700 J. H. GARDNER TPIE MID-CONTINENT OIL FIELDS 



an area of steeply folded anticlines and synclines running northeastward 

 and southwestward parallel to the Choctaw fault. This region has suf- 

 fered extreme compression of the strata, so that the coal beds run as high 

 as 70 per cent carbon on a moisture-ash-free basis, due to the metamor- 

 phic effects of this great thrust. David AVhite has called attention to the 

 fact that such areas seldom supply commercial oil fields, but frequently 

 furnish gas fields. This portion of Oklahoma and that extending into 

 Arkansas around Port Smith and Kibler illustrate this fact in a splendid 

 manner. The gas fields in this district do not carry oil with them; in 

 fact the gas is extremely dry. The limit of the region thus affected lies 

 far within the Pennsylvanian area and is marked by a fairly definite line 

 which the writer has drawn on the accompanying map of Oklahoma. 



The local structures that contain the oil and gas fields of Oklahoma 

 are related to the Ozark uplift, the Ouachita and Arbuckle Mountains 

 uplift, the Choctaw fault, and the Wichita Mountains uplift. The oil- 

 bearing folds fall into two classifications; one class is that of the distinct 

 isolated structure standing separately and definitely disconnected from 

 all others. These have well marked and consistent boundaries, such as, 

 for instance, the elongated dome or short anticline that produced the 

 Cushing field (see figure 5). The other class is the producing zone, or a 

 more or less disconnected, irregular area of crumpling that covers so 

 much territory that the term '*^oil pool" as used by the operator is not 

 applicable to it; as a concrete illustration of this type the production in 

 eastern Osage County and about Bartlesville may be cited (see figure 4). 



In Oklahoma the nature of local structure in its relation to the presence 

 of salt water determines the respective class into which any particular 

 oil field falls. In some districts, for instance, the oil-bearing sandstones, 

 or "oil sands," contain an abundance of salt water under strong hydro- 

 static head, in which case the oil and gas have been sharply segregated 

 from the water-bearing areas and pushed under the portions of the struc- 

 ture where the sands lie highest above a given datum plane. As a rule 

 in such districts both petroleum and gas lie relatively high on structure, 

 and the sands about them are strongly saturated with brine. In that 

 portion of Oklahoma and Kansas west of the Ninety-sixth Meridian, 

 which runs through Tulsa, Oklahoma, and a short distance west of Inde- 

 pendence, Kansas, most of the oil and gas fields lie on what are usually 

 referred to by geologists as "closed structures" — that is to say, on domes 

 or anticlinal bulges. As a matter of fact, the w^estern extension of this 

 region lies down the dip of the strata, where the main oil sands are at 

 depths below 1,800 feet, and the hydrostatic head of the salt-water satura- 

 tion is strong. It is an interesting fact that the closed pressure on the 



