with the slope of the adjacent country. It is the _motion of
translation_ which a wave acquires on reaching shallow water, that gives
it such great capacity for the transportation of material.

This _translative action_, as it is technically called, commences
ordinarily in about three fathoms water, and is most violent in six or
eight feet depths, within which the sea breaks. It is just within the
breaker that the windrows of sand are observed to form on exposed flats.

This disposition of the sea to cast up well defined boundaries of sand
along its margin, is so great and persistent, that the inland waters are
dammed up and suffered only to escape into the ocean by narrow avenues,
where their rapid currents maintain a supremacy of power--albeit with
unceasing contest.

Wherever, along our coast, the waves drive _obliquely_ upon the beach, a
movement of the sand takes place, and the inlets are consequently
continually shifting.

The Long Island inlets are moving _westward_, and Sandy Hook advances to
the _northward_, because the sea rolls in along the axis of the great
bay between Long Island and New Jersey, and necessarily sweeps along the
beaches, instead of taking the direction of a _normal_ to the shore
line.

The movement of Sandy Hook to the northward is, however, a problem not
so easily disposed of as we might conceive from the above
considerations; for although, in the most general sense, its existence
must be regarded as the work of the waves, there are other agents
influencing materially its form and its rate of progress. The currents
control, to a very great extent, the final disposition of the sands worn
away or kept in motion by the waves.

Professor Bache's investigations in the neighborhood of Sandy Hook have
been published, and we should not especially refer to them here, except
that the recent physical changes reported by Colonel Delafield to the
Engineer Department, have reawakened an interest in the matter.

The measurements of the Coast Survey, made in 1856 and 1857, showed that
the Hook was being washed away on the east and west shores, but was
extending slowly to the northwest, where it already encroached on the
main ship channel. This order of things has continued up to the present
time, and is now in progress.

The able Superintendent of the fortifications at Sandy Hook has evinced
considerable alarm lest the new fort shall fall a prey to the
encroachments, or be separated from the mai