Observations on the geology of Arabia.
My Dear Sir,
You will think me guilty of neglect in not answering your letter sooner, but I had gone for a short time to the Borders in search of picturesque beauty and poetic associations, and during the 3 days I remained in Edinburgh on my return I was much occupied in preparing a medical paper for the press, and in consulting books. I put your letter in my pocket on leaving for a pedestrian tour across from Blair Gowrie to the head of the Dee and the Cairn Gorm, intending to answer it from Braemar—but on opening it for the purpose on a very rainy day when we could not venture on the mountains, I found I had taken your former letter by mistake—so I put off till I came home, and now I have been waiting for 10 days, in vain, for part of my baggage which has been taken somewhere else by the steam boat. This is enough of your time occupied by excuses—so I need not add, that the delay has enabled me to get some information that, I hope, will be of use to you, from a friend who was some years amongst the islands between the Isle of France and Africa.—
Before I got your last letter the objection to the Glen Roy gulf theory
mentioned by yourself had occurred to me, and I talked it over
with Mr Geo. Anderson of Inverness (Author of the Guide) who
knows more of the highlands than any body else. He said that he knew of no other similar
appearance—but would not give me an opinion on your theory. I read
Now for Arabia.— Sahar is a considerable town on the
coast of Hadhramaut in about Lat 14
A little east of this, the wide bed of a torrent has
cut through the plain, and displays its structure in some low cliffs composed of
horizontal strata of hard conglomerate consisting of limestone pebbles, madrepores,
corals and shells cemented by a very calcareous sandstone. The corals and shells seemed
to belong to species common in these seas. The cliffs were not
above 16 feet in height from the fresh water that lay in pools in the bed of
the stream, but the plain rose towards the town, near which are wells from
30 to 40 feet deep containing saline and bitter water. The water in a pool at the foot of the coral rock was sweet and
being exposed to the air had a temperature of 70 (December), and that of the wells no
less than 83
Aden consists of vast cliffs of basalt with olivine calcedony, &c, and
on the summits pitch stone; and has probably been a vast crater with smaller ones in the
centre, one side of which has been removed by the sea. Were it sunk below the deep, it
would form a lagoon island, but I found no fossils above the influence of storms, which
have thrown masses of recently consolidated sand and shells high on the shore. Here I first observed the connection of springs of pure
water with the volcanic rocks and high temperature, while the saline springs were cold
and derived from the superficial strata. The country around Mocha is Basaltic and has
many sweet thermal springs—but the black soil near the town is very saline.
Various schistose rocks occur at Hodeida, Ghezan &c and in some places the sea
is encroaching. —but the island of Kamran north of Hodeida is composed of low
cliffs, which rise 30 and 40 feet above a saline sandy plain
containing sea shells, and not now covered by the sea at any time. It is here that the
country ships enter the inner navigation where the water is quite smooth in consequence
of a succession of reefs and islands. These cliffs are formed
of a solid rock of corals and vast numbers of shells with a little calcareous cement.
These appear to be all of recent species. In one place I found the coral rock resting on a
ferruginous fine grained argillo-calcareous stone which I at first took to be a volcanic
production, and still think that it has something of that nature. In a little valley
between two of these cliffs there is a fine well of very pure water, and between it and
the sea some fruitful date gardens, and on the cliff above some ruined tombs and an old
castle. The coral rock supports only a few stunted grasses and aromatic herbs. Here then
is an island that has been raised at least 40 feet above the highest level of
You will see that it is not far from Gebel Tor, nor from the volcanic rocks on the mainland.— I landed on some other islands formed of coral and blown sand,
but without any signs of elevation; and we often passed through narrow channels between
coral reefs over which the sea broke with fury, and we frequently sailed in a narrow
channel between them and the shore. (I was in an arab vessel). The harbour of Jedda
itself is approached through these reefs, from which nothing can be learned as to
the elevation of the coast, or as to the coral forming a mere coating: but the rising
ground on which the town stands, and towards the interior near the road to Mecca where
great cisterns for rain water are formed, and on a gentle
eminence north of the town on which a great military
- f1 533.f1Malcolmson 1839.
- f2 533.f2CD had presumably summarised his hypothesis that Glen Roy was once an arm of the sea. He considered the concentration of the ‘beaches’ in one small region to be one of the objections that might be made to the marine hypothesis. Another was the absence of sea shells on the terraces.
- f3 533.f3G. and P. Anderson 1834.
- f4 533.f4MacCulloch 1817.
- f5 533.f5Malcolmson visited Arabia and Sinai in 1836 on his homeward journey from India. Some of the places he describes are discussed in Malcolmson 1837. Sahar and Macula correspond to Shihr and Mukalla in modern atlases.
- f6 533.f6Referred to in Coral reefs, p. 137.
- f7 533.f7Kamaran passage is the southern end of the Inner Channel along the eastern shore of the Red Sea.
- f8 533.f8See Coral reefs, p. 136.
- f9 533.f9Jabal at Tair Island.