FORGOTTEN RIVERS 151

with sunrise and gradually increased in strength and gusti-
ness to die down altogether at sunset.

Before us lay the vast expanse of Bani Mukassar, a tract
of several long parallel dune ranges. We seemed now to be in
the very midst of the Great South Desert and the short
lengths of dunes we had seen amidst the lower sands hitherto
now gave way abruptly to dune barriers mountainous by
comparison. Between the first two ranges lay a broad valley
of rolling §and with considerable patches of the gritty or
pebble-strewn rock floor exposed. On reaching the first
range we skirted along its flank in the tracks of our bag-
gage animals until, nearing the crest by a lofty dune, I called
a halt to survey the scene from its summit. The wind swept
the sand in a continuous sheet from its crest as we sat on the
peak looking down into the gravel valley below and far out
beyond it over range upon range of dunes like the one on
which we were.

With Zayid and 'All I descended the steep soft slope of
sand—perhaps 200 or 250 feet in elevation—on the further
side to prospect the rock floor for flints or shells. Our camels,
loudly protesting, were pushed or dragged down the slope,
plunging almost knee-deep into the soft sand at every step.
The range seemed to extend to a total length of about 5 miles
along the flank of the valley, running NE. and SW. No
sooner had we reached the bottom than we began to find
flints, and a little further on we came upon the unmistakable
traces of another unknown well—Salim afterwards agreed
that no well had been known to exist in that position—which
we christened Bir Mukassar. It lay about 5 miles ESE. of
Tuwairifa and proved to be the last vestige of human activity
in this area of ancient floods.

Beyond it lay the desert sands •uninterrupted. The rest
of the party had continued in the tracks of the baggage, and
we saw them coming over and down the slope of the range
far ahead while we slanted across the valley to cut them off.
A steep downward slope of soft sand took us over the second
range, while an easy passage was found through the third,
beyond which we traversed a rolling sandy down tract to the
farther extremity of Bani Mukassar. Its width from side to