lxXViii REPORT OF THE STATE GEOLOGIST. 



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 Bonne] 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 manufac- 

 ture 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 ofT. 

 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. 



