CHAPTEE XVI. 



CONTINENTAL ISLANDS OF RECENT ORIGIN : GREAT BRITAIN. 



Characteristic Features of Recent Continental Islands — Recent Physical 

 Changes of the British Isles — Proofs of Former Elevation — Submerged 

 Forests — Buried River Channels — Time of Last Union with the Conti- 

 nent — Why Britain is poor in Species — Peculiar British Birds — Fresh- 

 water Fishes — Cause of Great Speciality in Fishes — Peculiar British 

 Insects — Lepidoptera confined to the British Isles — Peculiarities of the 

 Isle of Man — Lepidoptera — Coleoptera confined to the British Isles— 

 Trichoptera peculiar to the British Isles — Land and Freshwater 

 Shells — Peculiarities of the British Flora — Peculiarities of the Irish 

 Flora — Peculiar British Mosses and Hepaticae — Concluding Remarks 

 on the Peculiarities of the British Fauna and Flora. 



We now proceed to examine those islands wliich are the very 

 reverse of the ''oceanic" class, being fragments of continents or 

 of larger islands from which they have been separated by sub- 

 sidence of the intervening land at a period which, geologically, 

 must be considered recent. Such islands are always still con- 

 nected with their parent land by a shallow sea, usually indeed 

 not exceeding a hundred fathoms deep ; they always possess 

 mammalia and reptiles either wholly or in large proportion 

 identical with those of the mainland ; while their entire flora 

 and fauna is characterised either by the total absence or com- 

 parative scarcity of those endemic or peculiar species and genera 

 which are so striking a feature of all oceanic islands. Such 

 islands will, of course, differ from each other in size, in antiquity, 

 and in the richness of their respective faunas, as well as in their 

 distance from the parent land and the facilities for intercom- 

 munication with it; and these diversities of conditions will 

 manifest themselves in the greater or less amount of speciality 

 of their animal productions. 



