The Plains
The plains of North America form the third of the four main physical
divisions of the continent. For the most part they lie between the great
western cordillera on one side and the
Laurentian and
Appalachian highlands on the
other. Yet they lap around the southern end of the Appalachians and run
far up the Atlantic coast to New York. They remained beneath the sea till
a late date, much later than the other three divisions. They were not,
however, covered with deep water like that of the abysmal oceans, but only
with shallow seas from which the land at times emerged. In spite of the
old belief to the contrary, the continents appear to be so permanent that
they have occupied practically their present positions from the remotest
geological times. They have moved slowly up and down, however, so that
some parts have frequently been submerged, and the plains are the 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.
Peneplainpeneplain (PEE-nuh-playn, pee-nuh-PLAYN)
noun |
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 marshes and swamps. The rich soil and
the moisture are good for rice, but the region is so unhealthy and
so hard to drain that only small parts are inhabited.
Everywhere in the coastal plain this same belted character is more
or less evident. It has much to do with all sorts of activities from
farming to politics. On consulting the map showing the cotton
production of the United States in 1914, one notices the two dark
bands in the southeast. One of them, extending from the northwestern
part of South Carolina across Georgia and Alabama, is due to the
fertile soil of the Piedmont region. The other, lying nearer the
sea, begins in North Carolina and extends well into Alabama before
it swings around to the northwest toward the area of heavy
production along the Mississippi. It is due to the fertile soil of
that part of the coastal plain known as the "cotton belt." Portions
of it are called the "black belt," not because of the colored
population, but because of the darkness of the soil. Since this land
has always been prosperous, it has regularly been conservative in
politics.
The Atlantic coastal plain is by no means the only part of the
United States where the fertility of the soil is the dominant fact
in the life of the people. Because of their rich soil the prairies
which extend from western Ohio to the Missouri River and northward
into Canada are fast becoming the most steadily prosperous part of
America. They owe their surpassing richness largely to glaciation.
We have already seen how the coming of the ice-sheet benefited the
regions on the borders of the old Laurentian highland. This same
benefit extended over practically the whole of what are now the
prairies. Before the advent of the ice the whole section consisted
of a broadly banded coastal plain much older than that of the
Atlantic coast. When the ice with its burden of material scraped
from the hills of the north passed over the coastal plain, it filled
the hollows with rich new soil. The icy streams that flowed out from
the glaciers were full of fine sediment, which they deposited over
enormous flood plains. During dry seasons the winds picked up this
dust and spread it out still more widely, forming the great banks of
yellow loess whose fertile soil mantles the sides of many a valley
in the Mississippi basin. Thus glaciers, streams, and winds laid
down ten, twenty, fifty, or even one hundred feet of the finest,
most fertile soil. We have already seen how much the soil was
improved by glaciation in Wisconsin and Ohio. It was in the prairie
States that this improvement reached a maximum. The soil there is
not only fine grained and free from rocks, but it consists of
particles brought from widely different sources and is therefore
full of all kinds of plant foods. In most parts of the world a
fine-grained soil is formed only after a prolonged period of
weathering which leaches out many valuable chemical elements. In the
prairies, however, the soil consists largely of materials that were
mechanically ground to dust by the ice without being exposed to the
action of weathering. Thus they have reached their present
resting-places without the loss of any of their original plant
foods. When such a soil is found with a climate which is good for
crops and which is also highly stimulating to man, the combination
is almost ideal. There is some justification for those who say that
the north central portion of the United States is more fortunate
than any other part of the earth. Nowhere else, unless in western
Europe, is there such a combination of fertile soil, fine climate,
easy communication, and possibilities for manufacturing and
commerce. Iron from that outlier of the Laurentian highland which
forms the peninsula of northern Michigan can easily be brought by
water almost to the center of the prairie region. Coal in vast
quantities lies directly under the surface of this region, for the
rock of the ancient coastal plain belongs to the same Pennsylvanian
series which yields most of the world's coal. Here man is, indeed,
blessed with resources and opportunities scarcely equaled in any
other part of the world, and finds the only drawbacks to be the
extremes of temperature in both winter and summer and the remoteness
of the region from the sea. Because of the richness of their
heritage and because they live safely protected from threats of
foreign aggression, the people who live in this part of the world
are in danger of being slow to feel the currents of great world
movements.
The western half of the plains of North America consists of two
parts unlike either the Atlantic coastal plain or the prairies. From
South Dakota and Nebraska northward far into Canada and westward to
the Rocky Mountains there extends an ancient peneplain worn down to
gentle relief by the erosion of millions of years. It is not so
level as the plains farther east nor so low. Its western margin
reaches heights of four or five thousand feet. Here and there,
especially on the western side, it rises to the crest of a rugged
escarpment where some resistant layer of rocks still holds itself up
against the forces of erosion. Elsewhere its smooth surfaces are
broken by lava-capped mesas or by ridges where some ancient volcanic
dike is so hard that it has not yet been worn away. The soil, though
excellent, is thinner and less fertile than in the prairies.
Nevertheless the population might in time become as dense and
prosperous as almost any in the world if only the rainfall were more
abundant and good supplies of coal were not quite so far away. Yet
in spite of these handicaps the northwestern peneplain with its vast
open stretches, its cattle, its wheat, and its opportunities is a
most attractive land.
South of Nebraska and Wyoming the "high plains," the last of the
four great divisions of the plains, extend as far as western Texas.
These, like the prairies, have been built up by deposits brought
from other regions. In this case, however, the deposits consist of
gravel, sand, and silt which the rivers have gradually washed out
from the Rocky Mountains. As the rivers have changed their courses
from one bed to another, layer after layer has been laid down to
form a vast plain like a gently sloping beach hundreds of miles
wide. In most places the streams are no longer building this up.
Frequently they have carved narrow valleys hundreds of feet deep in
the materials which they formerly deposited. Elsewhere, however, as
in western Kansas, most of the country is so flat that the horizon
is like that of the ocean. It seems almost incredible that at
heights of four or five thousand feet the plains can still be so
wonderfully level. When the grass is green, when the spring flowers
are at their best, it would be hard to find a picture of greater
beauty. Here the buffalo wandered in the days before the white man
destroyed them. Here today is the great cattle region of America.
Here is the region where the soul of man is filled with the feeling
of infinite space.
To the student of land forms there is an ever present contrast
between those due directly to the processes which build up the
earth's surface and those due to the erosive forces which destroy
what the others have built. In the great plains of North America two
of the divisions, that is, the Atlantic coastal plain of the
southeast and the peneplain of the northwest, owe their present form
to the forces of erosion. The other two, that is, the prairies and
the high plains, still bear the impress of the original processes of
deposition and have been modified to only a slight extent by
erosion.
