[Sidenote: The Sou'-wester]
We have to study four regions of one great Sou'-wester wind, which is
known to navigators as the South-west Counter-Trade.
WESTERN REGION. The tropic sunshine lifts masses of hot, tremulous
vapour from the surface of the Equatorial Pacific. This vapour lifts
to a great height and there condenses into clouds. The clouds are
swept by the south-west wind and form their floor at a height above
the sea of about two miles. The Rocky Mountains reach up bare and
stony hands to clutch at the flying moisture and bring down whirling
snowstorms. On sweep the cloud fleets across the Canadian Plains
with rarely a drop of rain to spare through the summer for the
thirsting grass beneath. But {19} slowly the cloud-floor slopes
downward until at last the cloud-fleets come to ground, and the
breath of the sou'-wester becomes visible as the Northern Forest.
Beyond that forest the wind trails its cold vapours over the
sub-Arctic tundras of North-Eastern Canada, lashing bleak rains on
Baffin's Bay, to spend the last of its moisture in the form of snow
upon the Greenland Ice-cap.
[Sidenote: Central region]
CENTRAL REGION. From the eastern part of the Equatorial Pacific,
about the neighbourhood of the Gallipagoes, a second echelon of the
sou'-wester brings its immense load of flying clouds high in the air
across the United States to slant down out of the skies and brush the
Atlantic in the Forties. Strong gales trail their clouds along the
Gulf Stream, taking a deal of warmth out of that current. Exposed
trees in North-western Europe are slightly bent by the stress of
Atlantic gales, while all the trailing clouds discharge their cargoes
of warm rain across the Baltic Region. The British Isles, for
example, get an annual ration amounting to thirty cubic miles of
water fresh from the Equatorial Pacific.
These two large _echelons_ of the sou'-wester carried the vapour
which once fell as snow to form the Icefields of the Great Ice Age.
{20}
[Sidenote: The Ice-cap]
The skies were clearing. The planet was being stripped of its cloud
roof, so that its warmth from the sun was radiated at night and in
winter directly into Space. Except to leeward of the Gulf Stream,
the lands of the North Atlantic are still sub-Arctic as in Labrador.
These lands were more extensive then than now, forming a bridge about
a thousand miles wide from Arctic Canada across Smith's Sound to
Greenland, and thence by way of the Faroes to Scotland, which was
part of the European main. On this bleak bridge which spanned the
North Atlantic permanent snows heaped up to mountainous heights
forming the nucleus of the giant Ice-cap. Its western lobe touched
the Rocky Mountains and the Missouri Valley, its eastern wing covered
the Russian plains as far as Moscow, and southward flooded the German
Empire. It may be that the North Atlantic bridge, remnant of an
elder continent, sank slowly until it foundered under its load of
ice. So the sea melted the ice and the climate began to mend.
EASTERN REGION. A third _echelon_ of the sou'-wester comes from the
equatorial belt of South America down to 15°S. This does not take up
any great load of moisture, for the {21} wind blows nearly dry across
the heights of air which overhang the Atlantic. It has little
moisture to spare for the Mediterranean summer, none at all for the
levels of the Sahara, Arabia, Persia, and the deserts of Central
Asia. The lands to leeward of Brazil are deserts.
FAR EASTERN REGION. In Asia, the movements of the sou'-wester are
complicated by the south-west monsoon, and the immense ranges of the
Himalaya. Eastward lies one more _echelon_ of the South-west Counter
Trade. Just as the sou'-wester in the North Atlantic is warmed by
the Gulf Stream, so the sou'-wester of the North Pacific is warmed by
the Japan current. Before the uplift of the St. Elias Alps, the
region of Alaska, and of Bering-Sea was a warm and well-watered
lowland. Alaska still grows gigantic timber in latitudes where North
Scotland and South Norway have only scrubby bushes.