'THE GEOLOGY AND MINERAL RESOURCES OF DHUFAR PROVINCE, MUSCAT AND OMAN' [‎24v] (38/96)

24
e
southwards as well as underground. We were now travelling west
and south-west and had gone for perhaps four hours (nearly 9 or 10
miles), still largely on uplands of grass and shrubs before we reached
wooded valleys opening southward, and had a glimpse of Risut bay
far away to the south-west. The vegetation on the slopes was never
thick enough to hide the outcrops of the bedded limestones. These
strata are seen to be undulating in gentle arches (anticlinals) and
troughs (synclinals) as the curves of the outcrops are easy to trace.
45. And so about midday we arrived under some fig trees
near a water-hole or spring well up the hillside at Otak (Othk).
The water is dirty, due to cattle standing and drinking in the pool.
1 understood that there was water in the valley below, but I was
unable to get the real name of the valley or the exact position of the
reported pool or spring in it. From Otak we crossed the valley in
a southerly direction and again emerged on open upland with grass
and shrubs almost dangerous to walk on because of the irregular
solution pillars of limestone, 12 to 18 inches high and spaced barely
2 feet apart in any direction. They are not at first visible because
the dry grass is also about 18 inches high. Practically all the run-ofi
rain must be trapped, or at least hindered, on such karstland and
much of it must ultimately take an underground course through the
worn cracks and joint planes in the underlying limestone. After
perhaps 4 miles (from Otak) we began a long gradual descent south-
south-east. In this descent of perhaps 1,200 feet I collected a few
typical samples of the limestones. Some were fine textured and
crystalline, others almost of the texture of lithographic A lithograph is an image reproduced from a printing plate whose image areas attract ink and non-image areas repel it. limestone,
and others with veins of silica (some quartz) and appearing siliceous.
The analyses show nearly all the specimens to be very high grade
(pure) limestones, with little magnesia or silica.
46. About 4 p.m. we had descended to the foot of the hills,
then deflected eastwards and entered the valley of the Rizat a
mile or so below the big spring. I believe the actual place is called
Mulwa Al’Aud (but this may be a mile lower down the valley where
I finally camped). The Rizat (or Ar’Zat) spring feeds a large pool
and I was not able to see from where the underground water enters.
There is an abundance of tufa around the pool and downstream along
the Rizat wadi A seasonal or intermittent watercourse, or the valley in which it flows. , and the water is conducted in a channel along the
eastern side of the wide stream course. My measurement of the
flow near the pool, in the aqueduct or prepared channel, gave about
18 cusecs (roughly 64,000 cubic feet or 400,000 gallons an hour).
It is a river almost capable of providing 40,000 people with 25 gallons
a head a day. At present this water is carried out to the plains for
irrigation purposes and no use made of the fall from the spring to
Mahmulah which must be over a 100 feet and should yield about
120 kilowatts of electrical energy at Mahmulah (i.e. before the water
is seriously used for irrigation). The above estimate is an all-the-