REPORT OF THE STATE GEOLOGIST. XXXV 



ferent shades of color, from chocolate to very light greens and blues. 

 The colors usually become lighter as we approach the top of the series. 

 These clays are very hard, and weather to a pure white, giving rise to 

 bluffs which are sometimes miscalled chalk bluffs on that account. 

 Sulphur and gypsum are very abundant, as well as nodules and concre- 

 tions of carbonate of lime. Even the chocolate clays often weather 

 white upon the surface, and must be dug into before they will reveal 

 their true character. This is due to certain chemical reactions which 

 take place among the included minerals and vegetable matter, result- 

 ing in decomposing and leaching out the small amount of iron and 

 carbonaceous matters contained in the surface of the clays. , Lignite 

 beds are found in connection with them, but there has not been time to 

 examine them closely enough to reach any decision as to their probable 

 value. 



Many of the clays of this formation will prove of great value for 

 pottery, fire brick, and similar uses. Some of them are free from iron 

 and other objectionable ingredients, and burn to a pure clean white 

 color; others, somewhat less pure, still vitrify beautifully on burning, 

 and closely resemble the body of the common Chinese china. They 

 are especially adapted to the manufacture of paving tile and brick, 

 either alone or mixed with other clays. The sands furnish most ex- 

 cellent material for mortar and plaster, being sharp, light colored, and 

 clean. The sandstones are of great value as building material. They 

 are now being extensively quarried for use as rock material for the 

 jetties at Galveston bar and the mouth of the Brazos. These beds of 

 sandstone cross the Neches at Rockland, the Trinity at Trinitv, the 

 Colorado at La Grange, and are found at many other localities between 

 and beyond these points. It is in them and the overlying sands that 

 the water-bearing beds exist from which artesian water is obtained 

 throughout the Gulf coast prairies. 



Along the rivers of Central Texas these alternating beds of sands 

 and clays so store and hold the water as to make their exposed edges 

 the natural home of the most luxuriant fern growth, the exquisite 

 beauties of which can nowhere be surpassed. 



Overlying these beds are large deposits of gravel drift, which are 

 used largely in the cities for paving purposes. 



