A 

 BRIEF DESCRIPTION 



OF THE 



CRETACEOUS BOCKS OF TEXAS AND THEIR ECONOMIC USES.* 



Based Principally Upon a Preliminary Section along the Colorado River from 



near Smithicick Mills, Burnet County, to Webber ville, Travis County. 



ROBT. T. HILL. F. G. S. A. 



SYNOPSIS. 



The Cretaceous Areas of Texas Briefly Defined. — G-eneral Statement of the Import- 

 ance of the Underlying Eock Structure — Broadly Subdivided into the Black and G-rand 

 Prairie Regions. 



Tee Upper Cretaceoes. or Biace Prairie, Series. — The Black Prairie and its Subdivis- 

 ions — Its Underlying Eock Sheets — The Lower Cross Timber Sands — The Eagle Ford 

 Clays — The "White Eock." or Austin-Dallas Chalk — The Exogyra Ponderosa Marls, or 

 Main Black Prairie Beds — The Uppermost or Sandy G-lauconitic Beds. 



The Lower Cretaceous, or Comaxche, Series. — The G-rand. or Fort Worth, Prairie — Com- 

 pared with the Black Prairie — The Trinity Sands, or Upper Cross Timber Beds — The 

 Fredericksburg Division — The Basal Alternating, or Magnesian Beds — The Comanche 

 Peak Chalk, and the Caprotina Limestone — The Occurrence of Flints in the Latter Beds — 

 The Leander Beds — The "Washita Division, or Fort Worth Limestone — The Exogyra Ari- 

 etina Clays — The Shoal Creek Limestone and the Denison Beds. 



Tabeiar Eevtew of she Cretaceoes System of Texas. — Economic Features of the Cre- 

 taceous System — The Agricultural Soils and Natural Fertilizers — The Building Material — 

 Peculiar Adaptability for the Manufacture of Portland and Hydraulic Cements — Impor- 

 tant "Water Conditions — Mineral Products — Lines of Investigation for the Future. 



The two series of rocks comprising the Cretaceous System occupy the area 

 of the State known as the Black Prairie, the Grand Prairie, and. the two 

 Cross Timbers, and unstudied areas in the eastern and trans-Pecos regions 

 of the State. 



* Most of the scientific facts contained in this paper have been published from time to 

 time in various publications by the author, lists of which, with other references to the liter- 

 ature, fossils, and more technical points, have been published in Bulletin No. 4 of this Survey. 



