THE DUNES, OR SAND-HILLS. 35 



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.* 



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. 



It will easily be understood that this accumulation along the 

 shore cannot have taken place where the force and direction of 

 the sands experience periodical or capricious changes ; for then the 

 sands cast upon the beach by the winds of the north and west would 

 be driven back into the sea by the winds of the south and east. 

 This is noticeable in many places where the nature of the coast is 

 favourable for the production of such a phenomenon. But on other 

 shores as on the Atlantic littoral of France the winds which blow 

 most frequently and most violently are from the west and south-west. 

 And it is there we encounter the Dunes. Those of Gascony are by 

 far the most remarkable. Northward, they extend as far as the 

 Point de Grave, which shuts in the mouth of the Gironde ; south- 

 ward, to the bank of the Adour, and even further, to the cliffs of 

 Be'arn. Here the basin of Arcachon constitutes one vast hollow ; 

 and some openings exist, moreover, in the department of Landes, 

 between that basin and the Adour, for the overflow of the waters 

 which descend from the interior. To the north and south of the 



* Angus B. Reach, " Claret and Olives. 



