DEPOSITS OF TUSCAN RIVERS. 525 
from the hills of Ethiopia which man has stripped of their pro- 
tecting forests, contributes to raise the plains of Egypt, to shoal 
the maritime channels which lead to the city built by Alexan- 
der near the mouth of the Nile, to obstruct the artificial com- 
munication between the Mediterranean and the Red Sea, and 
to fill up the harbors made famous by Phenician commerce. 
Deposits of the Tuscan Rivers. 
The Arno, and all the rivers rising on the western slopes 
and spurs of the Apennines, carry down immense quantities 
of mud to the Mediterranean. There can be no doubt that the 
volume of earth so transported is very much greater than it 
would have been had the soil about the headwaters of those 
rivers continued to be protected from wash by forests; and 
there is as little question that the quantity borne out to sea by 
the rivers of Western Italy is much increased by artificial em- 
bankments, because they are thereby prevented from spreading 
over the surface the sedimentary matter with which they are 
for many miles from its mouths. Ships often encounter floating masses of 
Nile mud, and Dr. Clarke thus describes a case of this sort: 
‘“ While we were at table, we heard the sailors who were throwing the lead 
suddenly cry out: ‘Three and a half!’ The ship slackened her way, and 
veered about. As she came round, the whole surface of the water was seen 
to be covered with thick, black mud, which extended so far that it appeared 
like an island. At the same time, actual land was nowhere to be seen—not 
even from the mast-head—nor was any notice of such a shoal to be found on 
any chart on board. The fact is, as we learned afterwards, that a stratum of 
mud, stretching from the mouths of the Nile for many miles out into the open 
sea, forms a movable deposit along the Egyptian coast. If this deposit is 
driven forwards by powerful currents, it sometimes rises to the surface, and 
disturbs the mariner by the sudden appearance of shoals where the charts lead 
him to expect a considerable depth of water. But these strata of mud are, in 
reality, not in the least dangerous. As soon as a ship strikes them they break 
up at once, and a frigate may hold her course in perfect safety where an inex- 
perienced pilot, misled by his soundings, would every moment expect to be 
stranded.” —B6éTTGER, Das Mittelmeer, pp. 188, 189. 
This phenomenon is not peculiar to the locality in question, and it is fre- 
quently observed in the Gulf of Bengal, and other great marine estuaries. 
