120 



LAND CONNECTIONS BETWEEN THE OTHER 

 CONTINENTS AND SOUTH AFRICA IN THE PAST. 



By Alex. L. du Toit, D.Sc, F.G.S., 

 Geologist to the Irrigation Department. 



With Two Text Figures. 



Fublic Evening Lecture, delivered July 15, 1921. 



The subject chosen for this evening is by no means novel, being; 

 one that has repeatedly attracted the attention of biologists and 

 geologists, but yet, on account of the vast conceptions demanded, 

 has nevertheless maintained its fascinating character unimpaired. 



The principle of splendid isolation appeals universally to man- 

 kind, and therefore it may be a little disconcerting at first to learn 

 that in the dim past the African continent, geographically and 

 biologically, was linked at times to the several other land-masses 

 of the globe; that during a period to be measured by many millions 

 of years there occurred revolutionary movements of land and sea 

 involving the emergence and inundation of land-masses, the growth 

 and destruction of mountain ranges, the pouring out of lava floods, 

 amazing variations in climate, and marvellous evolution of animal 

 and plant life. 



Changes of Land and Sea. 



That the lands are not fixed and unchanging was clearly appre- 

 ciated in early history, but, conversely, that new land should have 

 arisen out of the sea was an idea not so easy of credence. We have 

 nevertheless as instances thereof the Himalayan ranges with their 

 marine Tertiary strata sharply folded and elevated to extreme alti- 

 tudes, while to take an example nearer home we possess the- 

 Devonian Bokkeveld series of the Cape with its dark slaty rocks 

 carrying molluscan and crustacean fossils of undoubted marine 

 affinities, such as can be dug out in the Hex River Valley or in 

 the Bokkeveld thousands of feet above sea-level. 



Evolution. 



The study of fossil forms, known as palaeontology, has proved 

 unquestionably the theory of evolution, according to which from 

 the dawn of life upon this planet there has been a continuous chain 

 of living forms, small variations from the type ultimately produc- 

 ing new species or genera. For any particular brief period life was 

 more or less the same over the globe, but different as a whole from 

 that of any other period ; hence, when the fossils obtained from 

 one series of beds in one part of the earth are found to be identica 1 

 or very closelv allied to those from another area, we may regard 

 the two sets of strata as being of similar age. 



