In 1890 Penrose,2 as a result of his trip down the Rio Grande with Dumble in 1889, described a deposit of limestone containing pebbles and cobbles, under the name “Reynosa limestone,” from the town of Reynosa, Tamaulipas, Mexico, across the Rio Grande from Hidalgo, Texas. At Reynosa the rocks unconformably overlie what was then called the Fayette sands, now known to include strata of upper Eocene, Oligocene, and Miocene age. Penrose found Recent shells embedded in the surface of the exposure and, thinking the formation was Recent, included it in his “post-Tertiary formations.”
In 1891 Hill3 described patchy remnants of a formation that consisted of gravel cemented by a calcareous matrix, and that occupied terraces 400 to 1,000 feet above the Rio Grande, in Uvalde and adjacent counties in Texas, and called it the “Uvalde formation,” for the town of Uvalde, in Uvalde County, and in 1898 Hill . . .