Sixteen depositional sequences, commonly called cyclothems, each composed mostly of limestone(retrogradational/transgressive) and siliciclastic (progradational/regressive) subsequences, or systems tracts, record the paleogeography during Late Pennsylvanian (Virgilian Epoch) and Early Permian (Wol

This cross section set comprises 14 dip (E-W) sections and 9 strike (N-S) stratigraphic cross sections (with text), correlating upper Pennsylvanian (Virgilian) and lower Permian (Wolfcampian) strata throughout the subsurface in all or parts of 28 counties of North-Central Texas.

The Lower Cretaceous Hosston and Hensel Sandstones are important sources of ground water in North-Central Texas.

Nelson and others (1962) define a bank as " ... a skeletal deposit formed by organisms which do not have the ecologic potential to erect a rigid wave-resistant structure." They explain that a bank may have any geometry.

Coal is found in six areas in Texas, including the large North-Central Texas field, a distinctive cannel coalfield in Webb County, and Late Cretaceous-age coals near Eagle Pass.

The Eastern Shelf was a constructional platform developed on the margin of the sediment-starved Midland Basin during Late Pennsylvanian and Early Permian time. A mixed terrigenous-carbonate sedimentary province characterized the shelf during most of its history.

Geologic map that depicts the surface geology of Shackelford, Stephens, Palo Pinto, Callahan, and Eastland Counties and parts of Jones, Taylor, Runnels, Coleman, Brown, Comanche, Erath, Parker, and Hood Counties, Texas.

Virgil and lower Wolfcamp rocks on the Eastern Shelf in North-central Texas are composed of several intergradational depositional systems comprising 1,200 to 1,500 feet of off-lapping, predominantly terrigenous sediments.

Upper Pensylvanian and lower Permian rocks of the Eastern Shelf in North-central Texas are composed of 10 to 15 repetitive sequences including open shelf, deltaic, fluvial, and interdeltaic depositional systems.

Lower Cretaceous sands have long been important aquifers in Central, North-Central, and North Texas. In recent years these sands also have been sources of high-silica industrial or specialty-purpose sand.