84 
ORIGIN OF LIFE IN AMERICA 
The problem at issue is obviously not to be solved by the 
application of purely geological reasoning. Dr. Brooks, in 
his splendid contribution to the geology of Alaska, carefully 
avoids any discussion of a former land connection with Asia. 
In bis brief statement that a land bridge between Asia and 
North America could only have been utilised for Glacial or 
post-Glacial migrations of Asiatic types, Professor Suess * 
does not make us acquainted with the reasons for his supposi¬ 
tion that the land connection did not also exist in Pliocene 
times. He alludes to the striking circumstance that the 
hypothetical land bridge was used apparently by Asiatic types 
only, and leaves us wondering why American types should 
not have taken a similar advantage of pouring into Asia. 
That, however, is part of the problem which we must reserve 
for a later stage of the discussion. 
Dr. Matthew f does not share Professor Suess’ opinion, 
for he indicates a wide land connection, and Professor Osborn 
follows him in that respect, between North America and 
north-eastern Asia in the Bering Sea region in Oligocene, 
Miocene, Pliocene and Pleistocene times. 
As a rule the opinions of geologists on this problem are 
based on biological evidence alone. It is the latter, there¬ 
fore, that we have to rely upon. Curiously enough, Mr. 
Knopf J maintains that all the stratigraphical testimony from 
which conclusions of some positiveness can be drawn, record 
only epochs of more widely-spread submergence and in¬ 
creased separation of the continents, although he recognises 
the strength of the palaeontological demands in favour of 
more or less continuous inter-continental communications. 
I shall endeavour, now, to critically examine the problem 
from that point of view. I have already had several oppor¬ 
tunities of expressing my own views on this subject (pp. 32 
and 68), and these are entirely in favour of a geologically 
recent Bering Strait land bridge (see Fig. 7). But we require 
to know more than this. We want evidence which will lead to 
the determination of the geological age of the bridge and the 
approximate date of its beginning and end. 
* Suess, R., “ Antlitz der Erde,” Vol. III., p. '764. 
t Matthew, W. D., “ Hypothetical Outlines of Continents.” 
f Knopf, A., “ Probable Tertiary Land Connection,” p. 419. 
