133

there are several permanent lakes containing both salt and fresh water, and depressions in which rain water collects and stands for several months at a time. The only other diversity breaking the wide monotonous level are some drift sand-hills raised by the winds in the south-west.

CANYONS.

On the eastern side extensive canyons penetrate for various distances into the Plains, running from northwest to southeast, in line with the dip of the strata. The Colorado, Brazos and Red rivers all have their sources in the Plains with numerous branches extending a greater or less distance, some of them as far as one hundred miles. These canyons are the work of erosion, and no greater force was required than that now at work. When once the upper stratum is broken, and the water begins to flow over the soft material of the beds below, the channel is cut deeper each year, until the present deep canyons are the result. All have flowing streams in them, coming from the water-bearing stratum lying at the bottom of the Tertiary formation. Their sides are generally precipitous, so that at only a few places is it possible to cross them, even on horseback. Before roads were dug down one might travel for many miles without being able to cross.

SAND-HILLS.

About twenty miles west of Duro, a station on the Texas and Pacific Railroad, and south of the southeast corner of New Mexico, is a body of land known as the White Sand Hills. These hills extend from north to south about sixty miles, and are about fifteen miles wide. The whole area is covered with mounds composed of white quartz sand, rising in height from ten to thirty feet. They present steep ascents through short distances in many places, and the loose movable character of the sand and its depth render the passage of wagons through it next to impossible.

On approaching these hills from the east or west, they can be seen for long distances. The reason of their occurrence at this place and in their present form has not been determined. There are a great many lakes and ponds in these sand-hills, ranging in depth from three to five feet.

Their whole surface is covered with a growth of scrubby oak, known as "Shinoak," which now forms an obstacle against which the sand will and does deposit, and this may have been the original cause.

There are two probable sources of the material composing these hills —one of them the superficial covering of sandy soil that occurs almost everywhere on the Staked Plains, and the other the sandstones and sand that compose the underlying strata which are exposed at the surface southwest of this area.