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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 semichalky 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 angularity of the uncemented particles, characteristic of typical littoral deposits, while occasionally there are found fossiliferous horizons.

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 denudation 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 casual 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 bituminous coal. It is doubtful whether either is in sufficient quantities for commercial 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 association 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 undetermined Cerithiidoe, Neritina, Ostrea, Aguillaria cumminsi (White), and other littoral species. From a well at Whitesboro, which was dug in the sharp sands of this division, I procured fish teeth (Otodus), an Ammonite (Scaphites), and indeterminate mollusks. Dr. B. F. Shumard 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.