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Nature
(Thursday, November 4, 1869)

Letters to the editor,   p. 24


Page 24


NA TURE
[N7Vov. 4, I 869.
  Thus, during the Triassic epoch, extensive dry land seems
to have existed in North America, Western and Central
Europe, Eastern Europe, Central India, and South Africa,
as it does now; and, throughout this vast area, the
Dinosauria-the links between reptiles and birds-seem
to have been represented by not fewer, probably by many
more, than nine or ten distinct genera.
  I hope, shortly, to have the honour of placing the details
of the researches into the structure and distribution of the
Dinosauria, in which I have been engaged for the last two
years, and of which the above notice is one of the results,
before the Geological Society.
                                           T. H. HUXLEY
            LETTERS TO THE EDITOR
[7he Editor does not hold himself responsiblefor opinions expressed
                    by his Correspondents.]
                    The Suez Canal
  THE all-engrossing topic of the day is the Suez Canal, about
which some diversities of opinion still exist. As for many years back
I have had my attention particularly drawn to some of the chief
matters in dispute, having been engaged on the largest irrigation
works in India, I venture to trouble you with the following
remarks.
  Engineering science and indomitable energy have, in the case
of the Suez Canal, overcome difficulties which at one time
were considered insurmountable; but even up to the present
moment doubts still exist, and some fear that the whole scheme
may yet prove a failure, owing to the debris of the Nile travelling
eastward transported by the currents of air and water. That
-we can overcome the former is, in my opinion, beyond all doubt;
for it is found that whenever an irrigation channel is run
out from the Jumna Canal into the great desert of Northern
India, rich vegetation takes the place of arid sand.  And
so in Egypt will irrigation force back the desert; so the
only question is, Can irrigation be carried out on an extensive
scale? And of this also I have no doubt, for the enormous
volume of water which now flows into the sea and is lost, is quite
sufficient to reclaim the whole of the desert.
  It may be asked, Can the water be made to flow over the
desert? And of this I hold that there can also be no doubt.
The very name of the Timsa Lake proves, I think, that the
Nile, or at least a branch of it, flowed eastward, for the word
Timsa signifies crocodile, showing that the water must at one
time have been brackish or fresh, for these creatures could not
have existed in this lake had it been salt as at present. If,
therefore, a portion of the Nile water at one time flowed eastward,
there can be no great engineering difficulty to make it do so again;
and I am almost inclined to think that it would have been better
to have made the canal a fresh-water one, for it is only by vegeta-
tion, the produce of irrigation, that the desert can be kept under
control. Other advantages may be cited, such as cleaning the
bottom of ships by bringing them into fresh water, and the preven-
tion of any of the disturbed and very muddy waters along the
Mediterranean coast getting admission into the canal; for by
keeping the water in the canal at a higher level than that of
the sea at both ends there could only be an outflow. So all
the water wasted would be expended on lockage.
  It may be objected that the fresh-water canal would get silted
up by the muddy waters of the Nile; but could not this Timsa
Lake be used as a silt-trap ? I do not mean to say, that the present
canal will be a failure because it has not been made a fresh-water
one; but what I do think is, that possibly in the end a fresh-water
canal would have been best and perhaps cheapest, as the dredging
of the canal might have been much reduced, * as the water could
have been kept at a higher level in the canal.
  The great difficulty, however, to contend against, appears to
me to be to keep a deep-water channel at the Mediterranean end
of the Canal; and what drew my attention to this more than a
dozen years ago, was the fact that the harbour of Alexandria does
* I observe that, in a discussion at the Civil Engineers Institution, the
total excavation of the Suez Canal is stated to be 7oo0o,ooo cubic metres.
The excavation of the Ganges Canal was 2,547,000,ooo cubic feet, or a little
over 70,000,000 metres; but this latter does not include some 3,000 miles
of
distribution channels.
not get silted up. Some have supposed that the subsidence of the
delta accounts for this, and that the small advance of the land on
the sea in this direction is owing to a constant sinking of the
land. In my opinion a very different cause can be assigned:
Nature here is working by a very different agency, namely,
the current in the Mediterranean which flows eastward all along
the African coast, and transports the debris of the Nile, depositing
it all along the western portion of the Mediterranean.  The
fact of the Timsa Lake being at one time fresh or brackish, goes
to support this view; so the only question is, Will the cost of
continuous dredging be so excessive that the Canal will become
a financial failure? On this point I cannot venture to give an
opinion, as I have no data, but I think this difficulty may be
met by forcing this easterly current to aid in keeping the mouth
of the Canal clear of silt deposits.
  What aids this current to transport the earthy matter is the
beat of the sea always stirring the mud and sand up-on the coast,
and enabling the water to hold a large proportion of matter in
suspension, and even to transport heavy matter.'
  The proportion of earthy matter a short distance out to sea
is comparatively little, so the great object appears to me to
prevent the agitated water travelling as it does at present, and this
can be done by arranging the breakwaters somewhat as shown
in this diagram.
       ME D / T E R R A N        E A N S E A
C
PRE VAILI NC
C URENT
* -t1_I -
r//tt /
A/     /
11 0
.4
D
  The breakwater AB is intended to prevent the very muddy
water travelling along the coast, and the point A should extend
well out into deep water. The breakwater CD is to direct the
comparatively pure water where the sea is deep to pass across the
mouth of the canal; and by the funnel-mouthed shape thus given,
the velocity at D will be increased, and thus keep deep water at
the head of the canal. Some may say that the expense will be
enormous, and that it will have to be year after year extended.
But, in reply to this, I say that deltas do not extend out into the
sea at so rapid a rate as some suppose; and that the formation
of a delta takes several thousands of years to accomplish,
so that in this very delta, the advance is hardly perceptible;
and that a sinking of the land has been brought forward, to account
for the very slow progress made; while, ini fact, Nature has at
present a power at work which is quite sufficient to explain the
reason why so little advance is made on the sea during the his-
toric period (see my paper on the Delta of the Irrawaddy,
read before the Royal Society of Edinburgh in i857).
  In conclusion, I have no doubt this Suez Canal will have many
ready to abuse it and say it is a total failure, as has been said of the
Ganges Canal; but like the latter work, which last year saved
some three million human beings from starvation, so will this
canal, I have little doubt, outlive the abuse, and become one of
the greatest blessings to the civilised world.
                  T. LOGIN, C. E., late of the Ganges Canal.
  London, Oct. 29, 1869.
  ' At Felixstowe, last March, during a gale of wind, I watched a mass of
brickwork, some eighteen inches square and about six inches thick, moved
along the coast by the action of the waves, which were in an oblique dire
titan to the coast, and no doubt the same takes place along the mouths of
the
Nile. By a sample I took of this agitated Mater, I found it contained 0o7375
per cent. of its weight of small pebbles, sand, and mud. This sample was
taken at a height of nearly ten feet above the sea, and was got by catching
the spray of the sea as it was falling.
kl
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