236 DOWNS ARREST OF MOVING SANDS. 



studied and successfully resolved by M. Bremontier, a French en- 

 gineer, who by sagacity in the choice of means and persever- 

 ance in their employment gave a complete and practical solution of 

 the question among the downs of the Gulf of Gascony.* 



The downs formed hy the sand which is thrown up by the ocean 

 between the mouths of the Adonr and the Girond, occupy a surface 

 of 75 square leagues and have a mean elevation of from 60 to 70 

 feet. They form a multitude of hillocks, which appear connected 

 by their bases, the crowns of many of them rising to a height of 

 160 feet and upwards. Under the inlluence of the prevailing west 

 winds, these masses of sand move with a mean celerity of about 80 

 feet per annum, covering forests and villages in their progress. A 

 part of the little town of Mimizan is already invaded, and it has 

 been calculated that in the course of twenty centuries, things pro- 

 ceeding at their present rate, the rich territory of Bordeaux will 

 have complelelv disappeared. In tl)eir progress these moving mass- 

 es of sand choke up the heds of rivers, and increase the disastrous 

 effects they produce otherwise by causing fcumidable inundations. 



The sands of the Gulf of Gascony, like those of Holland and the 

 Low Countries, are not altogether without moisture; a very short 

 way below the surface they are moist, and even present a certain 

 degree of cohesion. This, in fact, miuht have been predicated, for 

 otherwise the wind wliich brings them from the sea would have dis- 

 persed them in clouds of dust and l(» great distances ; but no such 

 dispersion takes place. Downs advance slowly, at the ralealieady 

 indicated, and by rolling over, as it were, uptui themselves. The 

 sand driven by the wind creeps up on the flanks of the ridges as 

 upon an inclined plane-; after iiaving got over the summit of the 

 hillocks already formed, it falls <l<)wn the opposite slo{)e, and accu- 

 mulates at the base. The action of the wind is only e.\erted upon 

 so much of the sand as is rendered loose and nioveubU' by its dry- 

 ness ; but the moist part is exposed, dried, and swept away in its 

 turn ; in this way the whole mass of s:ind which was at first deposit- 

 ed upon the west aspect of the hillocks is carried to the east, where 

 it is in the shelter. By this process, under the inlluence i»f a wind 

 which blew steadily for six days, a hillock has been seen to advance 

 towards the interior of the country throuLrh a space of 3{ feet.f 



The moisture containeil in the sand proceeds from the rains, from 

 the surface water that filters through it and displaces the salt water 

 which impregnated it originally. The very slight trace of sea-salt 

 that finally remains it it has no unfavorable infiuence on vegeta- 

 tion. 



Once aware of the fart that certain plants throve in the sands of 

 downs, Bremontier saw that they alone were capable of staying their 

 progress and consolidating them. The grand object was to gel 

 plants to grow in moving sand, and to protect them from lh«' violent 

 winds which blow otf the ocean, until their roots had got firm hold 

 of the soil, 



• Annnls of French .Agriculture, vol. xxvil. p. I<1^ 

 t D'.\ul>ui»son, Geognosy, vo' ii. p. 4G7. 



