226 



THE GEOLOGICAL HISTORY OF PLANTS. 



extended far into temperate regions, was not favorable to 

 vegetable life. But in some localities we have stratified 

 clays with plant-remains later than the Glacial epoch, 

 yet indicating that the great cold had not then entirely 

 disappeared. In the lacustrine beds at Holderness is 

 found a small birch {Betula nana, L.), now limited in 

 Great Britain to some of the mountains of Scotland, but 

 found in the arctic regions of the Old and New World 

 and on Alpine districts in L ipe, and with it Prunus 

 padus, L., Quercus rohur, L., Corylus avellana, L., 

 Alnus glutinosa, L., and Pinus sylvcstris, L. In the 

 white clay-beds at Bovey Tracey of the same age there 

 occur the leaves of Arctostaphylos uva-ursi, L., three 

 species of willow, viz., Salix cinerea, L., S. myrtilloides, 

 L., and S. polaris, Wahl., and in addition to our Alpine 

 Betula nana, L., the more familiar B. alba, L. Two of 

 these plants have been lost to our flora from the change 

 of climate that has taken place, viz., Salix myrtilloides, 

 L., and 8. polaris, Wahl.; and Betula nana, L., has re- 

 treated to the mountains of Scotland. Three others 

 {Dryas octopetala, L., ArctostapJiylos uva-tirsi, L., and 

 Salix herhacea, L.) have withdrawn to the mountains of 

 northern England, Wales, and Scotland, while the re- 

 mainder are still found scattered over the country. Not- 

 withstanding the diverse physical conditions to which 

 these plants have been subjected, the remains preserved 

 in these beds present no characters by which tliey can 

 be distinguished from the living representatives of the 

 species." 



One of the instances referred to is very striking. At 

 Bovey Tracey the arctic beds rest directly on those hold- 

 ing the rich, warm temj>erate flora of the Eocene ; so 

 that here we have the evidence of fossil plants to show the 

 change from the climate of the Eocene to that of arctic 

 lands, and the modern vegetation to indicate the return 

 of a warm temperature. 



