lil REPORT OF THE STATE GEOLOGIST. 



magnesia and frequently some clay, which become much more sandy 

 and thin-bedded toward the bottom. 



Below the lower beds of limestone of the Washita Division belongs 

 the most persistent and highly characteristic bed of the Lower Creta- 

 ceous Period, which is known as the Caprina Limestone. Formed 

 originally at the bottom of the deepest sea of Cretaceous times as a 

 soft chalky mass, with beds of flints, and enclosing remains of animal 

 life of most peculiar forms, it has gradually risen, portions of it becoming 

 harder and harder, until, after untold ages of exposure, they now form 

 the capstones whose protection has preserved much of the softer material 

 which underlies them. To these hardened layers is due, in a large 

 measure, the present extent of the Grand Prairie. The strata are not 

 all hardened to this extent, however, and many of them are even yet 

 almost true chalk. In Trans-Pecos Texas also, this limestone is one 

 of the resisting agencies which have had much to do in shaping the 

 topography of the country. Here it frequently forms the entire sur- 

 face and slope of hills, as in the various ranges of the Sierra Blanca 

 Eegion. It is readily distinguishable in most places by the peculiar 

 manner of its weathering, which, while of very similar character to 

 that of the other limestones, still has an individuality of its own, in the 

 ferruginated or calcitic impressions or casts of its distinctive fossils, the 

 Caprina crassifibra, Eoemer. Other fossils abound also, but the shell 

 named seems to be by far the most abundant. Strata of this age were 

 observed around Sierra Blanca Junction, where they are tilted and 

 even cut by porphyritic intrusions. These limestones, in the more 

 eastern part of the State, on account of their purity, are, like those of 

 the Austin Chalk, especially adapted to the manufacture of lime, and 

 are now extensively used for that purpose. 



Between the Caprina Limestones and the Basal Trinity Sands we 

 find everywhere present the chalky limestone belonging to the Co- 

 manche Peak Beds, filled with many beautiful fossils, and underlaid 

 by the lower or alternating beds of sands and limestones, more or 

 less magnesian. In these lower beds occur some interesting minerals, 

 which are the result of chemical action which has taken place since 

 the deposition of the rock. These include Epsom salts, Celestite, and 

 Anhydrite. 



TRINITY SANDS. 



The lowest beds of the great Cretaceous system are composed of sands 

 and pebbles derived from the ancient shore line of the earliest Cretace- 



