have been 

 very extensive, and perhaps reach into the glacial period of which I 

 have spoken above. 14 



According to Mr. Forbes's views, for which he has offered a great 

 body of very striking and converging reasons, the present vegetable 

 and animal population of the British Isles is to be accounted for by 

 the following series of events. The marine deposits of the meiocene 

 formation were elevated into a great Atlantic continent, yet separate 

 from what is now America, and having its western shore where now 

 the great semi-circular belt of gulf-weed ranges from the 15th to the 

 45th parallel of latitude. This continent then became stocked with 

 life, and of its vegetable population, the flora of the west of Ireland, 

 which has many points in common with the flora of Spain and the At- 



18 B. in. c. viii. p. 166. 



14 See, in Memoirs of the Geological Survey of Great Britain, vol. i. p. 336, 

 Professor Forbes's Memoir " On the Connection between the Distribution of the 

 existing Fauna and Flora of the British Isles, and the Geological Changes which 

 have affected their area, especially during the epoch of the Northern Drift," 



