SANDS OF NORTHERN AFRICA. 551 
the sand thrown upon the coast in question must be derived 
from a narrow belt of sea. It must hence, in time, become ex- 
hausted, and the formation of new sand-banks 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 
ageregation, and to have been brought to their present position 
by upheaval, they are not wholly composed of material collect- 
ed 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 
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 powerful 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 exten- 
sive series of observations on this subject has been recorded. On the Spit of 
Agger, at the present outlet of the Liimfjord, Andresen found the quantity 
during ten years, on a beach about five hundred and seventy feet broad, equal 
to an annual deposit of an inch and a half over the whole surface.—Om Alit- 
formationen, 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, on this subject, an article in Aws der Natur, vol. xxx., p. 590. 
The Florentine Frescobaldi, who visited the Sinaitic peninsula five hundred 
years ago, observed the powerful action of the solar heat in the disintegration 
of the desert rocks. ‘‘ This place,” says he, ‘‘ was a ridge of rocks burnt to 
powder by the sun, and this powder is blown away from the rock by the wind 
and is the sand of the desert; and there be many hills which are pure bare 
