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IV.—WATER SUPPLY.

With the geology what it is, a more favorable arrangement for the distribution of the water supply than that which exists could hardly be imagined. The Devil's, Las Moras, Nueces, Frio, Sabinal and Medina rivers flowing southward, with smaller intervening streams, all start from springs suddenly emerging in rocks of nearly the same horizon. Wells bored at various points between these springs and the very similar ones which feed the northward flowing streams across the divide—the South Concho river, Lipan and Kickapoo creeks and the South Fork of the Llano river—give no uncertain record. From these it appears that a vast body of underground water lies like an overflowing lake beneath this great divide The fact is all we can mention in this brief review, but it indicates much of geologic importance which may be discussed in our final report.

In questions of underground water supply the geologic structure is a very essential factor, whose relation to artesian possibilities is of vital moment. The arrangement of the strata in this region is not only admirably adapted to the collection of the rainfall of the district itself, but it affords an extensive catchment area and a well formed storage basin. Judging from what my own observations teach concerning the proximity and relations of the older rocks, and from a comparison with the known conditions further east, there appears good warrant for the belief that deeper-seated and more extended sources of supply are concerned in the filling of the reservoir in question. The topic is, however, too broad for full treatment in these pages. Complete instrumental data have been collected, and the results of the investigation will soon be forthcoming. Carefully prepared sections will be necessary to clearly illustrate the situation.

ARTESIAN WATER.

The conditions needed for the ready supply of water in the artesian wells are an extensive catchment basin, a porous collecting stratum between two retaining layers, and an outlet at a point where the pressure is less than at the surface of the reservoir. These conditions are all fulfilled save the last over the largest part of the region we are now considering. In some few places, chiefly where springs are abundant enough to make artesian water unnecessary, it might be feasible to secure flowing wells, but the reservoir is usually too low to make this possible unless it be in the southern portion of the tract. There the pressure is not usually sufficient to bring the water to the surface, and in some districts it cannot be obtained by boring even to great depths. Possibly, however, by going much deeper than has yet been attempted, the deeply buried reservoir might be tapped at a point of high pressure sufficient to elevate the water within pumping distance of the surface.