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gently-rounded hills and bold escarpments about two hundred feet in height, but as we travel westward from this place they increase rapidly in thickness, and at the San Pedro or Devils River, as well as at other points, they show a vertical development of upwards of a thousand feet, and constitute the prevailing surface formation until we arrive within a few miles of the Horsehead Crossing of the Rio Pecos. West of this point they are observed at frequent intervals as far as the sources of Delaware Creek, twenty-one miles east of the Guadalupe Mountains, and in this vicinity exhibit a thickness of five or six hundred feet. (Vide Journal) Farther south their development is equally well marked along the base of the Limpea Mountains, as well as at several intermediate points.

On our return route from the Rio Pecos by way of Fort McKavett, Fort Mason, and Fredericksburg, they are the prevailing rocks as far as San Antonio, being interrupted occasionally by igneous protrusions, upheaved strata of the Paleozoic Period, and bands of red marls of the Lower Cretaceous Group. At several localities along this route the thickness of the Upper Cretaceous strata was estimated at about eleven hundred feet.

North of this route we find these rocks also well developed. From Fort Towson to Fort Washita, and thence in a southwest direction, they are traced almost uninterruptedly as far as the Upper Cross Timbers of Texas. In the vicinity of Fort Washita, and at several localities between that point and the Cross Timbers, they exhibit a vertical thickness of three or four hundred feet, though in this part of the district their usually observed thickness is from one to two hundred feet.

Along the Big and Little Witchita Rivers these rocks form abrupt and gently-rounded hills from four to five hundred feet high. On the Upper Brazos River they occur in elevated plateaus, and near the head of that stream appear in nearly perpendicular escarpments six or seven hundred feet high, forming here those high table lands that stretch away for many miles to the north, south, and west.

Again, these rocks are equally well developed in the region watered by the Upper Red River. Near the source of the Ke-che-ah-que-ho-no, or main branch of Red River, they exhibit a thickness of about six hundred feet, and form the bold escarpments which there characterize the eastern borders of the Llano Estacado.

Finally, other observers have shown the existence of the rocks of this division of the Cretaceous System along the Canadian River, and at a number of points north of that stream.

In the vicinity of Fort Washita the Upper Cretaceous Limestone is usually hard, fine textured, and sometimes more or less crystalline. Its color varies from light gray to blue, yellow, and brown, and not unfrequently it is pure white.