THE AMERICAN FAUNA AND ITS ORIGIN. 
221 
of these views, and Ortman, the most recent, takes a view 
intermediate between those of Forbes and Hedley. 
Oceanic depths have been found to be from 2,000 to 4,500 
fathoms under vast areas, surrounded by lesser depths, under 
extensive areas also, extending to the shore lines of the 
continents. Elevations, therefore, of 12,000 feet would give 
a great extension of present land areas while leaving the ocean 
basins with depths of water ranging to 15,000 feet even if 
a general and equal uprise of the whole ocean door had taken 
place, which is by no means probable. 
Such an amount of elevation would, I think, suffice for 
zoogeographical requirements, since it would give land con- 
nections in the north that would furnish bridges for the 
temperate animals of European and Asiatic lands, and in the 
south it would give connections either complete or nearly so 
between Australian, African and American lands, that would 
serve for the migration of both the sub-tropical and the tropical 
animals of the eastern hemisphere. 
Such an elevation would also be sufficient for the geographical 
and geological changes of Tertiary and Quaternary times, for it 
would give the uprise that laid bare the now submerged 
continental shelf, united continental and some called oceanic 
islands, to the mainland, and gave those extensions seawards of 
existing river- valleys that Professor Hull and Professor Spencer 
have, on several occasions, brought before the notice of this 
Institute. It would also, I may add, be amply sufficient to 
raise the lower northern mountains above the snow-line and so 
produce the geographical and climatal conditions of the Glacial 
Period, while in the Pacific area it would suffice to give 
Darwin’s land on the submerged summits of which are now 
a thousand coral islands, and yet there would be no obliteration 
of the Atlantic, the Pacific or the Indian oceans. 
I venture, therefore, to conclude that an elevation of 12,000 
feet at one time or another in different areas during the 
Tertiary and Quaternary Periods, which we have seen, may be 
readily conceded, while not affecting the permanence of ocean 
basins, would yet be sufficient to allow of all the animal 
migrations necessary for the faunal development that living 
animals or fossils in America reveal. 
