238 
ORIGIN OF LIFE IN AMERICA 
satisfied that the isthmus of Panama was submerged during 
the Eocene Period, and that the submerged area of Central 
America greatly increased in Oligocence times. Professor 
Hill, who has dealt with various lines of enquiry in regard to 
the geological history of Central America, contends that, they 
all give evidence for the belief that no connection has existed 
between the Pacific and Atlantic Oceans since the close of the 
Oligocene (p. 270). A very careful re-examination of the 
fossils of Gatun, near the Panama Canal, by Professor Toula, 
however, throws considerable doubt on the supposed Eocene 
age of the deposits containing these fossils. He gives reason 
for his belief that they are of upper Miocene, possibly even of 
lower Pliocene age, and estimates the depth of water of the 
marine channel uniting the two oceans at about a hundred and 
fifty feet.* 
In conjunction with Dr. Bose, the same author also in¬ 
vestigated the Tertiary deposits of the isthmus of Tehuantepec 
in southern Mexico with very noteworthy results. The fossil 
mollusks contained in them indicate that the sea covered the 
land to a depth of from fifty to two hundred fathoms, that is to 
say from three hundred to one thousand two hundred feet. 
As the isthmus does not rise much beyond eight hundred 
feet, the existing land, even as far north as this region, 
was submerged by a shallow sea. Dr. Bose i's inclined to attri¬ 
bute to this fauna an early Miocene age, while Professor 
Toula believes it to be younger, in fact distinctly “ jung- 
tertuir." f 
Now it has been argued, and the argument appears most 
reasonable, that we are able to check these results indicating 
a submergence of parts of Central America by means of two 
other tests, viz., the distribution of living animals and the 
palaeontology of North America. The first deals mainly with 
the amount of affinity existing between the marine animals 
of the Atlantic and Pacific sides of Central America. From 
the nearness or remoteness in relationship of the species on 
the two opposite coasts it was thought we might determine at 
what particular geological period, if at any, the Atlantic and 
the Pacific Oceans were joined to one another across Central 
* Toula, F., “ Jungtertiare Fauna von Gatun,” pp. 744 — 745. 
f Bose, E., and F. Toula, “Fauna von Tehuantepec,” pp. 221 and 273. 
