96 
ORIGIN OF LIFE IN AMERICA 
Professor Arnold. At any rate, it is reasonable to infer that 
a rise to a higher temperature of the northern Pacific Ocean, 
coupled with an increased conveyance of Asiatic species to 
the American coasts and a northward advance of southern 
forms must have coincided with the closing of Bering Strait. 
And it was not until Pliocene times, according to Professor 
J.:P. Smith,* that the marine faunas of Japan and the western 
coast of America began to be remarkably similar, many species 
being identical. From this fact we must conclude that inter¬ 
migration between the two continents had set along a northern 
shore line. During the preceding Miocene Period the marine 
fauna of California consisted of endemic species mixed with 
southern and circumhoreal ones, but without any Asiatic 
admixture. Consequently there was probably a wide com¬ 
munication between the Pacific and the Arctic Ocean, favour¬ 
ing the entrance into the latter of a warm current which 
profoundly affected the Arctic Regions. The curious relation¬ 
ship to Pacific mollusks which is noticeable among some 
forms of the English Crag deposits may possibly date from 
this theoretical Miocene current, which may have carried 
marine species right across the Polar Seas to Europe. 
At the beginning of the Pleistocene Period, the same con¬ 
ditions existed, according to Professor Smith, as in the Upper 
Pliocene. As the waters of the Californian coast gradually 
became warmer, he remarks, Mexican species began to creep 
northward. But this, he says, does not mean that connection 
with Japan was cut off. The continuation of the conditions 
that permitted Japanese species to migrate to California, 
merely allowed marine animals to make their way up the 
American coast also. Here I must beg to differ from Pro¬ 
fessor Smith. If a change in the fauna of the upper Pleis¬ 
tocene of California took place as asserted, that change was 
in all probability due to a gradual sinking of the land in 
the north, for a moderate subsidence in northern Alaska at 
any rate has been recorded by Dr. Dali f during later Pleisto¬ 
cene times. A gradual modification was thus brought about 
in the disposition of land and water, the continents of Asia 
and North America slowly assuming their present shapes. 
* Smith, J. P., “Periodic Migrations,” pp. 225—226. 
t Dali, W. II., “ Neocene of North America,” p. 278, 
