498 W. H. DALL 
some boreal elements. ‘Thirty miles off shore, in less than fifty 
fathoms, the fringe of the Gulf Stream protects a fauna in large part 
identical with that which characterizes the Bahama Banks and 
Bermuda. ‘The large species of Venus, which penetrated to the north 
shore of the Gulf of Mexico with the cool Miocene water, have 
maintained themselves notwithstanding the subsequent rise of tem- 
perature and persist in these new conditions to the present day, a 
notable example of adaptation. On the other hand the subtropical 
Rangia and Corbicula, which advanced with the warm Pliocene waters 
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.t | 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 
t Proc. U. S. Nat. Mus., Vol. XVI, No. 946, 1893, pp. 471-78, pl. 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 down contemporaneously with the American Kenai formation. 
2 Cf. Am. Jour. Science, Vol. XXIII, June, 1907, pp. 457, 458. 
