gh tide. For the greater part of
the time it appears as broad savannas, whose brilliant green gives
them the aspect of rare fertility.

Owing to the conditions of their growth, the deposits formed in marine
marshes contain no distinct peat, the nearest approach to that
substance being the tangle of wirelike roots which covers the upper
foot or so of the accumulation. The greater part of the mass is
composed of fine silt, brought in by the streams of land water which
discharge into the basin, and by the remains of animals which dwelt
upon the bottom or between the stalks of the plants that occupy the
surface of the marshes. These interspaces afford admirable shelter to
a host of small marine forms. The result is, that the tidal marshes,
as well as the lower-lying mud flats, which have been occupied by the
mat of vegetation, afford admirable earth for tillage. Unfortunately,
however, there are two disadvantages connected with the redemption of
such lands. In the first place, it is necessary to exclude the sea
from the area, which can only be accomplished by considerable
engineering work; in the second place, the exclusion of the tide
inevitably results in the silting up of the passage by which the water
found its way to the sea. As these openings are often used for
harbours, the effect arising from their destruction is often rather
serious. Nevertheless, in some parts of the world very extensive and
most fertile tracts of land have thus been won from the sea; a large
part of Holland and shore-land districts in northern Europe are made
up of fields which were originally covered by the tide. Near the mouth
of the Rhine, indeed, the people have found these sea-bottom soils so
profitable that they have gone beyond the zone of the marshes, and
have drained considerable seas which of old were permanently covered,
even at the lowest level of the waters.

On the coast of North America marine marshes have an extensive
development, and vary much in character. In the Bay of Fundy, where
the tides have an altitude of fifty feet or more, the energy of their
currents is such that the marsh mat rarely forms. Its place, however,
is taken by vast and ever-changing mud flats, the materials of which
are swept to and fro by the moving waters. The people of this region
have learned an art of a peculiar nature, by which they win broad
fields of excellent land from the sea. Selecting an area of the flats,
the surface of which has been brought