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The strata of the Gaudalupe Mountains from bottom to top belong to the Carboniferous formation. Beds of this age also extend into the valley below. The strata in the mountains dip at various angles, and are more or less metamorphosed. The mountain strata are principally limestone. The strata in the valleys approach nearer to a horizontal position and are composed of sandstones, shales, and limestones with fossils characteristic of that age. Between the mountains and the western escarpment of the gypsum beds of the Permian there is a wide valley, over which there is spread a thick bed of Quaternary drift.

Cretaceous beds were not seen after leaving Tucumcari, until we reached the country south of the southern extension of the Guadalupe Mountains. The highest part of the Cretaceous beds that we saw north of the Davis Mountains was the Arietina beds, or the upper part of the Washita division; below them were the beds bearing Ostrea quadru-plicata Shumard. And only further eastward were the lower beds seen.

The Tertiary beds, the same as those forming the upper part of the Staked Plains, occur at various localities in this district in broad valleys that reach occasionally from the foot of the mountains to the river on its western side. I saw a few patches of it east of the river. There are also large areas covered with Quaternary drift, composed of the peb- bles brought down from the mountain sides. This drift is not confined to the river valleys, but is also spread out over the high plateaus.

There is some evidence that at a late geological period there existed an inland fresh water lake, in that part of the district under consideration, which was afterwards drained by the Pecos river, when it cut through the heavy Cretaceous strata on the south We have collected some facts during the past summer that indicate such a state of things, but they have not been sufficiently studied to warrant a positive assertion on the subject.

WATER SUPPLY.

Water sufficient for all purposes is obtained on the Staked Plains from shallow wells, lakes and the streams, and springs found in the various canyons.

The water-bearing stratum lies at the base of the Tertiary or upper division of the plateau. This water has very little hydrostatic pressure, and as a consequence it rises very little in any of the wells. As has been stated elsewhere in this paper, this strata thickens toward the northwest, and as a consequence the wells increase in depth in that direction. The supply of water in this stratum is practically inexhaustible, and an abundant supply of water may be had at any. given locality by sinking wells down to this water-bearing bed. The wells that have already been put down range in depth from twenty to three hundred