The place where Marks’s car had been discovered he found without difficulty. There was, however, no faintest indication of wheel-tracks. Standing approximately where the car stood in relation to the black’s sign, Bony traced the probable path it had taken when it left the road, and made out the sand ridge which had stopped it. The ridge was not two feet high, and ran due north and south. The wind had shaped it into perfect symmetry. Its northern end was lost amidst a wilderness of sand-hummocks, and its southern end rested against a much higher ridge of sand running due east and west. On the west side of the low ridge which had stopped the car the sand was ankle-deep and fine, but east of it lay a strip of ground three to four yards wide, hard as cement, and known as clay-pan, which ran the length of the low ridge. The car had crossed the clay-pan, and when it stopped its rear wheels would still have rested on it.

Even in sandycountry on which grow sturdy pines, these clay-pans are to be found. An exceedingly heavy downpour of rain-probably occurring but once in twenty years-overcomes the sand’s power of absorption and collects in pools. The water eventually evaporates, leaving a perfectly level surface of mud which dries to iron hardness, and thereafter the wind is able to sweep it continually free of the omnipresent sand.

In the centre of this particular clay-pan a colony of dark red ants with black legs had excavated their marvellous palace, whilst here and there along the edge of the clay-pan another species of ant, wholly black and about an inch in length, had founded colonies. These latter were notso ferocious as the red ants, nor were they so quick and purposeful in movement. The entrance to each nest was protected against flying sand, and presumably water as well, by a circular rampart, six inches high, which in turn was protected by a mass of pine-needles intricately woven together.