46-1 E. T. DUMBLE PROBLEM OF TEXAS TERTIARY SANDS 



111 tlio j\Iaiiiiiiig beds many lamellibranehs are found in the limonitic 

 shales, and in tlie overlying" light-gray sands there are pockets of fossils 

 wliicli are mostly casts, but occasionally liave the shells preserved. Simi- 

 lar occurrences were found in the cartioiiaceous shales and sands at the 

 top of the section. 



No specimens of Levifusus hrannerl were found, but in the upper 

 carbonaceous sands of the Manning stage there are imprints and casts of 

 a large gasteropod that may possibly be referred to that species. 



A marked increase in the sandiness of the Jackson is shown in the 

 Grove ton section. 



.The sandy clay with limestone concretions, found 12 miles north of 

 Groveton, grades upward through carbonaceous shaly clays into a succes- 

 sion of gray and brown sands and lignitic sands carrying silicified wood, 

 some limestone concretions, clay balls, fragments of volcanic tuff, and 

 many plant impressions. Wells drilled at Groveton to depths of 400 to 

 600 feet show principally sands or sandy strata, with a few clay beds and 

 streaks of lignitic material. South of GroNcton carbonaceous sands are 

 found with imprints of invertebrates similar to those at the top of sec- 

 tion north of Corrigan. 



Going northward the Caddell clay of this section is underlain by sandy 

 carbonaceous shales and sands, with silicified logs, massive, rather fine- 

 grained, sandstones and lignitic clays and sands seemingly of Jackson 

 facies. These extend to the vicinity of Apple Springs, beyond which the 

 Yegua badland sandv clays and gypsiferous clays with clay ironstone 

 concretions make their appearance. It would appear, therefore, that this 

 section gives us a member of the Jackson lower than any seen east of the 

 ISTeches or of a series of beds intermediate in age between the Yegua and 

 Jackson, most proliably the former. 



West of Groveton the change is decided. Xo further traces of the 

 Caddell sandy clay with limestone concretions are found, but the lignitic 

 sands and clays underlying it seem to be immediately overlain l)y the 

 carbonaceous sands of the Manning beds, as shown in section north of 

 Corrigan. Volcanic ash comes in as definite beds and is well shown in 

 the section along the International & Great Northern Railway. 



Between Calhoun's ferry, near the Houston-Trinity County line and 

 the bend north of Riverside, the Trinity River gives many good sections 

 of the Jackson. At the base are lignitic clays carrying plant remains 

 and sands with lignites. These are overlain by light-yellow, gray, and 

 brown sands, with sulphur, and by carbonaceous shales, sulphur-stained, 

 followed by other lignitic clays, sands, and lignites. There are beds, of 

 volcanic ash as much as 10 feet in thickness in the upper portion, and 



