G. C. A. Krause, Der Dünenbau auf den Ostsee-Küsten West-Preussens, 1850, 1 vol. 8vo.
W. C. H. Staring, De Bodem van Nederland, 1856, vol. i, pp. 310-341, and 424-431.
Same author, Voormaals en Thans, 1858, pages cited.
C. C. Andresen, Om Klitformationen og Klittens Behandling og Bestyrelse, 1861, 1 vol. 8vo, x, 392 pp., much the most complete treatise on the subject.
Andresen cites, upon the origin of the dunes: Hull, Over den Oorsprong en de Geschiedenis der Hollandsche Duinen, 1838, and Gross's Veiledning ved Behandlingen af Sandflugtstrækningerne, 1847; and upon the improvement of sand plains by planting, Pannewitz, Anleitung zum Anbau der Sandflächen, 1832. I am not acquainted with either of the latter two works but I have consulted with advantage, on this subject, Delamarre, Historique de la Création d'une Richesse millionaire par la culture des Pins, 1827; Boitel, Mise en valeur des terres pauvres par le Pin maritime, 1857; and Brincken, Ansichten über die Bewaldung der Steppen des Europäischen Russlands, 1854.
[426] "Dunes are always full of water, from the action of capillary attraction. Upon the summits, one seldom needs to dig more than a foot to find the sand moist, and in the depressions, fresh water is met with near the surface."—Forchhammer, in Leonhard und Bronn, for 1841, p. 5, note.
On the other hand, Andresen, who has very carefully investigated this as well as all other dune phenomena, maintains that the humidity of the sand ridges cannot be derived from capillary attraction. He found by experiment that drift sand was not moistened to a greater height than eight and a half inches, after standing a whole night in water. He states the minimum of water contained by the sand of the dunes, one foot below the surface, after a long drought, at two per cent., the maximum, after a rainy month, at four per cent. At greater depths the quantity is larger. The hygroscopicity of the sand of the coast of Jutland he found to be thirty-three per cent. by measure, or 21.5 by weight. The annual precipitation on that coast is twenty-seven inches, and, as the evaporation is about the same, he argues that rain water does not penetrate far beneath the surface of the dunes, and concludes that their humidity can be explained only by evaporation from below.—Om Klitformationen, pp. 106-110.
In the dunes of Algeria, water is so abundant that wells are constantly dug in them at high points on their surface. They are sunk to the depth of three or four mètres only, and the water rises to the height of a mètre in them.—Laurent, Mémoire sur le Sahara, pp. 11, 12, 13.
The same writer observes (p. 14) that the hollows in the dunes are planted with palms which find moisture enough a little below the surface. It would hence seem that the proposal to fix the dunes which are supposed to threaten the Suez Canal, by planting the maritime pine and other trees upon them, is not altogether so absurd as it is thought to be by some of those disinterested philanthropists of other nations who are distressed with fears that French capitalists will lose the money they have invested in that great undertaking.
Ponds of water are often found in the depressions between the sand hills of the dune chains in the North American desert.