ening between
South Africa and Australia is very wide, and the tendency of the
trade-winds would be to concentrate 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 conveyance of heated water
northward, by concentrating the currents, and thus producing massive bodies
of moving water analogous to the Gulf Stream of the Atlantic.[22] 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 northwards, 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. Owing to the warm currents being concentrated in
inland seas instead of being dispersed over a wide ocean like the {83}
North Atlantic, much more heat would be conveyed into the Arctic Ocean, and
this would altogether prevent the formation of ice on the northern shores
of Asia, which continent did not then extend nearly so far north and was
probably deeply inter-penetrated by the sea. This open ocean to the north,
and the warm currents along all the northern lands, would so equalise
temperature, that even the northern parts of Europe might then have enjoyed
a climate fully equal to th