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ANNALS NEW YORK ACADEMY OF SCIENCES 



Table I. — Correlation of the Four Principal Terrestrial Formations 



the principal centei- of dispersal of Mammalia was in the Holaretic re- 

 gion, the fossil mammals in southern regions invaded by that northern 

 fauna will appear in their homotaxial relations to l)e more ancient than 

 they really are. The modern fauna of South America, of Africa, of the 

 Oriental regions, will be in the same stage of evolution as tlie late Ter- 

 tiary and Quaternary fauna? of Holarctica. Its species will be more 

 nearly related or equivalent to Pliocene and Pleistocene species of Europe 

 and North America than to their modern fauna. The late Tertiaiy 

 mammals of the southern continents will approximate in homotaxis the 

 middle or early Tertiary mammals of Holarctica; and the middle Ter- 

 tiary southern faunae will approximate the early Tertiary or late Cre- 

 taceous faunas of the north. 



On the other hand, if we believe, as does Dr. Ameghiint. that the prin- 

 cipal theater of evolution of the mammals lay in the temperate regions 

 of South America, and that the mammal population of the Xorth was 

 derived by migration from that center (by way of Africa across a tropical 

 land bridge not now existing), it will be equally obvious that the southern 

 formations will be more ancient than their homotaxis, impartially con- 

 sidered, would lead us to believe. The result will be to assign to the 



