Texas Fossils: An Amateur Collector's Handbook

by William Henry Matthews

HIGH PLAINS NORTH-CENTRAL PLAINS GRAND PRAIRIE TRANS-PECOS TEXAS VAN HORN UPLIFT THE BIG BEND AREA SOLITARIO UPLIFT MARATHON UPLIFT EDWARDS PLATEAU LLANO UPLIFT BALCONES [FAULT] ZONE GULF COASTAL PLAIN

North-Central Plains

Surface strata of the North-Central Plains ([Pl. 9]) are westward-dipping [Pennsylvanian], [Permian], and [Triassic] rocks. Present also are extensive exposures of [Quaternary] sands and gravels which trend north-south across the central portion of the region. The area is bounded on the west by the High Plains, on the east by the Grand Prairie, and on the south by the Edwards Plateau and Llano uplift. Many [vertebrate] fossils have been collected from the Permian and Triassic rocks of this area. There are also many excellent outcrops of [fossiliferous] Pennsylvanian formations in the North-Central Plains region.

Edwards Plateau

The Edwards Plateau ([Pl. 9]) is located in south-central Texas and is bounded on the south by the Balcones [fault] zone and on the north by the North-Central Plains. The surface of the area is typically flat with a gentle slope to the south. The rocks of the Edwards Plateau consist primarily of Lower [Cretaceous] limestones and shales, many of which are very [fossiliferous].

Grand Prairie

This area ([Pl. 9]) has a relatively flat surface but there are areas of gently rolling hills. The eastern boundary of the Grand Prairie is marked partly by the Balcones [fault] zone. North of McLennan County, however, the Balcones fault zone is not expressed at the surface and in this area the eastern boundary is defined by the western edge of the Woodbine exposures. Upper and Lower [Cretaceous] rocks occur at the surface and [dip] to the southeast; many of these rocks contain a large number of invertebrate fossils.

Llano Uplift

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.