DESERT SANDS. 
457 
the sand thrown upon the coast in question must be derived 
from a narrow belt of sea. It must hence, in time, become 
exhausted, and the formation of new sandbanks and dunes 
upon the southern shores of the Mediterranean will cease at 
last for want of material.* 
But even in the cases where the accumulations of sand in 
extensive deserts appear to be of marine formation, or rather 
aggregation, and to have been brought to their present posi¬ 
tion by upheaval, they are not wholly composed of material 
collected or distributed by the currents of the sea; for, in all 
such regions, they continue to receive some small contributions 
from the disintegration of the rocks which underlie, or crop 
out through, the superficial deposits. In some instances, too, 
as in Northern Africa, additions are constantly made to the 
mass by the prevalence of sea winds, which transport, or, to 
divers employed at Constantinople in 1853 found in the Bosphorus, at the 
depth of twenty-five fathoms and at a point much exposed to the wash 
from Galata and Pera, a number of bronze guns supposed to have belonged 
to a ship of war blown up about a hundred and fifty years before. These 
guns were not covered by sand or slime though a crust of earthy matter, 
an inch in thickness, adhered to their upper surfaces, and the bottom of the 
strait appeared to be wholly free from sediment. The current was so pow¬ 
erful at this depth that the divers were hardly able to stand, and a keg of 
nails, purposely dropped into the water, in order that its movements might 
serve as a guide in the search for a bag of coin accidentally lost overboard 
from a ship in the harbor, was rolled by the stream several hundred yards 
before it stopped. 
* Few seas have thrown up so much sand as the shallow German 
Ocean ; but there is some reason to think that the amount of this material 
now cast upon its northern shores is less than at some former periods, 
though no extensive series of observations on this subject has been re¬ 
corded. On the Spit of Agger, at the present outlet of the Liimfjord, 
Andresen found the quantity during ten years, on a beach about five hun¬ 
dred and seventy feet broad, equal to an annual deposit of an inch and a 
half over the whole surface .—Ora Klitfonnationen , p. 56. 
This gives seventy-one and a quarter cubic feet to the running foot—a 
quantity certainly much smaller than that cast up by the same sea on the 
shores of the Dano-German duchies and of Holland, and, as we have 
seen, scarcely one fourth of that deposited by the Atlantic on the coast of 
Gascony. See ante . p. 6, note. 
