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the production of alum in this country is imported. Special attention will be given to the search for proper clays for this purpose during the next field season.
STRONTIA.
Two minerals having this earth as a base (celestite and strontianite) are found in the lower magnesian rocks of the Cretaceous of Central Texas. It is found at Mount Bonnel near Austin, and in the vicinity of Lampasas, and can be expected to occur wherever the proper horizon of the Cretaceous rocks containing it are found at the surface. It is not only used in the form of nitrate for fireworks, but also in the manufacture of sugar.
EPSOMITE.
Crystalline masses of Epsom salts are found in the same series of beds that contain the strontianite and celestite. It is extremely doubtful, however, whether it can be made commercially valuable.
THE ARTESIAN WATER CONDITIONS OF TEXAS.
Artesian water is rain water which has fallen on some porous bed or stratum of earth and has followed the sloping course of this bed between other beds, which were sufficiently impervious to confine it until it has found an opening to the surface, either natural or artificial, at a lower level than its original source, through which it rises and flows off. When this opening is a natural one it is a spring; when artificial it is an artesian well.
The artesian water conditions of a region are dependent upon its geology, topography, and its rainfall. The geologic conditions are that there shall be a continuous porous stratum enclosed between two strata that are impervious. Topographically it is necessary that the exposed portion of this porous stratum—the "catchment" basin—be at sufficient elevation above that of the mouth of the wells to force a steady flow of water by hydrostatic pressure; and finally the rainfall must be sufficient within the area covered by the catchment basin to secure the steady supply of water. Unless all of these conditions be favorable there can be no constant supply of flowing water obtained.
"The conditions of artesian wells were fully discussed by Prof. T. C. Chamberlin in the Fifth Annual Report of the United States Geological Survey. A brief statement of the main features, compiled from this valuable article, was published in the First Report of Progress of this Survey, pp. 21-28.