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As we progressed the surface became more rolling, and often thickly coated with fragments of limestone of the same character as that met with yesterday. This deposit is sometimes accumulated to the depth of ten or twelve feet, and not unfrequently is loosely cemented with calcareous matter. Two miles to the east of our road and about six miles from the last camp, there occurs an extensive exposure of hard gray sub-crystalline limestone and thin bedded quartzose sandstone, the whole presenting a dip E. S. E. of about 2 degrees. These rocks are hard and durable, and afford excellent building materials, for which purpose they are already somewhat extensively employed in the neighborhood.

After traveling eight miles the country became still more hilly and broken, and at the same time the strata presented more or less evidence of local disturbance, but did not differ lithologically or paleontologically from the beds already noted. The pulverulent limestone still continues to be frequently seen, often exhibiting a thickness of fifteen or twenty feet. About ten o'clock we came to a small stream of clear water, along the margin of which is an exposure of about ten feet of yellow and reddish silicious limestone, containing rounded masses of flint, and compact gray limestone, replete with organic remains, chiefly, however, Exogyra costata. In places the rock is highly discolored with oxide of iron, and is undergoing rapid disintegration. The general dip is about 2 degrees to the west.

Shortly after leaving the creek we entered. an extensive and nearly flat prairie, of but little geological interest. It extends to the Medina River, which is about seventy-five feet wide, and flows over a bed of solid limestone. The water is clear and strongly impregnated with carbonate of lime. Its temperature was found to be 77 degrees F. On either side of the stream are high bluffs, one of which exhibits a vertical section of thick-bedded yellow, brown, and white limestone, with alternating bands of soft blue shale, surmounted with loose detritus derived from the destruction of these beds. The whole cliff is replete with fossils, but owing to the softness of the rock they are very poorly preserved. The most abundant forms are, Ostrea vesicularis, Pholadomya (allied to P. elegantula D'Orb.) and Trigonia and Pecten of undetermined species. The accompanying section shows the strata at this locality.

The soil, during the greater portion of the day's march, was a deep and highly productive vegetable loam; sub-soil calcareo-argillaceous.

Distance, 161 miles.

April 18.-Shortly after crossing Medina River we ascended by a gradual slope to the base of an extensive range of limestone bluffs from one to two hundred feet in height, which stretch irregularly across the country in a northwesterly and southeasterly direction as far as vision extends. They constitute the beginning of a series of abrupt ascents leading to the elevated table land of the Llano Estacado. As well as I was able to determine,