Many ingenious theories have also been advanced as to the origin of these pans, which, although such a feature of the desert, are by no means confined to it. They are generally believed to have also been formed by the action of the prevailing wind (which seems to have quite a lot to answer for!), and doubtless in many places, where the sand is thin, this had been the case. But it can scarcely have been the case in these numerous pans of the “Game Reserve,” where the sand is at its deepest, and where many of the circular or oval pans are surrounded and protected by dunes of well over 100 feet in height, as with a wall. A learned German scientist (Passarge) has suggested that pans have been formed through vast herds of animals drinking and wallowing in the mud at these spots, causing depressions in which rain-water and sub-surface water collected, and I believe this is generally given as an explanation of the salt pans such as I have described. But for animals to “wallow in mud” presupposes water in these spots, and they must have been free of sand in the first place to allow of water standing there. I have visited scores of these pans, and I have found them to differ so greatly that it is hard to find a theory that would account for them all. In many the soil is what is known locally as _brak_ alkaline, spongy, powdery, into which the foot sinks deep at every step; in others the surface is a hard, sun-baked mud, red in colour and covered with a shining glaze. Some are salt pans such as I have described, in others I found several feet of blue or greenish “pot clay,” under which was a sort of black volcanic mud; still others were filled with a species of Kimberlite (blue ground) almost identical with that of the Premier Mine; and though the surface was often the usual blue shale that underlies most of the desert sand, in very many cases these depressions--on which the surrounding sand never accumulates--marked an entirely different “country rock” from that of the region generally. One useful peculiarity about these pans, and one by which we were able eventually to locate them, was that their position was invariably marked by exceptionally high dunes in the immediate vicinity--usually on the south side; those of Aar Pan, the highest in the Reserve, being a good 300 feet above the level of the pan they flank. But to return to our own particular troubles. Old Gert, when he had been given a very drastically edited account of our trip, was able to describe minutely how we could take our bearings from the Salt Pan to find a large pan called “Kobo-Kobo,” whence the locating of our first diamond pan would be easy, and a day or two later Du Toit, Telfer, and myself made an attempt to reach it; van Reenen, with the “boys,” meanwhile testing a small pan about a mile to the north, where volcanic action was unmistakable, but where we found only pot-clay and volcanic mud.