lxxxii REPORT OF THE STATE GEOLOGIST. 



bed on the surface is very wide — a circumstance of greatest importance, 

 as it gives an immense catchment area for the rain water. 



These Fayette Sands form a range of hills and give rise to the most 

 striking topographic feature of the Coast region. Every river in its 

 passage to the Grulf pays tribute to and is deflected by them. Many 

 smaller streams have their course entirely determined by them, while 

 the coast rivers, of which the San Jacinto and Buffalo are types, have 

 their origin on their southern slope. At Rockland, in Tyler County, 

 and along the various railroads that cross the area of these sands, as 

 shown upon the map, typical sections can be seen. The base of these 

 beds are sandy clays and sands, with some lignite. 



The strata often contain carbonate of lime in appreciable quantities, 

 and sulphur and gypsum are of frequent occurrence. 



The Timber Belt Beds are composed of siliceous and glauconitic 

 sands with white, brown, and black clays, and have associated with 

 them lignite beds sometimes as much as twelve feet in thickness ; iron 

 pyrites, gypsum, and various bituminous materials also occur. Carbon- 

 ate of lime is also widely disseminated throughout the beds, sometimes 

 as limestone, but more often as calcareous concretions or in calcareous 

 sandstones. 



The Basal Clays are, as the name implies, beds of stratified clays and 

 contain masses of concretionary limestone and large quantities of 

 gypsum. 



The Upper Cretaceous is composed in its upper members of great beds 

 of clay somewhat similar to the Basal Clays above, which were doubtless 

 derived from these. This is underlaid by the Austin Chalk, below 

 which we find another series of clay shales overlying the Lower Cross 

 Timber Sands. 



The rock formation of the Grand Prairie belongs to the Lower Creta- 

 ceous series, and consists of a great thickness of limestones and chalks — 

 magnesian, arenaceous, and even argillaceous in places — which is under- 

 laid by a great bed of sand and conglomerate, known as the Trinity 

 Sands. 



We have in these formations, therefore, well marked and definite 

 sandy or porous beds, which are enclosed by others practically imper- 

 vious. Some of these are : 



The Orange Sands. 



The middle portion of the Fayette Beds. 



The Lower Cross^Timber Sands, 



