VI.] RELATION TO AFRICA. 225" 



the Mascarene land or not." It is added that if future soundings 

 should indicate the absence of a bank extending the whole way 

 from India to Africa, it may be a question whether the whole of 

 the ocean-bed between those two countries has not sunk to its 

 present depth since the Cretaceous era 1 . 



This presumed connection satisfactorily explains much in 

 regard to the distribution of the molluscs. It is, however, certain 

 that fruit-bats did not exist in the early Tertiary, and the Pteropus 

 must accordingly have made the journey across the sea from 

 India, aided by what remained of the chain of islands, which may 

 have been more extensive during the Pliocene. The same 

 explanation also holds good with regard to most of the Oriental 

 types of birds. The case of the land-tortoises is, however, more 

 difficult. Nearly allied forms have been found in Mauritius, 

 Rodriguez, Madagascar, and Aldabra; and since this group is 

 unknown, even in Europe, before the Oligocene, it is evident that 

 they could not have travelled from India by means of the con- 

 necting land-bridge, which is considered to have been broken up 

 at the commencement of the Tertiary epoch. This being so, the 

 probability is that they originally came from Africa ; but whether 

 they entered Madagascar with the ancestral lemurs, or whether 

 they, or their eggs, were transported across the channel when 

 narrower than at present, there is no evidence to show. Be this 

 as it may, it is probable that they reached Rodriguez and Mauritius 

 across the intervening sea, since even if these islands ever joined 

 Madagascar, such union must apparently have been at a date 

 anterior to the existence of true tortoises. That none of these 

 tortoises could have been transported by sea from India is proved 

 by an observation of Dr Blanford to the effect that on this line the 

 currents invariably set from the Seychelles to India. It may be 

 added that some writers have considered it probable that the giant 

 tortoises of the Malagasy region, like those of the Galapagos 

 Islands, attained their large dimensions after they had reached 

 the islands they respectively inhabit. The existence of gigantic 



1 Neumayr (Erdgeschichte, 2nd ed. vol. n. p. 262, 1895) considers that when 

 India was connected with Madagascar during the Jurassic era, only the southern 

 extremity of that island was joined to South Africa. 



L. 15 



