Page:South African Geology - Schwarz - 1912.djvu/40

 away by the winds. A typical pan may be a few hundred yards, or 20 ml. across as at Verneuk Pan in Kenhardt. In many cases their connection with a river can still be traced, either in the elongated form or by the fact that a particularly heavy rain will cause them to overflow their lip, and the water will find its way to some neighbouring river channel. In many cases the pans appear to be quite isolated hollows; but their history, nevertheless, is in all cases the same. The pans are for the most part very shallow, and the mud covering their bottoms is very fine, tenacious clay, useless for anything, and in addition it usually contains salt. All rocks contain a certain amount of lime, soda, chlorine, and sulphur, and as these are soluble, the result is that rainwater, washing down from the rocks, absorbs a certain amount of these substances. If the river has free access to the sea, the water contains such a small amount of these dissolved substances that it is fresh: but the continual pouring of these substances into the ocean, and evaporation of the water, has, in the course of ages, caused the ocean to become salt. The same happens on a smaller scale where year after year water containing small amounts of salt and lime washes into the pans; the water evaporates and a concentration of the salt and lime takes place, and in many instances crystallizes out naturally as salt and gypsum. The inland salt pans, which occur all over the western part of the Orange Free State, as at Haagenstad, and in the north-west of Cape Colony, are different from the coast salt pans. These latter are shallow depressions in marine gravels and sands, which still retain some of the actual salt of the sea; and as the rain washes through the porous material it dissolves a small amount and carries