The Llano uplift (Pl. 9) is located in the central part of the State
where Precambrian igneous and metamorphic rocks and sedimentary rocks of
early Paleozoic age occur on the surface. The area, which now appears as
a basin-shaped depression, was at one time covered by Lower Cretaceous
rocks and perhaps also by Devonian, Mississippian, and Pennsylvanian
strata. These have since been removed by erosion. The east, south, and
west sides of the uplift are surrounded by Lower Cretaceous rocks, and
the northern margin is marked by the Mississippian and Pennsylvanian
formations of the North-Central Plains. The area is, in general,
composed of unfossiliferous rocks, but some invertebrate fossils
(primarily trilobites and brachiopods) have been collected.