Calvert Bluff Formation of Wilcox Group. Top formation of Wilcox. Mostly mudstone with various amount of sandstone, lignite, ironstone concretions, and in uppermost part locally glauconitic. Mudstone, massive to thin-bedded with silt and very fine sand laminate, pale brown to yellowish brown, weathers yellowish brown. Sandstone, medium- to fine-grained, moderately well sorted, cross-bedded, lenticular, thin beds locally burrowed, light gray to pale yellowish brown, weathers to various shades of brown. Lignite, mostly in lower part of formation, seams 1 to 20 feet thick, brownish black. Average thickness 1,200 feet. Lies above Simsboro Formation of Wilcox and below Carrizo Sand. Age is Eocene.
Mapped in Robertson, Limestone, Leon and Freestone Cos., eastern TX.

Source: Publication.