parts that remained longest under water.

The plains of North America may be divided into four parts
according to the character of their surface: the Atlantic coastal
plain, the prairies, the northwestern peneplain, and the
southwestern high plains. The Atlantic coastal plain lies along
the Atlantic coast from New York southward to Florida and
Alabama. It also forms a great embayment up the Mississippi
Valley as far as the Ohio River, and it extends along the shore
of the Gulf of Mexico to the Rio Grande. The chief characteristic
of this Atlantic and Gulf coastal plain is its belted nature. One
layer of rocks is sandy, another consists of limestone, and a
third of clay. When uplifted and eroded each assumes its own
special topography and is covered with its own special type of
vegetation. Thus in South Carolina and Georgia the crystalline
Piedmont band of the Appalachian province is bordered on the
southeast by a belt of sandstone. This rock is so far from the
sea and has been raised so high above it that erosion has
converted it into a region of gentle hills, whose tops are six
hundred or seven hundred feet above sea-level. Its sandy soil is
so poor that farming is difficult. The hills are largely covered
with pine, yielding tar and turpentine. Farther seaward comes a
broad band of younger rock which forms a clayey soil or else a
yellow sandy loam. These soils are so rich that splendid cotton
crops can be raised, and hence the region is thickly populated.
Again there comes a belt of sand, the so-called "pine barrens,"
which form a poor section about fifty miles inland from the
coast. Finally the coastal belt itself has emerged from beneath
the sea so recently and lies so nearly at sea-level that it has
not been greatly eroded, and is still covered with numerous