The Trinity Group is divided into a lower unit consisting of the terrigenous Hosston Formation overlain by the carbonate Sligo; a middle unit called the Pearsall, made up of the Hammett shale, Cow Creek limestone: and Bexar shale; and an upper unit which includes the Hensel sand, overlain by the Glen Rose limestone.

Limestone, dolomite, and marl of the section between the base of the Upper Trinity and the top of the Edwards were deposited in shallow water behind the Stuart City coral-rudistid barrier reef. Lower Glen Rose reefs and the Stuart City reef formed the southwestern, southern, and eastern barriers of the Ferry Lake anhydrite evaporation pan.

The Fredericksburg Group includes the strata between the base of the Bee Cave limestone and the base of the Kiamichi.

The Washita Group includes the Kiamichi, middle (Kiamichi) Edwards, upper Edwards, Georgetown, Del Rio, and Buda formations. The upper, or the lower Edwards should be renamed.

Structural elements which affected Lower Cretaceous deposition include the spasmodically positive Belton high (new term), the Round Rock syncline (new term), two synclinal troughs behind the Stuart City reef, and the Sample fault system (new term). Up-to-the-coast faults are dominant southeast of the axes of the synclinal troughs, and down-to-the-coast faults are dominant northwest.

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