578 AGE, CHARACTER, AND PERMANENCE OF DUNES. 
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 accumulation is de- 
rived 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, ex- 
tensive 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 difference 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 arti- 
ficial methods of confinement and plantation were employed by 
the primitive inhabitants of Gaul; and Laval, basing his calcu- 
lations on the rate of annual movement of the shifting dunes, 
assions the fifth century of the Christian era as the period when 
these processes were abandoned.* 
There is no historical evidence that the Gauls were ac- 
quainted with artificial methods of fixing the sands of the 
coast, and we have little reason to suppose that they were ad- 
vanced enough in civilization to be likely to resort to such 
processes, especially at a period when land could have had but 
‘a moderate value. 
In other countries, dunes haye spontaneously clothed them- 
* LAVAL, Mémoire sur les Dunes de Gascogne, Annales des Ponts et Chaussées, 
1847, 2me sémestre, p. 231. The same opinion had been expressed by 
BrimMontier, Annales des Ponts et Chaussées, 1833, ler sémestre, p. 185. 
