MATTHEW, CLIMATE AND EVOLUTION 311 



rafts; the degree of probability that attaches to this hypothesis is esti- 

 mated. 



The dispersal of mammals is then considered at some length, order by 

 order, and it is shown to accord fully and in detail with the principles 

 here set forth, and to be impossible of explanation except upon the 

 theory of permanence of the ocean basins during the Cenozoic era. While 

 the prominence of the Holarctic region as a center of dispersal is ascribed 

 to its central position and greater area, some evidence is given to show 

 that climate is also a factor in the greater progressiveness of the northern, 

 since it is also noticeable in the southern as compared with tropical faunae. 



The distribution of the Eeptilia appears to be in conformity with the 

 principles here outlined, and extends their application to the Mesozoic 

 era. The distribution of birds and fishes and of invertebrates and plants 

 is probably in accord with the same general principles, modified by differ- 

 ences in methods of dispersal. The opposing conclusions that have been 

 drawn from the distribution of these groups are believed to be due to an 

 incorrect interpretation of the evidence. A few instances, which have 

 been prominently used to support opposing conclusions, are analyzed and 

 shown to conform to the conclusions above set forth, if interpreted upon 

 similar lines as the data for mammalian distribution. 



Appendix 



Since this paper was written two very readable and instructive books 

 on geographic distribution have appeared, "The Wanderings of Animals" 

 by Professor Gadow,^^® and "Distribution and Origin of Life in America" 

 by Professor Scharff.^^" Both writers, and especially Doctor Scharff, be- 

 long to what may be called the bridge-building school of paleogeography, 

 and the general criticisms expressed in the earlier part of this article 

 apply largely to their interpretations. It is with no intent to depreciate 

 their value that I observe that there are numerous errors of fact in those 

 portions of the evidence with which I am best acquainted, for in a subject 

 of so wide a scope most of the evidence is necessarily compiled and not 

 very well understood, and errors more or less essential will slip in. It is 

 for that reason that I have avoided detailed discussion of the parts of 

 the evidence on the present subject with which I am not well acquainted ; 

 and, in spite of a good deal of checking and revision, I have no doubt 

 that the foregoing discussion contains various inaccuracies. 



i2« Hans Gadow : "The Wanderings of Animals." Cambridge Manuals of Science and 

 Literature, No. 64. 191.3. 



1" R. F. ScHARPF : Distribution and Origin of Life in America. Macmillan Co., pub- 

 lishers. New Yorli. 1912. 



