69

CHAPTER III.

FROM FORT CLARK TO THE LOWER EMIGRANT CROSSING OF THE RIO PECOS.

April 26.-Shortly after leaving Fort Clark I observed several miles north of our road a number of conical hills, very rugged in their outlines, and bearing a close resemblance to the hills of basalt before encountered. They doubtless have the same geological structure.

During the day we continued to travel over white arid grayish white limestone in thick beds, occasionally more or less folded. This rock agrees lithologically as well as paleontologically with the building stone of San Antonio, and is now employed in the construction of the government buildings at Fort Clark, for which purpose its softness and the ease with which it is wrought, together with its property of acquiring hardness on exposure, renders it exceedingly valuable. In ravines at several points I saw exposures of this rock from eighty to a hundred feet thick.

The surface of the country traversed to-day was gently rolling, and often thickly covered with fragments of limestone, among which loose masses of brown iron ore were frequently observed.

Soil dark, calcareous, and highly productive.

Distance, 9½ miles.

April 27.-No change in the character of the strata was observed during the first few miles of this day's travel. The general surface of the country is flat, although frequently traversed by ravines, in which the Cretaceous rocks are well exhibited. From some of these ravines specimens of Ammonites vespertinus, Inoceramus Crispii, and other cretaceous fossils, were obtained.

In about ten miles we again encountered heavy deposits of fragments of Cretaceous Limestone, often firmly cemented with calcareous matter, and agreeing in every respect with that encountered east of the Rio Frio. The country at the same time was quite uneven, and intersected in every direction by rocky canyons, from thirty to forty feet in depth, and which have been excavated by running water.

About eleven o'clock we reached the Arroyo Pedro, a clear stream of excellent water, with a broad, flat, rocky bed. Here is an exposure, upwards of a mile in length, of cream colored, compact, brittle, fine textured limestone, breaking with a conchoidal and splintery fracture. Many of the layers are susceptible of a good polish, and some present all the characters of an excellent lithographic limestone. The beds exhibit a thickness of about fifty feet, and their geological position is above the white chalky limestone. No fossils were detected in any part of the mass.