UPON THE BRITISH FLORA. II 



scratched, and polished stones, intercalated by deposits of sands 

 and gravels denoting warm periods, when vegetation was 

 luxuriant, and beds of lignite were laid down sufficiently thick to be 

 worked for coal. The trees are principally Willows and Alders. 

 Oaks, too, are frequently found rooted in the subject glacial clays. 

 These intercalated beds yield mammalian remains, Mammoth, Ox 

 (Bos primigenius), Irish Elk, and Horse. In the Swiss deposits of 

 this age are found the remains of Elephas antiquus, Rhinoceros 

 megarhinns, Bos primigenius, Cervus elaphus (Red-deer), and the 

 Cave-bear, of which all are extinct except the Red-deer. . Dr. A. 

 Russell Wallace, in his "Island Life," quotes the late Professor 

 Asa Gray, who points out that hundreds of species of trees and 

 shrubs which still flourish in America are now completely 

 wanting in Europe. There is good reason to believe that many 

 were exterminated elsewhere by the rigours of the Glacial Period 

 owing to being cut off from their southern migration by the 

 Alps and the Mediterranean, whereas in Eastern America and 

 Asia, the mountain chains running in a northern and southern 

 direction, there was nothing to prevent the flora from being 

 preserved by a southern migration to a milder region. 



We have now arrived at a point favourable for the examina- 

 tion of the age of the flora and fauna of the British Isles. It is 

 generally considered that the Lusitanian group is the oldest, and 

 that it arrived before the Glacial Age, and that the Eastern or 

 Siberian was the latest. It arrived in Germany from the east, 

 after the deposition of the Lower Boulder Clay, and therefore 

 after the former portion of the Glacial Period had passed away. 

 It makes its first appearance in the Forest-bed of Norfolk. On 

 this supposition the other migrations must have arrived in Great 

 Britain during the earlier part of the Glacial Age. Relics of an 

 Arctic Flora have been met with at Bovey Tracy in Devonshire, 

 comprising Betula nana, Salix cinerea, Arctostaphylos uva-ursi, 

 which are now natives of the British Islands. We have no less 

 than twenty-six species of the Siberian mammals which came as 

 far west as the British Islands. Nine of these now inhabit Great 

 Britain. We cannot obtain any evidence as to the geographical 



