MOVEMENT OF DUNES. 589 
width from a quarter of a mile to five miles, extends from the 
Adour to the estuary of the Gironde, and covers an area of nine 
hundred and seventy square kilometres, or two hundred and 
forty thousand acres. When not fixed by vegetable growths, 
these dunes advance eastwards at a mean rate of about 
one rod, or sixteen and a half feet, a year. We do not know 
historically when they began to drift, but if we suppose their 
motion to have been always the same as at present, they would 
have passed over the space between the sea coast and their 
present eastern border, and covered the large area above men- 
tioned, in fourteen hundred years. We know, from written 
records, that they have buried extensive fields and forests and 
thriving villages, and changed the courses of rivers, and that 
the lighter particles carried from them by the winds, even 
where not transported in sufficient quantities to form sand-hills, 
have rendered sterile much land formerly fertile.* They have 
also injuriously obstructed the natural drainage of the maritime 
districts by choking up the beds of the streams, and forming 
lakes and pestilential swamps of no inconsiderable extent. In 
fact, so completely do they embank the coast, that between the 
Gironde and the village of Mimizan, a distance of one hundred 
miles, there are but two outlets for the discharge of all the 
waters which flow from the land to the sea; and the eastern 
front of the dunes is bordered by a succession of stagnant 
pools, some of which are more than six miles in length and 
breadth.+ 
* The movement of the dunes has been hardly less destructive on the north 
side of the Gironde. See the valuable articles of ELtssk REcLus in the [e- 
oue des Deux Mondes for December, 1862, and several later numbers, entitled 
‘* Le Littoral dela France.” 
+ LavaL, Mémoire sur les Dunes du Golfe de Gascogne, Annales des Ponts 
et Chaussées, 1847, p. 223. The author adds, as a curious and unexplained 
fact, that some of these pools, though evidently not original formations but 
mere accumulations of water dammed up by the dunes, have, along their 
western shore, near the base of the sand-hills, a depth of more than one hun- 
dred and thirty feet, and hence their bottoms are not less than eighty feet, 
below the level of the lowest tides. Their western banks descend steeply, 
