CHAP. IX.] 
MILD ARCTIC CLIMATES. 
185 
and the Persian Gulf, thus opening a communication between 
the North 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 
during the whole Tertiary period. Another channel probably 
existed over Egypt 1 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 were 
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 mountain 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. Skertchley informs me that he has himself observed thick 
Tertiary deposits, consisting of clays and anhydrous gypsum, 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. 
