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



Page 

 Subclass IV (&) — Monoclinal bulges 575 



Subclass IV (c) — Closed saline domes 575 



History of saline dome developments 575 



Topography and structure 579 



List of known saline domes , 580 



Association of rock-salt and other minerals 580 



Apparent absence of salt in some domes 581 



Distribution of saline domes 5.81 



Origin of saline domes 583 



Subclass IV (d) — Volcanic plugs 585 



Subclass IV (e) — Perforated saline domes 587 



Features common to all types of quaquaversal structure 588 



Class V — Contact of sedimentary and igneous rocks 589 



Subclass V (a) — Contact of sedimentaries with volcanic plugs... 589 



Subclass V ( & ) ^Contact of sedimentaries with dikes 589 



Subclass V (c) — ^Contact of sedimentaries with intrusive beds or 



laccoliths 589 



Subclass V (d) — Contact of sedimentaries with older igneous 



rocks 591 



Class VI — ^Strata dipping unconformably away from an old shoreline. 591 



Class VII — Crevices of igneous rocks 592 



Class VIII — Crevices of sedimentary rocks 593 



Class IX — Oil associated with closed faults 594 



General discussion 594 



Subclass IX (a) — Oil on the upthrow side 594 



Subclass IX (h) — Oil on the downthrow side 594 



Oil on both sides of the fault 596 



Subclass IX (c) — Oil along overthrust faults 596 



Class X — Oil sands sealed in by bituminous deposits at outcrop 596 



Other conditions than structure 598 



Relation between structure and topography 600 



Causes of failure of geological work in search of oil 600 



Structural "habits" peculiar to individual fields 601 



Substance of a geological examination 602 



Conclusion 602 



Introduction 



When we consider "the variety of different conditions prevailing in oil 

 fields, it is evident that some sort of a classification is needed. Tn order 

 to be of most practical service, this should be based on the most con- 

 spicuous distinguishing factors prevailing in a majority of the fields. 

 What, then, is the most conspicuous type of phenomena displayed in an 

 undeveloped oil field? Without doubt, it is the geological structure; 

 hence we choose structure as the starting point in our classification, as 

 we do in our detailed field investigations. 



