Page:Lake Ngami.djvu/321

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313
CLIMATE—GEOLOGICAL STRUCTURE.

plains, traversed by hill and rock, and thickly strewn with quartz, which reflects a dazzling and perplexing light. Two to three days' journey south of Rehoboth, the dense thorny bush, so peculiar to Damara-land, ceases, and with the exception of a few mimosas along the water-courses, and occasional ebony-trees, the arboreous vegetation is scanty and stunted. For more than six months of the year it is scorched by an almost vertical sun. The rains, which are always accompanied by heavy thunder, are periodical and very partial. In its northern portion, the wet season sets in at the same time as in Damara-land; but in a southerly direction, the rains are later and more uncertain; and, as has been said in the last chapter, little or none falls about the lower course of the Orange River and the neighborhood. The springs (which are often either hot or salt) are indifferent and scantily distributed. The periodical water-courses, therefore, afford the chief supply.

The Namaquas, as well as the Damaras, are loud in their complaints that less rain falls now than half a century back. Indeed, the numerous ancient beds of rivers in the vast sandy plains, and the deeply-scored slopes and sides of the now "sunburnt" and crumbling hills, clearly indicate that almost the whole country north of the Orange River, as far as Europeans have penetrated from the Cape side, has at some former period been much more abundantly watered. In some parts, the destruction of forests, which are well known to retain and condense vapory particles, may partly account for such atmospheric changes; but in this region we must look for other causes.

In a geological point of view, Great Namaqua-land presents many interesting features. Between the Orange River and Walfisch Bay, beginning at the sea-side, three distinct terrace-like risings of the country are recognized. Besides the granite, which is the prevailing rock, great masses of quartz are met with either, as aforesaid, scattered over its