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



joint cracks and fissures in shale. The oil does not follow any particular 

 beds or series of beds and the oil zone contains no sandstone or other 

 porous beds. Washburne's evidence on this matter, which seemed de- 

 cisive, was as follows : 



1. Correspondence in direction of major joints with alignment of interfering 

 wells. 



2. Lack of productivity of some wells situated only a few feet from pro- 

 ductive wells. 



3. Occasional ruining of a deep well by tapping the source of pressure by a 

 neighboring shallow well. 



4. Draining of many wells by adjacent wells of much greater depth. 



5. Marked increase of maximum pressure with depth. 



6. Dissimilar pressure in adjacent wells of ^the same depth. 



7. "Crevices" reported by drillers. 



8. Disappearance of large quantities of water poured into the wells. 



9. Reported dropping of drilling tools. 



In northeastern Ohio, southern Texas, and in some localities in Wyo- 

 ming small oil and gas .wells are frequently obtained in shales outside of 

 known domes, anticlines, or other structures. This is generally called 

 "shale oil," or "crevice oil," to distinguish it from the normal structural 

 type. The shale oil is believed by many to be indigenous to the beds in 

 which it is found. 



CLASS IX— OIL ASSOCIATED WITH CLOSED FAULTS 



General discussion. — The known examples of this class consist of some 

 pools in the Los Angeles field and some in the Lompoc field in California, 

 described by Arnold. In these cases the highly inclined oil sands are cut 

 off abruptly below ground by a fault, thus sealing in the oil and gas and 

 preventing their escape to the surface. To explain the probability that 

 such occurrences are more frequent than is known, it may be worth while 

 to mention that oil springs frequently occur along fault-lines in British 

 Columbia, in Gaspe in Quebec, in Wyoming, and in Mexico. This type is 

 illustrated in figures 17 and 18. 



Subclass IX(a) — Oil on the upthrow side. — Definite examples of oil 

 on the upthrow side of faults are frequent in Oklahoma and they may 

 exist elsewhere. No localities are mentioned on account of professional 

 connections, which demand secrecy. 



Subclass IX(h) — Oil on the downthrow side. — A good example of oil 

 along the downthrow side of faults in the Coalinga field in California is 

 illustrated in figure 17, after Arnold. Numerous other cases doubtless 

 exist. 



