[3] Taff assigned the town of Stanley in Pushmataha County, Oklahoma as the type locality, but did not designate a stratotype.
After introduction into Arkansas in 1909 by Albert Homer Purdue,[5] the unit was redefined in 1918, when the formation known as the Fork Mountain Slate was abandoned and partially combined into the Stanley Shale.
The Stanley Shale is recognized as a geologic formation with two sub-units in Arkansas, the Hatton Tuff Lentil and the Hot Springs Sandstone Member,[1] however, several others have been proposed.
The Hatton Tuff Lentil, recognized in Arkansas, is also in Oklahoma as a unit of the Tenmile Creek Formation.
Several informal members have been noted including the Smithville chert lentil, the Faith chert member, and the Chickasaw Creek tuff among others [2] Mining in the Stanley Shale is limited to cinnabar, barite, and quartz.