192 ISLAND LIFE 



basin of the Mediterranean and the Black Sea ; while it is 

 probable that there was a communication 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 

 warranted by an actual knowledge of continuous Tertiary 

 dejDOsits over the situations of the alleged marine channels ; 

 but it is no less certain that the seas in which any partic- 

 ular 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 deposits (as the 

 chalk once covered the weald), while a portion of them 

 may lie concealed under 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 our doing so. Considering 

 then, that some one or more of the sea-communications 

 here indicated almost certainly existed during Eocene and 

 Miocene times, let us endeavour to estimate the probable 

 effect such communications would have upon the climate 

 of the northern hemis23here. 



The Indian Ocean as a Source of Heat in Tertiary Times. 

 — If we compare the Indian Ocean with the South 

 Atlantic we shall see that the position and outline of the 

 former are very favourable for the accumulation of a large 

 body of warm water moving northwards. Its southern 



