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 be discharged in a constant flow or at intervals as convenience may dictate.*

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

* M. G. Dumas, La Science des Fontaines, 1857.

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, 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.

CHAPTER V.

THE SANDS.

ORIGIN OF SAND-SAND NOW CARRIED DOWN TO THE SEA-THE SANDS OF EGYPT AND THE ADJACENT DESERT-THE SUEZ CANAL-THE SANDS OF EGYPT ---ÇOAST DUNES AND SAND PLAINS-SAND BANKS-DUNES ON COAST OF AMERICA-DUNES OF WESTERN EUROPE-FORMATION OF DUNES-CHARACTER OF DUNE SAND -INTERIOR STRUCTURE OF DUNES-FORM OF DUNES-GEOLOGICAL IMPORTANCE OF DUNES-INLAND DUNES-AGE, CHARACTER, AND PERMANENCE OF DUNES-USE OF DUNES AS BARRIER AGAINST THE SEAENCROACHMENTS OF THE SEA-THE LIIMFJORD-ENCROACHMENTS OF THE SEADRIFTING OF DUNE SANDS-DUNES OF GASCONY-DUNES OF DENMARK-DUNES OF PRUSSIA-ARTIFICIAL FORMATION OF DUNES TREES SUITABLE FOR DUNE PLANTATIONS-EXTENT OF DUNES IN EUROPE-DUNE VINEYARDS OF CAPE BRETON-REMOVAL OF DUNES-INLAND SAND PLAINS-THE LANDES OF GASCONY THE BELGIAN CAMPINE-SANDS AND STEPPES OF EASTERN EUROPE— ADVANTAGES OF RECLAIMING DUNES-GOVERNMENT WORKS OF IMPROVEMENT.

Origin of Sand.

SAND, which is found in beds or strata at the bottom of the sea or in the channels of rivers, as well as in extensive deposits upon or beneath the surface of the dry land, appears to consist essentially of the detritus of rocks. It is not always by any means clear through what agency the solid rock has been reduced to a granular condition; for there are beds of quartzose sand, where the sharp, angular shape of the particles renders it highly improbable that they have been formed by gradual abrasion and attrition, and where the supposition of a crushing mechanical force seems equally inadmissible. common sand, the quartz grains are the most numerous; but this is not a proof that the rocks from which these particles

In

were derived were wholly, or even chiefly, quartzose in char acter; for, in many composite rocks, as, for example, in the granitic group, the mica, felspar, and hornblende are more easily decomposed by chemical action, or disintegrated, comminuted, and reduced to an impalpable state by mechanical force, than the quartz. In the destruction of such rocks, therefore, the quartz would survive the other ingredients, and remain unmixed, when they had been decomposed and had entered into new chemical combinations, or been ground to slime and washed away by water currents.

The greater or less specific gravity of the different constituents of rock doubtless aids in separating them into distinct masses when once disintegrated, though there are veined and stratified beds of sand where the difference between the upper and lower layers, in this respect, is too slight to be supposed capable of effecting a complete separation.* In cases where rock has been reduced to sandy fragments by heat, or by obscure chemical and other molecular forces, the sandbeds may remain undisturbed, and represent, in the series of geological strata, the solid formations from which they were derived. The large masses of sand not found in place have been transported and accumulated by water or by wind, the former being generally considered the most important of these agencies; for the extensive deposits of the Sahara, of the deserts of Persia, and of that of Gobi, are commonly supposed to have been swept together or distributed by marine currents, and to have been elevated above the ocean by the same means as other upheaved strata.

* In the curiously variegated sandstone of Arabia Petræa—which is certainly a reaggregation of loose sand derived from particles of older rocks the contiguous veins frequently differ very widely in color, but not sensibly in specific gravity or in texture; and the singular way in which they are now alternated, now confusedly intermixed, must be explained otherwise than by the weight of the respective grains which compose them. They seem, in fact, to have been let fall by water in violent ebullition or tumultuous mechanical agitation, or by a succession of sudden aquatic or aerial currents flowing in different directions and charged with differently colored matter.

Meteoric and mechanical influences are still active in the reduction of rocks to a fragmentary state; but the quantity of sand now transported to the sea seems to be comparatively inconsiderable, because--not to speak of the absence of diluvial action the number of torrents emptying directly into the sea is much less than it was at earlier periods. The formation of alluvial plains in maritime bays, by the sedimentary matter brought down from the mountains, has lengthened the flow of such streams and converted them very generally into rivers, or rather affluents of rivers, much younger than themselves. The filling up of the estuaries has so reduced the slope of all large and many small rivers, and, consequently, so checked the current of what the Germans call their Unterlauf, or lower course, that they are much less able to transport heavy material than at earlier epochs. The slime deposited by rivers at their junction with the sea, is usually found to be composed of material too finely ground and too light to be denominated sand, and it can be abundantly shown that the sandbanks at the outlet of large streams are of tidal, not of fluviatile origin, or, in lakes and tideless seas, a result of the concurrent action of waves and of wind.

Large deposits of sand, therefore, must in general be considered as of ancient, not of recent formation, and many eminent geologists ascribe them to diluvial action. Staring has discussed this question very fully, with special reference to the sands of the North Sea, the Zuiderzee, and the bays and channels of the Dutch coast.* His general conclusion is, that the

* De Bodem van Nederland, i, pp. 243, 246–377, et seqq. See also the arguments of Brémontier as to the origin of the dune sands of Gascony, Annales des Ponts et Chaussées, 1833, 1er sémestre, pp. 158, 161. Brémontier estimates the sand annually thrown up on that coast at five cubic toises and two feet to the running toise (ubi supra, p. 162), or rather more than two hundred and twenty cubic feet to the running foot. Laval, upon observations continued through seven years, found the quantity to be twenty-five mètres per running mètre, which is equal to two hundred and sixty-eight cubic feet to the running foot.-Annales des Ponts et Chaussées, 1842, 2me sémestre, p. 229. These computations make the proportion of sand deposited on the coast of Gascony three or four times as great as that