238 OEIGIN 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 Tehuantepeo 

 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, tiiat 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 is inclined to .attri- 

 bute to this fauna an early Miocene age, while Professor 

 Toula believes it to be younger, in fact distinctly " jung- 

 tertidr."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. Prom 

 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, r., " Jungtertiare Fauna von Gatun," pp. 744 — 745. 



t Bfise, B., and P. Toula, " Fauna von Tehuantepec," pp. 221 and 273. 



