'THE GEOLOGY AND MINERAL RESOURCES OF DHUFAR PROVINCE, MUSCAT AND OMAN' [‎34v] (58/96)

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that there has been an uplift of the Arabian coast near Risut (and
presumably westwards into the Jabal Qamar of the Hac iramaut).
The wadi A seasonal or intermittent watercourse, or the valley in which it flows. down the scarp of the Jabal Samhan into Murbat bay
also shows evidence of erosion, but it js not as mar ed as that
in the Ghaiz wadi A seasonal or intermittent watercourse, or the valley in which it flows. . All the wadis draining north trom A 1 Qutun
into the Qarn Shaiba and towards the Nejd show strong signs of
erosion, so that the general evidence is towards uplift throughout
Dhufar. There are terraces of tufa-conglomerate at the debouche
of many of the wadis emptying into the Dhufar plain. Among
the most conspicuous of such deposits of calcareous tufa or travertine
is that in Darbat wadi A seasonal or intermittent watercourse, or the valley in which it flows. , at the ‘ abyss of the Bents (Bertram Thomas
precipice), known as the Dahaq. It has been deposited from water
which has cascaded over an obstacle and become aerated and
precipitated calcium carbonate. In this way a lake was impounded
and the overflow continued to build up the dam (as is the case at
Band-i-Amir in the Hindukush in Afghanistan today). After a time
the lake spilled through the lateral valley to the west until another
natural dam was built up there, and then both dams were built
up and the lake bed itself also largely filled up with tufa. The lake
of Darbat is a remnant of what it was, and the Dahaq must be
between 500 and 600 feet high where seen as a wall (up valley as
you come from Takah).
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Weathering and Erosion Effects
77 . Except for the evidence of the springs—Garzaz, Sahnut,
Rizat, etc.—and the curious hole (Dianae Oraculum?) in the wadi A seasonal or intermittent watercourse, or the valley in which it flows.
Nihaz, there are no great underground caves in the limestones of
Jabal Qara, other than that of Sahaur above the Ghaur Fazl (Dianae
Oraculum). Caves occur all around in these hills, but they are
. erosion rather than solution effects on certain beds of limestone (as is
well seen at almost every water-hole (pool) in the Qarn Shaiba
country). And yet on the upland of A1 Qutun (between Na Sat
and the descent to the Rizat spring via Othik, for example) the
‘trip pillars’ of limestone show that solution is operating effectively.
In the upper valley of the Darbat among the western slopes of Jabal
Samhan there is said to be a great ‘sink-hole’, and it is shown on
some Air Flight maps. However, more active in this respect is the
weathering in progress in Dhufar. In the region to the north chemical
action appears to work hand in hand with hot sun and occasional
heavy rain, and it was my impression that the ‘ chalky ’ dolomite beds
of the Qarn Shaiba area were chemically produced in non-dolomitic
limestones in situ. I had the impression also that some of the flint
and chert had been segregated in those limestones after the beds had
been laid down as sediments in a tropical sea, and that this silica-
freeing action was of comparatively recent date. This may explain