574 r. G. CLAPr — classification of petroleum and gas fields 



greatest gas fields in the world, on the lower border of which are the 

 Bremen, Wooster, Straitsville, and other oil fields. A cross-section of 

 the west side of the Appalachian basin, illustrating Snbclass III(^), is 

 shown in fignre 2. 



Oil occurs in lenses in either of two ways: (1) in the npper end of a 

 })inching-out lentil, and (2) where the latter is dome-shaped, in the 

 upper part of this dome. Doubtless a large number of instances of the 

 second class exist, but they form local phenomena of pools rather than a 

 cause of an independent pool. 



CLASS IV—QUAQUAVERSAL STRUCTURES, OR "DOMES''' 



General discussion. — In the classification of oil pools, the subdivision 

 entitled "Quaquaversal structures" is considered to include those struc- 

 tures in which the oil sand dips away in all directions from a central 

 point, including the saline domes of Louisiana, certain domes in Okla- 

 homa and West Virginia, the basalt plugs of Mexico, and the perforated 

 and non-perforated salt domes of Eoumania and Hungary. 



Si(.h class IV (a) — Anliclinal bulges or ''cross-anticlines/' — This type 

 of structure merges with those described in Subclasses 11(a) and 11(h) 

 of tlie classification, since practically all anticlines consist of alternate 

 contractions and bulges where their crests are respectively depressed or 

 elevated. The term "cross-anticline" has been sometimes applied to these 

 domes or bulges, but not always correctly so — as, for instance, at Jack- 

 sonville, Greene County, Pennsylvania*^ — where the deepest part of the 

 Ninevah syncline lies directly opposite the highest part of a dome on the 

 Washington anticline. 



' This is one of the types to which the anticline theory, as originally 

 promulgated by I. C. White, can be applied without modification. In the 

 illustration mentioned, the strata dip northwest toward the Ohio River 

 syncline, southeast toward the Mnevah syncline, and northeast and south- 

 west it plunges into a long structural fold which extends from the vicinity 

 of Cannonsburg, Pennsylvania, southwest into Wetzel County, West Vir- 

 ginia. In other words, the Jacksonville dome or bulge has the shape of 

 an inverted basin. 



Anticlinal bulges are of all shapes and sizes, but those of great length 

 would hardly be recognized as domes and are not here considered, since 

 they belong strictly to Subclass II (a) . Anticlinal bulges exist in many 

 places' in Pennsylvania and West Virginia, in a few counties in Ohio, and 

 are frequent in Wyoming. The fact that the Wheeler and Healdton pools 



*2F. G. Clapp: Rogersville folio, No. 146, U. S. Geol. Survey, 1907. 



