SEALS OF THE CASPIAN SEA AND LAKE BAIKAL. 127 



species in one part of the Mediterraiicau. We have thus instances in the Seals of sjjccies living 

 in all the gradations between ordinary sea water and fresh water ; first, those in the Atlantic itself; 

 where the water is whoUy salt ; next, one in the Mediterranean, where it is scarcely less so ; then 

 another in the Baltic, a sea much less salt than the Northern Ocean outside the Cattegat ; then 

 one in the Caspian, which is still less salt ; and, lastlj', one in Lake Bailcal, which is whoU}' 

 fresh. The inference which one can hardly fail to draw fi'oni tliis, is that Lake Baikal and the 

 Caspian were formerlj' bays of the Arctic Sea ;* and that by an elevation of the land these bays 

 were cut off from the open sea and converted into inland lakes, in which were respectively shut up 

 the Common Seal and the Pii. FfETiiiA, the one without any communication at all with the sea, the 

 other with an outlet for its waters, but with barriers preventing the escape of the Seals. 



When these salt-water bays were thus converted, that which had an outlet (Lake Baikal) 

 must have continued salt until, in the course of time, from the constant inpouring of fresh water 

 by streams and rivers falling into it, the water must have become fresher and fresher, until it has 

 become what it now is ; but the process has been so gradual, and the change from salt to fresh 

 so imperceptible, and spread over so immense a period of time, that the animals have undergone 

 a change in physical condition of life without ever being aware of it, or being affected by it, and 

 they have become fitted for their new medium as imperceptibly, and by as slow degrees, as it itself 

 has come into existence. Had the change been more rapid, according to my \'iew, we should have 

 had a new species instead of merely the old one. The process in the Caspian, which has no outlet, 

 must have been still simpler, because the water continues salt, although somewhat altered in its 

 chemical constituents,! and greatly fresher than the sea. 



If the reader will look at the Map 2, which shows the countries that would be submerged by a 

 depression of the land to the extent of 600 feet, he will observe how completely the Caspian Sea and 

 Lake Baikal would in that event be continuous with the Arctic Ocean ; and if by the rise of the land 

 which is now going on in Denmark and Sweden, the Cattegat should be obliterated, and the Baltic 

 turned into an inland lake, there might then be a repetition of what has taken place in Lake Baikal and 

 the Caspian, and the Halich.erus gryphi' s be turned into a fresh-water specimen of the marine 

 species. 



The geographical distribution of the Seals is somewhat complicated by the fact that some, if not 

 all of them, make periodical migrations, returning j^ear after year, like birds, to their former abode. 

 Speaking of a species of Otaria, or Sea Lion, common near San Francisco, Dr. Newberry mentions 

 having identified one, by a bullet found in it when killed, which had been shot at it the prcA'ious 

 year at the same place. J 



Periodical migration thus takes place in these mammals as well as in birds ; besides the Seals, 



* It is but fail' to point out that .so high an authority Beche's " Researches iu Theoretical Geology." 1834, p. 14. 

 as the late Ur. Falconer look.s with doubt on such a con- J " This specimen is of interest as illustrating, in one 



nexion. He says, " It stiU remains to be proved that the particular, the habits of these animals. The left zygo- 



Arctic Ocean of the glacial period ever invaded the Aralo- matic arch has been perforated by a bullet, and the lower 



Caspian province, of which the Sea of Azof was a part. We part of the loft inferior maxillary bone shattered by an- 



have the authority of Woodward for the fact that the other ; both those injuries having been received so long 



Aralo-C'aspian basin contains only a single species (Car- since that the action of the absorbents has almost smoothed 



DHJM EDCLE, var. rdsticum), common to it and the White the splintered edges of the bones. Inside of the wound 



Sea." (Manual of MoUusca, p. 431.) See Falconer in of the zygoma was found the piece of lead which had 



" Nat. Hist. Rev." No. 9, Jan. 1863, p. 75. caused it, and which was at once recognised, from certain 



t M. Eichwald states that sulphate of magnesia is a peculiarities of form, as one which had been fired, without 



common salt in the waters of the C;ispian Sea.— De La fatal eSect, at a Sea Lion, on the same rocks, in the sum- 



