COAST OF THE NETHERLANDS. 543 
of returning streams, and it is uncertain how far this loss has 
been balanced by earth washed by the sea from distant shores 
and let fall on the coasts of the Netherlands and other neigh- 
boring countries. 
We know little or nothing of the quantity of solid matter 
brought down by the rivers of Western Europe in early ages, 
but, as the banks of those rivers are now generally better 
secured against wash and abrasion than in former centuries, 
the sediment transported by them must be less than at periods 
nearer the removal of the primitive forests of their valleys, 
though certainly greater than it was before those forests were 
felled. laden informs us that the sedimentary matter trans- 
ported to the sea by the Rhine would amount to a cubic geo- 
graphical mile in five thousand years.* 
‘The proportion of this suspended matter which, with our 
present means, could be arrested and precipitated upon the 
ground, is almost infinitesimal, for only the surface-water, which 
carries much less sediment than that at the bottom of the chan- 
nel, would flow over the banks, and as the movement of this 
water, if not checked altogether, would be greatly retarded by 
the proposed cross-dikes, the quantity of solid matter which 
would be conveyed to a given portion of land during a single 
inundation would be extremely small. Inundations of the 
Rhine occur but once or twice a year, and high water continues 
but a few days, or even hours; the flood-tide of the sea hap- 
pens seven hundred times ina year,and at the turn of the 
tide the water is brought to almost absolute rest. Hence, small 
as is the proportion of suspended matter in the tide-water, the 
deposit probably amounts to far more in a year than would be 
let fall upon the same area by the Rhine. 
This argument, except as to the comparison between river 
and tide water, applies to the Mississippi, the Po, and most other 
great rivers. Hence, until that distant day when man shall de- 
* Hrdhunde, vol. i., p. 884. The Mississippi—a river ‘‘ undercharged with 
sediment”—with a mean discharge of about ten times that of the Rhine, 
deposits a cubic geographical mile in thirty-three years. 
