702 J. II. GARDNER THE MID-CONTINENT OIL FIELDS 



more or less than this figure, due probably to the fact that the water 

 saturation is not complete, or that gas pressures for other reasons are 

 unusually strong. The gas pressure is evidently not entirely a reactive 

 pressure against a water head. A well at Gushing 2,600 feet deep gave 

 a gas pressure of 1,120 pounds; figuring the theoretical hydrostatic pres- 

 sure of 43.4 pounds per hundred feet, gives 1,128.4 pounds. A well near 

 Claremore, at a depth of 860 feet, gave a pressure of 375 pounds; the 

 theoretical pressure as above calculated is 373.2. A well near Collins- 

 ville, at a depth of 1,100 feet, gave a pressure of 495 pounds; the theo- 

 retical head at this depth is 477.4 pounds. These were closed pressures 

 on new wells taken by the Oklahoma Natural Gas Company. In contrast 

 to this uniformity, Haworth reports a well in Kansas, 1,000 feet deep, 

 with a pressure of 250 pounds, while another well half a mile distant, at 

 a depth of 900 feet, showed a pressure of 375 pounds. 



The region around Bartlesville produces oil on various types of struc- 

 ture, including anticlines, domes, terraces, and the heads of synclines, all 

 lying together over a broad area of folding ; this fact, together with local 

 hardening or tightening of the sands, gives a very irregular outline to the 

 fields as contrasted to the sharper structures farther west, or in local dis- 

 tricts of the eastern or southern portion of the main field. South of the 

 Arbuckle Mountains at Wheeler, Madill, and Healdton, the petroleum and 

 gas lie in an area of abundant water saturation, and consequently on 

 well defined structures that show reversed dips. 



Texas 



geographic divisions 



The oil fields of Texas fall into two geographical divisions, namely, 

 those of the Gulf Coast and those of central and northern Texas, the 

 latter being classified with the Mid-Continent region (see figure 6). 



The several oil and gas fields of central and northern portions of Texas 

 lie in districts rather widely separated. The production is controlled by 

 distinct and rather sharply outlined local anticlines, domed terraces, and 

 monoclines, with their surfaces lying at various stratigraphic horizons. 



STRATIGRAPHY 



The oil and gas sands are found at levels ranging from the Strawn 

 group of the Pennsylvanian system up to the Taylor marls of the Upper 

 Cretaceous. Positions of the various fields with respect to the strati- 

 graphic boundaries are shown on the accompanying map and the horizon 

 of the various sands are shown in the following general section. 



