Part Iii. 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.

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.

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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.