This causes an effectual barrier, which the warm
tropical currents cannot penetrate to any great extent. For instance,
the tropical waters of the high ocean levels, which lie abreast Brazil
in the Atlantic and the east coast of Africa in the Indian Ocean, are
not attracted far into the southern sea, because the surface waters of
the latter sea are blown by the westerly winds from west to east
around the globe. Consequently the tropical waters moving southward
are turned away by the prevailing winds and currents from entering the
Southern Ocean. Thus the ice is accumulating on its lands, and the
temperature of its waters slowly falling through their contact with
the increasing ice; and such conditions will continue until the lands
of the high southern latitudes are again covered with glaciers, and a
southern ice period perfected. But while this gathering of ice is
being brought about, the antarctic continent, now nearly covered with
an ice sheet, will, through the extension of glaciers out into its
shallow waters, cover a larger area than now; for where the waters are
shoal the growing glaciers, resting on a firm bottom, will advance
into the sea, and this advancement will continue wherever the shallow
waters extend.
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