The remains of shell banks along the inner mar gin of this great, and but very slightly inclined plain, fully establish the fact, that over its whole surface the ocean once rolled, and by a slow reces sion left most of the surface dry land. The bays and sounds are, however, remains of the former shallow ocean border. We are naturally, or more correctly by custom, led to estimate the depth of water on coasts, relative to the draught of ships, and to designate bays, gulfs and river mouths and channels deep, if that depth exceeds the utmost in which the largest vessels float, but philosophically speaking, a depth of even 40 or 50 feet is really shallow when compared with that of any large sea, much less an ocean. But, on the scale we usually estimate water depth, the rivers and sounds of the United States, contained in the great alluvial physi cal section south-west from the Chesapeake, are shallow, one river only, the St. Marys, admitting the entrance of the largest vessels; and in many in stances of apparently spacious harbours, the small est coasters are navigated with difficulty. If the Atlantic Ocean is still receding, the result, in a se ries of ages, must produce radical changes, and many expensive experiments have been made to de termine a much less important problem. When in Europe the abasement of the Baltic Sea was first suggested, the fact was rejected with something like horror, but the only safe test of truth finally put the contest at rest, and compelled the adoption of the result with all its consequences. This very interesting part of geographical history will be again touched under the head of river basins; we now return to our review of the great and general outlines of the physical sections.
Receding westward from the Atlantic Ocean along the zone, between the 30th and 31st degrees of north latitude, the alluvial plain is perpetuated over the peninsula of Florida, and thence westward along the northern coast of the gulf of Mexico, through 71 degrees of longitude, or about 450 statute miles to the estuary of Pascagoula river. Here the vast Delta of the Mississippi protrudes the alluvion to the 29th degree of North Lat., gradually, however. again receding to the northward, between 29° and 30° North Lat. passes the Sabine, stretching be yond the limits of the United States.
There is one feature of the alluvial zone north of the Gulf of Mexico, which demands particular no tice, as it is connected with a phenomenon very lit tle known. Between Vacassansa Bay of the western coast of the Gulf of Mexico and the mouth of the Mississippi river, extends an elliptical bay, the longer axis of which is North Lat. 29°. This bay curves to North Lat. 23', between the mouths of the rivers Appalachicola and Pascagoula, and along this part of the coast of the Gulf of Mexico the alluvial plain is narrow, and confined, indeed, to the small counter-bays of St. Joseph's, St. An drew's, Choctaw, Pensacola, Mobile, and Pasca goula. To the westward from the outlet of Pas cagoula, the coast entirely changes character. The Delta of the Mississippi is protruded upwards of eighty minutes of latitude directly into the Gulf of Mexico; and again, to the westward of the Delta to the Sabine, the alluvial zone is spread, as already noticed, about one degree of latitude south of its extent in that direction, east of the Delta.
The writer of this article personally examined the coast of Louisiana and Florida, and, in the pro. gress of that survey, found that the debris, or wood floated out of the Mississippi river, was invariably borne westward from the outlets of that stream.
These fragments of timber, or not unfrequently whole trees of vast size, lie scattered along the gulf margin, and afford the only fuel on that dreary coast. The northern shore of the great bay between the Delta and West Florida is covered with a dense forest. This forest is continued on very nearly the same geographical zone to the Sabine, whilst on, and directly westward of the Delta, the much most extensive part of the land surface is denuded of tim ber, presenting an immense series of grassy plains, with partial clumps or very thin selvedges of trees along the streams.
It may be placed amongst the most remarkable facts in the hydrography of the earth, that a canal or series of canals, and bay or sound navigation, could be constructed from the mouth of Hudson river to that of Sabine, with a rise of very little, if any, above 200 feet, and seldom more than from 10 to 20 feet; a series which, if formed, would consti tute the most important and productive chain of inland navigation which the surface of our planet admits.
Over the long and wide alluvial plain we have glanced upon, flow the numerous rivers having their origin on the Appalachian nucleus in its rear. Those rivers we now proceed to notice, advancing from north-east to south-west; giving the name of the basin to the main stream, which terminates in the oceanic recipient.
Hudson river, as connecting two physical sec tions, comes appropriately under either head, but when carefully examined on a map, in connexion with the minor basins of Passaic and Raritan, the basins of Hudson and Delaware are more intimately blended than is the former with the contiguous ba sins of St. Lawrence, Connecticut, and Housatonick. Taken in its utmost extent, the Hudson basin pre sents a marked anomaly amongst the Atlantic ri vers. By the main channel, the ocean tides traverse the primitive chains, and reach the base of the cen tral secondary. The Hudson is formed by two branches; the northern, or Hudson proper, and the western, or Mohawk.
The Hudson has its remote source interlocking with those of the Racket river branch of St. Law rence, and with those of the Saranac and Sable ri vers flowing into Lake Champlain, at about N.Lat. 44°, Lon. E. from W.C. Flowing south south eastward until only separated by a narrow ridge of five miles from Lake George, the Hudson deflects to the south, and at about 50 miles comparative course from the source, receives the Sacondago river from the west. Both those streams rise in the valleys of a ridge or rather chain of mountains, the con tinuation of the Catsbergs, as we shall see in the sequel. Below their junction the course of the united waters is to the eastward 12 miles direct, but a much greater distance following the channel, to where it is precipitated down a mountain ledge called Glenn Falls, and enters the very peculiar valley formed by Hudson river, Lake Champlain, and Sorel or Richelieu river. There is only one other known valley of the earth having specifically similar features with that we are reviewing. Scot land is divided into two unequal parts by a vale, extending from the Atlantic Ocean on the north west side of the island, in a direct course nearly N.E. into Murray Frith or bay, of the German Sea, length 120 miles. This valley is well designated by the term glen, signifiying a confined vale between steep and impending hills or mountains. The Caledonian Canal now unites the small rivers and lochs or lakes of the Scottish Glen, and admits the navigation of frigates across the island of Britain.