A glance at a general coast chart discovers at once a marked contrast between two different sections of our seaboard: to the eastward of us, the principal harbors of New England are rockbound, with elevated back countries; while to the southward, in the region of alluvial drift, which extends all along the coast of the Middle and Southern States, the harbors have flat and sandy shores. The harbor and neighborhood of New York, holding an intermediate position between these diverse sections, exhibit a singular combination of the leading physical features of both, and present to the hydrographer a field for research that is quite without a parallel.
We recognize in the Bar of New York simply a submerged portion of that sandy cordon which skirts the coast from Montauk Point to Florida; and although, in the ordinary sense, the lower entrance to the harbor is not an inlet, it may nevertheless be regarded as belonging to the same class.
This sandy cordon, which may be said to be the principal characteristic of our coast, is an exceedingly interesting feature; it appears to have been formed by the action of the sea, which has disintegrated the borders of shallow flats, bearing away the light vegetable moulds, but suffering the coarse quartz sand to remain rolled up into ridges. In many places the dry winds have caught up these sands, when laid bare at low water, and elevated them into dunes or galls.
The distance of the sand ridge from the mainland is observed to vary 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.