MATTHEW, CLIMATE AND EVOLUTION V^:^ 



Cretaceous period those southern faunae which are homotaxial with tlie 

 early Eocene of the North: to the Eocene those faunge which are homo- 

 taxial with the Middle Tertiary of the North, and so on. 



To a certain extent, the intercalation of marine formations may pro- 

 vide a check on this relationship, but it must be remembered that the 

 same theories of dispersal may also apply to marine fauna?, wholly or in 

 part. Homotaxial marine faunae may be far from contemporaneous. 

 The chief center of dispersal of marine faunas may be assumed to be 

 either the equatorial oceans and coasts, the northern, or the southern 

 seas, or both north and south equally. Only when the movements of dis- 

 persal are in opposite directions on land and in the seas will the marine 

 faunffi furnish an adequate check on the homotaxis of land fauna?; and 

 in that case the true synchronism must be arrived at by balancing con- 

 flicting evidence derived from terrestrial and marine faunal comparisons. 



It is true that if we eliminate the idea of faunal dispersal altogether 

 and regard each race of animals as evolving and dispersing independ- 

 ently, governed by its own conditions and causes of change, we may in 

 the present imperfect state of our knowledge lay out various and inde- 

 pendent centers of dispersal for different races, whose successive appear- 

 ance in one or another continent will furnish data for a true correlation. 

 There has been a strong tendency in the last half century to work on this 

 theory, but in the j)resent writer's opinion at least, the supposed evidence 

 in favor of this view is due chiefly to the imperfection of the geologic 

 record, and its very wide acce})tance to a lack of appreciation of the 

 underlying causes of evolutionary progress and dispersal. 



I do not understand how anyone can reconcile the theory that each 

 race of animals evolves and disperses independently and that the common 

 biotic and physical environment is not a controlling factor, with the plain 

 fact that regional faun^ do exist to-day. The conditions that control the 

 dispersal of one race are largely identical or correlated with those that 

 control the dispersal of others, and every change in these conditions will 

 affect not one race only, but a large part or the whole of a fauna, in a 

 manner and to a degree largely identical, causing similar changes in the 

 range of the fauna. 



TERTIARY CORRKLATIOX TX SOUTH AMERICA 



Before setting forth the evidence as to the dispersal of the mammals, 

 it is necessary to attack a problem whicli has caused much acrid contro- 

 versy, namely, the age of the later formations of the Argentine Republic. 

 The difference of opinion among authorities has already been indicated, 



