[MESOZOIC] ROCKS
[Mesozoic] rocks occur over a wide area of Texas and include exposures of [Triassic], [Jurassic], and [Cretaceous] age. Many of the Upper and Lower Cretaceous outcrops are quite [fossiliferous] and easily accessible and thus of considerable interest to many amateur collectors.
[Triassic]
[Triassic] rocks crop out in parts of the High Plains, the Glass Mountains of Trans-Pecos Texas, and parts of Pecos, Crockett, Upton, Reagan, and Glasscock and other west Texas counties. These are predominantly nonmarine rocks consisting of conglomerates, sandstones, shales, and some gypsum beds.
[Triassic] fossils are almost exclusively vertebrates, although some poorly preserved plant and invertebrate remains have been reported. [Fossil] vertebrates of the Texas Triassic include phytosaurs ([Pl. 42]), crocodiles, amphibians, and fish.
[Jurassic]
In Texas, surface exposures of [Jurassic] rocks are known only from Malone Mountain in southwestern Hudspeth County. The rocks there are limestones, shales, sandstones, and conglomerates. Fossils reported from that locality include marine and fresh-water pelecypods, fresh-water gastropods, and ammonites.
[Cretaceous]
Rocks of [Cretaceous] age are widely distributed in Texas and represent one of the more important [rock] systems of the State. Cretaceous outcrops occur in central Texas, north Texas, the Edwards Plateau, parts of the High Plains, the Gulf Coastal Plain, and Trans-Pecos Texas.
As mentioned [earlier], the Texas [Cretaceous] has been divided into the Lower Cretaceous (Comanche [series]) and Upper Cretaceous (Gulf series). These rocks consist primarily of marls (a type of [calcareous] clay), shales, chalks, and limestones, but sands and conglomerates also occur. Cretaceous rocks occur on the surface of about 28 percent of Texas, and many of the larger cities of the State are situated on Cretaceous strata.