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:--
+------------------------------------------------------------------+
| | | | Fall in |
| |Length of | Fall. | inches |
| | course. | |per mile.|
+-----------------------------------+----------+---------+---------+
| |Miles. F. |Feet. in.| |
|From Wallingford to Reading Bridge,| 18·0 | 24·1 | 15·72 |
|From Reading to Henley Bridge, | 9·0 | 19·3 | 25·68 |
|From Henley to Marlow Bridge, | 9·0 | 12·2 | 16·20 |
|From Marlow to Maidenhead Bridge, | 8·0 | 15·1 | 22·32 |
|From Maidenhead to Windsor Bridge, | 7·0 | 13·6 | 23·16 |
|From Windsor to Staines Bridge, | 8·0 | 15·8 | 23·52 |
|From Staines to Chertsey Bridge, | 4·6 | 6·6 | 17·28 |
|From Chertsey to Teddington Lock, | 13·6 | 19·8 | 17·40 |
| +----------+---------+---------+
| | 77·4 | 125·11 | |
+------------------------------------------------------------------+
"In general, the velocity may be estimated at from half-a-mile to two
miles and three-quarters per hour; but the mean velocity may be
reckoned at two miles per hour. In the year 1794, the late Mr Rennie
found the velocity of the Thames at Windsor two miles and a half per
hour."[69]
Footnote 69: Rennie, Report on Hydraulics, in the Fourth Report
of the British Association for the Advancement of Science, 1834,
p. 487.
It will thus be seen that the velocity of the Nile is probably greatly
inferior to that of the Thames; for it appears that, except during the
inundation, for more than half the year the depth is inconsiderable.
The average fall when greatest, that is, including the province of
Batn-el-Hadjar, where the rapids chiefly occur, is considerably less
than that of any part of the above course of the Thames; so that there
must be long intervals between the rapids where the fall must be far
less than 13 inches in a mile. The breadth of the Nile is vastly
greater; but supposing the depth of the water to be the same as that
of the Thames, on account of the friction of the bed, the greater
breadth would add very little to the velocity. If we assume the
average depth of the Thames in the above distance to be 5 feet, and
that it flows with an average velocity of 2 miles in an hour, and if
we assume the average depth of the Nile in that part of its course
where the fall is 13·12 inches to be 10 feet, when not swollen by the
rise, the velocity would be 2 miles nearly in an hour,[70] if the
fall were equal to that of the Thames. We shall probably come near the
truth, by assuming the velocity of the Nile on this part at 2 miles in
an hour. That it must be considerably less in the other divisions of
the course I have named, and especially in that part immediately below
the second cataract, where the average fall is only 5·30 inches for a
distance of 96 miles, is quite evident.
Footnote 70: I state this on the authority of my friend, W.
Hopkins, Esq., of Cambridge.
The power of a river to abrade the soil over which it flows, so far as
water is by itself capable of doing so, must depend upon its volume
and velocity, and the degree of hardness of the material acted upon.
The power is increased when the water has force enough to transport
hard substances. But even transported gravel has little action on the
rocks with which it comes in contact, when it is free to move in
running water, unless the fall be considerable, and, consequently, the
velocity and force of the stream great. When stones are firmly set in
moving ice, they then acquire a great erosive power, cutting and
wearing down the rocks they are forcibly rubbed against; but this
condition never obtains in Lower Nubia, as ice is unknown there.
_Geological Structure of Lower Nubia._
One kind only of regularly stratified rock occurs in the 776 miles
from Abu Hammed to Philæ; viz. a silicious sandstone, similar to that
which occurs to a great extent on both sides of the Nile in Upper
Egypt, and which Russegger, after a very careful examination of it
there, considers to be an equivalent of the greensand of the
cretaceous rocks of Europe. The tertiary nummulite limestone, so
abundant in Egypt, has not hitherto been met with in Nubia.
The Nile flows over this sandstone for nearly 426 miles of the entire
distance, but not continuously. At Abu Hammed, it flows over granitic
rocks, and these continue from that place for about 120 miles. There
is then about 215 miles of the sandstone, which is succeeded by
igneous and metamorphic rocks, that continue for 195 miles without any
interruption, except a narrow stripe of sandstone of about 15 miles
near Amara. It is in this region of hard igneous rocks that nearly all
the rapids occur, between that of Hannek and the great or second
cataract at Wadi-Halfa. From the latter place there is sandstone
throughout a distance of about 196 miles, and then commences the
granitic region of the Cataract of Assuan, through which the Nile
flows about 35 miles. Thus we have about 350 miles of igneous and
metamorphic rocks, and about 426 of sandstone.
The general hard nature of the igneous and metamorphic rocks, over
which the Nile flows for about 155 miles above Semne, and for about 40
immediately below it, will be recognised by my naming some of the
varieties described by Russegger, viz. granites of various kinds,
often penetrated by greenstone dykes; sienite, diorite, and felspar
porphyries; gneiss, and clay slate, penetrated by numerous quartz
veins.
The siliceous sandstone is very uniform in its character; and in
Nubia, as in Egypt, the only organic bodies which it has as yet been
found to contain, are silicified stems of wood. Occasionally, as in
the neighbourhood of Korusko, interstratified beds of marly clay are
met with.[71]
Footnote 71: Russegger, Bd. ii., 1 Thl. 569 to 584.
When, therefore, we take into account the hard nature of the siliceous
sandstone, the durability of which is shewn by the very ancient
monuments of Egypt and Nubia, that are formed of it, and the still
greater hardness of the granites and other crystalline rocks, it is
manifest that the wearing action of a river flowing over so gentle a
fall, can scarcely be appreciable. If the occasional beds of marly
clay occur in the bank of the river, they may be washed out, and
blocks of the superincumbent sandstones may fall down; but such an
operation would have a tendency to raise rather than deepen the bed of
the river at those places; unless the transporting power of the stream
were far greater than can exist with so moderate a fall, especially in
that part of the river below Semne, where, for 96 miles, it is not
more than 5·3 inches, and for 115 miles below that, not more than 12
inches in a mile. Even if we suppose the river to have power to tear
up its bed for some distance above Semne and below it, as far as the
rapid of Wadi-Halfa, it is evident that the materials brought down
would be deposited, except the finest particles, in that tranquil run
of 96 miles, which may be almost compared to a canal. The drains in
Lincolnshire are inclined 5 inches to a mile.[72] When the annual
inundations commence, the water of the Nile comes down the rapid at
Assuan of a reddish colour, loaded with sand and mud only; whatever
detrital matter of a larger and heavier kind the Nile may have brought
with it, is deposited before it reaches that point.
Footnote 72: Rennie, Report cited above, p. 422.
From all these considerations, therefore, I come to the conclusion,
that the bed of the Nile cannot have been excavated, as Professor
Lepsius supposes, since the date of the sculptured marks on the rock
at Semne. He says, "Es lässt sich kaum eine andere Ursache für das
bedentende Fallen des Nils denken, als ein Answaschen und Aushölen
_der Katakomben_." By the word _Katakomben_ he can only mean natural
caverns in the rock; but such caverns are rarely, if ever, met with in
sandstones, and only occasionally in limestones. If the course of the
Nile were over limestone instead of sandstone, we could not for a
moment entertain the idea of a succession of caverns for 200 miles
beneath its bed, sometimes two miles in width, the roofs of which were
to fall in; and where the igneous rocks prevail, this explanation is
wholly inapplicable.
But besides the objections arising from the nature of the rocks, and
the inconsiderable fall of the river, there is still another
difficulty to overcome. It is to be borne in mind, that this lowering
of the bed of the Nile, from Semne to Assuan, is supposed to have
taken place within the last 4000 years. Between the first cataract at
Assuan and the second at Wadi-Halfa, there are numerous remains of
temples on both banks of the Nile, some of very great antiquity. "From
Wadi-Halfa to Philæ," says Parthey, "there is a vast number of
Egyptian monuments, almost all on the left bank of the river, and so
near the water that most of them are in immediate contact with
it."[73] We may rest assured that the builders of these would place
them out of the reach of the highest inundations then known. Although
we have many accurate descriptions of these monuments, the heights of
their foundations above the surface of the river are not often given;
they are, however, mentioned in some instances. I shall describe the
situations of some of these buildings relatively to the present state
of the river's levels, and shall begin with those on the island of
Philæ.
Footnote 73: Parthey, 318.
This island, according to the measurements of General von Prokesh, is
1200 Paris feet (1278 English) in length, and 420 (447) in breadth,
and is composed of granite. Lancrot informs us, that, "à l'époque des
hautes eaux, l'île de Philæ est peu élevé audessus de leur surface,
mais lorqu'elles sont abaissées elle les surpasse de huit metres." It
was formerly surrounded by a quay of masonry, portions of which may be
traced at intervals, and in some places they are still in good
preservation. The south-west part of the island is occupied by
temples. According to Wilkinson, the principal building is a temple of
Isis commenced by Ptolemy Philadelphus, who reigned from 283 to 247
years before Christ; and he adds, that it is evident an ancient
building formerly stood on the site of the present great temple.
Lancrot, in referring to this more ancient building, says:--"Il y a
des preuves certaines d'une antiquité bien plus reculeé encore,
puisque des pierres qui entrent dans la construction de ce même grand
temple, sont des débris de quelque construction antérieure."
Rossellini considers that it was built by Nectanabis. The first king
of Egypt, of the Sebennite dynasty of that name, ascended the throne
374 years B.C., the second and last ceased to reign about 350 years
B.C.[74]
Footnote 74: Russegger, Reison, Bd. ii. 300 and 320. Lancrot,
Description de l'Égypte, Memoire sur l'île de Philæ, 15-58.
Rossellini, I Monumenti dell'Egitto e della Nubia. Monumenti del
Culto, 187. Wilkinson's Thebes and General View of Egypt, 466.
Smith's Dictionary of Greek and Roman Biography, Arts. Ptolemy,
Ph. and Nectanabis.
Rossellini[75] informs us, that on the island of Bageh, opposite to
Philæ, there are the remains of a temple of the time of Amenophis II.,
and a sitting statue of granite representing him. He was a king in the
earlier years of the 18th dynasty, which, according to the Chevalier
Bunsen,[76] began in the year 1638, and ended in 1410 B.C.
Footnote 75: P. 187.
Footnote 76: Egyptens Stelle in der Weltgeschichte.--Drittes
Buch, 122.
GAU,[77] in describing a temple at Debu, about 12 miles above Philæ,
which he visited in January, and consequently during the time of low
water, states that he discovered under the sand, at the edge of the
river, the remains of a terrace leading towards a temple.
Footnote 77: Antiquités de la Nubie, p. 6.
A short distance north of Kalabsche, about 30 miles above Philæ, at
Beil-nalli, Rossellini[78] speaks of a small temple in the following
terms:--"Among the many memorials that still exist of Ramses II., the
most important, in a historical point of view, is a small temple or
grotto excavated in the rock;" and Wilkinson mentions it "as a small
but interesting temple excavated in the rock, of the time of Rameses
II., whom Champellion supposes to be the father of Sesostris or
Rameses the Great."[79] He was the first king of the 19th dynasty,
which began in the year 1409 B.C.[80]
Footnote 78: Tome III., Parte II., p. 6.
Footnote 79: Thebes, &c., p. 482.
Footnote 80: Bunsen, as above.
Gau[81] thus describes a monument at Gerbé Dandour:--"La chaine de
montagnes qui borde le Nil est, dans cet endroit, si approchée du lit
de ce fleuve, qu'il ne reste que très peu d'espace sur la rive. Cet
espace est presque entièrement occupé par le monument, et la rivière,
dans ses débordemens, arrive jusqu'au pied du mur de la terrasse."
Footnote 81: P. 9.
Parthey informs us that the temple of Sebua is about 200 feet distant
from the river, in which distance there are two rows of sphinxes, and
that the road between them, from the temple, ends in wide steps at the
water's edge; and he adds, that Champellion refers this temple to the
time of Rameses the Great.[82]
Footnote 82: Warnderungen, &c., 334.
It thus appears that monuments exist close to the river, some of which
were constructed at least 1400 years before our era; so that taking
the time of Amenemha III. to be, as Professor Lepsius states, 2200
years B.C., the excavation of the bed of the Nile which he supposes to
have taken place, must have been the work, not of 4000 years but of
800. If the erosive power of the river was so active in that time, it
cannot be supposed that it then ceased; it would surely have continued
to deepen the bed during the following 3000 years.
At all events, the buildings on the island of Philæ demonstrate that
the bed of the Nile must have been very much the same as it is now,
2200 years ago; and even a thousand years earlier it must have been
the same, if the foundation of the temple on the island of Begh,
opposite to Philæ, be near the limit of the highest rise of the Nile
of the present time; so that there could be no barrier at the Cataract
of Assuan to dam up the Nile when they were constructed; and thus the
deafening sound of the waterfall recorded by Cicero and Seneca must
still be held to be an exaggeration.
The existence of alluvial soil, apparently of the same kind as that
deposited by the Nile, in situations above the Cataract of Assuan, at
a level considerably above the highest point which the inundations of
the river have reached in modern times, to which allusion is made by
Professor Lepsius, has been noticed by other travellers, and even at
still higher levels than those he mentions. Whether that alluvial soil
be identical with, or only resembles the Nile deposit, would require
to be determined by a close examination, and especially with regard to
organic remains, if any can be found in it. There is no evidence to
shew that it was deposited during the historical period, and it may be
an evidence of a depression and subsequent elevation of the land
antecedent to that period. It may not be of fresh-water origin, but
the clay and sand, or till, left by a drift while the land was under
the sea. For remote as is the antiquity of Nubia and Egypt, in
relation to the existence of the human race, it appears to be of very
modern formation in geological time. The greater part of Lower Egypt,
probably all the Delta, is of post-pliocene age, and even late in that
age; and the very granite of the Cataract of Assuan, that of which the
oldest monuments in Egypt are formed, and which, in the earlier days
of geology, was looked upon as the very type of the rock on which the
oldest strata of the earth were founded, is said to have burst forth
during the later tertiary period. We learn from Russegger, that the
low land which lies between the Mediterranean and the range of hills
that extends from Cairo to the Red Sea at Suez, and of which hills a
nummulite limestone constitutes a great part, is composed of a
sandstone which he calls a "Meeresdiluvium," a marine diluvial
formation, and considers to be of an age younger than that of the
sub-appennines.[83] This sandstone he found associated with the
granite above Assuan, and covering the cretaceous sandstone far into
Nubia. It appears, therefore, that, in the later ages of the tertiary
period, this north-eastern part of Africa must have been submerged,
and that very energetic plutonic action was going forward in the then
bed of the sea. The remarkable fact of the granite bursting through
this modern sandstone is thus described by Russegger:--
"We arrived at a plateau of the Arabian Chain south-east of
Assuan. It is about 200 feet above the bed of the Nile, and
consists of the lower and upper sandstone, which are penetrated by
innumerable granite cones from 20 to 100 feet in height, arranged
over the plateau in parallel lines, very much resembling volcanic
cones rising from a great cleft. The sandstone is totally altered
in texture near the granite, and has all the appearance as if it
had been exposed to a great heat. 'I cannot refrain,' he says,
'from supposing that the granite must have burst, like a volcanic
product, through long wide rents in the sandstone, and that, in
this way, the conical hills were formed.'"[84]
Footnote 83: Reisen, Bd. I., s. 273.
Footnote 84: Id., Bd. II., I. Thl. s. 328.
An eruption of a true granite during the period of the sub-appennine
formations, one possessing the same mineral structure as that we
know to have been erupted during the period of the palæozoic rocks,
would be a fact of so extraordinary a kind, that its age would
require to be established on the clearest evidence, and especially
by that of organic remains in the sandstone.
Having thus ventured--I trust without any want of the respect due to
so eminent a person--to reject the hypothesis proposed by Professor
Lepsius for the high levels of the Nile at Semne, indicated by the
sculptured marks he discovered, it may perhaps be expected that I
should offer another more probable explanation. If in some narrow
gorge of the river below Semne, a place had been described by any
traveller, where, from the nature of the banks, a great landslip, or
even an artificial dam, could have raised the bed to an adequate
height; that is, proportionate to the fall of the river, as it was
more distant from Semne, a bar that, in the course of a few
centuries, might have been gradually washed away, I might have
ventured to suggest such a solution of the problem. But without any
information of the existence of such a contraction of the river's
channel, or any exact knowledge of the natural outlets and dams to
running water along the 250 miles of the Nile Valley, from Semne to
Assuan, it would be idle to offer even a conjecture. These marks are
unquestionably very difficult to account for, in the present
imperfect state of our knowledge of the structure of that portion of
the Nile Valley; and any competent geologist, well versed in the
questions of physical structure involved, who may hereafter visit
Nubia, would have a very interesting occupation in endeavouring to
solve the difficulty.
_7th April 1850._
[Illustration: _Marks of the Levels of the Nile near the Cataracts of
Semne in the time of King Amenemha III. (Moeris) about 2200 Years B.C.
compared with the present levels._]
_On the Salmon Tribe (Salmonidæ.)_
So long as the family _Salmonidæ_ remains circumscribed as it was
established by Cuvier, it seems to be a type almost universally
diffused over the globe, occurring equally in the sea and in
fresh-water, so that we are left almost without a clue to its natural
relations to the surrounding world. Joh. Muller, working out some
suggestions of Prince Canino, and introducing among them more precise
anatomical characters, had no sooner subdivided the old family of
_Salmonidæ_ into his _Salmonidæ_, _Characini_, and _Scopelini_, than
light immediately spread over this field. Limited now to such fishes
as, in addition to the mere general character of former _Salmonidæ_,
have a false gill on the inner surface of the operculum, the
_Salmonidæ_ appeared at once as fishes peculiar to the northern
temperate region, occurring in immense numbers all around the Arctic
Sea, and running regularly up the rivers at certain seasons of the
year to deposit their spawn, while some live permanently in fresh
water. We have thus in the true _Salmonidæ_ actually a northern family
of fishes, which, when found in more temperate regions, occurs there
in clear mountain rivers, sometimes very high above the level of the
sea, near the limits of perpetual snow, or in deep, cold lakes. That
this family is adapted to the cold regions is most remarkably
exemplified by the fact that they all spawn late in the season, at the
approach of autumn or winter, when frost or snow has reduced the
temperature of the water in which they live nearly to its lowest
natural point. The embryos grow within the egg very slowly for about
two months before they are hatched; while fecundated eggs of some
other families which spawn in spring and summer, give birth to young
fishes a few days after they are laid. The _Salmonidæ_, on the
contrary, are born at an epoch when the waters are generally frozen
up; that is at a period _when the maximum of temperature is at the
bottom of the water_, where the eggs and young salmons remain among
gravel, surrounded by a medium which scarcely ever rises above thirty
or forty degrees.
It is plain from these statements, and from what we know otherwise of
the habits of this family, that there is no one upon the globe living
under more uniform circumstances, and nevertheless the species are
extremely diversified, and we find peculiar ones in all parts of the
world, where the family occurs at all. Thus we find in Lake Superior
species which do not exist in the course of the Mackenzie or
Saskatchewan, and _vice versa_; others in the Columbia river which
differ from those of the Lena, Obi, and Yenisei, while Europe again
has its peculiar forms.