Livingstone found that in every salt pan of the country there is a spring of water on one side. The water of the spring is brackish. In one instance he found two springs, one salter than the other.
He was of the opinion that the supply could not come from beds of rock salt; for, where the natives have removed the salt from the pans, no new deposit has ever formed.
He thought it probable that these salt deposits are the remains of the slightly brackish lakes of antiquity. Large portions of these lakes must, in the course of ages, have evaporated to leave a deposit where the waters have receded.
An instance of this kind is Lake N'gami; for the waters of the lake when low become brackish.
The largest quantities of salt have been found in the deepest hollows or in the lowest valleys, where there is no outlet. Livingstone cites an instance of a fountain, the temperature of which was upwards of 100°. This fountain, though strongly impregnated with salt, had no deposit, because situated on a flat portion of the country.
When these salt deposits occur in a flat country with a tufa layer covering the soil, a chemical change takes place in the soil; the tufa is dissolved and the ground kept in a state unfavorable to the growth of plants.
Livingstone discovered one large salt pan with a deposit of salt an inch and a half in thickness. This deposit contained bitter salt in addition, probably the nitrate of lime. In order to make the deposit wholesome and palatable, the natives mix the salt with the juice of a gummy plant. They then place the mixture in the sand and build a fire over it to bake it. The action of the fire renders the lime insoluble and tasteless.
The natives in the vicinity of this salt pan keep large flocks of sheep and goats at various points on the outskirts of the desert. These flocks thrive wonderfully wherever salt and bushes are to be found.
The milk of goats does not coagulate readily, like that of cows, on account of its rich quality. The natives have discovered that by mixing a tea made from the fruit of a special plant with the milk of goats they can cause it to coagulate quickly.
It is the custom among some of the natives to put the milk into sacks of untanned hide from which the hair has been removed. When these sacks are hung in the sun the milk soon thickens. The whey is then drawn off by a plug at the bottom of the sack. Fresh milk is then added, until a thick sour curd fills the sack. When one becomes accustomed to this, its taste is delicious.