EVOLUTION AND DISTRIBUTION OF TERTIARY FAUNAS 217 



far to the north of their original station, have left only sparsely scat- 

 tered fossils as an indication of their invasion. 



In the later Tertiaries the proportion of recent species is sufficient, 

 taking into account the present distribution of these species, to afford 

 the means for a very probable estimate of the temperature which 

 prevailed during the particular portion of Tertiary time when they 

 formed part of the fauna. An interesting example of this is afforded 

 by a small collection of fossils obtained by Stimpson in 1865, from 

 above the lignitic coal measures in the northeast angle of the Okhotsk 

 Sea, in Penjinsk Gulf.' I have reported in full upon these fossils, 

 and it is sufficient to say on this occasion that the climate and recent 

 fauna of the locality are Arctic and the open water of the sea persists 

 only for some three months of the year, while the species of fossils 

 indicate that during their existence in the living state the annual 

 mean air temperature, at the most moderate estimate, must have 

 been 30° to 40° F. warmer than at present. Another instance has 

 recently been brought to my attention. During the two seasons just 

 past, collections have been made from the Pliocene auriferous gravels 

 of the coast of Alaska near the town of Nome.^ Thirty-three species 

 have been identified of which seven appear to be new, eleven are 

 now known living only south of the line of floating ice in winter, one 

 is a Miocene species, and the remaining fourteen are common to the 

 Alaskan fauna in general from the Arctic to British Columbia. This 

 indicates clearly that during the Pliocene, when these gravels were 

 being laid down, the climate of Norton Sound, now subarctic, was not 

 colder than that of North Japan or the Aleutian Islands where the 

 sea remains unfrozen throughout the entire year. This agrees well 

 with the evidence from the marine Pliocene of the northeastern corner 

 of Iceland, which has afforded over one hundred species, of which 

 seventy-four are said to be common to the Crag fauna of the British 

 Islands, corresponding to an annual mean air temperature not lower 

 than 42° F., while it is hardly necessary to say that the present 



1 Proc. U. S. Nat. Mus., Vol. XVI, No. 946, 1893, pp. 471-78, pi. LVI. The age 

 of the fossil shells in the report upon these fossils was given as Miocene, but it is probable 

 that like the analogous lignite deposits of the adjacent shores of America, the underlying 

 coal measures may be referable to the Upper Eocene or Oligocene and may have been 

 laid dow^n contemporaneously with the American Kenai formation. 



2 Cf. Am. Jour. Science, Vol. XXIII, June, 1907, pp. 457, 458. 



