RECORDS OF MEETINGS 191 



3. The geographic changes required to explain the past and present 

 distribution of land vertebrates are not extensive and do not affect the 

 permanence of the ocean basins as defined by the continental shelf. 



4. The theory of alternations of moist and uniform with arid and 

 zonal climates associated, respectively, with partial submergence and ex- 

 treme emergence of the continental areas, as elaborated by Chamberlin, 

 are in exact accord with the apparent course of evolution of land verte- 

 brates, when interpreted with due allowance for the probable gaps in the 

 geologic record. 



5. The numerous hypothetic land bridges in temperate, tropical and 

 southern regions, connecting continents now separated by deep oceans, 

 which have been advocated by various authors, are improbable, incon- 

 sistent and unnecessary to explain geographic distribution. On the con- 

 trary, the known facts point distinctly to the permanency of the deep- 

 ocean basins during the later epochs of geologic time, to the alternate 

 connection and separation of the land areas within the line of the conti- 

 nental shelf and to the continued isolation of those land areas which are 

 surrounded by deep ocean. 



These theories are substantially an adaptation of the conservative 

 views of Wallace and other zoologists to the geological theories of Cham- 

 berlin. They are defended by a consideration (1) of the nature and 

 extent of the defects in the geological record ; ( 2 ) of the relations of the 

 zoological regions to each other and the changes effected by elevation or 

 submergence of 100 fathoms; (3) of the principles of dispersal of land 

 animals; (4) of the character of the fauna of oceanic islands (including 

 Madagascar, Cuba and New Zealand) and the degree of probability which 

 attaches to accidental transportation as a means of populating them; 

 (5) of the present and known past distribution of the mammalia, group 

 by group, in considerable detail; (6) of the distribution of the different 

 orders of reptilia in a less detailed manner; (7) of the distribution of 

 birds and fishes, with a few instances from invertebrate distribution which 

 have been especially urged in support of hypothetical bridges; (8) of the 

 objections to such bridges and an interpretation of the real significance 

 of such evidence as has been adduced in support of them. 



I believe that the supposed cumulative evidence obtained in various 

 groups of animals or plants for various continental bridges is due simply 

 to identical errors in interpretation running through all such instances. 

 On the other hand, to admit such bridges would seem to involve certain 

 distribution results, which, in the groups which I have studied, assuredly 

 do not exist. 



