522 OBSTRUCTION OF RIVER MOUTHS. 
would have been carried out to sea. This would have been a 
considerable quantity ; for the Nile holds some earth in suspen- 
sion at all seasons except at the very lowest water, a much 
larger proportion during the flood, and irrigation must have 
been carried on during the whole year.. The precise amount of 
sediment which would have been thus distributed over the soil 
is matter of conjecture, but though large, it would have been 
much less than the inundations have deposited, and continuous 
longitudinal embankments would have compelled the Nile 
to transport to the Mediterranean an immense quantity over 
and above what it has actually deposited in that sea. The 
Mediterranean is shoal for some miles out to sea along the 
whole coast of the Delta, and the large bays or lagoons within 
the coast-line, which communicate both with the river and the 
sea, have little depth of water. These lagoons the river deposits 
would haye filled up, and there would still have been surplus 
earth enough to extend the Delta far into the Mediterranean.* 
Obstruction of Liver Mouths. 
The mouths of a large proportion of the streams known to 
ancient navigation are already blocked up by sand-bars or 
fluviatile deposits, and the maritime approaches to river harbors 
frequented by the ships of Phenicia and Carthage and Greece 
and Rome are shoaled to a considerable distance out to sea. 
The inclination of the lower course of almost every known river- 
bed has been considerably reduced within the historical period, 
and nothing but great volume of water, or exceptional rapidity 
of flow, now enables a few large streams like the Amazon, the 
La Plata, the Ganges, and, in a less degree, the Mississippi, to 
* The present annual extension of the Delta is, if perceptible, at all events 
very small. According to some authorities, a few hectares are added every 
year at each Nile mouth. Others, among whom I may mention Fraas, deny 
that there is any extension at all, the deposit being balanced by a secular de- 
pression of the coast. 
Elisée Reclus states that the Delta advances about 40 inches per year.—La 
Terre, i., p. 500. 
