10 J. H. GAtlDNER THE MID-COls^TINEl^T OIL ElELDS 



Upper Cretaceous (Gulf series). Feet 



4. Austin group. Contains at top the Annona chalk, 100 feet, 



and at base Brownstown marl composed of clay, chalk, and 



sand 200-520 



5. Eagle Ford clay. Contains at top the Blossom oil sand. Blu- 



ish and carbonaceous clay with hard layers of limestone.. 350-400 



6. Woodbine sand. Main oil sand of field at Caddo and at ap- 



proximate position of Naborton sand 20-100 



Loioer Gretaceon,s (Comanche series). 



1. Shale, limestone, and lenses of sandstone. Denison forma- 



tion (250-300). Limestone. Fort Worth (15-30). Shale 



and thin limestone. Preston (150-250) 415-580 



2. Fredericksburg group. (Goodland limestone) 25- 50 



3. Trinity sand. Largely untested in Louisiana, but contains 



oil sand at Madill, Oklahoma, and in South Bosque field, 



Texas 200-400 



As will be seen from the, above section, all the oil and gas bearing strata 

 to date in this territory lie in the Upper Cretaceous series. The Nacatoch 

 gas sand is light gray to, drab in color and contains thin laminae of clay; 

 locally the sand contains lime and is occasionally rendered entirely im- 

 pervious to water and gas by a cement of calcinm carbonate; but this 

 condition is very exceptional. It contains some grains of glanconite, a 

 constituent characteristic of many of the sands in deposits of the Gulf 

 series and Tertiary. The Blossom oil sand (at 1,800 feet in the Caddo 

 field) is a quartz sandstone, usually soft, but sometimes indurated and 

 containing lenses of clay. The Woodbine sand, or the main oil sand of 

 the region, is a porous quartz sand, containing argillaceous, ferruginous, 

 and glauconitic material, together with an abundance of carbonaceous 

 plant remains. 



The Arkadelphia clay, the Marlbrook marl, and the Eagle Ford clay 

 all contain organic material, chiefly in the form of dark to black car- 

 l)onaceous clay or shale. The ^acatoch sand, the x\nnona chalk, which 

 contains some oil and gas, and the Woodbine sand lie in alternate posi- 

 tions with these deposits. The clays are impervious to the passage of oil 

 and gas and hence restrain those materials in the porous sands, notwith- 

 standing the fact that the oil and gas are under tremendous initial pres- 

 sure. 



STRUCTURE 



The Sabine uplift is a broad, flat-topped, irregularly shaped arch in 

 the sedimentary beds which, on the south, shows a lelatively steep down- 

 ward dip. Veatch, in his excellent report on the Geology and Under- 

 ground Water Eesources of Northern Louisiana and Southern Arkansas, 

 termed this steep zone the Angelina-Caldwell Monoclinal Flexure (Pro- 



