"نجد الجنوبية: رحلة إلى الخرج والأفلاج والسليل ووادي الدواسر في سنة ١٩١٨." [و‎‎٩] (١٠٠/٢٢)

Faria, in which is the oasis of Hilwa; the Faia, dividing Alaiya
from the southern part of Tuwaiq drains part of both sections
into the Kharj valley at a point south of Dilam. Finally there
is the Ajaimi which, besides collecting the drainage of a number
of streams flowing west from the Biyadh, drains the southern
Tuwaiq plateau for about fifty miles from north to south and
receives the outflow of Wadi Birk, another great level crossing,
draining the quadruple range of western Nejd via Wadi Sirra
along the northern edge of Nafudh Dahi through the barrier
of Tuwaiq eastward to the Ajaimi. From the above it will
be seen that the Sahaba is eventually the sole drainage outlet
of the whole of what we may call Central Nejd, i.e. the tract
lying roughly between Longitude 44° and 47^° and Latitude 23°
and 26°. As to its onward course it is fairly safe to presume
that it very seldom carries water as far as, and still more seldom
across, the Dahana, though there seems no reason to doubt
the tiuth of local report that its course through a depression
in the sands is easily traceable. It is idle to speculate whether
it ever reaches the sea—it would certainly do so given a sufficient
volume of water. Its general direction from Kharj onwards
appears to be somewhat south of east.
It is not surprising that Kharj, saturated as its soil must
be by the floods brought down into the valley year after yeai
by the great drainage system above described, is or, lather I
should say, once was, a fertile tract renowned for its prosperity.
That prosperity is but a dim memory now, having long given
way to decay which broods over the scattered evidences of a
glorious past, inscrutable as Fate, and is intensified by a century
of strife only recently ended. Yamama, that great city of the
past, is choked with sand ; Firzan and a nameless city on the
eastern ridge, both of an older date than Yamama, are now
but heaps of debris, and the life-giving springs of water are
nearly dead from disuse or misuse—in fact the northern section
of the valley is a sorry sight and the scene of prosperity, on a
greatly modified scale, has shifted to the central part of the
district wheie Dilam, the modern capital, is surrounded by a
number of fairly prosperous settlements, entirely dependent
on wells.
Apart from the fact that it is one of the most important
drainage collecting centres in Arabia, the distinctive features
of the Kharj volley, whose height above sea-level rises from