Yegua Formation (TXEOy;0)

State	Texas
Name	Yegua Formation
Geologic age	Phanerozoic \| Cenozoic \| Tertiary \| Eocene-Middle
Original map label	Ey
Comments	clay with minor beds of sandstone, some concretionary limestone beds and lenses of oyster shells. sandst fine grained, calcar., glauconitic, massive, laminated, crossbedded; fossil wood; Volcanic ash included. silicified tuff containing an oyster and gastropod fauna (Eargle, 1968); 1,000 ft thick in San Antonio Sheet (1974). In East Texas and Gulf Coast to Rio Grande: Overlies Cook Mt. Formation; overlain by Caddell Fm. Unit is sandstone, clay, and lignite. Sandst. is mostly quartz and some chert, fine-grained, laminated, corssbedded; clay, lignitic, sandy, bentonitic, well laminated, lentils of lignite. In Seguin Sheet unit is about 1000 ft thick.
Primary rock type	clay or mud
Secondary rock type	sandstone
Other rock types	limestone; coal
Lithologic constituents	Major Sedimentary > Clastic > Sandstone (Bed) Sedimentary > Clastic > Mudstone > Claystone (Bed) Incidental Igneous > Volcanic (Pyroclastic, air fall) Sedimentary > Coal > Lignite (Bed) Sedimentary > Carbonate > Limestone (Bed)
Map references	Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000
Unit references	Eargle, D.H., 1968, Nomenclature of formations of Claiborne Group, Middle Eocene, coastal plain of Texas: U.S. Geological Survey Bulletin 1251-D. [http://pubs.er.usgs.gov/publication/b1251D] Bureau of Economic Geology, 1970, Waco Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000. Bureau of Economic Geology, 1974, San Antonio Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000. Bureau of Economic Geology, 1974, Seguin Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000. Bureau of Economic Geology, 1976, Crystal City-Eagle Pass Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000. Bureau of Economic Geology, 1967, Palestine Sheet, Geologic Atlas of Texas, Bureau of Economic Geology, University of Texas at Austin, scale 1:250,000.
Geographic coverage	Angelina - Atascosa - Bastrop - Brazos - Burleson - Fayette - Frio - Gonzales - Grimes - Houston - Karnes - La Salle - Lee - Leon - McMullen - Madison - Nacogdoches - Sabine - San Augustine - Starr - Trinity - Uvalde - Walker - Webb - Wilson - Zapata