Nature has looked well to the law of cause and effect; for, while the rivers are dry during some portions of the year, after a tempest the waters flow down over the sides of the mountains in torrents. These, in the course of ages, have worn deep cuts, or valley gorges, called kloofs.
The karroos, or elevated tracts, of which we have read, are not like the vast seas of sand of the Sahara. "They consist of shallow beds of rich soil, which want only the fertilizing power of water to render them most productive. The soil of the karroos is clay and sand, resting on blue slate rock. As the streams are dry for three-fourths of the year, the ground becomes during that period as hard as brick. After a few days of rain, grasses and other plants with bulbous roots, spring up everywhere from the hard soil in which they have been encased, and soon the land is covered with bright flowers and verdant pasturage."
Probably no part of the globe presents a more beautiful appearance than these karroos when carpeted by the hand of nature. The description of the flowers of Cape Colony by the author of "Life on an Ostrich Farm" gives one a fair idea of their beauty and variety.
CHAPTER XXIX.
SOME PECULIAR FEATURES OF AFRICAN SOIL.
In making some of his early explorations Livingstone passed over a country, the firm, compact soil of which was perfectly level. Here he found a little soil covering a limelike tufa deposit. This extended over a tract of several hundred miles. It supported a vegetation of fine, sweet, short grass, and baobab and other trees.
In several parts of this tract he found large salt pans, as they are termed. One was fifteen miles broad and one hundred miles long.
Although these curious spots seemed perfectly level, yet they have a slight slope to the northeast, towards which the rain water, which sometimes covers them, gently trickles. The salt dissolved in the water has in this way been gradually transferred to one large pan lying to the northeast. On this may be seen a cake of salt and lime an inch and a half thick. Some of these pans have merely a covering of salty lime; others are covered with a thick deposit of shells.
These shells are identical with those of the mollusk species of Lake N'gami. There appear to be three varieties, spiral, univalve, and bivalve.