The Isthmus of Suez Question

by Ferdinand de Lesseps

The numerous transverse sections taken with the levelling of 1847, enable us to ascertain approximately the superfice of the Bitter Lakes at the water line. This superfice is about 330,000,000 square metres. If, then, the action of the tide, which brings two metres of moving water, be admitted into these lakes, a disposable volume of 660,000,000 cubic metres of water would be accumulated, and which might be raised to 800,000,000 by adding Lake Timsah and the retaining basins at Suez and Pelusium to these immense reservoirs.

Before pointing out the various directions of the adopted track, it appears necessary to arrive at a fixed opinion as to the formation of the Isthmus and of the downs by which it is partly covered, and also as to the accumulations of sand which exist both on the coast of Pelusium and at the bottom of the Gulf of Suez; for it is from the explanation of these phenomena that we shall start in our justification of the arrangements of the direct track in general and in detail.

By attentively observing what is passing before our eyes at the present time, in respect of the destruction and recomposition of continuity, we may come to an exact conclusion regarding the laws which operated towards the first ages of the world in the formation of alluvial lands.

Let us first examine what is going on in the English Channel; for this narrow sea having a large number of ports both on the French and English coasts, has on that account been the object of numerous observations by engineers.

The first well recognised fact is the destruction of the coast from the point of Barfleur as far as the Somme, a distance of 338 kilometres; and on the other side of the channel, from the Isle of Wight to Dover, a distance of 250 kilometres. This action is produced by the alternation of frost and thaw, by dry and moist winds, and by the saline evaporation of the sea. The abrasion observed on the coast of Calvados is an average of 0 met., 25, per ann. and on the coasts of Normandy and England 0 met., 30. The mean height of the cliffs on either side being sixty metres, it follows that the channel swallows up an amount of 10,000,000 cubic metres of earth and stones every year, which must find a place somewhere.

The second fact, equally well established, and which, though opposed to the opinion of the ancients, can no longer leave any doubt on the mind, is, that rivers, with a few rare exceptions,—such as the Loire for instance,—only carry to the sea an extremely thin mud, destined to be lost in the mass of matter held in suspension by the latter; that the sands of rivers do not in general reach the sea, and that the muddy or sandy deposits observed in tidal rivers, are entirely owing to the matters brought by the tide. This discovery has been arrived at as follows.

In making the analysis of the alluvial lands forming the Bay of St. Michael, it was found that the principal substances of their formation are silex and the carbonate of lime; that the nearer the sea is approached, the more the proportion of silex increases; the more it is receded from, the more considerable the proportion of carbonate of lime becomes. Now if the basins of the three rivers which discharge themselves into this bay, the Sée, the Selime and the Couësnon, be examined, they will be found entirely destitute of calcareous substances. It is the same with the coasts of the channel and of Brittany. It cannot, therefore, be either from these rivers or from the coasts that the enormous proportion of silex proceeds which has just been described. If samples are examined with a magnifying glass, commencing with those nearest the sea, and afterwards proceeding farther into the bay, in the first, fragments of shells are perceived quite distinguishable, then these fragments are reduced and become so impalpable, that the best glass will no longer enable us to distinguish the form in the most calcareous portions.

It is, therefore, certain that the calcareous part comes exclusively from the sea, and even from the bottom of the roadstead of Cancale. As for the silex and clay, a part in their deposit may be attributed to the rivers; but it should first be understood how unimportant these three small rivers are, each discharging not more than an average of eight to ten cubic metres of water per second. Farther, if the contributions of the rivers reckoned for anything in the deposits which are made in this locality, clayey or gravelly stratifications would be seen on their banks at the parts where the tide is least felt. Nothing of the kind occurs. The mixture of the calcareous matter, the grains of silex, and the argillaceous atoms is so intimate, that it is evident it could only be made at the very centre of the production of the calcareous matter; that is to say, at the bottom of the sea. If the fluviatile deposit was appreciable, it would counterbalance entirely, or in part, the calcareous overplus in the drift taken from the top of the roadstead, as compared with that taken at the bottom. Far from this being the case, the progression of the calcareous element, which can only come from the sea, is seen in proportion to the elevation of the shores. Finally, if the fluviatile deposit ought to be reckoned for anything, a larger proportion of clay would be seen upon the brink of the Sée, which traverses fissile lands, than in the neighbouring channel of the Couësnon, which traverses lands of a much harder character, furnishing less clay than the fissile ground of the Sée and the Selime. Now, the contrary is the case; the drifts of the neighbouring channel of the Couësnon are more clayey than the others, solely because this channel being more sheltered than the beds of the other two rivers, the muddy matter which the sea always holds so abundantly in suspension, and which it deposits in the basins of ports, can be carried there concurrently with the drifts.

On making the same investigations for the Seine, it was found that the sands transported by this river do not pass Rouen, and that all the accretions that are seen lower down, as far as the flats which are met with at its mouth, are deposits by the sea.

The same results were arrived at for the Scheld.