484 
AGE OF THE DUNES, 
Age, Character, and Permanence of Dunes. 
The origin of most great lines of dunes goes back past all 
history. There are on many coasts, several distinct ranges of 
sand hills which seem to be of very different ages, and to have 
been formed under different relative conditions of land a7id 
water.* In some cases, there has been an upheaval of the coast 
siderably longer, lying perpendicularly to the direction of the wind, the 
sand is deposited with a windward angle of from 6° to 12°, and the bank 
presents a concave face to the wind, while, behind the obstruction, the 
outline is convex; ” and he lays it down as a general rule, that a slope, 
from which sand is blown, is left with a concavity of about one inch of 
depth to four feet of distance; a slope, upon which sand is dropped by the 
wind, is convex. It appears from Andresen’s figures, however, that the 
concavity and convexity referred to, apply, not to the horizontal longi¬ 
tudinal section of the sand bank, as his language unexplained by the 
drawings might be supposed to mean, but to the vertical cross-section , and 
hence the dunes he describes, with the exception above noted, do not cor¬ 
respond to those of the American deserts.— Om Klitformationen, p. 86. 
The dunes of Gascony, which sometimes exceed three hundred feet in 
height, present the same concavity and convexity of vertical cross-section. 
The slopes of these dunes are much steeper than those of the Netherlands 
and the Danish coast; for while all observers agree in assigning to the sea¬ 
ward and landward faces of these latter, respectively, angles of from 5° 
to 12°, and 30° with the horizon, the corresponding faces of the dunes 
of Gascony present angles of from 10° to 25°, and 50° to 60°.— Laval, 
Memoire sur les Dunes de Gascogne , Annales des Pouts et Ghaussees , 1847, 
2me s6mestre. 
* Krause, speaking of the dunes on the coast of Prussia, says: “ Their 
origin belongs to three different periods, in which important changes in 
the relative level of sea and land have unquestionably taken place. * * * 
Except in the deep depressions between them, the dunes are everywhere 
sprinkled, to a considerable height, with brown oxydulated 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 differing 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 luxuriantly, at least on the west coast, though 
Krause doubts whether the dunes of the east coast were ever thus pro¬ 
tected.— Der Diinenbau, pp. 8, 11. 
