On the third day two white men overtook and passed us, on horseback, not keeping the trail but away to the right of us, and apparently anxious to avoid us. This was peculiar, as in a country where days may pass without seeing a soul by the way, the custom is to seek the infrequent wayfarer rather than to avoid him, and I began to think of all I had been told about being followed. The driver, who had seen them pass, said he was sure they were not police, and Piet, the _voorlooper_ of the telescopic eyes, corroborated this. Again and again we caught sight of them, sometimes ahead, sometimes behind or on our flank, but they never came near us, and it soon became pretty clear that we were being “shepherded.” Once or twice we tried to signal to them by waving a handkerchief and shouting, but they took no notice, and G., exasperated at their attitude, seriously suggested having a shot at them with the rifle. CHAPTER VI ZWARTMODDER--THE MOLOPO--RIETFONTEIN--THE GAME RESERVE. On the third day we reached Zwartmodder, a tiny police post and store in the old dry bed of the Molopo, whose course we were now to follow for some days. The two policemen (C.M.P.) stationed at this lonely little spot told us the horsemen had gone straight through without coming near the station, and confirmed us in our suspicion as to what these sneaks were after. Zwartmodder is a weird and desolate little place standing in a deep, narrow, rock-walled valley, whose sandy floor was the bed of the ancient river that once flowed right across what is now the Kalahari Desert from near Mafeking, westward, and then south, for many hundreds of miles, till it joined the Orange below the great falls of Aughrabies. In most places it is sand-choked to the level of the surrounding desert. In others, though still dry, it is filled with vegetation, and indeed many stretches farther north are well timbered, with fine mimosa and other thorn-trees. But, with the exception of one or two melancholy survivors, there are none of these trees left near Zwartmodder, the channel being loose sand where it is not the “black mud” from which the place is named. Made anxious by this particular “shadowing” by men who kept ahead of us, I consulted the driver as to whether we could leave the track and give them the slip, and for the first time showed him the map old Anderson had made.