General Stratigraphic Section of Cretaceous Units, Balcones Escarpment

rock unit Characteristics
Navarro Group Thick section of claystone--Blackland Prairie substrate
Taylor Group Calcareous claystone and marl--Blackland Prairie substrate
Austin Group Chalk and marl with local pyroclastic material
Eagle Ford Formation Shale; local siltstones
Buda Formation Limestone; not an aquifer
Del Rio Clay Claystone and shale--forms seal above Edwards aquifer
Georgetown Formation Nodular limestone--upper part of Edwards aquifer
Edwards Group Limestone--karstified host rocks for Edwards aquifer
Comanche Peak Formation Marly limestone
Walnut Formation Hard and soft limestone
Glen Rose Formation Alternating beds of limestone, dolomite, and marl--numerous small, perched aquifers
Hensel Sand Sandstone and conglomerates--upper member of "Trinity Sand aquifer"
Cow Creek Limestone Limestone--locally water-bearing
Hammett Shale Shale and claystone with sandstone lenses
Sycamore Sand Sandstone and conglomerates--basal Cretaceous rock unit in Central Texas

Last Updated on 3/25/99
By the University of Texas Libraries