AGE, CHAEACTER AND PEEMANENCE OF DUNES. 



555 



an upheaval of the coast hne since the formation of the oldest 

 hillocks, and these have become inland dunes, while younger rows 

 have been thrown up on the new beach laid bare by elevation of 

 the sea-bed. Our knowledge of the mode of their first accumula- 

 tion is derived from observation of the action of wind and water 

 in the few instances where, with or without the aid of man, new 

 coast-dunes have been accumulated, and of the influence of wind 

 alone in elevating new sand-heaps inland of the coast tier, when 

 the outer rows are destroyed by the sea, as also when the sodded 

 surface of ancient sands has been broken, and the subjacent strata 

 laid open to the air. 



It is a question of much interest, in what degree the naked 

 condition of most dunes is to be ascribed to the improvidence and 

 indiscretion of man. There are, in "Western France, extensive 

 ranges of dunes covered with ancient and dense forests, while the 

 recently formed sand-hills between them and the sea are bare of 

 vegetation, and in some cases are rapidly advancing upon the 

 wooded dunes, which they threaten to bury beneath their drifts. 

 Between the old dunes and the new there is no discoverable dif- 

 ference in material or in structure ; but the modern sand-hills are 

 naked and shifting, the ancient, clothed with vegetation and fixed. 

 It has been conjectured that artificial methods of confinement and 

 plantation were employed by the primitive inhabitants of Gaul ; 

 and Laval, basing his calculations on the rate of annual movement 

 of the shifting dunes, assigns the fifth century of the Christian 

 era as the period when these processes were abandoned.* 



There is no historical evidence that the Gauls were acquainted 

 with artificial methods of fixing the sands of the coast, and we 



in the deep depressions between them, the dunes are everywhere sprinkled, to 

 a considerable height, with brown oxidulated iron, which has penetrated into 

 the sand to the depth of from three to eighteen inches, and colored it red. 

 .... Above the iron is a stratum of sand diifering in composition from 



ordinary sea-sand, and on this, growing woods are always found The 



gradually accumulated forest soil occurs in beds of from one to three feet 

 thick, and changes, proceeding upward, from gray sand to black humus." 

 Even on the third or seaward range, the sand grasses appear and thrive luxuri- 

 antly, at least on the west coast, though Krause doubts whether the dunes ol 

 the east coast were ever thus protected. — Der Duneribau, pp. 8, 11. 



* Laval, Memoire sur les Dunes de Oascogne, Annales des Ponis et Ghausseea, 

 1847, 2me semestre, p. 231. The same opinion had been expressed by Brb 

 MONTiER, Annales des Fonts et Chaussees, 1833, ler semestre, p. 185. 



