22 PEOCEEDINGS OF THE 



Land-Tortoises is so great that, having failed to account in 

 a generally convincing manner for the presence of these animals 

 in the Galapagos, we naturally turn to the other group to see 

 whether a consideration of the geological conditions in the Indian 

 Ocean leads to more satisfactory results. Will that consideration 

 give us a clue as to the direct genetic relations between those 

 Pleistocene giants and their insular representatives ? In a 

 masterly treatise on ancient land-connections which Mr. W. T. 

 Blanford embodied in his Anniversary Address to the Geological 

 Society in 1S96, all the evidence, geological as well as biological, 

 is collected, by which he proves that such a connection did exist 

 across the Indian Ocean between India and Madagascar. Even 

 Mr. "Wallace, who is one of the most emphatic opponents of the 

 doctrine of extensive changes of land and water in Tertiary times, 

 feels compelled to assume that the areas now occupied by the 

 Laccadive, Maldive, and Chagos atolls, and the Saya de Malha 

 and Cargados reefs, are the remains of great islands which existed 

 in late Tertiary times. He admits subsidence so far, because the 

 existence of such intervening islands would facilitate the intro- 

 duction of certain Birds and Bats which are common to India and 

 Madagascar. But the distances by which these Tertiary islands 

 were separated from the Mascarenes and Madagascar are stiil too 

 great to meet the requirements of the case of the Tortoises. 

 Absolutely helpless, these animals could not make active progress 

 iu the water and would perish long before a favourable current 

 carried them to a distant shore. Dispersal by accidental means 

 may be set aside in their case as utterly incomprehensible and 

 inadequate; they require, for spontaneous dispersal, continuity 

 of land. Now the researches of W. T. Blanford, of his brother 

 H. P. Blanford, and other Indian geologists, of Suess, and Neu- 

 inayer, definitely prove the existence of a wide area which con- 

 jiectfdSouth Africa and India, and of course included Madagascar, 

 the Seychelles, Mascarenes, and other islands. The continuity of 

 this area began to be encroached upon by the Ocean in Mesozoic 

 times, and was gradually broken up into islands at an early 

 Tertiary date {Blanford). On the other hand, the slow evolution 

 of this Chelonian type, which has scarcel}' changed since the 

 Eocene, and its wide distribution in that era over the Northern 

 Hemisphere, justify the supposition that it was in existence 

 already before the Tertiary, before the bridge was broken through 

 which allowed of its passage southwards or northwards. 



From the available nalajoutological evidence, the majority of 

 naturalists would indine to the belief that the Pliocene conti- 

 nental foi ms were the ancestors of the insular races, or, in other 

 v.ords, that the ij^e has migrated southwards. Thus Mr. 

 Lydekker (1885, p. 163) says that "it appears not improbable 

 that the Aldabra Tortoises are a branch which has taken origin 

 irom the old Indian stock of gigantic Land-Tortoises." How- 

 ever, Continental and Insular Jorins difter structurally so slightly 

 from each other, that we cannot draw from their structure sate 

 conclusions as to their relative ages. Porms with a bifurcated 



