some funnel-shaped chasms in the soil, varying from twenty-five to forty feet in depth, distinguishable from a distance by the thickness of the growth of the trees. I afterwards learnt that similar chasms are by no means uncommon in some parts of the Transvaal, between the Harts River and the Molapo, as well as between the Lower Molapo and the Vaal in the Barolong and Batlapin territory; they are found likewise in Griqualand West. These crater-like openings are characteristic of the vast bed of superficial limestone that lies, sometimes indeed only in thin layers, but ordinarily some hundreds of feet thick, covered in some places with sand or chalk, and in others with blocks of granite or slate; they are caused by the union of several deep fissures in the rock far below the surface of the soil. This limestone-bed has a clearly defined stratification; it bears external marks of the action of water, and throughout its extent of hundreds of miles is full of cracks, but so hard is its substance, and so huge is its mass, that in nine cases out of ten the convulsions of nature have not made any appreciable displacement; it is only in these chasms that the effect is at all apparent.
The underground fissures, sometimes several miles long, serve as subterranean channels for the streams, which after a while force themselves out through little rifts into the valleys. This is the case with the Upper Molapo, and in the same way does a portion of the Mooi flow below the surface of the ground, disappearing entirely in places, to reissue
