Part 15

"There is certainly no reason for believing," he says, "that there has been any diminution in the general volume of water coming from the south. The great change in the level can, therefore, only be accounted for by some changes in the land, and these must also have altered the whole nature of the Nile Valley. There seems to be but one cause for the very considerable lowering of the Nile; namely, the washing out and excavations of the catacombs (_Answaschen und Aushölen der Katakomben_); and this is quite possible from the nature of the rocks themselves, which, it is true, are of a quality that could not well be rent asunder, and carried away by the mere force of the water, but might be acted upon directly by the rising of the water-level, and the consequent effects of the sun and air on the places left dry, causing cracks, into which earth and sand would penetrate, which would then give rise to still greater rents, until, at last, the rocks would of themselves fall in, by having been hollowed out, a process that would be hastened in those parts of the hills where softer and earthy beds existed, and which would be more easily washed away. But that, in historical times, within a period of about 4000 years, so great an alteration should take place in the hardest rocks, is a fact of the most remarkable kind,--one which may afford ground for many other important considerations.

"The elevation of the water-level at Semne must necessarily have affected all the lands above; and, it is to be presumed, that the level of the province of Dongola was at one time higher, as Semne cannot be the only place in the long tract of cliffs where the bed of rock has been hollowed out. It is to be conceived, therefore, that not only the widely-extended tracts in Dongola, but those of all the higher country in Meroë, and as far up as Fasogle, which, in the present day, are dry and barren on both sides of the river, and are with difficulty irrigated by artificial contrivances, must then have presented a very different aspect, when the Nile overflowed them, and yearly deposited its fertile mud to the limits of the sandy desert.

"Lower Nubia also, between Wadi Haifa and Assuan, is now arid almost throughout its whole extent. The present land of the valley, which is only partly irrigated by water-wheels, is, on an average, from 6 to 12 feet higher than the level to which the Nile now rises; and although the rise at Semne might have no immediate influence upon it, yet what has occurred there makes it more than probable, that at Assuan there was formerly a very different level of the river, and that the cataracts there, even in the historical period, have been considerably worn down. The continued impoverishment of Nubia is a proof of this. I have no manner of doubt that the land in this lower part of the valley, which, as already stated, is at present about 10 feet above the highest rise of the Nile, was inundated by it within historical time. Many marks are also met with here, that leave no doubt regarding the condition of the Nile Valley antecedent to history, when the river must have risen much higher; for it has left an alluvial soil in almost all the considerable bays, at an average height of 10 metres (32 feet 9 inches) above the present mean rise of the river. That alluvial soil, since that period, has doubtless been considerably diminished in extent by the action of rain. On the 17th of August Hr. Erbkam and I measured the nearest alluvial hillock in the neighbourhood of Korusko, and found it 6·91 metres (22 feet 7 inches) above the general level of the valley, and 10·26 metres (33 feet 7 inches) above the present mean rise of the river. That rise, which at Semne, on account of the greater confinement of the stream between the rocks, varies as much as 2·40 metres (7 feet 10 inches) in different years, varies at Korusko less than 1 metre (3 feet 3 inches).

"Near Abusimbel, on the west bank, I found the ground of the temple 6·50 metres (21 feet 2 inches) above the highest water-level. This temple, it is well known, was built under Rameses the Great, between 1388 and 1322 years before Christ. Near Ibrim there are, on the east bank, four grottoes excavated in the vertical rock that bounds the river, which belong partly to the 18th and partly to the 19th dynasties; the last, under Rameses the Great, is also the lowest, and only 2·50 metres (8 feet 1 inch) above the highest inundation; the next in height is 2·70 metres (8 feet 9½ inches) above the former, and was made 250 years earlier, under Tutmes III. Although I only measured the present level of the valley near Korusko, nevertheless it appears to me that, during the whole of the new kingdom, that is, from about 1700 years before Christ to this time, the Nile has not reached to the full height of the low land of the valley.

"It is, however, conceivable that, at the time when the present low land of the Nubian Valley was formed, the cataracts at Assuan were in a totally different state; one that would, in some degree, justify the overcharged descriptions of the ancients, according to whom they made so great a noise that the dwellers near them became deaf. The damming up of the inundation at Assuan could have no material influence on Egypt, any more than that at Semne, or the land from thence to Assuan."

It appears therefore, from the above statements, that at the time mentioned, the Nile, during the inundations, stood 26 feet 8 inches higher than the highest level to which it now rises in years of the greatest floods; and that, to account for this, Professor Lepsius conceives that, between the time of Moesis and the present day, the bed of the Nile, from a considerable distance above Semne to Assuan, must have been worn down to that extent. In the index to the volume of the Berlin Monatsbericht, in which the letters of Professor Lepsius are inserted, there is the following line:--

"NIL, _senkung seines Bettes um 25 Fuss seit 4000 Jahren_."

"_Nile_, sinking of its bed about 25 feet (Paris) within the last 4000 years."

Rivers are, undoubtedly, among the most active agents of change that are operating on the earth's surface; the solid matter which renders their waters turbid, and which they unceasingly carry to the sea, afford indisputable proof of this agency. But the power of rivers to abrade and wear down the rocks over which they flow, and to form and deepen their own bed, depends upon a variety of circumstances not always taken into account; and although the great extent of that power, in both respects, is shewn in the case of many rivers, to conclude, as some have done, from these instances, that all rivers have excavated the channels in which they flow, is a generalization that cannot be safely assented to. The excavation of the bed of a river is one of those problems in geological dynamics which can only be rightly solved by each particular case being subjected to the rigorous examination of the mathematician and the physicist. The solid matter which rivers carry forward is in part only the produce of their own abrading power; and the amount of it must be proportional to that power, which is mainly dependent on their velocity; they are the recipients of the waste of the adjoining lands by other combined agencies, and the carriers of it to the lower districts and to the sea. They often afford the strongest evidence of the vast lapse of time that must be included between the beginning and close of a geological period; and, when they flow through countries whose remote political history is known to us, they supply a scale by which we may measure and estimate that lapse of time. This is especially so in the case of the Nile.

When so startling an hypothesis as that now referred to, viz., that the entire bed of so vast a river as the Nile, for more than 250 miles, from Semne to Assuan, has been excavated, within historical time, to a depth of 27 feet, is made by a person whose name carries so much weight in one department of philosophical inquiry, the statement involves such important geological considerations, that it becomes the duty of the geologist to examine, and thoroughly test the soundness of the explanation, in order that the authority of Professor Lepsius, for the accuracy of the facts observed, may not be too readily admitted as conclusive for the correctness of his theory of the cause to which they owe their existence. That there has been such an undoubting admission, appears from the following passage in the work of one of the latest writers on Nubia:--

"The translation of the name of this town (Aswán) is 'the opening;' and a great opening this once was, before the Nile had changed its character in Ethiopia, and when the more ancient races made this rock (at the first cataract) their watch-tower on the frontier between Egypt and the south. That the Nile has changed its character, south of the first cataract, has been made clear by some recent examinations of the shores and monuments of Nubia. Dr Lepsius has discovered water-marks so high on the rocks and edifices, and so placed as to compel the conviction that the bed of the Nile has sunk extraordinarily by some great natural process, either of convulsion or wear. The apparent exaggerations of some old writers about the cataracts at Syene may thus be in some measure accounted for. If there really was once a cataract here, instead of the rapids of the present day, there is some excuse for the reports given from hearsay by Cicero and Seneca. Cicero says, that 'the river throws itself headlong from the loftiest mountains, so that those who live nearest are deprived of the sense of hearing, from the greatness of the noise.' Seneca's account is: 'When some people were stationed there by the Persians, their ears were so stunned with the constant roar, that it was found necessary to remove them to a more quiet place.'"[54]

Footnote 54: Miss Martineau's Eastern Life, vol. i., p. 99.

_Note._--The learned author of an article on Egyptian Chronology and History in the "Prospective Review" for May 1850, in referring to the contributions of Professor Lepsius to Egyptian history, says, "He has discovered undescribed pyramids, equal in number to those known before; has traced the Labyrinth, and ascertained its founder. _He has detected inscriptions on the banks of the Nile, which show that its bed has subsided many feet in historic times." 9th June 1850_.

In the assumption of an excavation of the bed of the river, we have no small amount of wear to deal with, for the distance from Semne to Assuan, following the course of the river, is not less than 250 miles; and if, as Professor Lepsius supposes, the excavation extended to Meroë, we have a distance, between that place and Assuan, of not less than 600 miles.

Although these records of a former high level of the Nile at Semne had not been noticed by any traveller prior to Professor Lepsius, we may rest fully assured of the accuracy of his statements, from the habitual care and diligence, and the established character for fidelity, of the observer. The silence of other travellers may be readily accounted for by this, that none of them appear to have remained more than a very short time at this spot--not even the diligent Russegger--whereas we have seen that Professor Lepsius passed twelve days in the examination of this gorge in the Nile Valley.

The theory of a lowering of the bed of the river by wearing, involves two main considerations, viz., the power of the stream, and the degree of hardness of the rocks acted upon. The power depends upon the volume and velocity of the river--the velocity on its depth, and the degree of inclination of the bed: the hardness of the rocks we can form a tolerable estimate of when we know their nature. To judge, therefore, of the probability of the hypothesis of Professor Lepsius, we must inquire into the physical and geological features of the Nile Valley, in Nubia.

In the observations I have now to offer, my information has been derived of course entirely from the works of other travellers, particularly those of Burckhardt, Rüppell, and Russegger,[55] and especially the latter, who travelled in Nubia in 1837; for he not only enters far more into the details of the natural history of the country, but he is the only traveller in Nubia who appears, from previous acquirements, to have been competent to describe its natural history with any degree of accuracy--I refer more particularly to the physical and geological features of the country. Besides full descriptions in his volumes, he has given a geological map of Nubia, and also several sections, or what may more properly be called _vertical sketches_--a term that would, perhaps, be a more appropriate designation for all sections that are not drawn to a true scale, or at least when the proportion of height to horizontal distance is not stated.

Footnote 55: Reisen in Europa Asien und Afrika, in der Jahren 1835, bis 1841.--Stuttgart 1841-1846.

_The Physical Geography of Lower Nubia._[56]

Footnote 56: With reference to the object of this paper.

Russegger informs us,[57] that he believes he was the first traveller who had succeeded in making a series of barometrical measurements along the Nile Valley, from the Mediterranean to Sennaar and Kordofan, and thence to the 10th degree of north latitude. He gives the following altitudes, above the sea:--

Paris Feet. English Feet.

The upper part of the Cataract of Assuan, 342 = 364·37 Korusko, on the right bank of the Nile, in Nubia, 450 = 479·43 Wadi-Halfa, 490 = 522·00 New Dongola, 757 = 806·52 Abu Hammed, 963 = 1026·00

Footnote 57: Reisen, Bd. ii., 545.

I shall now give the length of the Nile along its course from Abu Hammed to the island of Philæ, at the head of the cataract of Assuan. I employ for this purpose the map in the atlas which accompanies the work of Russegger, which bears the date of 1846, and which, doubtless, was constructed on the best authorities. He mentions a map of General von Prokesch with great praise.[58] It flows:--

German M. English M.

From NE. to SW., from Abu Hammed to Meroë, about 31 = 150 It makes a curve between Meroë and Old Dongola, of about 16 = 77 It flows between Old and New Dongola, from SE. to NW., about 16 = 77 Then, with some short windings, nearly due north to the island of Sais, for about 30 = 145 And from Sais to the island of Philæ, from SW. to NE., about 68 = 327 ---- ---- Making the whole length of the course, from Abu Hammed to Philæ, about 161 = 776

Footnote 58: "Über den Stromlauf und das zunächst liegende Uferland des Nils, von der zweiten Katarakte bis Assuan, besitzen wir eine vortreffliche Karte namlich:" "Land zwischen der kleinen und grossen Katarakten des Nil. Astronomisch bestimmt und aufgenommen in J. 1827, durch v. Prokesch. Nil Grundrisse der Monumente. Wien, 1831."--Reisen Bd. ii., Thl. iii. 86.

Ascending the river, we have, between Philæ and Korusko, a distance of 24 German, or 115½ English miles, and without any rapid, except one near Kalabsche. Korusko being 115 feet above the head of the cataract of Assuan, at Philæ, we have an average fall of the river between these two places of a foot in a mile.

Between Korusko and Wadi-Halfa there is no rapid. The distance being 20 German, or 96 English miles, and the difference of altitude being 42½ feet, we have an average fall throughout that part of the river's course of not more than 5·3 inches in a mile.

This very inconsiderable fall need not surprise us; for the average fall of the Nile in Lower Egypt, at the lowest water, is little more than one-third of that now stated. At the time of the highest water the surface of the Nile, at Boulak, near Cairo; that is, about 116 miles in a direct line from the coast is only 43·437 English feet above the level of the Mediterranean, and at the time of the lowest water, only 17·33 feet. Thus, in the first case, there is an average fall of about 5·00 inches; in the second, of not more than 1·80 inches in a mile.[59]

Footnote 59: Russegger, Reisen, Bd. i., 258.

Between Wadi Halfa and Dale, a distance of about 94 miles, six cataracts, or schellals, as they are called in the language of the country, are marked in Russegger's map. And here, it may be as well to notice, that there are no cataracts, in the ordinary sense of the term, on the Nile; no fall of the river over a precipice; all the so-called cataracts are rapids, where the river rushes through rocks in its bed; the rapids varying in their length and degrees of inclination. We have no measurements of their lengths or of their falls, except as regards the first and second cataracts. The former, according to Russegger, has a fall of about 85 English feet in a distance of about 8 miles; and he describes the latter as extending from 5 to 6 _stunden_; that is, from 12 to 14½ miles, but he does not give the height. Speaking of the schellals above Semne, Russegger says, that all may be passed in boats without difficulty for about six weeks, or two months in the year. This is the case also, at the cataract or rapid of Assuan. But between Wadi-Halfa and Dale, with some inconsiderable spaces of free navigable water, in the ordinary state of the river, there is an almost uninterrupted series of rapids. We have no measurement of the height of Dale above Wadi-Halfa, near to which the second great cataract of the Nile occurs; but this is the part of the river's course where the fall is greatest, and from Semne to Dale there are about 45 miles of this more rapid fall.

From Dale to New Dongola, a distance of 35 German, or about 168 English miles, only three rapids are marked on Russegger's map--the highest being at Hannek, about 26 English miles below New Dongola. New Dongola being 806 English feet above the sea, and the distance from that place to the rapid of Hannek being 26 miles only, we may with probability estimate the surface of the river at the rapid of Hannek at 780 feet above the sea. Now, Wadi-Halfa being 522 feet, we have a difference of height, between these two last-named places, of 258 feet; and the length of the river's course between them being 236 miles, we have an average fall of 13·12 inches in a mile; that is, in the part of the river's course where nine rapids occur, in the provinces of Batn-el-Hadjar, Sukkot, and Dar-el-Mahass, where the river flows over granite and other plutonic rocks; gneiss, mica-schist, and other hard rocks, which Russegger considers to be metamorphic. But between Semne and the head of the second cataract at Wadi-Halfa, there is not a continuous rapid stream; for Hoskins says, that about two miles above that cataract, the river has a width of a third of a mile, and, when he passed it the water was scarcely ruffled.[60]

Footnote 60: Travels in Ethiopia, p. 272.

From the rapid of Hannek to Abu Hammed, the distance is 329 English miles, and the difference of altitude is 246 English feet. We have thus an average fall in that distance of 9·00 inches in a mile.

Thus, in the 776 miles between Abu Hammed and Philæ, we have an average fall of the Nile

Of 9·00 inches in a mile, for a distance of 329 miles. Of 13·12 ......... ......... 236 ... Of 5·30 ......... ......... 96 ... Of 12·00 ......... ......... 115 ...

_Of the Breadth, Depth, and Velocity of the Nile, in Nubia._

Our information is very scanty respecting the breadth and depth of the river, either at the time of lowest water or during the inundations. About two miles above Philæ, it is stated by Jomard[61] to be 3000 metres, or nearly two English miles wide. At the second cataract, or rapid of Wadi-Halfa, it spreads over a rocky bed of nearly two miles and a-quarter in width (2000 klafter),[62] but contracts above the rapid to a third of a mile. Russegger also states, that the Nile, near Boulak, in Lower Egypt, is 2000 toises, nearly two-and-a-half English miles in breadth, and yet that it is considerably wider in some parts of Southern Nubia; but Burckhardt says, that the bed of the Nile in Nubia is, in general, much narrower than in any part of Egypt. Near Kalabsche, about 30 miles above Philæ, the river runs through a gorge not more than 300 paces wide, and its bed is full of granite blocks. It shortly afterwards again widens for some distance; but near Sialla, 78 miles above Philæ, it is contracted by the sandstone hills on both sides coming so near each other, that the river's bed is again not more than from 250 to 300 paces wide. It is about 600 yards broad about two miles above the second cataract near Wadi-Halfa, but is again very much contracted in the rocky region of Batn-el-Hadjar. At Aulike it is only 200 paces broad.[63]

Footnote 61: Description de l'Égypte.--Separate Memoir entitled, "Description de Syène et des Cataractes."

Footnote 62: Russegger, Bd. ii., 3 Thl. 85.

Footnote 63: Russegger, Bd. ii., 3 Thl. 76.

I have not met with any measurements of the depth of the river in any part of its course in Nubia; but Hoskins describes it as being so shallow at the island of Sais, 327 miles above Philæ, on the 9th of June, which would be before the commencement of the inundation, as only to reach the knees of the camels.[64] Near Derr, about 86 miles below the Cataract of Wadi-Halfa, Norden, in January, found the river so shallow that loaded camels waded through it, and his boat frequently struck the ground. In May, Burckhardt found the river fordable at Kostamne, 53 miles above Philæ; and Parthey states, that between Philæ and the island of Bageh, to the west of it, the river is so shallow before the commencement of the inundation, that it may be waded through.[65] Burckhardt says, that from March to June the Nile-water, in Nubia, is quite limpid.[66] Miss Martineau, who visited Nubia in December and January, speaking of the river above Philæ says, that it "was divided into streamlets and ponds by the black islets. Where it was overshadowed it was dark-gray or deep blue, but when the light caught it rushing between a wooded island and the shore, it was of the clearest green."[67] At the second cataract she describes the river as "dashing and driving among its thousand islets, and then gathering its thousand currents into one, proceeds calmly in its course."[68]

Footnote 64: Travels, p. 257.

Footnote 65: Wanderungen durch das Nilthal, von G. Parthey, Berlin 1840. 378.

Footnote 66: Travels, pp. 9 and 11.

Footnote 67: Eastern Life, i. 10½.

Footnote 68: _Ib._, 144.

Although we have no accurate measurements of the velocity of the Nile in Nubia, we may arrive at an approximate estimate of it by comparing its fall with that of a river well known to us.

I have stated the fall of the Nile in different parts of its course to be 5·30, 9·00, 12·00, and 13·12 inches in a mile. The fall of the Thames from Wallingford to Teddington Lock, where the influence of the tide ends, is as follows:--