PHYSICAL CONDITIONS— PLEISTOCENE. 353 



vanished from that region, and as the cold increased the less 

 hardy of the temperate forms would follow. The alpine plants, 

 at the same time, would advance from the north and descend 

 from the mountains, whither they had retired during the 

 preceding interglacial epoch. Thus, by and by, a flora of 

 polar willows, dwarf birches, and arctic and alpine mosses, 

 saxifrages, and lichens would occupy the low grounds of Central 

 Europe, while pines and firs would spread over Northern and 

 Central France. We know that the arctic flora pushed its way 

 south into Spain, Italy, and Austria, for a number of character- 

 istic species are now living in the mountain- regions of those 

 countries, whither they retreated upon the subsequent disap- 

 pearance of cold climatic conditions in the low grounds. Among 

 these are Mulgedium alpinum, Less., Gnaphalmm norvegicum, 

 Gunn., Azalea procumbens, L., Arctostaphylos alpinus, L., Veronica 

 alpina, L., V. saxatilis, L., Salix reticulata, L., S. herbacea, L., Jun- 

 cus triglumis L., Woodsia hyperborea, Br. Few of the arctic-alpine 

 plants, however, seem to have crossed into Africa ; at all events 

 they have not been recorded as occurring south of the Mediter- 

 ranean, although many northern species are common to the flora 

 of Europe and North Africa. According to Hooker and Ball, 

 the most remarkable feature of the higher region of the Atlas 

 is the very large proportion of common plants of the colder 

 temperate regions of Central and North-western Europe, which 

 are there found associated with species of very different types. 

 With the doubtful exception of Sagina Zinnwi, not one of the 

 plants is characteristically alpine, or typical of the arctic or 

 glacial flora. 1 During the southward advance of the tempe- 

 rate forms we can readily imagine what changes would take 

 place in the interglacial flora of Southern Europe. The 

 fig-tree, the Canary laurel, the vine, the judas-tree, and prob- 

 ably many others, became extinct in Southern France, some 

 of them — for example, the fig-tree — dying out in Europe alto- 

 gether. A similar fate befell the fauna — the great pachyderms 

 of southern habitats vanished from our continent, and th© 



1 Journal of a Tour in Marocco and the Great Atlas, p. 231. 



2 A 



