The Geology of Texas - Volume 1 - Stratigraphy

Graham Formation

" The Graham Formation at the base of the Cisco group is best developed in the Brazos River valley, where it has been subdivided into several members as follows: Gonzales limestone shale and sandstone; Bunger limestone; Necessity shale and sandstone; Gunsight limestone; and Wayland shale. Formerly the Jacksboro limestone and Finis shale of Jack County were placed in this Strata but they are now recognized as part of the Home Creek limestone of the Caddo Creek Strata. To the southwest the Strata thins, the lower members, according to Plummer and Moore, being lost by overlap. The members recognized in the Colorado River valley are the Bluff Creek shale, Gunsight limestone, and Wayland shale.

The uppermost member, the Wayland shale, is notably fossiliferous.  An erosional unconformity is found at the top of the Strata by which the Wayland shale is cut out locally. Some geologists prefer making the division line between the Canyon and Cisco at this break in sedimentation—a position supported also by a break in the microfauna — thus placing the Graham Formation in the Canyon group (652, p. 139). The Strata is traced northward into Montague County (176, p. 63). The limestones thin northward and have largely disappeared where the Strata passes under the Cretaceous in Montague County (176, p. 63). A chert conglomerate is found in this Strata at its type locality and at several other localities.

A large ammonite fauna obtained from the Necessity shale at several localities includes Uddenites, Gastrioceras modestum, Schistoceras hyatti, Shumardites simondsi, and Gonioloboceras welleri (1234f).  Type locality: The type locality is at Graham in Young County; thickness, 160 feet in the Colorado River valley, and 350 or 450 feet in the Brazos River valley.  "