524 PREHISTORIC E UROPE. 



land-connections across the Mediterranean. The approaches to 

 our preserves were effectually closed to these southern reivers. 



The succeeding stage in the history of postglacial changes 

 was marked by a gradual deterioration of climate, and the sub- 

 mergence of vast tracts of land in the north and north-west. 

 The British area was insulated, and a like fate befell Greenland, 

 Iceland, and the Fseroe Islands. This insulation of our area pre- 

 vented the immigration hither of many plants of an eastern 

 derivation which subsequently spread into the neighbouring 

 regions of the Continent, where they are now plentiful. 1 We 

 have no reason to believe that these changes were suddenly 

 effected. Probably the depression commenced during the pre- 

 ceding genial period — perhaps in the far north, and gradually 

 extended southward, so that the separation of Greenland, and 

 the isolation of the Faeroe Islands and Iceland, may have taken 

 place long before the North Sea crept in between Britain and 

 the Continent. It is possible, indeed, that the broad space be- 

 tween Greenland and Scandinavia may mark a special area of 

 depression — from the centre of which the downward movement 

 may have diminished outwards in all directions. And this is 

 not a mere conjecture, but is suggested by the fact already 

 referred to, that the evidences of recent submergence are con- 

 spicuous in the north of Scotland, the Outer Hebrides, Orkney 

 and Shetland, the Fseroe Islands; and the north-west shores of 

 Norway. Eaised- beaches, which prove recent elevation, are 

 common upon the coasts of England, Ireland, Central Scotland, 

 and the southern margin of the Scandinavian peninsula. But 

 north of those regions all the appearances betoken a recent sub- 

 mergence. There are no raised-beaches, nor, as a rule, have the 



1 As examples, Professor Engler gives the following list of species : — Anemone 

 ranunculoides, L., Hepatica triloba, Chaix, Thalictrum angustifolium, Jacq., 

 Corydalis cava, Schweigg. and Koerte, C. fabacea, Pers., Viola mirabilis, L., 

 Dianthus superbus, h.,D. Carthusianorum, L., Tilia platyphyllos, Scop., Gera- 

 nium palustre, L., Acer platanoides, L., Genista germanica, L., Astragalus Cicer, 

 L., Lathyrus vernus (L.), Bernh., Potentilla alba, L., Sambucus racemosa, L., 

 Melampyrum nemorosum, L., Abies alba, Mill. , Picea excelsa (Lamk. ), Lk. — Versuch 

 einer Entwicklungsgeschichte der Pflanzenwelt insbesondere der Florengebiete sett 

 der Tertidrperiode, I Theil., p. 182. 



