NATURAL HISTORY OF SOUTH AFRICA 



round. At that period the Klip or Rock Dassie, 

 no doubt, was arboreal, that is, it was an inhabitant 

 of the trees. 



In the course of time the climate changed. This 

 change was gradual, and the rainfall slowly but surely 

 diminished. The lakes began to dry up, and the 

 springs and rivers decreased in volume, and in con- 

 sequence the less hardy vegetation died off. The 

 struggle for the survival of the fittest in both the 

 vegetable and animal world began in grim earnest. 

 Great numbers of species of plants perished, and 

 their kind became extinct. Others slowly but surely 

 adapted themselves to the changing conditions by 

 modifying their structure, and to-day we have plant 

 life which has specially adapted itself to survive in 

 the vast inland stretches of the country where the 

 rainfall is small. 



During this long period the forests were slowly 

 vanishing and being replaced by stunted Karoo 

 bushes and the hardy Mimosa trees and grasses. 



The hills and mountains became increasingly bare, 

 and to-day over great stretches of country we see 

 but their skeletons, for the fertile soils and vegeta- 

 tion which once clothed them, have been washed 

 down into the valleys, and now constitute the soil 

 of the veld. 



So to-day we have the spectacle of hills and moun- 

 tains covered with loose boulders and bare outcrops 

 of rocks, crannied, fissured, caverned and eroded. 



There was no room in the ever-diminishing forests 

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