MATTHEW, CLIMATE AND EVOLUTION 281 



The depth of this ridge Dr. Hay omits to state, but the soundings indi- 

 cate it as being upwards of ten thousand feet, so that it does not mate- 

 rially affect the improbability of an elevation to this extent. The Gala- 

 pagos Islands are purely volcanic in origin and stand upon a platform 

 less than a thousand feet in depth, similar on a smaller scale to that 

 which surrounds the continents and presumably open to similar inter- 

 pretation. If so, the islands have, probably, been more or less completely 

 united at periods of continental emergence and completely isolated at 

 periods of continental submergence (if any such have occurred since 

 they were first upbuilt from the ocean floor by volcanic ejectamenta) 

 but never connected with the mainland. As the island platform is less 

 extensive than Madagascar or Cuba, farther from the mainland and 

 without intervening island stepping-stones, the opportunities for success- 

 ful colonization through rafts or other means of transport have been 

 fewer, and have not succeeded in introducing any mammals or amphib- 

 ians and but few reptiles and invertebrates. The most favorable oppor- 

 tunity for such colonization would be when the islands were at their 

 maximum elevation — towards the end of the Tertiary, if this corre- 

 sponded with the elevation of the mainland — as at that time the extent 

 of coast and consequent probability of making a landing would be much 

 greater. The subsequent isolation of the islands by submergence ac- 

 counts for the presence of distinct although related species on different 

 islands. Thus the series of "miracles of transportation," which Dr. Hay 

 finds it so difficult to accept, dwindles down to a single "miracle" and 

 to one which he must invoke to account for the populating of the more 

 remote Pacific islands, and which, when considered in relation to the 

 time involved, does not really involve any serious improbability. On 

 the other hand, if a miracle be an exceptional occurrence in apparent 

 contravention of all probabilities, and without assignable causes in nat- 

 ural law, I think the processes of selective drowning, or of selective 

 migration of sporadic elements of a fauna, involved in the alternate 

 hypothesis, in addition to the elevation during the late Tertiary of 

 abyssal depths to the surface, unwarranted by any valid evidence, does 

 involve a series of miracles, almost as unworthy of belief on the evidence 

 offered, as the special creation of the species of the Galapagos Islands 

 appeared to Darwin. 



The present distribution of species of Testudo on the islands of the 

 Indian Ocean has been partly changed by man, so that there is some 

 uncertainty about its details. Lydekker states it as follows : 



"Madagascar, probably the Comoros. North and South Aldabra — small islands 

 lying to the northwest of the northern point of Madagascar — the Mascarenes 



