Petroleum or Rock Oil 295 



ence of less pervious beds arching over such folds and affording 

 favorable conditions for the confinement of oil and gas tending 

 to escape (M. R. Campbell) . 



Geologic conditions in California fields are so complicated 

 that it is extremely difficult to formulate general laws regarding 

 migration or occurrence of oil and gas. The element of time 

 also enters into the question, for since the deposition of Tertiary 

 rocks sufficient time has not elapsed for the escape of all the 

 hydrocarbons, whereas in the Palaeozoic rocks of the east time 

 has been so great that there has been opportunity for the escape 

 of all hydrocarbons in the rocks wherever the minutest fracture 

 occurs. Owing to the complicated conditions in California it 

 it doubtful if the laws governing the movement of oil and the 

 full effect of local conditions will ever be fully understood. 



Rock Structure Controls Accumulation 

 of Oil 



A study of the rock structures shows that the anticline is the 

 dominating factor controlling the accumulation of petroleum 

 irrespective of topography. The close association of oil with 

 structural features of this type is not unique to California, but 

 is found in all the larger fields of the world. The presence of 

 anticlines can of course only be of importance where rocks 

 known to be oil-bearing are involved in or near the folds, and 

 where part of the strata are porous enough to act as reservoirs. 

 The original anticlinal theory assumed that oil, being lighter 

 than water, rises above it, following porous beds to the highest 

 part of the anticline, where it is trapped below impervious 

 strata that cover the oil-bearing sands. In the east flank of the 

 Coast Ranges anticlinal folds are the dominating factor influ- 

 encing the accumulation of oil. 



Another theory advanced by competent geologists is that 

 the orogenic (mountain making) forces which have so greatly 

 disturbed the rocks of the earth's crust are the most potent cause 

 of the migration of oil along lines of least resistance. This force 



