116 CRETACEOUS ROCKS OF TEXAS. 



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 glauco- 

 nite as we ascend, and there are conspicuous changes in the fossils, which 

 become more plentiful, and the species partake of the same faunal char- 

 acteristics 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 devel- 

 oped 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 green- 

 sand 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 geo- 

 graphic 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. 



