NORTH PACIFIC MARINE FAUNA 95 



while 6 ! 1 per cent, at present occur exclusively north of 

 this locality. Professor Arnold* is thus led to the con- 

 clusion that semi-tropical conditions prevailed during the 

 deposition of the Pleistocene formation. He also emphasises 

 the fact that the later Tertiary and Pleistocene faunas of 

 Japan and the west coast of the United States resembled one 

 another much more than the faunas of the two sides of the 

 Pacific do at the present time. 



Nothing could be more contradictory than the two state- 

 ments of Dr. Dall and Professor Arnold as to the climatic 

 conditions prevailing in two portions of the Pacific coast of 

 North America in Pliocene and Pleistocene times. It seems 

 almost as if the deposits from which Dr. Dall derived his con- 

 clusions were not contemporaneous with those that led Pro- 

 fessor Arnold to pronounce the views just stated. It is 

 scarcely possible to conceive that, while a warm-water fauna 

 existed on the Oregon and Alaskan coasts in Pliocene times, 

 California should have had a cold climate. Arctic conditions 

 are then supposed to have supervened on the north Pacific 

 coast. On the Californian coast, on the other hand, the cold 

 Pliocene climate is stated to have been succeeded by a semi- 

 tropical one during the Pleistocene Period. 



It is now generally recognised, I think, that Central 

 America, in its present configuration, originated by a final 

 union of pre-existing independent land-masses in Pliocene 

 times. That an inter-oceanic current, now no longer exist- 

 ing, might have produced altogether peculiar climatic con- 

 ditions on the Californian coast in Miocene times but 

 not later seems admissible. If we suppose that the Japanese 

 " Kuroshiwo " current formerly sent part of its warm 

 waters through a wider opening at Bering Strait into the 

 Arctic Ocean, would it have had the effect of inducing 

 the Mexican fauna to advance northward and the arctic 

 fauna to pour southward towards the coast of Oregon ? 

 I doubt, even under such geographical conditions, whether 

 the Pleistocene faunas of California and Oregon could 

 have differed to such an extent as described by Dr. Dall and 



* Arnold, Ealph, " Marine Pliocene and Pleistocene of San Pedro," 

 pp. 65 67. 



