276 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1928 



all have come about ! We appear, therefore, to be able to say that 

 with so much time available we might even do away with the middle 

 Atlantic land bridge and explain the distribution of all land life on 

 the basis of radial dispersion from Holarctis and Antarctis. 



The writer has long been a believer in a land bridge — a far nar- 

 rower one, however, than usually shown on paleogeographic maps — 

 all through the Paleozoic and Mesozoic across the Atlantic from 

 Brazil to Africa. This bridge appears to him necessary to explain 

 the peculiar distribution of the various Paleozoic and Mesozoic 

 marine faunas of northern Brazil, the Andean geosyncline. Central 

 America, and the southern part of the United States, on the one side, 

 and those of southern South America, south and east Africa, and 

 India, on the other. But this western Gondwana land bridge appears 

 even more necessary to explain the similarities of the land floras and 

 faunas, and yet all biogeographers admit the great possibilities of 

 radial dispersion from Holarctis. Such migration routes have been 

 possible ever since the beginning of the Cambrian, but have been 

 made locally and chronologically inoperative through periodically 

 appearing mountain ranges, desert climates over vast areas, and 

 variations in the spread of the great mediterranean Tethys and 

 other oceans. 



Grant the biogeographer Holarctis, a land bridge from northern 

 Africa to Brazil, another from South America to Antarctis (it almost 

 exists to-day), still another from this polar land to Australia and 

 from the latter across the Arafura Sea to Borneo and Sumatra and 

 so on to Asia, plus the accepted means of dispersal along shelf seas 

 and by wind and water currents and migratory birds, and he has all 

 the possibilities needed to explain the life dispersion of the land and 

 ocean realms throughout geological time on the basis of the present 

 arrangements of the continents. With these means he can also 

 explain life dispersion far more easily than by way of Wegener's 

 Pangaea; this hypothetic land should have made for easy dispersion 

 and therefore for cosmopolitan floras and faunas, and that is just 

 what the world has very rarely seen and does not have to-day. 



CONCLUDING REMARKS 



The previous account has again and again shown that the rump 

 mountain ranges on the two sides of the Atlantic are not at all as 

 closely related in position, structure, and history as Wegener makes 

 them out to be, and the same is equally true for the fossil marine 

 faunas. The writer does not wish to say that there are no geological 

 and paleontological similarities at all on the two sides of the At- 

 lantic, for there are many f aunal ones easily seen and there are struc- 

 tural ones as well, which were pointed out long before Wegener's 

 time. But the whole trouble in Wegener's hypothesis and in his 



