Water erosion has certainly formed the Theban wadis.  But this water erosion was probably not that which would be the result of perennial streams flowing down from wooded heights, but of torrents like those of to-day, which fill the wadis once in three years or so after heavy rain, but repeated at much closer intervals.  We may in fact suppose just so much difference in meteorological conditions as would make it possible for sudden rain-storms to occur over the desert at far more frequent intervals than at present.  That would account for the detritus bed at the mouth of the wadi, and its embedded flints, and at the same time maintain the general probability of the idea that the desert plateaus were desert in Palaeolithic days as now, and that early man only knapped his flints up there because he found the flint there.  He himself lived on the slopes and nearer the marsh.

This new view seems to be much sounder and more probable than the old one, maintained by Flinders Petrie and Blanckenhorn, according to which the high plateau was the home of man in Palaeolithic times, when the rainfall, as shown by the valley erosion and waterfalls, must have caused an abundant vegetation on the plateau, where man could live and hunt his game. [Petrie, Nagada and Ballas, p. 49.] Were this so, it is patent that the Palaeolithic flints could not have been found on the desert surface as they are.  Mr. H. J. L. Beadnell, of the Geological Survey of Egypt, to whom we are indebted for the promulgation of the more modern and probable view, says:  “Is it certain that the high plateau was then clothed with forests?  What evidence is there to show that it differed in any important respect from its present aspect?  And if, as I suggest, desert conditions obtained then as now, and man merely worked his flints along the edges of the plateaus overlooking the Nile valley, I see no reason why flint implements, dating even from Palaeolithic times should not in favourable cases still be found in the spots where they were left, surrounded by the flakes struck off in manufacture.  On the flat plateaus the occasional rains which fall—­once in three or four years—­can effect but little transport of material, and merely lower the general level by dissolving the underlying limestone, so that the plateau surface is left with a coating of nodules and blocks of insoluble flint and chert.  Flint implements might thus be expected to remain in many localities for indefinite periods, but they would certainly become more or less ‘patinated,’ pitted on the surface, and rounded at the angles after long exposure to heat, cold, and blown sand.”  This is exactly the case of the Palaeolithic flint tools from the desert plateau.

[Illustration:  012.jpg UPPER DESERT PLATEAU, WHERE PALEOLITHIC IMPLEMENTS ARE FOUND, Thebes:  1,400 leet above the Nile.]