50 H. I. JENSEN. 



Mr. Ealph Arnold (Memoirs of the Calif ornian Academy of 

 Sciences, Vol. in.) we find on p. 69 that the elevation of California 

 took place in the geological periods from Miocene to Post-Pliocene, 

 and that the Pleistocene Fauna of San Pedro bears a close resem- 

 blance to that of Japan, on account of similar geographical con- 

 ditions at the time. Hill shows in his valuable paper, " Geology 

 of the Isthmus of Panama," (Bulletin, Museum of Comparative 

 Zoology, Vol xxvin , pp. 95 - 98.) that there was continued sedi- 

 mentation in the Eocene and Oligocene Epochs, but there is no 

 trace of Miocene or Pliocene sedimentation, a fact which points 

 to the land area being much larger in these periods than now. 

 Hence elevation took place at the beginning of the Miocene. 

 These periods were followed by a Pleistocene subsidence, and lastly 

 a further elevation of at least ten feet. During the Pleistocene 

 subsidence the isthmus was at least partly submerged. To the 

 north of Panama, in Costa Rica and Nicaragua, deposits of 

 Pliocene Age exist-, hence there is a possibility that a passage 

 existed then between the Atlantic and Pacific. 



If some such strait existed during the Miocene and Pliocene 

 periods, the Atlantic Equatorial Current, instead of being diverted 

 into the Gulf Stream, Mould pass into the Pacific and meet the 

 cold South American (now Chili) current off the Peru- Ecuador 

 coast, and organisms would die in profusion and fall to the bottom. 

 At this time the Antilles probably was a plain connected no doubt 

 by land with Venezuela and Florida. The highest mountains of 

 South America were the Matto Grosso and Venezuelan ranges. 

 From these long rivers flowed westward into the Pacific. Around 

 Galapagos Island a kind of Sargasso Sea existed, caused by the 

 above mentioned currents. From the researches of modern geo- 

 graphers we know also that at no remote geological period, probably 

 in late Pleistocene time, the sea covered the Argentine pampas 

 and the Paraguayan plains. Probably it stretched even further, 

 right across the Bolivian plain, taking in Lake Titicaca and join- 

 ing on to the Pacific. The final disappearance of Atlantic waters 

 from the pampas took place perhaps about 20,000 years ago. 



