61

CHAPTER II.

FROM SAN ANTONIO DE BEXAR TO FORT CLARK.

April 16.-After leaving San Antonio, we traveled over a level and highly fertile prairie, thickly strewn in places with coarse angular fragments of white and grayish white limestone, often crowded with the same fossils as found in the vicinity of San Antonio. At the distance of four miles we encountered thick beds of indurated blue marly clay, which continued to be frequently exhibited until we arrived near Leon Creek, where it disappeared beneath the limestone, and was not again met with during the day. The suface now became undulating, more or less broken, and in places thickly covered with coarse silicious nodules, many of them encrusted with a white coating of carbonate of lime, which sometimes acted as a cementing material to form them into a coarse conglomerate. When broken they exhibited various shades of blue and brown, not unfrequently crossed by parallel lines. They have been derived from the disintegration of the adjacent limestone, in which they were often found embedded in great numbers.

At the crossing of Leon Creek a good section is exposed of nearly horizontal layers of white pulverulent limestone, with nodules of flint, and fine-grained greenish calcareo-silicious sandstone. The limestone is superimposed upon the sandstone, and is itself surmounted by about ten feet of partially consolidated detritus of coarse angular and rounded fragments of compact bluish-gray limestone, containing an abundance of water-worn fossils of the following species:

• Exogyra costata,
• E. arietina,
• and Pecten quadricostata.

From the general appearance of the fossils they evidently could not have been transported far.

Near this locality occurs a low exposure of soft light-gray earthy limestone, containing fossils evidently of the Tertiary Era. This rock is only visible at a few points, resting directly on the Cretaceous Limestone. The larger part of the formation appears to have been removed by denudation.

The soil, during the day's march, was thick and very productive. Subsoil mostly calcareo-argillaceous.

Distance, 12 miles.

April 17.-A half mile from our last camp we reached a gently sloping prairie, thickly studded with small hillocks and ridges, varying from a few inches to several feet in height. These are of frequent occurrence throughout various portions of Texas and the adjacent Indian Territories, and are everywhere known by the name of " Hog Wallows." Wherever they occur they impart to the face of the country a peculiar waved appearance, and are generally supposed to indicate a rich soil.