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in Sutton, Crockett and Val Verde counties, where the grade is not sufficient to overbalance the thickening of the strata.

The great water divide which separates the Colorado drainage from the southward flowing streams has not received the attention it deserves from geologists. As a mere topographic landmark it is remarkable, but when viewed as a structural boundary, it will repay very careful scrutiny. A hasty glance fails to indicate any connection with earlier rocks than the Cretaceous, except at the northwest of our area, in Tom Green county, where the Permian beds are exposed, but the evidence of the existence of a pre-Cretaceous fold throwing the earlier strata above the shore-line of the Cretaceous sea are apparent upon closer examination. Hints of the near approach of the pre-Permian, perhaps even Silurian, members are not wanting further east, and meagre exposures of granite have been reported by two members of the Texas Survey from near the line between Menard and Schleicher counties. In Val Verde county, west of Devil's river, a complicated ridge of jumbled strata of Carboniferous or Permian age forms a barrier against which the Arietina beds were laid down without subsequent disturbance. These areas of uplift are closely parallel with those which I have heretofore shown to be unmistakably pre-Cretaceous in the Central Mineral Region; and the later basaltic outflows seem to have used these very lines of weakness to some extent.

There is a question regarding the age of the basaltic outbursts. I am not yet prepared to speak conclusively upon the subject. The most northern ejections in Uvalde County follow most closely the pre-Cretaceous line of uplift, and these protrude into strata usually considered Lower Cretaceous. My observation is too limited to deny the occurrence of such igneous intrusions in the Upper Cretaceous, but the best judgment from the facts known to me is that the greater part of the basalt was contemporaneous with the deposition of the Lower Cretaceous strata. This opinion is, however, confessedly wavering from lack of detailed study of many exposures.

II.TOPOGRAPHIC FEATURES.

The topography of the Cretaceous area is distinctive and pronounced, a characteristic example of simple drainage erosion carried to a numer- ical extreme without widespread denudation. To express it otherwise, the results are those accomplished by myriads of streams of small extent, which have cut deep and narrow canyons, leaving innumerable peaks, buttes and "hog-backs" in the intervening spaces. Thus the plateau levels corresponding to successively exposed hard layers are extensive, but so badly cut up by the ramifying streams that it is impossible to travel across them except by frequent ascent and descent of steep inclines. This peculiarity gives to one following the valley roads of the country only, an id="txu-oclc-5762622-2-a046a" rend="arabic"/> who pursues the cross-country course, although either one will be liable to regard the region as more complicated in structure than it really is.

There is an individuality to each of the separate river basins, which might at first seem to be due to causes wholly independent of the rock masses, but a study of the strata leads to a contrary conclusion.

The Concho, San Saba and Llano valleys are striking examples of the influence of geologic structure upon topography. These three rivers flow in courses not widely diverse; the Concho and San Saba are coerced largely by conditions antedating the Cretaceous, but subsequent to the Carboniferous period, the general course of the Llano being guided largely by much more ancient structure, in large degree of Burnetian time. The Pedernales, the Guadalupe in part, and perhaps the Medina to some extent, occupy intermediate positions between the foregoing and the southward flowing streams, which flow down the grade of the retiring sea bottom of Cretaceous date. Occasionally the effect of earlier events, barely obscured by Cretaceous deposition, are visible in the windings of the last group of rivers, and the influence of the basaltic ejections in turning the courses of some of them locally is very evident. In some places the changes in the stream courses are inexplicable until traced to causes which would escape notice without close examination of the geology for many miles upon all sides.

In general, it may be stated that the drainage of the Cretaceous area is far less affected by post-Cretaceous movements than by the floor left by the retreating sea. But it must be remembered that this retrograde movement was not along an east west line, except for a limited distance, but rather in an irregular curve partially surrounding the Central Mineral Region. This, at least, is the view held by the writer after thorough instrumental work over that portion of the field most important to understand. It is fit to remark here that one or two able workers who have made general reconnoissances over portions of this and adjoining territory are opposed to my conclusions. The facts have, therefore, been collected with diligence and with a degree of accuracy beyond what is customary in the early stages of geologic work. The topography is a factor of great import in such investigations, for which reason our work in that direction has been minute along the lines of geologic section. The complete contographic representation of the border area must await the completion of the field work undertaken by the United States Geological Survey, an enterprise too ambitious for this Survey at present.

III.-AGRICULTURAL POSSIBILITIES.

The pastoral and agricultural capabilities of the major part of the region are by far greater than has been generally appreciated. Much of the area which is now neglected or given over to grazing can be