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we place their inland limit below Roma, the line of separation on the Rio Grande between the Fayette Beds and Timber Belt Beds would curve outward toward the Gulf of Mexico, whereas we should expect it to curve inward, just as the line between the Cretaceous and the Timber Belt Beds does, on account of the probable embayment on the Rio Grande at the time of their deposition. These beds lying between here and the coastal region will be treated under the heading of "Fayette Beds." A more detailed discussion of the Rio Grande strata is reserved until the fossils have been thoroughly studied.
THE FAYETTE BEDS.
These beds underlie the interior part of the coast plains of East Texas, and as we near the Gulf shore they are seen to gradually dip under the Post-Tertiary deposits. The surface of the country consists of a rolling prairie, and parts of it are undoubtedly destined to become very rich agricultural regions, combining as they do all the advantages of a rich soil, a well-watered country, and the temperate climate of the sea coast.
The thickness of these strata is at the minimum 350 feet, and probably nearer 400. They consist of a series of clays and sands, very characteristic in their color, mode of occurrence, and associations, and are easily distinguished from any other beds in the Tertiary series of Texas. They include all those beds found on the Brazos, Colorado, and Rio Grande which lie between the uppermost fossiliferous strata of the marine Tertiary below and the Post-Tertiary clays, limestones, and pebble beds above. Above the uppermost of the marine Tertiary already described on the Brazos and Colorado rivers, occurs a series of clay and sandy strata, the clay rapidly becoming more and more predominant as we go up the series, until the beds are composed almost exclusively of it. Then again the sandy beds suddenly assume predominance and extend upward to the Post-Tertiary beds. The lower or clayey part of this series composes a little over half of the formation, and the sandy beds compose the rest.
These beds represent the "Grand Gulf" series of Hilgard's Mississippi section. Professor Angelo Heilprin, in speaking of the Grand Gulf Beds, says: "No unequivocal deposits of Miocene age have thus far been detected on the Gulf slope, although strong grounds exist for the supposition that the formation designated by Hilgard as Grand Gulf Group belongs to this period of geologic time, but to which division or horizon of the same it is as yet impossible to state." In Mississippi and Louisiana, as in Texas, the base of this formation is composed of clays with lignite beds, and the upper part consists"
"Contributions to the Tertiary Geology and Paleontology of the United States," Prof. Angelo Heilprin, 1884, p. 4.