308 ANNALS NEW YORK AfWIUCMY OF SCIENCES 



be inexact. But, as knowledge increases and Ijccomes more exact, these 

 phyla are more and more broken and complex, and direct genetic series 

 become more limited in extent. This is to be expected, for the regions 

 which up to date have been at all thoroughly explored are ))ut a small 

 fracti<ui df llie area which the group concerned must have iniiabited. 

 And on ii jiriori grounds, the chances are greatly against the ))articular 

 species which was to become dominant inhabiting the particular regions 

 which we have explored. 



Professor H. F. Osborn has very well expressed the conditions of evo- 

 lutionary progress by stating that each group is highly polypliyletic, con- 

 sisting of numerous subphyla evolving along more or less parallel lines. 

 But we are here concerned less with the disentaglement of the subphyla 

 of a group than with its dominant center of dispersal as a whole. And 

 from this point of view it seems to me misleading and erroneous to as- 

 sume that it must have migrated only from one to others of the regions 

 where its remains have actually been found, instead of attempting to 

 locate from the indirect evidence available the true center of dis])ersal. 



In contrast with the views here criticized, I may venture to quote from 

 an address in which Dr. Stehlin^-^ has recently summarized the phylo- 

 genetic results of his monumental studies upon the Eocene fauna of Eger- 

 kingen, a work of extraordinary thoroughness and ability which, as a 

 recent reviewer observed, has involved a revision of the entire Eocene 

 mammal fauna of Europe : "Where then dwelt these yet unknowii herds 

 of mammals evolved during the Eocene, whose existence is recorded 

 through their influence upon Europe and North America the more clearly 

 as we analyze more closely the data obtained in these continents? We 

 can scarcely be wrong if we look to the huge continental mass of xA.sia, 

 still almost unexplored by the paleontologist. The future, and, it may be 

 hoped, the near future will show how far our ]n-osent anticipations are 

 correct." 



SUMMAKY OF EVIDENCE 



The geologic evidence for the general permanency of the abyssal oceans 

 is overwhelmingly strong. The continental and oceanic areas are now 

 maintained at their different levels chiefly through isostatic balance, and 

 it is difficult to believe that they could formerly have been reversed to any 

 extensive degree. The floor of the ocean differs notably in its relief from 

 the surfaces of the continents, and only in a few limited areas is the relief 

 suggestive of former elevation above sea-level. The continental shelf is 



125 H. O. Stkiilin : Verb. Schw. Naturf. Gesell., O:? .Tahresversammlimg. Slept. lOlC 

 P. 29 of separata. 



