110 CRETACEOUS ROCKS OF TEXAS. 



NO. 1. THE LOWEE CROSS TIMBER SANDS. 



From the Brazos River northward to Red River the base of the Upper 

 Series is composed of a brown, more or less ferruginous, predominantly sandy, 

 littoral deposit, resting unconformably upon various horizons of the semi- 

 chalky beds of the Washita division, or top of the Comanche Series. These 

 sandy deposits present an infinite variety of conditions of cross-bedding, clay 

 intercalations, lignitic patches, and variation in fineness of size and angu- 

 larity of the uncemented particles, characteristic of typical littoral deposits, 

 while occasionally there are found fossiliferous horizons.* 

 F~In the vicinity of Denison these sands are covered by a Post-Tertiary 

 sand, which confuses their identity there. South of the Brazos River, and 

 at Austin, these beds are entirely missing, a fact which may be explained in 

 connection with certain changes of level accompanied by volcanic events 

 which took place just after they were laid down, exposing them to denuda- 

 tion before the next division was deposited. No systematic study of these 

 beds, as a whole, has yet been made, and the thickness is estimated from cas- 

 ual observations by the writer. 



The Lower Cross Timbers region abounds in rich sandy soils, which have 

 not been studied minutely. These support a vigorous timber growth — this 

 structure being especially favorable for deep-rooted plants, and are specially 

 adapted to fruit growing, as seen near Denison and Paris. 



There is also considerable iron in the beds of the Lower Cross Timbers, as 

 well as lignite. The latter is frequently discovered and mistaken for bitu- 

 minous coal. It is doubtful whether either is in sufficient quantities for com- 

 mercial use. The Cross Timbers are also in the line of the Central Texas 

 artesian belt, and it is probable that in any portion of its area an artesian 

 well sunk through the rock of the underlying Comanche series would find 

 an abundant flow of water. These sands are also valuable for water-bearing 

 purposes, and the wells along the margin of the minor Black Prairie area are 

 supplied from them. 



* One of these, on Timber Creek, near Lewisville, in Denton County, occurred in associa- 

 tion with lignite and cross-bedded sands, and was largely composed of marine shells, such 

 as inhabit the brackish waters of estuarine and near-shore deposits, consisting of undeter- 

 mined Cerithiidce, Neritina, Ostrea, Aguillaria cumminsi (White), and other littoral species. 

 From a well at Whitesboro, which was dug in the sharp sands of this division, T procured 

 fish teeth (Otodus), an Ammonite (Scaphites), and indeterminate mollusks. Dr. B. F. Shu- 

 mard discovered leaves of flowering trees in this formation, and reported the same in the 

 proceedings of the St. Louis Academy of Science, Vol. 2, p. 140. He also correlated these 

 sands with those of Kansas and Nebraska called the Dakota group, or No. 1 in Meek and 

 Hayden's section. They are probably the same as the Arenaceous group of Dr. Shumard's 

 Texas section. 



