INTERIOR STRUCTURE OF DUNES. 
477 
Interior Structure of Dunes. 
The interior structure of the dunes, the arrangement of 
their particles, is not, as might be expected, that of an unor¬ 
ganized, confused heap, but they show a strong tendency to 
stratification. This is a point of much geological interest, 
because it indicates that sandstone may owe its stratified char¬ 
acter to the action of wind as well as of water. The origin 
and peculiar character of these layers are due to a variety of 
causes. A southwest wind and current may deposit upon a 
dune a stratum of a given color and mineral composition, and 
this may be succeeded by a northwest wind and current, 
bringing with them particles of a different hue, constitution, 
and origin. 
Again, if we suppose a violent tempest to strew the beach 
with sand grains very different in magnitude and specific grav¬ 
ity, and, after the sand is dry, to be succeeded by a gentle 
breeze, it is evident that only the lighter particles will be 
taken up and carried to the dunes. If, after some time, the 
wind freshens, heavier grains will be transported and depos¬ 
ited on the former, and a still stronger succeeding gale will 
roll up yet larger kernels. Each of these deposits will form a 
stratum. If we suppose the tempest to be followed, after the 
sand is dry, not by a gentle breeze, but by a wind powerful 
enough to lift at the same time particles of very various mag¬ 
nitudes and weights, the heaviest will often lodge on the dune 
while the lighter will be carried farther. This would producG 
a stratum of coarse sand, and the same effect might result from 
the blowing away of light particles out of a mixed layer, while 
the heavier remained undisturbed.* Still another cause of 
i 
puts an end to its formation. When, in the course of time, marine currents 
cut away the coast, the dunes move landward and fill up the ponds, and 
thus are formed the remarkable strata of fossile peat called Martbrv, which 
appears to be unknown to the geologists of other parts of Europe.”— Forch- 
hammee, in Leonhard und Bronn, 1841, p. 18. 
* The lower strata must be older than the superficial layers, and the 
particles which compose them may in time become more disintegrated, and 
therefore finer than those deposited later and above them. 
