PKEl'ACE. IX 



dent birds, the green woodpecker and the nuthatch ; of annual 

 summer migrants, the wood wren and the tree pipit. But we 

 should not have the stock clove, — a resident species in the midland 

 and eastern counties of England ; — nor would the melodious 

 nightingale favour us with its presence, so definitively marked is 

 the line of its migration. As to other species, which are found 

 though rarely to the westward, — in Cornwall and Wales, — as the 

 lesser whitethroat, &c, they might then, as a matter of course, 

 be expected as rare visitants; such they possibly may be now, 

 though more unfrequently than they would be in the other 

 instance. 



In like manner, the junction of Great Britain throughout its 

 parallels of latitude, with the nearest continental land, would add 

 greatly to the number of British birds, that island being as 

 deficient comparatively in those of the most western European 

 countries, as Ireland is, in comparison with it. The sea lying 

 between the shores of Great Britain and the continent, has the 

 same effect as that extending between the former and Ireland. 

 Were there an island even of equal size to Ireland, situated as far 

 distant to the westward of that country as it is from Great Britain, 

 the diminution of species would be still greater than that actually 

 existing between Ireland and Great Britain, and so on, in an 

 increased ratio, were island after island, about equidistant from 

 each other, placed still farther to the westward. 



The falling off would be owing to the principle, that species 

 continue diminishing (each within its different range) the farther 

 we recede from their metropolis, and that the diminution is accele- 

 rated by the insular nature of the land, as opposed to its being 

 conterminous or continental. 



The preceding remarks apply only to islands like Great Britain 

 and Ireland lying near a continent and deriving their birds 



