stern 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.

A similar but greater contrast separates the mountains of eastern North
America and those of the western cordillera--the fourth and last of the
main physical divisions of the continent. In both the Laurentian and
the Appalachian highlands the eastern mountains show no trace of the
original forms produced by the faulting of the crust or by volcanic
movements. All the original distinctive topography has been removed.
What we see today is the product of erosion working upon rocks that were
thousands of feet beneath the surface when they were brought to their
present positions. In the western cordillera, on the contrary, although
much of the present form of the land is due to erosion, a vast amount is