The Geology of Texas - Vol. 1 - pages 457-458

Nomenclature.—The Brownstown marl of Hill (753, pp. 86-87) was named from the vicinity of Brownstown, Sevier County, Arkansas. Veatch (1691, p. 25) restricted the term to the marls underlying the Annona chalk and overlying the Tokio (Veatch's Bingen). Dane (392, p. 46) later restricted the Brownstown to include only the lower part (on which the town Brownstown stands) of Veatch's Brownstown, the upper part being called Ozan.

Areal outcrop.—In Arkansas the Brownstown unconformably overlies the Tokio (392, p. 48). On the Ozan road 2.4 miles south of Nashville, Arkansas, there is exposed white Tokio clay containing poorly preserved fragments of plants. Overlying its slightly irregular surface there is a deposit of dark, calcareous Brownstown clay showing "borings" and irregularities filled with limy, sandy clay that extends down into the Tokio. In Arkansas, the thickness of the Brownstown is about 250 feet thick in Howard County, about 220 feet thick in Sevier County, and farther west it is thinner. In northeastern Texas it is 75 to 200 feet thick.

In Texas it extends from Red River County westward to near Bonham, overlying the Blossom sand, and in Lamar and eastern Fannin counties underlying the Gober chalk. It merges westwards into the top of the Bonham clay, which in southwestern Fannin County changes into the upper part of the Austin chalk (of Taylor age).

The oyster Exogyra ponderosa Roemer is so abundant in the Brownstown and in the overlying Ozan that the two formations together have been called Exogyra ponderosa marl. The Brownstown Exogyras include: (1) typical large, nearly smooth ponderosa with irregular and wide growth imbrications; (2) E. ponderosa var. erraticostata Stephenson, ornamented with irregular costae which become weaker toward the margin; (3) a form somewhat like the last, which has a relatively small and thin shell, and the left valve marked by numerous fine, narrow, bifurcating costae, the shell differing from E. upatoiensis in being larger and more coarsely ribbed. According to Stephenson a shell somewhat similar to the last, but narrower and higher, occurs in the Blossom sand in Texas. Ammonites found in the Brownstown include: Baculites asper, Placenticeras, and Scaphites hippocrepis (DeKay).