596 F. G. CLAPP CLASSIFICATION OF PETROLEUM AND GAS FIELDS 



Oil on both sides of the fault. — In many of the Oklahoma fields oil is 

 found both on the upthrow and downthrow sides. In the Bibi-Eibat field 

 of Eussia oil occurs on both sides of normal faults which cut the crest of 

 the anticline, as shown by D. Golubiatnikoff.^^ According to Thomp- 

 son, ^^ the faults in the Bibi-Eibat field exercise an important influence 

 on the production of the wells. The faults are inclined and wells are 

 drilled to strike them at great depths. In some cases the production of 

 wells on one side of the fault was much greater than on the other. 



Subclass IX (c) — Oil along overthrust faults. — Examples of oil fields 

 along overthrust faults are brought from Eoumania, where they are well 

 known. A cross-section of the Bustenari field, after Bosworth,^^ is here 

 shown in figure 19. A minor instance is in the Pincher Creek pool of 

 southern Alberta. One of the best published examples is described by 



S.W. 



a. Apsheron Beds- 13. Freshwater deds (Upper Miocene) m Meofic. 



Scale: i T f T i 



Figure 18. — Section through Bihi-Eihat Field of Baku, Russia 



Showing occurrence of oil on both sides of faults, Subclasses IX (a) and IX (6), and 

 also coming in Subclass II (6). After Thompson 



Arnold and Johnson^* in the McKittrick field in California (figure 20), 

 where the shales of the Monterey and Santa Margarita formations of 

 Middle Miocene age are supposed to have been overthrust along a low- 

 angled plane, on top of the McKittrick gravels, clays, and oil sand of 

 Upper Miocene age. 



CLA88 X — OIL SANDS SEALED IN BY BITUMINOUS DEPOSITS AT OUTCROP 



This class, apparently having been first postulated by the writer, has 

 since been referred to by other writers. The Pitch Lakes of Trinidad 

 and Venezuela are believed to be the best known examples. In some of 

 the California fields^^ the outcrop of the sands is believed to be closed by 

 brea. Some of the oil found near the vein of grahamite, described by 



81 D. GolubiatnikofE : Bull. Geol. Com., St. Petersburg, vol. 23, 1904. 



82 A. Beeby Thompson : Petroleum mining and oil-field development, New York and 

 London, 1910, p. 57. 



83 T. O, Bosworth : Pet. Review, March 23, 1912, p. 172. 



84 Ralph Arnold and Harry R. Johnson : Bull. 406, U. S. Geol. Survey, 1910, pp. 97-99. 



85 Arnold and Johnson : Loc. cit., pi. v. 



