200 
ARE SOILS ENRICHED, IMPOVERISHED, [Part III. 
channel sloping from a height to the sea; still 
less the myriads on myriads of dry upper valleys 
which ramify in all directions, from all river 
valleys through and to all sides of the tops of all 
elevations, whether high or low. 
But, in fact, the action of the sea impedes the 
formation of valleys, instead of making them. 
The sea often beats back, in the form of a bar, 
what the operation of rain on rivers forces into 
it; and valleys often form land in the sea, in¬ 
stead of the sea forming valleys in the land. 
The delta of the Ganges stretches 220 miles into 
the sea, with a base of 200 miles. The Missis¬ 
sippi has pushed a delta fifty miles out into the 
sea, with an area of 14,000 square miles; yet 
so far is it from “ acting on lines” in erodmg its 
banks, that at New Orleans it is less than half a 
mile wide: and it may be said to act on lines 
in building its banks, for it has raised its own 
banks above the land they pass through, and in¬ 
creases the area of its alluvial plain at the upper 
end and sides, as well as the depth of it. 
These effects are owing to the increase of the 
delta; and the same cause has produced the 
same effects in the valley of the Nile: for the 
lengthening of the delta lengthens the channel 
of the river with it; but the sea (leaving out 
the effect of the tide) tends to keep the surface 
