412 G. R. Wieland — Polar Climate in Time. 



How best explain this extensive fannal parallelism ? As the 

 deep oceans and the continents, though slowly increasing in 

 area as the result mainly of delta formation, have occupied 

 relatively the same position as now far back in geological time, 

 there have been no means of horizontal dispersion back and 

 forth. Although this view has been at times called into requi- 

 sition it appears to be utterly unsound. The great antiquity 

 of the principal elements of the life of the Hawaiian Islands, 

 Australia, New Zealand, Madagascar, bears unmistakable testi- 

 mony to the difficulty of dispersion of the higher types of life 

 across ocean barriers in any direction, and indeed shows such 

 dispersion of the vertebrates to be nearly impossible. Nor is 

 it conceivable that there was a constant exchange of American 

 and European monkeys, ganodents, cumbrous ungulates, horses, 

 dogs, rodents, bears, etc., etc., back and forth by way of the 

 polar regions. The difficulties of the enormous distances, 

 doubtless in most of Tertiary time increased by mountain 

 ranges, of the Behring's Strait, or the Aleutian Island route, 

 for such interchange between the Tertiary basins of Wyoming 

 and France are obvious enough. The shortest nearly all land 

 route that may by any possibility have existed so nearly as may 

 he judged from present shallow ocean depths, would have been 

 by way of the transverse submarine plateau marked by Ice- 

 land, the Faeroes, and Shetlands, the average depth between 

 these islands, exclusive of the deep waters off the Greenland 

 coast, now being some 250 fathoms. The remaining possibility 

 lies almost directly in line with the north pole and would be a 

 route by way of Melville Peninsula and Cockburn Land, 

 North Devon, Ellesmere Land, Grinnell Land, Melville Land, 

 The Spitzbergen Group, and Franz Josef's Land, Nova Zembla 

 and Nortliern Siberia. Even now this route involves but short 

 water gaps. But even if conditions were more favorable than 

 now, it is not conceivable that with the exception of a very 

 few times in the past, if ever, could animals have succeeded 



horses (Revision des Formes Europeenes de la Famille des Hja-acotherides, 

 Lyon, March, 1901) finds as the result of close analysis that Eohippus Marsh 

 of the Wasatch is close to Hyr^acotherinm Owen and to PropachynoJophus 

 Lemoine of the Suessonian, that Protorohippus Wortman from the Wind 

 Eiveris very similar to Pi-opalceotheriian Gervais and Pachynolophiis Pomel, 

 and that Epihippus and Eohippus Marsh are similar to Lophiotherixnn of 

 Gervais. Deperet shows that the early horses of Earope are most closely 

 allied to those of America in their successive evolutionary stages, or even 

 identical, and Professor Osborn in speaking of this similarity says (Science, 

 p. 674, April 24, 1903): "It is probably premature to establish generic 

 identity between these American and European forms ; but it is evident that 

 the time is not far distant when such identity is likely to be established, unless 

 we take the ground that the European and American forms were entirely 

 independent in their evolution from the time of their first appearance," In 

 Europe, as in America, it appears, however, that in the later history of the 

 horses there was mainly an indigenous evolution of species. 



