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as the lagoons of Venice, were gradually walled off from the Adriatic, the Adige and the Brenta now find channels parallel with that of the Po; and the waters of these streams mingle only in the Adriatic. Thus, while Venice may be said, from a geological point of view, to be situated on the delta formation of the Po, it is the action of the Brenta which is now filling her lagoons, and threatening to convert the most picturesque of Italian cities into an inland town. The whole coast from Trieste to Ancona may be regarded as the actual boundary line of a geological delta, in the middle of the sweeping curve formed by the base of which the present mouths of the Po are protruding their active formation, far in advance of the cordons of the two lagoon systems before mentioned. The lido, or cordon of sand bounding the Venetian lagoons, is pierced with deep water openings, or foci, which have owed their maintenance, from the date of the foundation of Venice in 1104, mainly to the fact that the ebb of the faint tide of the Adriatic lasts for only about a sixth part of the time of the flow. Thus a force of scour is attained, to which we have no exact parallel in the cases of the Rhone, the Tiber, or the Nile. The rise of ordinary spring tides does not exceed 2.8 feet. When counteracted by a north wind the flow is less than 14 inches in rise; aided by the scirocco, it has been known to attain a height of 4:3 feet.
It is the more necessary to collect due materials for forming a clear opinion of the action of the rivers in the vicinity of Venice, from the fact that M. Lenthéric attempts to establish an exact parallel between the littoral apparatus of this portion of the Adriatic and that which exists at Port Said. The ability shown by this writer in his examination of the delta of the Rhone, and in his description of the dead cities of the Gulf of Lyons, is such as to give weight to his remarks on any similar district. It is therefore desirable to note the very contrary conditions which prevail in the Venetian lagoons and in the Nilotic basin.
The rainfall descending on the southward versant of the Carnic Alps makes its way into the upper portion of the Adriatic, and sweeps the Gulf of Venice with an appreciable southward current. The sands and mud brought down by the Tagliamento, the Piave, and other streams, are thus partially carried towards Ancona. During the scirocco, which blows with great fury in the gulf, the alluvial matter is thrown upon the cordon. So far, however, has this influence been from permanently widening the Lido (which is only 350 metres in ineau breadth), that it has been found necessary to face this outer barrier with stone, protected by groins or ribs run out to the sea, for a length of four miles between Lido and Malamocco. These two entrances, thus defended, and the two smaller foci or openings of Foggia, Tre Porti, and the Piave, admit the tide when raised by the scirocco; and being aided by dredging, maintain an ample scour. The waters of the Brenta, which are full of solid material, were diverted into a canal, furnished with sluices, and by this means the silting up of the lagoons was for a long time reduced to a minimum. Great contention, however, has arisen among the Italian engineers on this subject; and the importance of the first principle contended for by Rennie and his school, that of a catch water drain for arresting the deposits brought down by flood water, was departed from in 1840, when the Austrian engineers turned the Brenta into the lagoon. Professor Zanon, in the * Rivista Maritima’ for October 1875, argues in favour of this course. But the result has been that over the entire bed of the lagoon, an area of some 50 kilometres by 10, the bottom has been warped up 75 metre since 1840, while the delta has advanced 7 kilometres, and is now within 3 kilometres of Chioggia. The silting up of the bottom alone shows a deposit of 11,000,000 of cubic yards per annum, independently of the growth of the delta.
By departing from the principle that prevention is better than cure, the Italian engineers have thrown away much of the special advantage with which nature had endowed the port of Venice. But even in its present condition it has no such menacing a foe to dread as exists in the case of Port Said, where a strong littoral current sweeps not from but towards the head of the Levant, bearing with it as much of the enormous mass of the annual deposit of the Nile as is not now disposed of in prolongation of the delta, or in raising the sea bottom between the Rosetta mouth and the Pelusiac Bay. This travelling mass, on reaching the shore of Syria, is partly blown from the margin of the sea, and advances, in desolating dunes, over the once celebrated gardens of Jaffa, as well as over the now barren isthmus. There is no scour from Lake Menzaleh or from Port Said, and all that can be done is to keep up a continuous dredging, the amount of which has risen from 161,000 cubic yards in 1871 to 937,000 cubic yards in 1875. Sir Henry Rawlinson, in his address to the Royal Geographical Society on May 22, 1876, refers to the observations made by Staff-Commander Millard, in February and March 1875, on the littoral between Port Said and the Damietta mouth of the Nile. He refers to the gradual shoaling of the Bay of Pelusium, of which Colonel Stokes has given very instructive details. The currents are found to be mainly dependent on the wind, the prevailing direction of which is north-westerly, as shown on the chart prepared by Admiral Spratt. The only positive contribution to our previous knowledge of the subject contained in Sir Henry Rawlinson's speech are the statements that the line of strongest current is that bordering on the • Damietta mouth of the Nile and the projecting coast east of • Port Said,' and that the coast-line between these localities was found to have advanced considerably seaward, in some • places nearly to the extent of three-quarters of a mile,' since the date of the survey made by Captain Mansell, R.N., in 1856. It is very possible to understand how the growth of the Nile delta, when it has passed beyond the shelter of Aboukir Point, may have been reduced from a secular average of more than 20 yards per annum to a fifth or a sixth of that rate of increase, if we find that the material brought to the mouth of the river is swept towards the Syrian shore with such energy as to cause a seaward growth of 52 yards per annum of the shore of the Pelusiac Bay.
The most valuable contribution, however, which has been made to our positive knowledge of the deposits of the Nile is a measurement of the volume of the river, and of the proportion of matter held in solution and in suspension by its water, which has been made by Mr. Fowler, C.E., in the capacity of engineer-in-chief to the Khedive. Mr. Fowler has favoured us with abstracts of measurements taken when the river stood at different heights, as measured on the nilometer. During a period of sixteen years daily observations have been thus recorded; and the mean annual volume has been calculated for a year when the Nile attains the mean height of 6.87 metres in flood. The lowest tide included in the observations was 5.87 metres (in 1868); the highest 8.48 metres (in 1874). Analyses of the solid material contained in the water were made for Mr. Fowler every month during the year 1874 by the late Dr. Letheby.
The annual discharge of the Nile, on these data, amounts to ninety thousand seven hundred and sixty-eight millions of tons of water. More than two-thirds of this large volume is brought down during the watery tetrameny of the ancient Egyptian year, containing the months Mesori, Thoth, Paophi, and Athyr (in the fixed, not the vague, year), and nearly corresponding to our own August, September, October and November. In October the flow amounts to 19 milliards of tons. In June it is rather less than 14 milliards of tons. The importance of a knowledge of this variation of volume is due to the fact that the quantity of solid matter brought down by the High Nile is far larger in proportion than is the case when the river is low. The quantity of matter in suspension, in a given quantity of water, is four times as great in August as it is in May. The total estimate of solid matter, both in solution and suspension, brought down in the year is 62 millions of tons. But Mr. Fowler remarks that, as the water analysed was taken from the surface of the river, the results of analysis are far below the real proportion of solid matter. Professional experience leads him to the inference that the bulk of wet material actually deposited must be fully five times that of the solids obtained by chemical analysis.
Experience at the Cairo waterworks has shown that the solids deposited in a few hours by High Nile water amount to an inch in depth for 10 feet of water, or go part of the bulk. It is long since Mr. Shaw gave exactly the same proportion, as the result of experiment. If only two-thirds of this proportion be taken for the flow of the four months of High Nile alone, the result will be equal to the above estimate of five times the deposit estimated from Dr. Letheby's analysis. Thus, from two independent modes of investigation, it results that the minimum quantity of solid matter annually brought down by the Nile amounts to at least 300 millions of tons. If we attribute to this matter the specific gravity assigned by Professor Rankine to mud (which is intermediate between that of dry and of damp sand), we have a quantity of 240 millions of cube yards of annual deposit.
The waters of the Nile may be distinguished by their colour, at the time of inundation, for more than 10 leagues after their entrance into the sea. The soundings taken by Admiral Spratt, R.N., off the coast of Africa, from Aboukir Bay to El Arish, give depths of from 14 to 20 fathoms at about 20 miles from the shore. We may, therefore, consider the deposits from the Nile to form a submarine hill, or sloping surface, from low-water level to the depths above indicated. If we take a mean depth of 10 fathoms, or 60 feet, as a vertical dimension, we find that the annual deposit of the Nile will cover an area of very nearly four square miles to that depth. If we double the estimate of depth we, of course, shall halve the estimate of area. It thus may be reduced to a mere matter of figures to show that the greater part of the superficies of Egypt to the north of the ancient site of Memphis, must have been raised above the level of the Mediterranean by the deposits of the Nile since the historic date of the founding of that city. The
statement of Herodotus to that effect is thus fully verified by the measurements of Mr. Fowler.
At the time of the founding of Memphis, according to the statement recorded by the great historian,' except the Theban • nomos, all Egypt was marsh, and none of those parts which
now exist below Lake Maris were above water. The area of the delta itself, between the two existing streams forming the Damietta and Rosetta mouths, is stated at something under 2,000 square miles. But the area indicated by Herodotus amounts to at least four times that dimension, as fairly as it is possible to compute from the irregularities of the actual coast and internal lines. M. Lenthéric makes it amount to 2,300,000 hectares. We shall find good reason to conclude that in the time of Herodotus the outlines of the coast occupied a position intermediate between that maintained in the time of Menes and that which is represented on our last hydrographic survey.
The earliest Egyptian literature yet deciphered speaks of Memphis as a city. The hieroglyphic characteristic is a pyramid; and the name in the inscriptions is read by Dr. Birch as
the city of the Mennefer pyramid,' or pyramids. The word 'men' means a port; although when it is used in that sense, it is usually accompanied by a determinative not employed in writing the name of Memphis. The meaning of the name men • nofre may be fairly illustrated by the more modern names of Havre de Grace, or Portobello, or Newhaven.
Indeed, the foundation of a city at or near to the northern limit of the terra firma of Egypt suggests the establishment of a port, especially as the king to whom the choice of the site is attributed had his capital at Abydos. The hills now rising above the sand in the parallel of Memphis and of Suez, and the position of the pyramids, agree with the hypothesis that, at the early date in question, the statement made to Herodotus was accurately true, and that only marsh and occasional islets then presented any barrier between the Mediterranean and the Arabian Gulf.
Thus Herodotus is fully borne out in his assertion that the Egypt to which the Greeks of his time were in the habit of navigating was altogether made ground, and the gift of the river. If we understand him aright, he seems to intimate that a distance of seven days' sail from the sea to the vicinity of Lake Mæris, added to three days' sail further up the Nile, marked the extension of the Nile-formed land in his own time. There has been some difficulty in deciding on the actual distances which it was intended to define. He reckons in schæni,