Chapter XXX: Section 6: , and especially the passages in Ritter s Erdkunde, vol. i., (1)

there referred to.

The tenacity with which the parched soil of Egypt retains the supply of moisture it receives from the Nile is well illustrated by observations of Girard cited by Lombardini from the Memoires de l'Academie des Sciences, t. ii., 1817. Girard dug wells at distances of 3,200, 1,800, and 1,200 metres from the Nile, and after three months of low water in the river, found water in the most remote well, at 4m. 97, in the next at 4m. 23, and in that nearest the bank at 3m. 44 above the surface of the Nile. The fact that the water was highest in the most distant well appears to show that it was derived from the inundation and not, by lateral infiltration, from the river. But water is found beneath the sands at points far above and beyond the reach of the inundations, and can be accounted for only by subterranean percolation from the Nile. At high flood, the hydrostatic pressure on the banks, combined with capillary attribution, sends water to great horizontal distances through the loose soil; at low water the current is reversed, and the moisture received from the river is partly returned, and may often be seen oozing from the banks into the river.--Clot Bey, Apercu sur l'Egypte, i., 128.

Laurent (Memoires sur le Sahara Oriental, pp. 8, 9), in speaking of a river at El-Faid, "which, like all those of the desert, is, most of the time, without water," observes, that many wells are dug in the bed of the river in the dry season, and that the subterranean supply of water thus reached extends itself laterally, at about the same level, at least a kilometre from the river, as water is found by digging to the depth of twelve or fifteen metres at a village situated at that distance from the bank.

Recent experiments, however, have shown that in the case of rivers flowing through thickly peopled regions, and especially where the refuse from industrial establishments is discharged into them, the finely comminuted material received from sewers and factories sometimes clogs up the interstices between the particles of sand and gravel which compose the bed and banks, and the water is consequently confined to the channel and no longer diffuses itself laterally through the adjacent soil. This obstruction of course acts in both directions, according to circumstances. In one case, it prevents the escape of river-water and tends to maintain a full flow of the current; in another it intercepts the supply the river might otherwise receive by infiltration from the land, and thus tends to reduce the volume of the stream. In some instances pits have been sunk along the banks of large rivers and the water which filters into them pumped up to supply aqueducts. This method often succeeds, but where the bed of the stream has been rendered impervious by the discharge of impurities into it, it cannot be depended upon.

The tubular wells generally known as the American wells furnish another proof of the free diffusion and circulation of water through the soil. I do not know the date of the first employment of these tubes in the United States, but as early as 1861, the Chevalier Calandra used wooden tubes for this pose in Piedmont, with complete success. See the interesting pamphlet, Sulla Estrazione delle Acque Sotterrance, by C. Calandra. Torino, 1867.

The most remarkable case of infiltration known to me by personal observation is the occurrence of fresh water in the beach-sand on the eastern side of the Gulf of Akaba, the eastern arm of the Red Sea. If you dig a cavity in the beach near the sea-level, it soon fills with water so fresh as not to be undrinkable, though the sea-water two or three yards from it contains even more than the average quantity of salt. It cannot be maintained that this is sea-water freshed by filtration through a few feet or inches of sand, for salt-water cannot be deprived of its salt by that process. It can only come from the highlands of Arabia, and it would seem that there must exist some large reservoir in the interior to furnish a supply which, in spite of evaporation, holds out for months after the last rains of winter, and perhaps even through the year. I observed the fact in the month of June. See Robinson, Biblical Researches, 1857, vol i., p. 167.

The precipitation in the mountains that border the Red Sea is not known by pluviometric measurement, but the mass of debris brought down the ravines by the torrents proves that their volume must be large. The proportion of surface covered by sand and absorbent earth, in Arabia Petraea and the neighboring countries, is small, and the mountains drain themselves rapidly into the wadies or ravines where the torrents are formed; but the beds of earth and disintegrated rock at the bottom of the valleys are of so loose and porous texture, that a great quantity of water is absorbed in saturating them before a visible current is formed on their surface. In a heavy thunder-storm, accompanied by a deluging rain, which I witnessed at Mount Sinai in the month of May, a large stream of water poured, in an almost continuous cascade, down the steep ravine north of the convent, by which travellers sometimes descend from the plateau between the two peaks, but after reaching the foot of the mountain, it flowed but a few yards before it was swallowed up in the sands.

Fresh-water wells are not unfrequently found upon the borders of ocean beaches. In the dry summer of 1870, drinkable water was procured in many places on the coast of Liguria by digging to the depth of a yard in the beach-sands. Tubular wells reach fresh water at twelve or fifteen feet below the surface on the sandy plains of Cape Cod. In this latter case, the supply is more probably derived directly from precipitation than from lateral infiltration.]

Artesian Wells.

The existence of artesian wells depends upon that of subterranean reservoirs and rivers, and the supply yielded by borings is regulated by the abundance of such sources. The waters of the earth are, in many cases, derived from superficial currents which are seen to pour into chasms opened, as it were, expressly for their reception; and in others, where no apertures in the crust of the earth have been detected, their existence is proved by the fact that artesian wells sometimes bring up from great depths seeds, leaves, and even living fish, which must have been carried down through channels large enough to admit a considerable stream. [Footnote: Charles Martins, Le Sahara, in Revue des Deux Mondes, Sept. 1, 1864, p. 619; Stoppani, Corso di Geologia, i., 281; Desor, Die Sahara, Basel, 1871, pp. 50, 51.] But in general, the sheet and currents of water reached by deep boring appear to be primarily due to infiltration from highlands where the water is first collected in superficial or subterranean reservoirs. By means of channels conforming to the dip of the strata, these reservoirs communicate with the lower basins, and exert upon them a fluid pressure sufficient to raise a column to the surface, whenever an orifice is opened. [Footnote: It is conceivable that in shallow subterranean basins superincumbered mineral strata may rest upon the water and be partly supported by it. In such case the weight of such strata would be an additional, if not the sole, cause of the ascent of the water through the tubes of artesian wells.

The ascent of petroleum in the artesian oil-wells in Pennsylvania, and, in many cases, of salt-water in similar tubes, can hardly be ascribed to hydrostatic pressure, and there is much difficulty in accounting for the rise of water in artesian wells in many parts of the African desert on that principle. Perhaps the elasticity of gases, which probably aids in forcing up petroleum and saline waters, may be, not unfrequently, an agency in causing the flow of water in common artesian borings. It is said that artesian wells lately bored in Chicago, some to the depth of 1,600 feet, raise water to the height of 100 feet above the surface. What is the source of the pressure ] The water delivered by an artesian well is, therefore, often derived from distant sources, and may be wholly unaffected by geographical or meteorological changes in its immediate neighborhood, while the same changes may quite dry up common wells and springs which are fed only by the local infiltration of their own narrow basins.

In most cases, artesian wells have been bored for purely economical or industrial purposes, such as to obtain good water for domestic use or for driving light machinery, to reach saline or other mineral springs, and recently, in America, to open fountains of petroleum or rock-oil. The geographical and geological effects of such abstraction of fluids from the bowels of the earth are too remote and uncertain to be here noticed; [Footnote: Many more or less probable conjectures have been made on this subject but thus far I am not aware that any of the apprehended results have been actually shown to have happened. In an article in the Annales des Ponts et Chaussees for July and August, 1839, p. 131, it was suggested that the sinking of the piers of a bridge at Tours in France was occasioned by the abstraction of water from the earth by artesian wells, and the consequent withdrawal of the mechanical support it had previously given to the strata containing it. A reply to this article will be found in Viollet, Theorie des Puits Artesiens, p. 217.

In some instances the water has rushed up with a force which seemed to threaten the inundation of the neighborhood, and even the washing away of much soil; but in those cases the partial exhaustion of the supply, or the relief of hydrostatic or elastic pressure, has generally produced a diminution of theflow in a short time, and I do not know that any serious evil has everbeen occasioned in this way.

In April, 1866, a case of this sort occurred in boring an artesian well near the church of St. Agnes at Venice. When the drill reached the depth of 160 feet, a jet of mud and water was shot up to the height of 130 feet above the surface, and continued to flow with gradually diminishing force for about eight hours.] but artesian wells have lately been employed in Algeria for a purpose which has even now a substantial, and may hereafter acquire a very great geographical importance. It was observed by many earlier as well as recent travellers in the East, among whom Shaw deserves special mention, that the Libyan desert, bordering upon the cultivated shores of the Mediterranean, appeared in many places to rest upon a subterranean lake at an accessible distance below the surface. The Moors are vaguely said to bore artesian wells down to this reservoir, to obtain water for domestic use and irrigation, and there is evidence that this art was practised in Northern Africa in the Middle Ages. But it had been lost by the modern Moors, and the universal astonishment and incredulity with which the native tribes viewed the operations of the French engineers sent into the desert for that purpose, are a sufficient proof that this mode of reaching the subterranean waters was new to them. They were, however, aware of the existence of water below the sands, and were dexterous in digging wells--square shafts lined with a framework of palm-tree stems--to the level of the sheet. The wells so constructed, though not technically artesian wells, answer the same purpose; for the water rises to the surface and flows over it as from a spring. [Footnote: See a very interesting account of these wells, and of the workmen who clean them out when obstructed by sand brought up with the water, in Laurent's memoir on the artesian wells recently bored by the French Government in the Algerian desert. Mimoire sur le Sahara Oriental, etc., pp. et seqq. Some of the men remained under water from two minutes to two minutes and forty seconds. Several officers are quoted as having observed immersions of three minutes' duration, and M. Berbrugger witnessed ona of six minutes and five seconds and another of five minutes and fifty-five seconds. The shortest of these periods is longer than the best pearl-diver can remain below the surface of salt-water. The wells of the Sahara are from twenty to eighty metres deep.-Desor, Die Sahara, Basel, 1871, p. 43.

The ancient Egyptians were acquainted with the art of boring artesian wells. Ayme, a French engineer in the service of the Pacha of Egypt, found several of these old wells, a few years ago, in the oases. They differed little from modern artesian wells, but were provided with pear-shaped valves of stone for closing them when water was not needed. When freed from the sand and rubbish with which they were choked, they flowed freely and threw up fish large enough for the table. The fish were not blind, as cave-fish often are, but were provided with eyes, and belonged to species common in the Nile. The sand, too, brought up with them resembled that of the bed of that river. Hence it is probable that they were carried to the oases by subterranean channels from the Nile.--Desor, Die Sahara, Basel, 1871, p. 28; Stoppani, Corso di Geologia, i., p. 281. Barth speaks of common wells in Northern Africa from 200 to 360 feet deep.--Reisen in Africa, ii., p. 180.

It is certain that artesian wells have been common in China from a very remote antiquity, and the simple method used by the Chinese--where the drill is raised and let fall by a rope, instead of a rigid rod--has lately been employed in Europe with advantage. Some of the Chinese wells are said to be 3,000 feet deep; that of Neusalzwerk in Silesia is 2,300. A well was bored at St. Louis, in Missouri, a few years ago, to supply a sugar refinery, to the depth of 2,199 feet. This was executed by a private firm in three years, at the expense of only $10,000. Four years since the boring was recommenced in this well and reached a depth of 3,150 feet, but without a satisfactory result. Another artesian well was sunk at Columbus, in Ohio, to the depth of 2,500 feet, but without obtaining the desired supply of water. Perhaps, however, the artesian well of the greatest depth ever executed until very recently, is that bored within the last six or seven years, for the use of an Insane Asylum near St. Louis. This well descends to the depth of three thousand eight hundred and forty-three feet, but the water which it furnishes is small in quantity and of a quality that cannot be used for ordinary domestic purposes. The bore has a diameter of six inches to the depth of 425 feet, and after that it is reduced to four inches. For about three thousand feet the strata penetrated were of carboniferous and magnesian limestone alternating with sandstone. The remainder of the well passes through igneous rock. At St. Louis the Missouri and Mississippi rivers are not more than twenty miles distant from each other, and it is worthy of note that the waters of neither of those two rivers appear to have opened for themselves a considerable subterranean passage through the rocky strata of the peninsula which separates them.

When in boring an artesian well water is not reached at a moderate depth, it is not always certain that it will be found by driving the drill still lower. In certain formations, water diminshes as we descend, and it seems probable that, except in case of caverns and deep fissures, the weight of the superincumbent mineral strata so compresses the underlying ones, at no very great distance below the surface, as to render them impermeable to water and consequently altogether dry. See London Quarterly Journal of Science, No. xvii., Jan., 1868, p. 18, 19.

In the silver mines of Nevada water is scarcely found at depths below 1,000 feet, and at 1,200 feet from the surface the earth is quite dry.--American Annual of Scientific Discovery for 1870, p. 75.

Similar facts are observed in Australia. The Pleasant Creek News writes: "A singular and unaccountable feature in connection with our deep quartz mines is being developed daily, which must surprise those well experienced in mining matters. It is the decrease of water as the greater depths are reached. In the Magdala shaft at 950 ft. the water has decreased to a MINIMUM; in the Crown Cross Reef Company's shaft, at 800 ft., notwithstanding the two reefs recently struck, no extra water has been met with; and in the long drive of the Extended Cross Reef Company, at a depth of over 800 ft., the water is lighter than it was nearer the surface."

Boring has been carried to a great depth at Sperenberg near Berlin, where, in 1871, the drill had descended 5,500 feet below the surface, passing through a stratum of salt for the last 3,200 feet; but the drilling was still in progress, the whole thickness of the salt-bed not having been penetrated.--Aus der Natur, vol. 55, p. 208.

The facts that there are mines extending two miles under the bed of the sea, which are not particularly subject to inconvenience from water, that little water was encountered in the Mt. Cenis tunnel, 3500 feet below the surface, and that at Scarpa, not far from Tivoli, there is an ancient well 1700 feet deep with but eighteen feet of water, may also be cited as proofs that water is not universally diffused at great distances beneath the surface.]

These wells, however, are too few and too scanty in supply to serve any other purposes than the domestic wells of other countries, and it is but recently that the transformation of desert into cultivable land by this means has been seriously attempted. The French Government has bored a large number of artesian wells in the Algerian desert within a few years, and the native sheikhs are beginning to avail themselves of the process. Every well becomes the nucleus of a settlement proportioned to the supply of water, and before the end of the year 1860, several nomade tribes had abandoned their wandering life, established themselves around the wells, and planted more than 30,000 palm trees, besides other perennial vegetables. [Footnote: "In the anticipation of our success at Oum-Thiour, everything had been prepared to take advantage of this new source of wealth without a moment's delay. A division of the tribe of the Selmia, and their sheikh, Aissa ben Sha, laid the foundation of a village as soon as the water flowed, and planted twelve hundred date-palms, renouncing their wandering life to attach themselves to the soil. In this arid spot, life had taken the place of solitude, and presented itself, with its smiling images, to the astonished traveller. Young girls were drawing water at the fountain; the flocks, the great dromedaries with their slow pace, the horses led by the halter, were moving to the watering trough; the hounds and the falcons enlivened the group of party-colored tents, and living voices and animated movement had succeeded to silence and desolation."--Laurent, Memoires sur le Sahara, p. 85.

Between 1856 and 1864 the French engineers had bored 83 wells in the Hodna and the Sahara of the Province of Constantine, yielding, all together, 9,000 gallons a minute, and irrigating more than 125,000 date-palms. Reclus, La Terre, i., p. 110.] The water is found at a small depth, generally from 100 to 200 feet, and though containing too large a proportion of mineral matter to be acceptable to a European palate, it answers well for irrigation, and does not prove unwholesome to the natives.

The most obvious use of artesian wells in the desert at present is that of creating stations for the establishment of military posts and halting-places for the desert traveller; but if the supply of water shall prove adequate for the indefinite extension of the system, it is probably destined to produce a greater geographical transformation than has ever been effected by any scheme of human improvement.

The most striking contrast of landscape scenery that nature brings near together in time or place, is that between the greenery of the tropics, or of a northern summer, and the snowy pall of leafless winter. Next to this in startling novelty of effect, we must rank the sudden transition from the shady and verdant oasis of the desert to the bare and burning party-colored ocean of sand and rock which surrounds it. [Footnote: The variety of hues and tones in the local color of the desert is, I think, one of the phenomena which most surprise and interest a stranger to those regions. In England and the United States, rock is so generally covered with moss or earth, and earth with vegetation, that untravelled Englishmen and Americans are not very familiar with naked rock as a conspicuous element of landscape. Hence, in their conception of a bare cliff or precipice, they hardly ascribe definite color to it, but depict it to their imagination as wearing a neutral tint not assimilable to any of the hues with which nature tinges her atmospheric or paints her organic creations. There are certainly extensive desert ranges, chiefly limestone formations, where the surface is either white, or has weathered down to a dull uniformity of tone which can hardly be called color at all; and there are sand plains and drifting hills of wearisome monotony of tint. But the chemistry of the air, though it may tame the glitter of the limestone to a dusky gray, brings out the green and brown and purple of the igneous rocks, and the white and red and blue and violet and yellow of the sandstone. Many a cliff in Arabia Petraea is as manifold in color as the rainbow, and the veins are so variable in thickness and inclination, so contorted and involved in arrangement, as to bewilder the eye of the spectator like a disk of party-colored glass in rapid evolution.

In the narrower wadies the mirage is not common; but on broad expanses, as at many points between Cairo and Suez, and in Wadi el Araba, it mocks you with lakes and land-locked bays, studded with inlands and fringed with trees, all painted with an illusory truth of representation absolutely indistinguishable from the reality. The checkered earth, too, is canopied with a heaven as variegated as itself. You see, high up in the sky, rosy clouds at noonday, colored probably by reflection from the ruddy mountains, while near the horizon float cumuli of a transparent, ethereal blue, seemingly balled up out of the clear cerulean substance of the firmament, and detached from the heavenly vault, not by color or consistence, but solely by the light and shade of their salient and retreating outlines.] The most sanguine believer in indefinite human progress hardly expects that man's cunning will accomplish the universal fulfilment of the prophecy, "the desert shall blossom as the rose," in its literal sense; but sober geographers have thought the future conversion of the sand plains of Northern Africa into fruitful gardens, by means of artesian wells, not an improbable expectation. They have gone farther, and argued that, if the soil were covered with fields and forests, vegetation would call down moisture from the Libyan sky, and that the showers which are now wasted on the sea, or so often deluge Southern Europe with destructive inundation, would in part be condensed over the arid wastes of Africa, and thus, without further aid from man, bestow abundance on regions which nature seems to have condemned to perpetual desolation.

An equally bold speculation, founded on the well-known fact that the temperature of the earth and of its internal waters increases as we descend beneath the surface, has suggested that artesian wells might supply heat for industrial and domestic purposes, for hot-house cultivation, and even for the local amelioration of climate. The success with which Count Lardarel has employed natural hot springs for the evaporation of water charged with boracic acid, and other fortunate applications of the heat of thermal sources, lend some countenance to the latter project; but both must, for the present, be ranked among the vague possibilities of science, not regarded as probable future triumphs of man over nature.

Artificial Springs

A more plausible and inviting scheme is that of the creation of perennial springs by husbanding rain and snow water, storing it up in artificial reservoirs of earth, and filtering it through purifying strata, in analogy with the operations of nature. The sagacious Palissy--starting from the theory that all springs are primarily derived from precipitation, and reasoning justly on the accumulation and movement of water in the earth--proposed to reduce theory to practice, and to imitate the natural processes by which rain is absorbed by the earth and given out again in running fountains. "When I had long and diligently considered the cause of the springing of natural fountains and the places where they be wont to issue," says he, "I did plainly perceive, at last, that they do proceed and are engendered of nought but the rains. And it is this, look you, which hath moved me to enterprise the gathering together of rain-water after the manner of nature, and the most closely according to her fashion that I am able; and I am well assured that by following the formulary of the Supreme Contriver of fountains, I can make springs, the water whereof shall be as good and pure and clear as of such which be natural." [Footnote: Oeuvres de Palissy, Des Eaux et Fontaines, p. 157.] Palissy discusses the subject of the origin of springs at length and with much ability, dwelling specially on infiltration, and, among other things, thus explains the frequency of springs in mountainous regions: "Having well considered the which, thou mayest plainly see the reason why there be more springs and rivulets proceeding from the mountains than from the rest of the earth; which is for no other cause but that the rocks and mountains do retain the water of the rains like vessels of brass. And the said waters falling upon the said mountains descend continually through the earth, and through crevices, and stop not till they find some place that is bottomed with stone or close and thick rocks; and they rest upon such bottom until they find some channel or other manner of issue, and then they flow out in springs or brooks or rivers, according to the greatness of the reservoirs and of the outlets thereof." [Footnote: Id., p. 166. Palissy's method has recently been tried with good success in various parts of France.]

After a full exposition of his theory, Palissy proceeds to describe his method of creating springs, which is substantially the same as that lately proposed by Babinet in the following terms: "Choose a piece of ground containing four or five acres, with a sandy soil, and with a gentle slope to determine the flow of the water. Along its upper line, dig a trench five or six feet deep and six feet wide. Level the bottom of the trench, and make it impermeable by paving, by macadamizing, by bitumen, or, more simply and cheaply, by a layer of clay. By the side of this trench dig another, and throw the earth from it into the first, and so on until you have rendered the subsoil of the whole parcel impermeable to rain-water. Build a wall along the lower line with an aperture in the middle for the water, and plant fruit or other low trees upon the whole, to shade the ground and check the currents of air which promote evaporation. This will infallibly give you a good spring which will flow without intermission, and supply the wants of a whole hamlet or a large chateau." [Footnote: Babinet, Etudes et Lectures sur les Sciences d'Observation, ii., p. 225. Our author precedes his account of his method with a complaint which most men who indulge in thinking have occasion to repeat many times in the course of their lives. "I will explain to my readers the construction of artificial fountains according to the plan of the famous Bernard de Palissy, who, a hundred and fifty [three hundred] years ago, came and took away from me, a humble academician of the nineteenth century, this discovery which I had taken a great deal of pains to make. It is enough to discourage all invention when one finds plagiarists in the past as well as in the future!" (P. 224.)] Babinet states that the whole amount of precipitation on a reservoir of the proposed area, in the climate of Paris, would be about 13,000 cubic yards, not above one half of which, he thinks, would be lost, and, of course, the other half would remain available to supply the spring. I much doubt whether this expectation would be realized in practice, in its whole extent; for if Babinet is right in supposing that the summer rain is wholly evaporated, the winter rains, being much less in quantity, would hardly suffice to keep the earth saturated and give off so large a surplus. The method of Palissy, though, as I have said, similar in principle to that of Babinet, would be cheaper of execution, and, at the same time, more efficient. He proposes the construction of relatively small filtering receptacles, into which he would conduct the rain falling upon a large area of rocky hillside, or other sloping ground not readily absorbing water. This process would, in all probability, be a very successful, as well as an inexpensive, mode of economizing atmospheric precipitation, and compelling the rain and snow to form perennial fountains at will.

Economizing Precipitation.

The methods suggested by Palissy and by Babinet are of limited application, and designed only to supply a sufficient quantity of water for the domestic use of small villages or large private establishments. Dumas has proposed a much more extensive system for collecting and retaining the whole precipitation in considerable valleys, and storing it in reservoirs, whence it is to be drawn for household and mechanical purposes, for irrigation, and, in short, for all the uses to which the water of natural springs and brooks is applicable. His plan consists in draining both surface and subsoil, by means of conduits differing in construction according to local circumstances, but in the main not unlike those employed in improved agriculture, collecting the water in a central channel, securing its proper filterage, checking its too rapid flow by barriers at convenient points, and finally receiving the whole in spacious, covered reservoirs, from which it may he discharged in a constant flow or at intervals as convenience may dictate. [Footnote: M. G. Dumas, La Science des Fontaines, 1857.]

There is no reasonable doubt that a very wide employment of these various contrivances for economizing and supplying water is practicable, and the expediency of resorting to them is almost purely an economical question. There appears to be no serious reason to apprehend collateral evils from them, and in fact all of them, except artesian wells, are simply indirect methods of returning to the original arrangements of nature, or, in other words, of restoring the fluid circulation of the globe; for when the earth was covered with the forest, perennial springs gushed from the foot of every hill, brooks flowed down the bed of every valley. The partial recovery of the fountains and rivulets which once abundantly watered the face of the agricultural world seems practicable by such means, even without any general replanting of the forests; and the cost of one year's warfare--or in some countries of that armed peace which has been called "Platonic war"--if judiciously expended in a combination of both methods of improvement, would secure, to almost every country that man has exhausted, an amelioration of climate, a renovated fertility of soil, and a general physical improvement, which might almost be characterized as a new creation.

Inundations and Torrents.

In pointing out in a former chapter the evils which have resulted from the too extensive destruction of the forests, I dwelt at some length on the increased violence of river inundations, and especially on the devastations of torrents, in countries improvidently deprived of their woods, and I spoke of the replanting of the forests as probably the most effectual method of preventing the frequent recurrence of disastrous floods. There are many regions where, from the loss of the superficial soil, from financial considerations, and from other special causes, the general restoration of the woods is not, under present circumstances, either possible or desirable. In all inhabited countries, the necessities of agriculture and other considerations of human convenience will always require the occupation of much the largest proportion of the surface for purposes inconsistent with the growth of extensive forests. Even where large plantations are possible and in actual process of execution, many years must elapse before the action of the destructive causes in question can be arrested or perhaps even sensibly mitigated by their influence; and besides, floods will always occur in years of excessive precipitation, whether the surface of the soil be generally cleared or generally wooded. [Footnote: All the arrangements of rural husbandry, and we might say of civilised occupancy of the earth, are such as necessarily to increase the danger and the range of floods by promoting the rapid discharge of the waters of precipitation. Superficial, if not subterranean, drainage is a necessary condition of all agriculture. There is no field which has not some artificial disposition for this purpose, and even the furrows of ploughed land, if the surface is inclined, and especially when it if frozen, serve rather to carry off than to retain water. As Bacquerel has observed, common road and railway ditches are among the most efficient conduits for the discharge of surface-water which man has yet constructed, and of course they are powerful agents in causing river inundations. All these channels are, indeed, necessary for the convenience of man, but this convenience, like every other interference with the order of nature, must often be purchased at a heavy cost.] Physical improvement in this respect, then, cannot be confined to merely preventive measures, but, in countries subject to damage by inundation, means must be contrived to obviate dangers and diminish injuries to which human life and all the works of human industry will occasionally be exposed, in spite of every effort to lessen the frequency of their recurrence by acting directly on the causes that produce them. As every civilized country is, in some degree, subject to inundation by the overflow of rivers, the evil is a familiar one, and needs no general description. In discussing this branch of the subject, therefore, I may confine myself chiefly to the means that have been or may be employed to resist the force and limit the ravages of floods, which, left wholly unrestrained, would not only inflict immense injury upon the material interests of man, but produce geographical revolutions of no little magnitude.

Inundations of 1856 in France.

The month of May, 1856, was remarkable for violent and almost uninterrupted rains, and most of the river-basins of France were inundated to an extraordinary height. In the val-leys of the Loire and its aflluents, about a million of acres, including many towns and villages, were laid under water, and the amount of pecuniary damage was almost incalculable. [Footnote: Champion, Les Inondations en France, iii., p.156, note.] The flood was not less destructive in the valley of the Rhone, and in fact an invasion by a hostile army could hardly have been more disastrous to the inhabitants of the plains than was this terrible deluge. There had been a flood of this latter river in the year 1840, which, for height and quantity of water, was almost as remarkable as that of 1856, but it took place in the month of November, when the crops had all been harvested, and the injury inflicted by it upon agriculturists was, therefore, of a character to be less severely and less immediately felt than the consequences of the inundation of 1856. [Footnote: Notwithstanding this favorable circumstance, the damage done by the inundation of 1840 in the valley of the Rhone was estimated at seventy-two millions of francs.--Champion, Les Inondations en France, iv., p. 124.

Several smaller floods of the Rhone, experienced at a somewhat earlier season of the year in 1846, occasioned a loss of forty-five millions of francs. "What if," says Dumont, "instead of happening in October, that is, between harvest and seedtime, they had occurred before the crops were secured The damage would have been counted by hundreds of millions."--Des Travaux Publics, p. 99, note.]

In the fifteen years between these two great floods, the population and the rural improvements of the river valleys had much increased, common roads, bridges, and railways had been multiplied and extended, telegraph lines had been constructed, all of which shared in the general ruin, and hence greater and more diversified interests were affected by the catastrophe of 1856 than by any former like calamity. The great flood of 1840 had excited the attention and roused the sympathies of the French people, and the subject was invested with new interest by the still more formidable character of the inundations of 1856. It was felt that these scourges had ceased to be a matter of merely local concern, for, although they bore most heavily on those whose homes and fields were situated within the immediate reach of the swelling waters, yet they frequently destroyed harvests valuable enough to be a matter of national interest, endangered the personal security of the population of important political centres, interrupted communication for days and even weeks together on great lines of traffic and travel--thus severing, as it were, all South-western France from the rest of the empire--and finally threatened to produce great and permanent geographical changes. The well-being of the whole commonwealth was seen to be involved in preventing the recurrence and in limiting the range of such devastations. The Government encouraged scientific investigation of the phenomena and their laws. Their causes, their history, their immediate and remote consequences, and the possible safeguards to be employed against them, have been carefully studied by the most eminent physicists, as well as by the ablest theoretical and practical engineers of France. Many hitherto unobserved facts have been collected, many new hypotheses suggested, and many plans, more or less original in character, have been devised for combating the evil; but thus far, the most competent judges are not well agreed as to the mode, or even the possibility, of applying an effectual remedy. I have noticed in the next preceding chapter the recent legislation of France upon the preservation and restoration of the forests, with reference to their utility in subduing torrents and lessening the frequency and diminishing the violence of river inundations. The provisions of those laws are preventive rather than remedial, but most beneficial effects have already been experienced from the measures adopted in pursuance of them, though sufficient time has not yet elapsed for the complete execution of the greater operations of the system.

Basins of Reception.

Destructive inundations of large rivers are seldom, if ever, produced by precipitation within the limits of the principal valley, but almost uniformly by sudden thaws or excessive rains on the mountain ranges where the tributaries take their rise. It is therefore plain that any measures which shall check the flow of surface-waters into the channels of the affluents, or which shall retard the delivery of such waters into the principal stream by its tributaries, will diminish in the same proportion the dangers and the evils of inundation by great rivers. The retention of the surface-waters upon or in the soil can hardly be accomplished except by the methods already mentioned, replanting of forests, and furrowing or terracing. The current of mountain streams can be checked by various methods, among which the most familiar and obvious is the erection of barriers or dams across their channels, at points convenient for forming reservoirs large enough to retain the superfluous waters of great rains and thaws. [Footnote: On the construction of temporary and more permanent barriera to the curreuts of torrents and rivulets, see Marchand, Les Torrents des Alpes, in Recue des Eaux et Forets for October and November, 1871.]

Besides the utility of such basins in preventing floods, the construction of them is recommended by very strong considerations, such as the furnishing of a constant supply of water for agricultural and mechanical purposes, and, also, their value as ponds for breeding and rearing fish, and, perhaps, for cultivating aquatic vegetables. [Footnote: In reference to the utilization of artificial as well as natural reservoirs, see Ackerhof, Die Nutruny der Teiche und Gewasser, Quadlinburg, 1869.]

The objections to the general adoption of the system of reservoirs are these: the expense of their construction and maintenance; the reduction of cultivable area by the amount of surface they must cover; the interruption they would occasion to free communication; the probability that they would soon be filled up with sediment, and the obvious fact that when full of earth, or even water, they would no longer serve their principal purpose; the great danger to which they would expose the country below them in case of the bursting of their barriers; [Footnote: For accounts of damage from the bursting of reservoirs, see Vallee, Memoire sur les Reservoir d'Alimentation des Canaux, Annales des Ponts et Chaussees, 1833, 1er semestre, p.261.

The dam of the reservoir of Puentes in Spain, which was one hundred and sixty feet high, after having discharged its functions for eleven years, burst, in 1802, in consequence of a defect in its foundations, and the eruption of the water destroyed or seriously injured eight hundred houses, and produced damage to the amount of more than a million dollars.--Aynard, Irrigations du Midi d l'Europe, pp. 257-259.] the evil consequences they would occasion by prolonging the flow of inundations in proportion as they diminished their height; the injurious effects it is supposed they would produce upon the salubrity of the neighbouring districts; and, lastly, the alleged impossibility of constructing artificial basins sufficient in capacity to prevent, or in any considerable measure to mitigate, the evils they are intended to guard against.

The last argument is more easily reduced to a numerical question than the others. The mean and extreme annual precipitation of all the basins where the construction of such works would be seriously proposed is already approximately known by meteorological tables, and the quantity of water, delivered by the greatest floods which have occurred within the memory of man, may be roughly estimated from their visible traces. From these elements, or from meteorological records, the capacity of the necessary reservoirs can be calculated. Let us take the case of the Ardeche. In the inundation of 1857, that river poured into the Rhone 1,305,000,000 cubic yards of water in three days. If we suppose that half this quantity might have been suffered to flow down its channel without inconvenience, we shall have about 650,000,000 cubic yards to provide for by reservoirs. The Ardeche and its principal affluent, the Chassezae, have, together, about twelve considerable tributaries rising near the crest of the mountains which bound the basin. If reservoirs of equal capacity were constructed upon all of them, each reservoir must be able to contain 54,000,000 cubic yards, or, in other words, must be equal to a lake 3,000 yards long, 1,000 yards wide, and 18 yards deep, and besides, in order to render any effectual service, the reservoirs must all have been empty at the commencement of the rains which produced the inundation.

Thus far I have supposed the swelling of the waters to be uniform throughout the whole basin; but such was by no means the fact in the inundation of 1857, for the rise of the Chassezae, which is as large as the Ardeche proper, did not exceed the limits of ordinary floods, and the dangerous excess came solely from the headwaters of the latter stream. Hence reservoirs of double the capacity I have supposed would have been necessary upon the tributaries of that river, to prevent the injurious effects of the inundation. It is evident that the construction of reservoirs of such magnitude for such a purpose is financially, if not physically, impracticable, and when we take into account a point I have just suggested, namely, that the reservoirs must be empty at all times of apprehended flood, and, of course, their utility limited almost solely to the single object of preventing inundations, the total inapplicability of such a measure in this particular case becomes still more glaringly manifest.

Another not less conclusive fact is, that the valleys of all the upland tributaries of the Ardeche descend so rapidly, and have so little lateral expansion, as to render the construction of capacious reservoirs in them quite impracticable. Indeed, engineers have found but two points in the whole basin suitable for that purpose, and the reservoirs admissible at these would have only a joint capacity of about 70,000,000 cubic yards, or less than one-ninth part of what I suppose to be required. The case of the Ardeche is no doubt an extreme one, both in the topographical character of its basin and in its exposure to excessive rains; but all destructive inundations are, in a certain sense, extreme cases also, and this of the Ardeche serves to show that the construction of reservoirs is not by any means to be regarded as a universal panacea against floods.

Nor, on the other hand, is this measure to be summarily rejected. Nature has adopted it on a great scale, on both flanks of the Alps, and on a smaller, on those of the Adirondacks and of many lower chains. The quantity of water which, in great rains or sudden thaws, rushes down the steep declivities of the Alps, is so vast that the channels of the Swiss and Italian rivers would be totally incompetent to carry it off as rapidly as it would pour into them, were it not absorbed by the capacious basins which nature has scooped out for its reception, freed from the transported material which adds immensely both to the volume and to the force of its current, and then, after some reduction by evaporation and infiltration, gradually discharged into the beds of the rivers. In the inundation of 1829 the water discharged into Lake Como from the 15th to the 20th of September amounted to 2,600 cubic yards the second, while the outflow from the lake during the same period was only at the rate of about 1,050 cubic yards to the second. In those five days, then, the lake accumulated 670,000,000 cubic yards of superfluous water, and of course diminished by so much the quantity to be disposed of by the Po. [Footnote: Baird Smith, Italian Irrigation, i., p. 176.] In the flood of October, 1868, the surface of Lago Maggiore was raised twenty-five feet above low-water mark in the course of a few hours. [Footnote: Bollettino della Societa Geog. Italiana, iii., p. 466.] There can be no doubt that without such detention of water by the Lakes Como, Maggiore, Garda, and other subalpine basins, almost the whole of Lombardy would have been irrecoverably desolated, or rather, its great plain would never have become anything but a vast expanse of river-beds and marshes; for the annual floods would always have prevented the possibility of its improvement by man. [Footnote: See, as to the probable effects of certain proposed hydraulic works at the outlet of Lake Maggiore on the action of the lake as a regulating reservoir, Tagliasecchi, Notizie sui Canali dell' Alta Lombardia, Milano, 1869.]

Lake Bourget in Savoy, once much more extensive than it is at present, served, and indeed still serves, a similar purpose in the economy of nature. In a flood of the Rhone, in 1863, this lake received from the overflow of that river, which does not pass through it, 72,000,000 cubic yards of water, and of course moderated, to that extent, the effects of the inundation below. [Footnote: Elisee Recluse, La Terre, i., p. 460.]

In fact, the alluvial plains which border the course of most considerable streams, and are overflowed in their inundations, either by the rise of the water to a higher level than that of their banks, or by the bursting of their dikes, serve as safety-valves for the escape of their superfluous waters. The current of the Po, spreading over the whole space between its widely separated embankments, takes up so much water in its inundations, that, while a little below the outlet of the Ticino the discharge of the channel is sometimes not less than 19,500 cubic yards to the second, it has never exceeded 6,730 yards at Ponte Lagoscuro, near Ferrara. The currents of the Mississippi, the Rhone, and of many other large rivers, are modified in the same way. In the flood of 1858, the delivery of the Mississippi, a little below the month of the Ohio, was 52,000 cubic yards to the second, but at Baton Rouge, though of course increased by the waters of the Arkansas, the Yazoo, and other smaller tributaries, the discharge was reduced to 46,760 cubic yards. We rarely err when we cautiously imitate the processes of nature, and there are doubtless many cases where artificial basins of reception and lateral expansions of river-beds might be employed with advantage. Many upland streams present points where none of the objections usually urged against artificial reservoirs, except those of expense and of danger from the breaking of dams, could have any application. Reservoirs may be so constructed as to retain the entire precipitation of the heaviest thaws and rains, leaving only the ordinary quantity to flow along the channel; they may be raised to such a height as only partially to obstruct the surface drainage; or they may be provided with sluices by means of which their whole contents can be discharged in the dry season and a summer crop be grown upon the ground they cover at high water. The expediency of employing them and the mode of construction depend on local conditions, and no rules of universal applicability can be laid down on the subject. [Footnote: The insufficiency of artificial basins of reception as a means of averting the evils resulting from the floods of great rivers has been conclusively shown, in reference to a most important particular case--that of the Mississippi--by Humphreys and Abbot, in their admirable monograph of that river.]

It is remarkable that nations which we, in the inflated pride of our modern civilization, so generally regard as little less than barbarian, should have long preceded Christian Europe in the systematic employment of great artificial basins for the various purposes they are calculated to subserve. The ancient Peruvians built strong walls, of excellent workmanship, across the channels of the mountain sources of important streams, and the Arabs executed immense works of similar description, both in the great Arabian peninsula and in all the provinces of Spain which had the good fortune to fall under their sway. The Spaniards of the fifteenth and sixteenth centuries, who, in many points of true civilization and culture, were far inferior to the races they subdued, wantonly destroyed these noble monuments of social and political wisdom, or suffered them to perish, because they were too ignorant to appreciate their value, or too unskilful as practical engineers to be able to maintain them, and some of their most important territories were soon reduced to sterility and poverty in consequence.

Diversion of Rivers.