206 E. C. Andrews — The Geological History of the 



regions in America, Australia and Africa and Asia, and that 

 the great endemic genera of Australia such as Eucalyptus, Hib- 

 I'cr/in. Bwckea, Pultoura, Duricsia. and the Australian phyl- 

 lodineous development of Acacia, are local secondary types of 

 the great primary cosmopolitan tropical types, which secondary 

 types have been developed as xerophytes on the vast areas of 

 sandy wastes in Australia, and have never migrated far from 

 the old home, by reason of their isolation, and because, despite 

 the vigorous and aggressive nature of these local types, they are 

 xerophytes and could not find a suitable environment on the 

 outlying islands which are possessed of mild and moist climates 

 and clad with jungle growths. 



(b) The South- African Problem. 



(1) General Remarks on Supposed Land Connections of South 

 Africa and Australia. 



This problem has been considered already in some measure 

 under the previous heading. In the present part the special 

 case of the peculiar relations of the South African and Austra- 

 lian vegetation is considered. 



It has been thought by some biologists that South Africa and 

 Southwest Australia must have been directly connected long 

 after the development both of the Monocotyledons and of the 

 most complex families of the Dicotyledons, to wit, the Oom- 

 positae, say at the close of the Cretaceous Period, because the 

 genera Helichrysum, Helipterum and Cassinia, in Composita?, 

 the genera Restio, Hypolcena and Leptocarpus, in Restiacese, 

 the genera Ccesia, Wurmbea and Bulbine, in Liliacece, the tribes 

 Protege and Persooniese in Proteacese, occur in both countries, 

 while the family Ericaceae is abundantly represented in South 

 Africa, and the allied family Epacridacese occurs mainly in 

 extratropical Australia. 



But before proceeding with the main discussion it would seem 

 advisable to confront this slender evidence of possible former 

 direct connection of South Africa and Australia with the evi- 

 dence of much greater weight on the other side. 



Thus the great family of the Myrtaceae is almost absent from 

 South Africa although it possesses very many genera and species 

 in Australia, and although the Australian Myrtaceae are exactly 

 the types which might be expected to occur on the poor sandy 

 soils of South Africa on the assumption of the existence of 

 a land bridge directly connecting the latter country with 

 Australia. 



