de of growth of mangroves.]

The tidal marshes of North America, which may be in time converted to
the uses of man, probably occupy an area exceeding twenty thousand
square miles. If the work of reclaiming such lands from the sea ever
attains the advance in this country that it has done in Holland, the
area added to the dry land by engineering devices may amount to as
much as fifty thousand square miles--a territory rather greater than
the surface of Kentucky, and with a food-yielding power at least five
times as great as is afforded by that fertile State. In fact, these
conquests from the sea are hereafter to be among the great works which
will attract the energies of mankind. In the arid region of the
Cordilleras, as well as in many other countries, the soil, though
destitute of those qualities which make it fit for the uses of man,
because of the absence of water in sufficient amount, is, as regards
its structure and depth, as well as its mineral contents, admirably
suited to the needs of agriculture. The development of soils in desert
regions is in almost all cases to be accounted for by the former
existence in the realms they occupy of a much greater rainfall than
now exists. Thus in the Rocky Mountain country, when the deep soils
of the ample valleys were formed, the lakes, as we have before noted,
were no longer dead seas, as is at present so generally the case, but
poured forth great streams to the sea. Here, as elsewhere, we find
evidence that certain portions of the earth which recently had an
abundant rainfall have now become starved for the lack of that supply.
All the soils of arid regions where the trial has been made have
proved very fertile when subjected to irrigation, which can often be
accomplished by storing the waters of the brief rainy season or by
diverting those of rivers which enter the deserts from well-watered
mountain fields. In fact, the soil of these arid realms yields
peculiarly ample returns to the husbandman, because of certain
conditions due to the exceeding dryness of the air. This leads to an
absence of cloudy weather, so that from the time the seed is planted
the growth is stimulated by uninterrupted and intense sunshine. The
same dryness of the air leads, as we have seen, to a rapid evaporation
from the surface, by which, in a manner before noted, the dissolved
mineral matter is brought near the top of the soil, where it can best
serve the greater part of our crop plants. On these a