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To suppose that these soils can not be improved by further geologic study, however, is a great mistake.
NO. 5. THE UPPER ARENACEOUS, OR GLAUCONITIC, DIVISION.
In East Texas along the eastern margin of the Black Prairie region, and in Southwest Arkansas—which is but the northeastern termination of the Texas section—where the rivers have cut through these overlying Tertiary beds, the uppermost beds of the Black Prairie series are glauconitic and arenaceous. This division is the upper continuation of the Ponderosa marls, its chief difference being that the clays gradate into sands and glauconite as we ascend, and there are conspicuous changes in the fossils, which become more plentiful, and the species partake of the same faunal characteristics that distinguish the Cretaceous of the New Jersey and Alabama regions. This division as it occurs in Southwest Arkansas has been minutely described in my Arkansas report, but its whole detail remains to be developed in Texas, its occurrence having only been affirmed in one or two places without specific detailed study.
In the extreme northeastern counties of the Cretaceous area these greensand beds are more abundant, and investigations into their details are now being conducted.
Like the main Black Waxy Prairie lands, from which they are hardly distinguishable, they are fine agricultural lands, possessing an advantage in being less sticky and tenacious. The glauconite, or greensand, will no doubt be found in greater and purer quantities in some localities than in others, and will prove of great local value as a fertilizer. In New Jersey similar marls are used to the amount of $2,000,000 worth per annum, and immense tracts of previously supposed poor lands, similar to some which exist in great quantities in our own State, have been reclaimed and converted by their use into fertile fruit and vegetable regions.
II. THE LOWER, OR COMANCHE, SERIES.
THE FORT WORTH, OR GRAND PRAIRIE.
The name prairie covers a multitude of diverse geographic features in Texas, of which the absence of timber growth is, to the casual observer, the most conspicuous; and hence the fact that west of the Black Prairie region (and its basal Lower Cross Timbers) there is another entirely distinct geographic and geologic region, which, until recently, has been confused with it. This is the beautiful prairie country surrounding the city of Fort Worth "
The Neozoic Geology of Southwestern Arkansas. Second Annual Report of the State Geologist, Little Rock, 1889.