The improvements of the dunes on the coast of West Prussia began in 1795, under Soren Bjorn, a native of Denmark, and, with the exception of the ten years between 1807 and 1817, they have been prosecuted ever since. The methods do not differ essentially from those employed in Denmark and France, though they are modified by local circumstances, and, with respect to the trees selected for planting, by climate. In 1850, between the mouth of the Vistula and Kahlberg, 6,300 acres, including about 1,900 acres planted with pines and birches, had been secured from drifting; between Kahlberg and the eastern boundary of West Prussia, 8,000 acres; and important preliminary operations had been carried on for subduing the dunes on the west coast. [Footnote: Kruse, Dunenbau, pp. 34, 38, 40.]
The tree which has been fonnd to thrive best upon the sand-hills of the French coast, and at the same time to confine the sand most firmly and yield the largest pecuniary returns, is the maritime pine, Pinus maritima, a species valuable both for its timber and for its resinous products. It is always grown from seed, and the young shoots require to be protected for several seasons, by the branches of other trees, planted in rows, or spread over the surface and staked down, by the growth of the Arundo arenaria and other small sand-plants, or by wattled hedges. The beach, from which the sand is derived, has been generally planted with the arundo, because the pine does not thrive well so near the sea; but it is thought that a species of tamarisk is likely to succeed in that latitude even better than the arundo. The shade and the protection offered by the branching top of this pine are favorable to the growth of deciduous trees, and, while still young, of shrubs and smaller plants, which contribute more rapidly to the formation of vegetable mould, and thus, when the pine has once taken root, the redemption of the waste is considered as effectually secured.
In France, the maritime pine is planted on the sands of the interior as well as on the dunes of the seacoast, and with equal advantage. This tree resembles the pitch pine of the Southern American States in its habits, and is applied to the same uses. The extraction of turpentine from it begins at the age of about twenty years, or when it has attained a diameter of from nine to twelve inches. Incisions are made up and down the trunk, to the depth of about half an inch in the wood, and it is insisted that if not more than two such slits are cut, the tree is not sensibly injured by the process. The growth, indeed, is somewhat checked, but the wood becomes superior to that of trees from which the turpentine is not extracted. Thus treated, the pine continues to flourish to the age of one hundred or one hundred and twenty years, and up to this age the trees on an acre yield annually 300 pounds of essence of turpentine, and 250 pounds of resin, worth together not far from ten dollars. The expense of extraction and distillation is calculated at about four dollars, and a clear profit of more than five dollars per acre is left. [Footnote: These processes are substantially similar to those employed in the pineries of the Carolinas, but they are better systematized and more economically conducted in France. In the latter country, all the products of the pine, even to the cones, find a remunerating market, while, in America, the price of resin is so low, that in the fierce steamboat races on the great rivers, large quantities of it are thrown into the furnaces to increase the intensity of the fires. In a carefully prepared article on the Southern pineries published in an American magazine—I think Harper's—a few years ago, it was stated that the resin from the turpentine distilleries was sometimes allowed to run to waste; and the writer, in one instance, observed a mass, thus rejected as rubbish, which was estimated to amount to two thousand barrels. Olmsted saw, near a distillery which had been in operation but a single year, a pool of resin estimated to contain three thousand barrels, which had been allowed to run off as waste.—A Journey in the seaboard Slave States, 1863, p. 345.] This is exclusive of the value of the timber, when finally cut, which, of course, amounts to a very considerable sum. In Denmark, where the climate is much colder, hardier conifers, as well as the birch and other northern trees, are found to answer a better purpose than the maritime pine, and it is doubtful whether this tree would be able to resist the winter on the dunes of Massachusetts. Probably the pitch-pine of the Northern States, in conjunction with some of the American oaks, birches, and poplars, and especially the robinia or locust, would prove very suitable to be employed on the sand-hills of Cape Cod and Long Island. The ailanthus, now coming into notice as a sand-loving tree, some species of tamarisk, and perhaps the Aspressus macrocarpa, already found useful on the dunes in California, may prove valuable auxiliaries in resisting the encroachment of drifting sands, whether in America or in Europe, and the intermixing of different species would doubtless be attended with as valuable results in this as in other branches of forest economy. It cannot, indeed, be affirmed that human power is able to arrest altogether the incursions of the waves on sandy coasts, by planting the beach, and clothing the dunes with wood. On the contrary, both in Holland and on the French coast, it has been found necessary to protect the dunes themselves by piling and by piers and sea-walls of heavy masonry. But experience has amply shown that the processes referred to are entirely successful in preventing the movement of the dunes, and the drifting of their sands over cultivated lands behind them; and that, at the same time, the plantations very much retard the landward progress of the waters. [Footnote: See a very interesting article entitled "Le Littoral de la France," by Elisee Reclus, in the Revue des Deux Mondes for December, 1862, pp. 901, 936.]
Besides the special office of dune plantations already noticed, these forests have the same general uses as other woods, and they have sometimes formed by their droppings so thick a layer of vegetable mould that the sand beneath has become sufficiently secured to allow the wood to be felled, and the surface to be ploughed and cultivated with ordinary field crops.
In some cases it has been found possible to confine and cultivate coast sand-hills, even without preliminary forestal plantation. Thus, in the vicinity of Cap Breton in France, a peculiar process is successfully employed, both for preventing the drifting of dunes, and for rendering the sands themselves immediately productive; but this method is applicable only in exceptional cases of favorable climate and exposure. It consists in planting vineyards upon the dunes, and protecting them by hedges of broom, Erica scoparia, so disposed as to form rectangles about thirty feet by forty. The vines planted in these enclosures thrive admirably, and the grapes produced by them are among the best grown in France. The dunes are so far from being an unfavorable soil for the vine, that fresh sea-sand is regularly employed as a fertilizer for it, alternating every other season with ordinary manure. The quantity of sand thus applied every second year, raises the surface of the vineyard about four or five inches. The vines are cut down every year to three or four shoots, and the raising of the soil rapidly covers the old stocks. As fast as buried, they send out new roots near the surface, and thus the vineyard is constantly renewed, and has always a youthful appearance, though it may have been already planted a couple of generations. This practice is ascertained to have been followed for two centuries, and is among the oldest well-authenticated attempts of man to resist and vanquish the dunes. [Footnote: Boitel, Mise en valeur des Terres pauvres, pp. 212, 218.]
The artificial removal of dunes, no longer necessary as a protection, does not appear to have been practiced upon a large scale except in the Netherlands, where the numerous canals furnish an easy and economical means of transporting the sand, and where the construction and maintenance of sea and river dikes, and of causeways and other embankments and fillings, create a great demand for that material. Sand is also employed in Holland, in large quantities, for improving the consistence of the tough clay bordering upon or underlying diluvial deposits, and for forming an artificial soil for the growth of certain garden and ornamental vegetables. When the dunes are removed, the ground they covered is restored to the domain of industry; and the quantity of land recovered in the Netherlands by the removal of the barren sands which encumbered it, amounts to hundreds and perhaps thousands of acres.
Inland Dunes.
Vast deposits of sand, both in the form of dunes and of plains, are found far in the interior of continents, in the Old World and in the New. The deserts of Gobi, of Arabia, and of Africa have been rendered familiar by the narratives of travellers, but the sandy wilderness of America, and even of Europe, have not yet been generally recognized as important elements in the geography of the regions where they occur. There are immense wastes of drifting sands in Poland and other interior parts of Europe, in Peru, and in the less known regions of our own Western territory, where their extent is greater than that of all the coast dunes together which have hitherto been described by European and American geographers. [Footnote: On the Niobrara river alone, the dunes cover a surface of twenty thousand square miles.—Hayden, Report on Geological Survey of Wyoming, 1870, p. 108.] The inland sand-hills of both hemispheres are composed of substantially the same material and aggregated by the action of the same natural forces as the dunes of the coast. There is, therefore, a general resemblance between them, but they appear, nevertheless, to be distinguished by certain differences which a more attentive study may perhaps enable geologists to recognize in the sandstone formed by them. The sand of which they are composed comes in both principally from the bed of the sea being brought to the surface in one case by the action of the wind and the waves, in the other by geological upheaval. [Footnote: American observers do not agree in their descriptions of the form and character of the sand-grains which compose the interior dunes of the North American desert. C. C. Parry, geologist to the Mexican Boundary Commission, in describing the dunes near the station at a spring thirty-two miles west from the Rio Grande at El Paso, says: "The separate grains of the sand composing the sand-hills are seen under a lens to be angular, and not rounded, as would be the case in regular beach deposits."—U. S. Mexican Boundary Survey, Report of, vol i., Geological Report of C. C. Parry, p. 10.
In the general description of the country traversed, same volume, p. 47, Colonel Emory says that on an "examination of the sand with a microscope of sufficient power," the grains are seen to be angular, not rounded by rolling in water.
On the other hand, Blake, in Geological Report, Pacific Railroad Rep., vol. v., p. 119, observes that the grains of the dune sand, consisting of quartz, chalcedony, carnelian, agate, rose quartz, and probably chrysolite, were much rounded; and on page 241, he says that many of the sand grains of the Colorado desert are perfect spheres. On page 20 of a report in vol. ii. of the Pacific Railroad Report, by the same observer, it is said that an examination of dunes brought from the Llano Estacado by Captain Pope, showed the grains to be "much rounded by attrition." The sands described by Mr. Parry and Colonel Emory are not from the same localities as those examined by Mr. Blake, and the difference in their character may be due to a difference of origin or of age. In New Mexico, sixty miles south of Fort Stanton, there are island dunes composed of finely granulated gypsum.—American Naturalist, Jan. 1871, p. 695.] The sand of the coast dunes is rendered, to a certain extent, cohesive by moisture and by the saline and other binding ingredients of sea-water, while long exposure to meteoric influences has in a great measure deprived the inland sands of these constituents, though there are not wanting examples of large accumulations of sand far from the sea, and yet agglutinated by saline material. Hence, as might be expected, inland dunes, when not confined by a fixed nucleus, are generally more movable than those of the coast, and the form of such dunes is more or less modified by their want of consistence. Thus, the crescent or falciform shape is described by all observers as more constant and conspicuous in these sandhills than in those of littoral origin; they tend less to unite in continuous ridges, and they rarely attain the height or other dimensions of the dunes of the seashore. Meyer describes the sand-hills of the Peruvian desert as perfectly falciform in shape and from seven to fifteen feet high, the chord of their arc measuring from twenty to seventy paces. The slope of the convex face is described as very small, that of the concave as high as 70 degrees or 80 degrees, and their surfaces were rippled. No smaller dunes were observed, nor any in the process of formation. The concave side uniformly faced the north-west, except towards the centre of the desert, where, for a distance of one or two hundred paces, they gradually opened to the west, and then again gradually resumed the former position. Tschudi observed, in the same desert, two species of dunes, fixed and movable, and he ascribes a falciform shape to the movable, a conical to the fixed dunes, or medanos. "The medanos," he observes, "are hillock-like elevations of sand, some having a firm, others a loose base. The former [latter], which are always crescent-shaped, are from ten to twenty feet high, and have an acute crest. The inner side is perpendicular, and the outer or bow side forms an angle with a steep inclination downwards. [Footnote: The dunes of the plains between Bokhara and the Oxus are all horse-shoe shaped, convex towards the north, from which the prevailing wind blows. On this side they are sloping, inside precipitous, and from fifteen to twenty feet high.—Burnes, Journal in Bokhara, ii., pp. 1, 2.] When driven by violent winds, the medanos pass rapidly over the plains. The smaller and lighter ones move quickly forward, before the larger; but the latter soon overtake and crush them, whilst they are themselves shivered by the collision. These medanos assume all sorts of extraordinary figures, and sometimes move along the plain in rows forming most intricate labyrinths…. A plain often appears to be covered with a row of medanos, and some days afterwards it is again restored to its level and uniform aspect…. "The medanos with immovable bases are formed on the blocks of rocks which are scattered about the plain. The sand is driven against them by the wind, and as soon as it reaches the top point, it descends on the other side until that is likewise covered; thus gradually arises a conical-formed hill. [Footnote: The sand-hills observed by Desor in the Algerian desert were fixed, changing their form only on the surface as sand was blown to and from them.—Sahara und Atlas, 1865, p. 21.] Entire hillock chains with acute crests are formed in a similar manner…. On their southern declivities are found vast masses of sand, drifted thither by the mid-day gales. The northern declivity, though not steeper than the southern, is only sparingly covered with sand. If a hillock chain somewhat distant from the sea extends in a line parallel with the Andes, namely, from S. S. E. to N. N. W., the western declivity is almost entirely free of sand, as it is driven to the plain below by the south-east wind, which constantly alternates with the wind from the south." [Footnote: Travels in Peru, New York, 1848, chap. ix.] It is difficult to reconcile this description with that of Meyen, but if confidence is to be reposed in the accuracy of either observer, the formation of the sand-hills in question must be governed by very different laws from those which determine the structure of coast dunes. Captain Gilliss, of the American navy, found the sand-hills of the Peruvian desert to be in general crescent-shaped, as described by Meyen, and a similar structure is said to characterize the inland dunes of the Llano Estacado and other plateaus of the North American desert, though those latter are of greater height and other dimensions than those described by Meyen. There is no very obvious explanation of this difference in form between maritime and inland sand-hills, and the subject merits investigation. It is, however, probable that the great mobility of the flying dunes of the Peruvian desert is an effect of their dryness, no rain falling in that desert, and of the want of salt or other binding material to hold their particles together.