THE TEXAS FIELDS 703 



The general stratigraphic section in northern Texas, given in descend- 

 ing order, is as follows : 



Tertiary system (Eocene). Peet 



1. Cook Mountain and Mount Selman. (Saint Maurice of 



Louisiana, Claiborne.) Consists of clays, clay-iron con- 

 glomerates, and calcareous glauconitic beds. 



2. Wilcox group. (Sabine formation.) Sands, clays, and 



conglomerates with beds of lignite 400- 500 



.''>. Midway group. Chiefly clays with some limestone 200- .''>00 



Hyper Cretaceous (Gulf series). 



1. Navarro group. Clay marls and glauconitic sands 400- 700 



2. Taylor marls group. Beds of clay and sandy to calcare- 



ous, soft shale, with local lenses of sandstone. Con- 

 tains Nacbatoch gas sand of Caddo field, oil sands of 

 Corsicana field, and oil-bearing igneous rock of Thrall 

 field 200- 500 



3. Austin group. (Annona chalk and Brownstown marl.) 



Contains some oil and gas in Caddo field 200- 600 



4. Eagle Ford group. Chiefly clays containing the Blossom 



oil sand of Caddo field 150- 400 



5. Woodbine sand. Massive, soft sandstone with some shale. 



Main oil sand of Caddo oil field. Occupies approxi- 

 mate time interval of Dakota sandstone in New Mex- 

 ico and northward into Canada. Also the Tamasopa 



limestone of the great oil fields in Mexico 50- 100 



Loicer Cretaceous (Comanche series). 



1. Washita group. Impure limestone with beds of shale and 



marl. Contains important water sand locally at Paris, 

 Texas ; includes, in descending order, the Pennington 

 limestone, Bokchito formation, Caddo limestone, and 

 Kiamichi formation (Denison, Fort Worth, and Pres- 

 ton formations) 175- 400 



2. Fredericksburg group. Massive white limestone beds, in- 



cluding the Goodland limestone (Edwards limestone 



and Walnut formation) 2.5- 200 



3. Trinity sand. Contains the oil of the South Bosque field 



in top member (Paluxy) 200- 400 



Permian series. 



1. Double Mountain group. Sandstone, limestone, sandy 



shale, red and blue clays with beds of gypsum and salt 1,900-2,100 



2. Clear Fork group. Thin-bedded sandstone, magnesian 



and carbonaceous limestone, red and blue clay-shale 

 and irregular beds of cemented clay-iron concretions. 

 Some gypsum 1,900-2,000 



3. Wichita group. Sandstone of various colors. Red and 



bluish clay-shale and beds of clay-iron concretions or 

 Mud-lump conglomerate." Beds of limestone rare east 



