1893.] evidence for the Recurrence of Ice Ages. 231 



more than 10,000 feet high, thus offering an appropriate area for 

 the condensation of vapour and the accumulation of snow. At 

 present however the mountains do not reach the snow -line, and 

 there is no proof that they have been much higher in recent 

 times, since the coast of Natal is now said to be rising. It is 

 evident that no slight elevation would now lead to the accumu- 

 lation of snow and ice in these mountains, situated as they are 

 between 27° and 30° S. Lat.; since the Andes, which in 32° S. 

 Lat. reach 23,300 feet high and in 28° S. Lat. 20,000, with far 

 more extensive plateaux, produce no ice fields. We cannot there- 

 fore believe that a few thousand feet of additional elevation, even 

 if it occurred so recently as indicated by the presence of striations, 

 would have produced the remarkable amount of glaciation above 

 described." But Wallace's argument from the present direction 

 of movement on the coast goes for nothing, seeing that it, as I 

 have endeavoured to emphasise above, is a recurring phenomenon 

 and that levels have been rapidly changing in quite recent times 

 in many places. Moreover we must bear in mind that we require 

 not only great cold but also abundant precipitation to produce 

 ice fields, and a plateau may be too high or out of the way of 

 the moisture-bearing currents of air. 



Mr G. W. Stow^ describes similar phenomena in the same 

 mountains, and also mounds and ridges of unstratified clay 

 packed with angular boulders ; while further south the Sturmberg 

 mountains are said to be similarly glaciated with immense ac- 

 cumulations of morainic matter in all the valleys. 



The fact of glaciation in tropical regions is itself evidence of 

 former great elevation, for even the astronomical theory requires 

 high land for the collection of snow and the formation of glaciers. 



But this is not the only proof of changes of level in that part 

 of the world. 



The uplift of earth above water or the sinking of the land 

 below the sea brings about the greatest change in the continuity 

 of life and of deposit and therefore furnishes the most important 

 data for stratigraphical classification, and perhaps of the two it is 

 the icy mountain range that forms the most effective barrier. On 

 such isolation of species Wallace has founded many of his happiest 

 generalizations. 



That there did exist along the East African side of the basin 

 a continuous range of very high ground is proved by the large 

 number of north temperate genera of plants in South Africa. 

 It is clear, says Wallace ^ "that South Africa has received its 

 European plants by the direct route through the Abyssinian high- 

 lands and the lofty equatorial mountains, and mostly at a distant 



1 Q. J. G. S., Vol. XXVII. p. 539. ^ Island Life, p. 492. 



