562 P. G. CLAPP CLASSIFICATION OF PETROLEUM AND GAS FIELDS 



in the Trenton limestone. The pools of Class III are on the broad mono- 

 clinal dip of over 200 miles extending across central and eastern Ohio, 

 in which the oil and gas occur mainly in the Clinton and Berea sands. 

 Near the Pennsylvania boundary line the dip becomes stronger and more 

 variable, changing the monoclinal dip laterally into definite anticliiies 

 and synclines, and it is in these structures that pools of Subclass 11(5) 

 exist. Anticlinal and synclinal structures are more and more prominent 

 eastward, until in near central Pennsylvania and in central West Vir- 

 ginia metamorphism appears to have been sufficient to drive out all im- 

 portant accumulations of oil or gas, which, although they presumably 

 once existed, escaped to the surface and disappeared loug ago. 



Symmetrical anticlines. — A good example of a symmetrical anticline 

 is, according to Thompson,^^ the Yenangyuang oil field of Burma, which 

 has yielded the main oil supply in that country from sands of Lower 

 Neocene age, where dome structure is well displayed. The Bibi-Eibai 

 field of Russia is mentioned by the same writer as another symmetrica] 

 anticline, modified by doming and faulting. 



Asymmetrical anticlines. — Asymmetrical anticlines are, however, most 

 prevalent in oil fields, examples of these being the Grosuy field of Russia, 

 the Yenangyat field of Burma, and the Campina field of Roumania. A 

 cross-section of the Grosny field is given by Kalitsky,"^^ of the Yenangyat 

 field by Pascoe,^* and of the Campina field by Mrazek.^^ Many of the 

 fields of Galicia are of this nature, a good instance being the Boryslav- 

 Tustanowice field, which is the principal field of that country.-^ 



Subclass 11(a) — Where strong anticlines exist standing alone.^ln this 

 division are included fields that bear a direct relation to very pronounced 

 uplifts, easily recognizable, and constituting a marked geologic feature of 

 the region. The only prominent example in the eastern fields of the 

 United States is the Volcano anticline in West Virginia. This anticline 

 is 25 miles in length, ranging in trend from north 10° west to uorth 20° 

 east, from an eighth of a mile to half a mile broad on its flat crest, and 

 has side dips of from 20 to 60 degrees. The anticliue differs somewhat 

 in direction from the main Appalachian folds and was probably produced 

 by a different set of forces. It is one of the earliest recognized auticlines 

 in the country, having had a great number of wells drilled on it, and has 



22 A. Beeby Thompson: Trans. Instn. of Min. and Met., vol. 20, 1910-1911, p. 219 

 (1911). 



23 K. Kalitsky : Mem. Geol. Com., St. Petersburg, no. 24, 1906. 



24 E. H. Pascoe : Records Geol. Survey India, vol. 34, 1906. 



25 R. L. Mrazek : Congress International du Petrole, 1907. 



26 J. Grybowski: Bull. Acad. Sci., Cracow, 1907. 



