The Scottish Naturalist. 313 



exist, but swept everything before it into the sea, on all sides, 

 itself filling up the hollow of the German Ocean, and forming 

 one continuous sheet with that covering Norway and Sweden, 

 forbidding the idea of the existence of either animal or vegetable 

 life. On the Continent the climate of the southern half of 

 Europe would then be of such a character that only an arctic 

 fauna and flora could exist in the low grounds, being driven 

 there gradually before the advancing ice- sheet, whence previ- 

 ously the temperate or European flora had been driven still 

 farther south. That this was so is no mere conjecture, as in 

 several localities in south Europe the peat-bogs have yielded 

 remains which go far to prove it. Some of these peat-beds are 

 only a few feet in thickness, and between the peat and the clay 

 on which it rests have been found leaves of Betula nana, Dryas 

 octopetala, Salix reticulata, and Salix polaris, the latter being a 

 characteristic Spitzbergen plant, — all being plants which now are 

 confined to the high hills in temperate Europe, or the most 

 northerly latitudes where vegetation will exist. Thus we learn 

 how the arctic and alpine flora, driven southward by the en- 

 croachment of the great northern mcr de glace, at last came to 

 occupy the low grounds of temperate Europe. 



In course of time a change occurred. The climate began to 

 ameliorate, and the ice-sheet gradually retreated northward and 

 up the hills. The arctic fauna and flora followed, and gradually 

 reoccupied the ground from which they had been formerly 

 driven. 



Dr Buchanan White, in his paper 1 on the Mountain Lepi- 

 doptera of Britain, has so graphically described the process of 

 immigration of the alpine flora which now occupies our country, 

 at the close of the great ice age, that I cannot do better than 

 give his account of it briefly. He says : " In course of time the 

 altered condition of things would be felt in Britain, but the 

 English Channel would as yet cut it off from the advancing tide 

 of life. Still it is probable that the winds and sea -currents 

 would carry thither the spores of mosses, lichens, and other 

 cryptogamic vegetation, and perhaps even the seeds of some of 

 the higher plants, which would find suitable resting-places out of 

 reach of the great floods which continued to sweep over much 

 of the low ground. 



" Finally, after several variations in the relative heights of the 

 land or sea (the latter being at one time 100 feet higher on our 



1 ' Scottish Naturalist,' vol. v. p. 97. 



