THE LOWER OR COMANCHE SERIES. 123 



valuable building material, among which may be mentioned building stones 

 of value for domestic uses and exportation. Some of these stones have rich 

 magnesian buff-yellow colors, while the limestones often resemble in every 

 detail the famed stone of Oaen, France, which is imported into the non-chalky 

 regions of the East for the purpose of adding brightness to the sombre colors. 

 They are especially used in interiors, where the ease with which they can be 

 carved renders them of great value. 



The magnesian beds are also exceedingly valuable for the manufacture of 

 hydraulic cements, although to-day they are unappreciated. There are also 

 valuable beds of epsom salts, glauber salts, gypsum, strontianite, and other 

 materials in these rocks, for all of which there is a commercial use in our 

 civilization. 



2 h. THE COMANCHE PEAK SUBDIVISION. 



Immediately above the E. texana beds the great series of alternations termi- 

 nate in a massive persistent chalky division, marking, no doubt, the begin- 

 ning of the culmination of the great subsidence of the sea bottom (as re- 

 corded in the succeeding Caprina chalk) which had been going on since the 

 pre-Trinity land epoch. This subdivision is composed of white chalky lime- 

 stone, which readily yields to disintegration, usually forming the sloping 

 sides of buttes and mesas, and capped by the Caprina chalk, next to be 

 described. It is characterized by its abundant fossil remains.* 



The chalky beds of the Comanche Peak subdivision are the most extensive 

 and uniform of the Comanche series, and must ever stand as the basis for 

 comparison from which to estimate the relative value of the overlying and 

 underlying horizons. It presents on weathering a sterile, rocky aspect, and 

 is covered by sparse, stunted, coriaceous vegetation. An interesting fact 

 concerning this subdivision is that several hundred feet above it, in the 

 Washita limestone, its lithologic conditions and features are simulated, but 

 modified as to species, only the Neithea quadricostata, Roemer, and Gryphcea 

 pitcheri running into the Washita division, and these presenting broad varietal 

 changes. This lithologic repetition is no doubt due to the fact that after a 

 time the descending ocean bottom again began to rise, and in so doing 

 passed through the same conditions of depth, producing the same character 

 of sedimentation. 



* The especially characteristic species are a star fish (Toxaster texanus, Rcemer), and Ammo- 

 nites pedernalis, Yon Buch. At the base of the chalk there is usually another marked bed 

 of G-rypheate oysters ( G. pitcheri, with E. texana), as seen near the summit of Mount Barker, 

 in the Bonnell ridge, Round Mountain, Comanche County, and especially in the town of 

 Weatherford, extending on to Red River. This is the second, in ascending order, of the great 

 oyster beds of the Comanche series, and is composed of countless numbers of individual shells 

 of Gryphcea, and is of marvelous areal extent. 



