It is a noteworthy fact that, owing to the encroachment of the Dunes, these lakes have been constantly forced back upon the inland country. Fortunately, this menacing invasion of the sands has been checked by the great engineering works executed a few years ago; which, on the one hand, have fixed, and, as it were, solidified the Dunes, and, on the other, have provided for the regular outflow of the waters. The Landes have thus been opened to the persevering labours of the cultivator. The culture of the pine, and the manufacture of resinous substances, have largely extended, and the time, perhaps, is not far distant when these deserts will almost completely disappear; when these desolate and unproductive plains will pleasantly bloom, transformed into shadowy woods or verdurous meadows.[10] To so fortunate a result nothing will more powerfully contribute than the embankment of the Dunes. These have been, in reality, the true scourge of this country; these were the moving desert, the constantly ascending sea, which had already engulfed forests, villages, even towns, under its billows of sand, and driven before it the terrified inhabitants of the coast. CHAPTER III. THE DUNES, OR SAND-HILLS. The Dunes form the extreme line of the Brittany coast for nearly two hundred miles, from the Adour to the Garonne. They are hills of white sand, as fine and soft as if it had been sifted through an hour-glass. Their outline, therefore, changes every hour. When the wind blows from the land, millions of tons of sand are hourly driven into the sea, to be washed up again on the beach and blown inland by the first Biscay gale. A water hurricane from the west will fill up with sand square miles of shallow lake, driving the displaced waters into the interior, dispersing them in shining pools among the "murmurous pines," flooding and frequently destroying the scattered hamlets of the people, and inundating their fields of rye and millet.[11] [Illustration: A FLOOD IN BRITTANY.] Their origin is due to the prevalence of the sea-winds on those points of the coast which are not protected by rock and cliff, and whose slopes of sand descend very gradually to the margin of the waves. Their formation is easily explained. The sand of which they are composed is a silicious material, reduced to minute grains, generally rounded, by trituration. These grains, nevertheless, are often too big and too heavy for the wind to take them up and scatter them afar, like the dust of the highways or the ashes of volcanoes. But at low tide the sand, dried by the sun's rays and the action of the wind, offers to the latter a sufficient _holdfast_ to be dragged up the slopes which descend seaward, and deposited at a certain distance. This process being constantly repeated, the heaps are daily increasing in dimensions.