588 p. G. CLAPP- — CLASSIPICATION OP PETROLEUM AND GAS PIELDS 



Subclasses IV (c) and IV (^). So far as we know, the oil-bearing domes 

 of this type are limited to Eonmania; but others appear in Transylvania 

 which appear not to have been adequately tested. Figure 13 is an illus- 

 tration of a perforated dome in Eonmania after Bosworth.*^^ 



It is probable that some of the saline domes of the Gulf Coastal Plain 

 of the United States may be of the perforated type ; but if so little, if any, 

 oil has been found in them and none has been found in the perforated 

 domes of Transylvania. In Eonmania oil occurs in association with per- 

 forated domes, among otlier places in the Baicoi field, as illustrated by 

 Thompson.^ ^ 



iss indicate© roassea of rock- soft 

 P => Pontian 

 D • Daclen 



Figure IB.— Cross-section of Oil Field at Baicoi, Roumania 



Illustrating occurrence of oil according to Subclass IV (e). After Bosworth. Petroleum 



Review, March 23, 1912 



Features common to all types of quaquaversal structure. — Although 

 many differences exist between oil fields of Types TV (a), (h), (c), (d), 

 and (e), these subclasses are similar in many respects. First, in order 

 to hold oil, they must combine all of the several factors which appear 

 essential in every field, namely : ( 1 ) a porous stratum, to hold the oil ; 

 (2) an impervious cover, to keep it from escaping, and (3) some sort of 

 geological structure by which the oil, gas, and water may have been sepa- 

 rated and the oil concentrated in one locality. In anticlinal and syn- 

 clinal fields the structure or folding of the beds has acted as factor (3) : 

 hence we may expect to find gas on the up-dip side or nearest the crest of 



63 Pet. Review, March 23, 1912, p. 172. 



'"A. Beeby Thompson: Trans. Instn. Min. and Met, vol. 20, 1910-3 911, p. 223, fig. 40. 



