DESCRIPTION OF DUNES. 13 



Of the Danes which have been so transformed M. Mangin gives 

 the following description : — " 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 fre- 

 quently destroying the scattered hamlets of the people, and inun- 

 dating 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. Bat 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 ; southward, to the 

 bank of the Adour, and even further, to the cliffs of Beam. Here 

 the basin of Arcachon constitutes one vast hollow ; and some open- 

 ings exist, moreover, in the department of Landes, between that basin 



