ago have been transformed into a solid mass, and if the assumptions as to the capacity of the Red Sea be correct, the waters would be dried up in the course of a hundred years, were no water to enter from without. In the course of three thousand years (and for this time it has been known to us) it must have been converted into a solid mass of salt, had the whole saline matter, carried in from without by the current required to feed evaporation, remained within the strait. Yet we know that, in point of fact, it is, at the surface at all events, not one whit more saline than the outer ocean; and we have no reason to believe that its lower waters differ materially from those which float at the surface. The various officers of the survey were, from the commencement of their labours, struck with the extraordinary diversity of the currents within the Gulf of Aden. "My endeavours," says Capt. Haines in a paper prepared in 1849, "to reduce them to principles which might guide others have hitherto entirely failed, but I am at this moment not satisfied how the currents themselves are set in motion, whether by submarine impulse, by a change in the component parts of the water occasioned by different degrees of evaporation, or by the pressure of prevailing winds. At sea I have experienced a current running in circles, or in bands, 60 miles in extent, and have not unfrequently borne up, and set topmast studding-sails with a favourable wind, in order to escape the counter current, when, by observation, I have found the vessel in another stream out of the former current, and have hauled to windward again, and beaten fast sailers, which were working inshore." This corresponds almost word for word with the account given by Dr. Scoresby of the bewildering currents produced by the tepid waters of the Gulf-stream running N., and meeting the cold and heavy polar currents moving southward: the cause of both being the encounter of streams of water of different weight; the specific gravity of the two depending in the one case on the diversities of temperature, in the other on differences of saltness. The error into which those who assume the salting up of the sea, seem to have fallen, is that of supposing the water concentrated by evaporation to remain at the surface till close on the point of saturation, and then sinking only when ready to deposit its salt, whereas, in point of fact, the instant the upper waters become one atom heavier than those beneath them, they will sink down either till they reach the bottom, or meet with others of the same gravity as themselves. A mass of brine, by ever so little salter than the surrounding waters, may thus accumulate in the recesses of the sea, until it rises to the level of the Mocha barrier, when, by its own gravity, it will at once flow over, and produce an outward under-current, by which the whole mass of the sea will come to be discharged as it is concentrated. Between this and the upper

inward-flowing current, required not only to supply the whole 165 cubic miles vaporized, but the vitiated water discharged, there will in all likelihood be a mass of stagnant water brought to × rest by its upper and lower surfaces being acted upon in opposite ways by the conflicting currents. These things are matters of physical necessity, dependent on the first principles of hydrostatics, and not requiring experiment for their establishment. It seems more than probable that the Red Sea changes the whole of its waters at least once a year; and we may yet be able to determine the fact by observation. As it is, we know that a strong current sets along the coast of Arabia, towards Meckran and Scinde, then sweeping southward by the shores of Hindostan, where it is diluted by the enormous falls of rain, of which probably not less than 10 feet are discharged into the ocean annually from an area of 24,000 miles, or 40 cubic miles of water, it next crosses the Arabian Sea towards Zanzibar, and gives off its surplus vapour as it returns along the shores of Africa northward to the Red Sea, again to perform the task it originally accomplished. The whole amount of water, evaporated from the nearly rainless shores to the N.W. of the Arabian Sea, probably exceeds 400 cubic miles, the further deficiency being supplied by currents from the southward.

The Shores of the Red Sea.--Around the whole of the shores of the Red Sea is a belt of sand and gravel, sloping inward from high-water mark to a distance varying from some hundred yards to that of many miles. It abounds with shells and corals, identical with those in the sea itself, and is obviously an upheaved beach of comparatively modern date. It is not very easy to determine either the extent or the elevation of its landward margin, as a long series of upheavals appear in these parts to have followed each other, so that a much more minute survey than has hitherto been bestowed upon it, would be required before what belongs to each could be determined. I have found Red Sea shells scattered in profusion all over the Desert, between Cairo and Suez, at an altitude of 800 feet, and they are mentioned as existing at an elevation of at least 2000. Dr. Carter describes a cavern near Ras-Morbat, in southern Arabia, the floor of which is a few feet above high-water mark, the roof being 30 feet high, obviously excavated by the waves. The face of the cliff on a level with the roof is full of borings of lithodomi, and Dr. Carter supposes that it was formed whilst slowly emerging from the sea.*

There are many similar caverns in the interior; the roofs and floors of all are incrusted with sulphate of lime, as stalagmites and stalactites. The cliffs along the shore of Africa, towards the mouth

*Geography of S.E. Coast of Arabia: Trans. Bomb. Asiat. Soc., 1851, p. 252.

of the Gulf of Aden, are found all pierced with similar caves, as I have no doubt those around the Red Sea would be found to be, were they examined; and I have come to the conclusion that the altitude of the most recent of these upheavals varies from 5 to 30 feet, being different at different points.

During his investigations with a view to the construction of a canal between the Mediterranean and the Red Sea, Mr. Cubitt found the level of the two seas the same; and there can be little doubt that the bitter lakes in the isthmus at one time formed the head of the Red Sea. Mr. Stephenson has ascertained that the sea-shells in this district, as well as those on both the raised beaches in that neighbourhood, are the same as those now prevailing in the Gulf of Suez; so that, at a period comparatively recent, all the tertiary beds forming the bottom of the sea and the contiguous land must have been elevated from 12 to 18 feet. Historical events afford us a date within which this must have occurred. Six centuries before the Christian era, Darius Hystaspes completed a canal from the Nile, a little above Bubastes, to the Red Sea near Patamos; it was in some places 150 feet wide and 30 feet deep, and was navigable for vessels of considerable burden; while the Nile which supplied it was high, the waters serving for irrigation. The vicinity of several important cities, the ruins of which are still scattered around, indicates that the district at this period was possessed of great fertility and a large population. Within three thousand years, then, the alteration of level must have occurred which rendered it impossible longer to supply the canal from the waters of the Nile. In this view I have adopted both the facts and the inferences of Mr. Cubitt, Mr. Stephenson, Capt. Newbold, Miss Corbaux, and Mr. Glynn, not having crossed it myself; but I had come to exactly the same conclusions, and published an account of these four years before the earliest of the writings referred to appeared. In Kattywar in Western India we have a proof of the same thing, near the Runn of Cutch, where the ruins of a city, known to have existed less than three thousand years ago, are now found 15 feet beneath the surface of the ground-8 or 10 feet above high-water mark. Within this time. a descent of at least 20 feet must have occurred to permit this mud to be deposited, the whole having reascended to its present level probably about the same time when the Runn of Cutch ceased to be an inland sea, by reason of the elevation of its basin. We are now minutely acquainted with the character of the Isthmus of Suez, destined, it is to be hoped, at no great distance

Capt. Newbold's Visit to the Bitter Lakes, Isthmus of Suez, Trans. Roy. Asiat. Soc., 1845, vol. viii. p. 355; Mr. Glynn on the Isthmus of Suez, on Ancient Canals of Egypt, Institution of Civil Engineers, 1852; Miss Fanny Corbaux's Letters in the "Athenæum," 1852.

of time to be traversed by a canal or railway connecting the two seas together.*

It is singular that we should know so little that is authentic or accurate of the Wadi Arabá, or the region which intervenes between the Gulf of Akabá, the other terminal point of the Red Sea, and the great depression of Palestine, considering its perfect accessibility and the frequency with which it has been traversed. Even the little knowledge we flattered ourselves that we possessed, has now vanished. A writer in the 18th volume of this Society's Journal, basing, as I had supposed, his conclusions on well-established facts, had placed its length at 105 miles, and its summit level at 495 feet; but Capt. Allen, R.N., has since shown that we are altogether ignorant both of the altitude

:

*The Isthmus of Suez appears at the southern extremity to constitute the trough or hollow which at one time formed the basin of the upper part of the Red Sea. Here it is walled in on both sides by mountain lands, which rise into loftier regions towards the peninsula, and into rounded hills of soft limestone in the direction of Cairo. It is with the level plain alone we are at present concerned this was first carefully surveyed by the French engineers in 1799, and the error was then committed of supposing the level of the Red Sea 30 feet above that of the Mediterranean. Although its suitableness for canal purposes had frequently been discussed, and it had been examined by Linant and other European engineers resident in Egypt, fifty years elapsed before the mistake of the French was discovered, when Mr. Stephenson made his survey in 1848. The distance by the shortest line from the Mediterranean to the Red Sea is 75 miles; the length of the canal proposed by the French 92 miles. From the high-water mark at Suez to the bed of the bitter lakes, a distance of 13 miles, the ground is almost even; it is covered with shells and sea-gravel, and rises from 3 to 12 feet above the highest tide. Here a depression, averaging about 16 feet, commences and extends for a distance of 27 miles; the surface of the bitter lakes themselves, which appear fragments of the Mediterranean or Red Sea lowered by evaporation, being 54 feet. From this to the Mediterranean the ground is low and marshy, abounding in pools of salt water. Over the whole of this tract the shells are identical with those now found in the Red Sea, which was probably here united with the Mediterranean much within the historic period. The question of its practicability for a canal was, until 1850, argued under two assumed difficulties, which have now both vanished-the navigation of the Red Sea before the introduction of steamers, and the difference of the levels of the two seas. The French engineers considered a canal perfectly prac ticable, and estimated the expense at 700,000l.; and Mr. Maclaren, who first presented us with their views in an English dress, concurs with them in opinion. Linant and Henderson agree as to the practicability, but double the charge. Capt. Vetch considers the canal will cost 2,500,000l. Capt. Glascock and Mr. Galway regarded it as wholly impracticable. Col. Chesney, M. Prony, M. Michel Chevalier, consider the canal practicable in a country where labour was cheap, and no physical difficulties existed. It seems singular that any doubt should be suffered to remain on a question of such supreme importance. The introduction of screw-steamers would permit the voyage to be made in one vessel from Europe to India; the distance between the two seas being calculated at 20 hours with a speed of no more than 5 miles an hour. At present, coal, which must be carried on camels' backs across the desert, costs 101. a ton at Suez; ships being thereby compelled to carry the bulk of their coal along with them from Aden and back, to their very great inconvenience.

See Mr. Maclaren's paper, Edin. Phil. Journ., 1825; various pamphlets published in 1842 and 1843; the Reports of the Society of Civil Engineers for 1850-51, Miss Fanny Corbaux' Letters in the Athenæum, 1851-52; Captain Newbold's visit to the Bitter Lakes; Journal of the Royal Asiatic Society, London, 1846.

Trans. of the Royal Geographical Society, 1853, vol. 23, p. 166.

and position of its water-shed. We do not profess to know anything of its geology, or the age of its upheaval. The islands in the Red Sea doubtless afford abundant evidence of these various changes of level; but, with the exception of the volcano of Gibel-Teer, and of those described by Ehrenberg, in the neighbourhood of Ras-Mahommed, scarcely one of them has been examined or described in modern times. The "Two Brothers," in lat. 26° 20' N., long. 34° 45′ E., are set down in the chart as coral islands, about 60 feet above the level of the sea. The sea immediately around them sinks at once to 50 fathoms. The Red Sea, around its whole circuit, is walled in by vast masses of mountain, which, down to Judda, in 21° 30' Ñ. latitude, approach close to its shores. On the African side, down to the 16th parallel, isolated hills alone skirt its borders; the higher ranges, 40 or 50 miles off, are seldom seen at sea; and on the opposite shore, between the same parallels, the land slopes gently in towards the interior of Arabia. The rocks chiefly consist of nummulite limestone—a portion of the vast band so admirably described by Sir Roderick Murchison, as stretching all the way, in one unbroken line, from the Bay of Biscay to the shores of Åracan, for nearly one-third of the circuit of the globe. From the parallel 16 to 12 the mountains on both shores and the islands in the middle of the Red Sea are volcanic. Gibel-Teer, in lat. 15° 30', is still smoking, as it has been since 1774, when visited by Bruce, by whom it is set down as 500 feet in elevation. Dr. Kirk makes it 300 feet; the surveyors place it at 900: so little do we know of a volcano passed by our steamers at least four times every month. A violent eruption, of short continuance, took place in one of the Zugar islands, lat. 15°, in 1846, which was fortunately seen from different points of view by steamers passing in opposite directions, but it has never since been visited. A range of hills, above 14 miles from the shore, to which it is nearly parallel, is laid down in the chart as volcanic on the African side, with a similar range of greater magnitude and of the same character, extending from lat. 12° to lat. 15° 30' on the Arabian coast. Dr. Kirk describes these as extending for about 300 miles to the westward; so that this vast volcanic field, which has scarcely been so much as noticed by geologists, occupies probably an area of above 10,000 square miles, without interruption; and is perhaps the third or fourth in point of extent on the surface of the globe. The only one of all its volcanoes with which we are somewhat acquainted is that of Aden, in the crater of which our troops are quartered. It has been so often described that it is not necessary here to refer to it, further than to state that it has clearly been submerged and elevated again from the waters, since the latest period of its activity. Up to the altitude of 500 feet it is thickly strewed with sea-shells mixed with scoriæ and volcanic