There is overwhelming evidence that Vaal River, into which millions of diamonds from the kimberlite pipes and fissures in the Kimberley, Barkly West and Campbell Plateau regions have been washed over the past ten million years, has repeatedly carried out enormously energetic erosive scouring of the bedrock along its flow path during exceptioiial flood events - (not just during 100 or 200-year flood events, but during rnassive 5000 and 10000-year flood events!). Wherever softer and more easily erodible bedrock types are encountered, the river with its load of fast flowing boulders and cobbles of very hard rock types such as quartzite, would have cut down into these areas producing deep potholes and gullies (many of which have already been found along the Vaal and Orange Rivers). The harder rock types such as Ventersdorp Lava, would by contrast have formed ridges across the path of the rivers. The deepest parts of these potholes and gullies would then have become the places where the boulders would have settled, especially in places where the river had been forced to change its direction with the formation of a vortex or whirlpool in the flow.

The low magnetic values (which indicate thick masses of sand and gravel sediments in deep bedrock channels) in the area to west of the "New Quarry" excavation, and the results of the drilling, where the rig was unable to reach the bedrock and encountered sand and gravel materials at depths in excess of 40 metres between the "New Quarry" and the power lines (see Fig. 1.), lies in an area where soft Dwyka shales abut against the resistant Quartz Porphyry Dyke and the Ventersdorp Lava Formation, and a hollow may already have formed here during the scouring which occurred during the movement of the continental ice sheets which preceded the deposition of the Dwyka shales and tillites. Downward movement of the Dwyka shale against Ventersdorp Lava may also have taken place here as a result of re-activation of the fault in post-Karoo times.

Whatever the reason, it is clear that powerful fluvial scouring has occurred to produce deep, elongate Muirton Porphyry Trench or gully in the softer shale all along its contact with the resistant porphyry dyke, after which the river was forced to cut its way through the resistant Ventersdorp Lava barrier to the south and then continue its journey towards its confluence with the Orange River at the present-day Douglas. The deep gully or elongate pothole in the riverbed, having a prominent, resistant lava ridge to the south, would have been a perfect trap for a mass of large boulders together with a large number of diamonds, especially very big diamonds, weighing in excess of 100 carats. Such a feature, carrying a high concentration of diamonds, is best described as a "Diamond Trench" or "Jewellery Pothole".