The Geology and Mineral Resources of Bexar County Volume 1932 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 Excerpt: ...the underlying formations over considerable areas. The low and relatively recent flood-plains have been shown where best developed bordering the larger water courses; of the next older and higher deposits, the Leona formation, there have been shown on the map the large areas lying southwest, south, and southeast of San Antonio; of the highest plain, referred to the Uvalde formation, there have been shown some areas in which the formation occupies uninterruptedly several square miles. All of these flood plains are more extensive than is here shown. Because of the presence of these surface materials, the boundary between the successive marine formations is necessarily placed in parts of the county on data from limited exposures, supplemented by well records. Where the surface is entirely obscured, the approximate boundary of the underlying marine formations has in some instances been indicated by broken lines, the data for placing the boundary being obtained chiefly from well records. As information is accumulated on the geology of this and the adjoining counties, the boundary lines of the formations can be more exactly determined. In mapping structure the Del Bio has been used as a key horizon and the contours are drawn as on the top surface of this formation. In using well records and reducing elevations to sea level it has been necessary to determine the approximate surface level of the wells from the topographic map. In that part of the county for which there is no topographic map the elevations for wells near the public roads have been obtained from the profiles of public roads made by the County Engineer of Bexar County, kindly made accessible for this purpose. In a few wells not on the area topographically mapped and remote from the public roads, an es...