The surface zones of the globe : a handbook to accompany a physical chart / by Keith Johnston.

Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: The surface zones of the globe : a handbook to accompany a physical chart / by Keith Johnston. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    Where the great westerly currents of the sea and of the air, the 'anti-trade' winds, begin to prevail in both hemispheres' carrying great volumes of moisture over the lands which occur m the directions towards which they move, forests again ap- pear, but these are now of a different character, hardier and less luxuriant in their growth, since, in these latitudes, the sun's rays are weaker, and the average temperature is less. The great forests of North America and of Siberia, repre- sent this belt in the northern hemisphere. The southern hemisphere has only a small proportion of land extending into the chmate in which temperate forests occur; but wherever there is such land in the southern half of the globe, there again are forests similar in character and aspect to those of the northern belt; in the extreme point of South America, in Tasmania and New Zealand, and just touching upon the Cape of Good Hope. Between these great primary belts, in the regions of transi- tion from the moist climates of the equatorial and temperate forests, to the excessive drought of the deserts, the natural grass lands of the globe appear in double belts, one on each side of the deserts in each hemisphere. Beyond the temperate forests nearer the poles, where, though moisture is not absent, the heating power of the sun's slanting rays becomes very small, there is not sufficient warmth further, to find the opinion stated, that these regions have, in recent geo- logical times, been beneath the ocean. The saHnity, also, of many parts of their surface is frequently ascribed to this, and is given as the cause of their barrenness. But no explanation of their origin could be more erroneous, since, in every part of the desert zone where moisture is intro- duced, either naturally by rivers or artificially by canals, there luxuriant vegetation springs up, showing clearly that dryness alone is the cause of the desert; and it is probable that every salt-encrusted portion of the true desert surface tlaroughout the world can be sho\vfl to be the dried up bed of some continental lake, fed by fresh streams.