CHAP. IX MILD AKCTIC CLIMATES 193 



opening between South Africa and Australia is very wide, 

 and the tendency of the trade-winds would be to concen- 

 trate the currents towards its north-western extremity, 

 just where the two great channels above described formed 

 an outlet to the northern seas. As will be shown in our 

 nineteenth chapter, there was probably, during the earlier 

 portion of the Tertiary period at least, several large islands 

 in the space between Madagascar and South India ; but 

 these had wide and deep channels between them, and 

 their existence may have been favourable to the con- 

 veyance of heated water northward, by concentrating 

 the currents, and thus producing massive bodies of moving 

 water analogous to the Gulf Stream of the Atlantic.^ 

 Less heat would thus be lost by evaporation and radiation 

 in the tropical zone, and an impulse would be acquired 

 which would carry the warm water into the north polar 

 area. About the same period Australia was probably 

 divided into two islands, separated by a wide channel in a 

 north and south direction (see Chapter XXII.), and 

 through this another current would almost certainly set 

 northAvards, and be directed to the north-west by the 

 southern extension of Malayan Asia. The more insular 

 condition at this period of Australia, India, and North 

 Africa, with the depression and probable fertility of the 

 Central Asiatic plateau, would lead to the Indian Ocean 

 being traversed by regular trade-winds instead of by 

 variable monsoons, and thus the constant vis a tergo, 

 which is so efficient in the Atlantic, would keep up a 

 steady and powerful current towards the northern parts 

 of the Indian Ocean, and thence through the midst of 

 the European archipelago to the northern seas. 



Now it is quite certain that such a condition as we have 

 here sketched out would produce a wonderful effect on the 

 climate of Central Europe and Western and Northern Asia. 

 Owincr to the warm currents beinof concentrated in inland 

 seas instead of being dispersed over a wide ocean like the 



^ By referring to our map of the Indian Ocean showing the submarine 

 banks indicating ancient islands (Chap. XIX. ), it will be evident that the 

 south-east trade-winds — then exceptionally powerful — would cause a vast 

 body of water to enter the deep Arabian Sea. 



O 



