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report. These are often exceedingly rugged, and though generally very tortuous, all of them appear to have a general east and west direction; hence they would afford no very serious obstacle to the construction of a railroad to the Pacific.

Denudation.-Besides its numerous escarpments and canyons there are other phenomena in the region we are considering showing the great extent to which the strata of this formation have been removed by denuding agencies. There can be no doubt that the Upper Cretaceous strata at one period occupied almost the entire space included between the western borders of the settlements and the Rocky Mountains. Some of the facts upon which this opinion is based are given in detail in the accompanying Journal, and others equally conclusive are abundantly exhibited along the Colorado, Big Witchita, Upper Brazos, and Red Rivers, and at many points north of these streams. The isolated, truncated, conical hills we have so frequently encountered, and which are described by travelers as constituting one of the most characteristic features of a very considerable portion of the Plains, are nothing more than the remains of a once continuous plateau that has gradually been removed by erosion. These are often six or seven hundred feet high, and in many instances almost wholly composed of nearly horizontal strata of the Upper Cretaceous Group. They are often widely separated from each other, and as already instanced on the Brazos River, sometimes fifty or sixty miles distant from the table lands which they once formed a part. Sections .... and .... of the Journal exhibit the character of some of these hills.

Disturbance.-As will have been gathered from the foregoing remarks, the Upper Cretaceous formation exhibits generally but little evidence of violent disturbance in the district we are noticing. The strata are usually spread out in smooth parallel layers, which usually conform to the general slope of the country. The only localities in which we have observed them violently dislocated or contorted are in the southern extension of the formation; as along the base of the Limpea Mountains; near the mouth of Delaware Creek; a few miles west -of Castroville; on the San Saba and Frio Rivers; and in the vicinity of Forts Inge, Clarke. and Mason. Of these the most important is that near the Limpea Mountains, where the strata are seen contorted, fractured, and inclined against eruptive rocks at angles of from 30 to 50 degrees. The next in point of importance are the disturbed districts of Fort Mason and the San Saba River, which appear to occupy extensive areas. These are elsewhere described in this report.