Geologic units in Montgomery county, Arkansas

Stanley Shale (Early Mississippian) at surface, covers 30 % of this area

Stanley Shale - Includes Chickasaw Creek Chert equivalent of Harlton (1938) near top and Hatton Tuff Lentil and Hot Springs Sandstone Member near base

Womble Shale (Middle Ordovician) (Middle Ordovician) at surface, covers 13 % of this area

Womble Shale (Middle Ordovician)

Pole Creek Shale (Upper Ordovician) and Bigfork Chert (Upper and Middle Ordovician) (Late Ordovician to Middle Ordovician) at surface, covers 13 % of this area

Polk Creek Shale (Upper Ordovician) and Bigfork Chert (Upper and Middle Ordovician)

Jackfork Sandstone (Early Pennsylvanian- Morrowan) at surface, covers 11 % of this area

Jackfork Sandstone

Mazarn Shale (Early Ordovician) at surface, covers 9 % of this area

Mazarn Shale

Arkansas Novaculite (Early Mississippian to Late Devonian) at surface, covers 7 % of this area

Includes upper division (Mississippian), middle division (Mississippian and Devonian), and lower division (Devonian)

Missouri Mountain Shale and Baylock Sandstone (Late Silurian) at surface, covers 5 % of this area

The Baylock Sandstone is present only in the Cross, Cossatot, and Trap Mountains. Missouri Mountain Shale is mapped with Polk Creek Shale and Bigfork Chert in the area between Paron, Saline County, and Little Rock.

Crystal Mountain Sandstone (Early Ordovician) at surface, covers 5 % of this area

Crystal Mountain Sandstone

Blakely Sandstone (Middle and Lower Ordovician) (Middle Ordovician to Early Ordovician) at surface, covers 4 % of this area

Blakely Sandstone (Middle and Lower Ordovician)

Collier Shale (Early Ordovician) at surface, covers 3 % of this area

Collier Shale

Johns Valley Shale (Early Pennsylvanian- Morrowan) at surface, covers 0.5 % of this area

Johns Valley Shale