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 Palæolithic 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 Palæolithic 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 Palæolithic 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
Palæolithic 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