CONCLUSIONS AS TO FORMER GEOGRAPHIC RELATIONS 665 



As to the former connection of the Antilles with each other and with 

 the mainland, my conclusions with the proviso just stated are as follows : 



1. That the Greater Antilles have probably been united with each other, 

 as far east as the Anguilla bank, in the late Tertiary or Pleistocene. This 

 I conclude from the near affinity of representative species of the same or 

 closely allied genera and the general similarity, of the fauna, so far as 

 known, in the different islands. 



2. That they have not at any time during the Tertiary been united with 

 North America. If they had been we should find North American ungu- 

 lates, rodents, carnivores, etcetera, differentiated in accord with the length 

 of subsequent isolation, but of clearly recognizable affinities, and it would 

 be a balanced or representative fauna. We might object that such a fauna 

 had perhaps existed, but been wiped out by subsequent submergence. But 

 the presence of Solenodon and Nesophontes negatives that, for they repre- 

 sent a very ancient survival, and if there had been a representative fauna 

 it is hardly credible that submergence would have spared just two insecti- 

 vores and destroyed all the rest of the fauna. 



3. That they probably have not been connected with South America, 

 either via the Lesser Antilles or via Central America, during the Ter- 

 tiary ; for if they had the fauna should be of continental South American 

 type, with South American ungulate groups, marsupial carnivores, and a 

 full representation of the rodents, edentates, etcetera. 



4. The mammalian fauna appears to me to be reducible to perhaps three 

 primary rodent stocks, one or more primary ground-sloth stocks, and two 

 Insectivora. These I conceive to have arrived at various times during the 

 Tertiary, the rodents and ground-sloths from South or Central America, 

 the insectivores from North America, by accidents of transportation, of 

 which the most probable for the mammals would perhaps be the so-called 

 '^natural rafts" or masses of vegetation dislodged from the banks of great 

 rivers during floods and drifted out to sea. The probabilities of this 

 method I have elsewhere discussed.^ For birds and bats, for the smaller 

 reptiles, amphibians, fishes, and invertebrates, the problem of oversea 

 transportation is a much simpler one.^° That successful colonization in 

 this way can occur is shown by their presence on nearly all oceanic islands ; 

 for it will hardly be maintained by reasonable men that every oceanic 

 island has been joined to the mainland and has been continuously above 

 water since its separation. Obviously, the larger the island and the nearer 

 to continental land, the more often such colonization will occur. 



» Matthew : Climate and evolution. Annals N. Y. Acad. Sci., vol. xxlv, 1015, p. 206. 



i» Tropical storms, as Wallace pointed out years ago, probably play a principal part 

 in transportation of very small animals or their eggs. Mammals could hardly be carried 

 that way nor survive if they were. 



XLIX — BuiL. Gkol. Soc. Am., Vol. 29, 1917 



