d in 1635 eight feet below the Wisbeck River, and
the smith's forge and tools found at Skirbeck Shoals, near Boston, buried
with silt sixteen feet deep, show what an astonishing quantity of sediment
formerly choked up the mouths of these great rivers. But the chief
hindrance caused by the ocean, arose from the tide rushing twice every day
for a very great distance up these channels, driving back the fresh
waters, and overflowing with them, so that the whole level became deluged
with deep water, and was, in fact, one great bay.

"In considering the state of this region as it first attracted the
enterprise of man to its improvement, we are to conceive a vast, wild
morass, with only small, detached portions of cultivated soil, or islands,
raised above the general inundation; a most desolate picture when
contrasted with its present state of matchless fertility."

Salt marshes are formed of the silty deposits of rivers and of the sea.
The former bring down vegetable mould and fine earth from the uplands, and
the latter contribute sea weeds and grasses, sand and shells, and millions
of animalculae which, born for life in salt water only, die, and are
deposited with the other matters, at those points where, from admixture
with the fresh flow of the rivers, the water ceases to be suitable for
their support. It is estimated that these animalculae alone are the chief
cause of the obstructions at the mouths of the rivers of Holland, which
retard their flow, and cause them to spread over the flat country
adjoining their banks. It is less important, however, for the purposes of
this chapter, to consider the manner in which salt marshes are formed,
than to discuss the means by which they may be reclaimed and made
available for the uses of agriculture. The improvement may be conveniently
considered under three heads:--

First--The exclusion of the sea water.

Second--The removal of the causes of inundation from the upland.

Third--The removal of the rain-fall and water of filtration.

*The Exclusion of the Sea* is of the first importance, because not only
does it saturate the land with water,--but this water, being salt, renders
it unfertile for the plants of ordinary cultivation, and causes it to
produce others which are of little, or no value.

The only means by which the sea may be kept out is, by building such dykes
or embankments as shut out the highest tides, and, on shores which are
exposed to the action of the waves, wil