428 ORIGINOF LIFE IN AMERICA 



and from it streamed forth practically all life, which eventually 

 reached the most southern tips of the continents. We thus not 

 only find there the oldest forms congregated together, accord- 

 ing to Professor Dahl, but these would naturally resemble one 

 another in all the southern parts of the continents. It is 

 a simple theory, and at first sight, as I mentioned before, 

 when discussing the similar views of Dr. Haacke, it- seems 

 to put before us the solution of all the problems of dispersal 

 in a satisfactory manner. No one, however, who has taken 

 the trouble to read this book, can for a moment, I venture to 

 think, perceive any justification for holding such a belief as 

 that of Professor Dahl's. There may possibly have been such a 

 centre of dispersal as that suggested, but it was long before 

 any geological records existed. Any forms of animal life that 

 we are acquainted with show clearly and unmistakably that 

 there have been scores of great centres of dispersal in the 

 world, and that from them streamed forth new forms in every 

 available direction. Northern animals advanced southward 

 and southern forms northward, aided, no doubt, by the ever- 

 changing conditions of climate and the gradual evolution of 

 oceans and continents. 



To return to the question at issue, let us examine what light 

 the marine fauna throws on the problem. The geographical 

 distribution of the elephant seal (Macrorhinus leoninus), 

 which occurs on the shores of southern South America, of 

 the antarctic lands, of New Zealand and Tasmania, will not 

 contribute much to its .solution, but some of the inverte- 

 brates are of more importance. The Eocene beds of Pata- 

 gonia, as well as those of New Zealand, contain several species 

 of marine mollusks common to both, such as Cucullaea alta, 

 Scalaria rugulosa and Turritella ambulacrum. Other Pata- 

 gonian species, for example, Brachydontes magellanica, Tur- 

 ritella patagonica and Crepidula gregaria only appear in New 

 Zealand in later deposits. Besides these species the older 

 Tertiaries of the two countries have a large number of genera 

 common to both. Dr. von Ihering * thus concludes with con- 

 siderable justification that the geographical conditions during 

 early -Tertiary times must have been favourable for a dis- 



* Ihering, H. von, "Mollusques Fossiles de L' Argentine," p. 499. 



I 



