CHAP. IX.] 



MILD ARCTIC CLIMATES. 



185 



and the Persian Gulf, thus opening a communication between 

 the ITorth Atlantic and the Indian Ocean. From the Caspian 

 also a wide arm of the sea extended during some part of the 

 Tertiary epoch northwards to the Arctic Ocean, and there is 

 nothing to show that this sea may not have been in existence 

 duriug the whole Tertiary period. Another channel probably 

 existed over Egypt ^ into the eastern basin of the Mediterranean 

 and the Black Sea ; while it is probable that there was a com- 

 munication between the Baltic and the White Sea, leaving 

 Scandinavia as an extensive island. Turning to India, we find 

 that an arm of the sea of great width and depth extended 

 from the Bay of Bengal to the mouths of the Indus ; while the 

 enormous depression indicated by the presence of marine fossils 

 of Eocene age at a height of 16,500 feet in Western Tibet, 

 renders it not improbable that a more direct channel across 

 Afghanistan may have opened a communication between the 

 West Asiatic and Polar seas. 



It may be said that the changes here indicated are not war- 

 ranted by an actual knowledge of continuous Tertiary deposits 

 over the situations of the alleged marine channels ; but it is 

 no less certain that the seas in which any particular strata w^ere 

 deposited were always more extensive than the fragments of 

 those strata now existing, and often immensely more extensive. 

 The Eocene deposits of Europe, for example, have certainly 

 undergone enormous denudation both marine and subaerial, 

 and may have once covered areas where we now find older de- 

 posits (as the chalk once covered the weald), while they certainly 

 exist concealed under some Miocene, Pliocene, or recent beds. 

 We find them widely scattered over Europe and Asia, and often 

 elevated into lofty motmtain ranges ; and we should certainly 

 err far more seriously in confining the Eocene seas to the 

 exact areas where we now find Eocene rocks, than in liberally 

 extending them, so as to connect the several detached portions 

 of the formation whenever there is no valid argument against 



1 Mr. S. B. J. Skertcliley informs me that he has himself observed thick 

 Tertiary deposits, consisting of clays and anhydrous gypsmn, at Berenice 

 on the borders of Egypt and Nubia, at a height of about 600 feet above 

 the sea-level; but these may have been of fresh-water origin. 



