No. 58 ([page 479]). It appears from Laurent, that marine shells, of extant species, are found in the sands of the Sahara, far from the sea, and even at considerable depths below the surface.—Mémoires sur le Sahara Oriental, p. 62.
This observation has been confirmed by late travellers, and is an important link in the chain of evidence which tends to prove that the upheaval of the Libyan desert is of comparatively recent date.
No. 59 ([p. 480]). "At New Quay [in England] the dune sands are converted to stone by an oxyde of iron held in solution by the water which pervades them. This stone, which is formed, so to speak, under our eye, has been found solid enough to be employed for building."—Esquiros, L'Angleterre et la vie Anglaise, Revue des Deux Mondes, 1 March, 1864, pp. 44, 45.
No. 60 ([page 496, first paragraph]). In Ditmarsh, the breaking of the surface by the manœuvering of a corps of cavalry let loose a sand-drift which did serious injury before it was subdued.—Kohl, Inseln u. Marschen. etc., III. p. 282.
Similar cases have occurred in Eastern Massachusetts, from equally slight causes.—See Thoreau, A Week on the Concord and Merrimack Rivers, pp. 151-208.
No. 61 ([page 497, last note]). A more probable explanation of the fact stated in the note is suggested by Èlisée Reclus, in an article entitled, Le Littoral de la France, in the Revue des Deux Mondes for Sept. 1, 1864, pp. 193, 194. This able writer believes such pools to be the remains of ancient maritime bays, which have been cut off from the ocean by gradually accumulated sand banks raised by the waves and winds to the character of dunes.
No. 62 ([page 506, note]). The statement in the note is confirmed by Olmsted: "There is not a sufficient demand for rosin, except of the first qualities, to make it worth transporting from the inland distilleries; it is ordinarily, therefore, conducted off to a little distance, in a wooden trough, and allowed to flow from it to waste upon the ground. At the first distillery I visited, which had been in operation but one year, there lay a congealed pool of rosin, estimated to contain over three thousand barrels."—A Journey in the Seaboard Slave States, 1863, p. 345.
No. 63 ([page 507]). In an article on the dunes of Europe, in Vol. 29 (1864) of Aus der Natur, p. 590, the dunes are estimated to cover, on the islands and coasts of Schleswig Holstein, in Northwest Germany, Denmark, Holland, and France, one hundred and eighty-one German, or nearly four thousand English square miles; in Scotland, about ten German, or two hundred and ten English miles; in Ireland, twenty German, or four hundred and twenty English miles; and in England, one hundred and twenty German, or more than twenty-five hundred English miles.
No. 64 ([page 512, last paragraph]). For a brilliant account of the improvement of the Landes, see Edmond About, Le Progrès, Chap, VII.
In the memoir referred to in Appendix, No. 48, ante, Duponchel proposes the construction of artificial torrents to grind calcareous rock to slime by rolling and attrition in its bed, and, at the same time, the washing down of an argillaceous deposit which is to be mixed with the calcareous slime and distributed over the Landes by watercourses constructed for the purpose. By this means, he supposes that a highly fertile soil could be formed on the surface, which would also be so raised by the process as to admit of freer drainage. That nothing may be wanting to recommend this project, Duponchel suggests that, as some of the rivers of Western France are auriferous, it is probable that gold enough may be collected from the washings to reduce the cost of the operations materially.