. Bulletin of the Southern California Academy of Sciences. Science; Natural history; Natural history. waliT ri>ir.;'; in >li;ilum .\\'> has driwii the oil and }^as into the ui)i)fi' liorlion of the stratum where they have arranged themselves accord- iiif^ to their rclatixc specifir ^ra\ity. Unless the line of faulting is filled with lime ov i la\ nv otlicr inipcr\'ious material there would be an oil spring or asphaltuni bed at point C—the probabilitx' is that most of the gas would have escaped along the fault line. Oil. POOLS I') THROUGH CHANGE IX PERME- .MULITY OF STRATA. There
. Bulletin of the Southern California Academy of Sciences. Science; Natural history; Natural history. waliT ri>ir.;'; in >li;ilum .\\'> has driwii the oil and }^as into the ui)i)fi' liorlion of the stratum where they have arranged themselves accord- iiif^ to their rclatixc specifir ^ra\ity. Unless the line of faulting is filled with lime ov i la\ nv otlicr inipcr\'ious material there would be an oil spring or asphaltuni bed at point C—the probabilitx' is that most of the gas would have escaped along the fault line. Oil. POOLS I') THROUGH CHANGE IX PERME- .MULITY OF STRATA. There doubtless are instances where a change in the permeability of strata have occasioned oil pools or a variation in the yield of wells situated near one another, and the occurrence of dry holes in other- wise producLi\e territory may often be attributed to this cause. In Fig. 7 stratum AB is shown to change from sand to clay and the oil and gas being pressed up by the water have percolated through the porous strata until they reached the barrier of clayey material in front of whicn they form an oil pool. It is evident that while C will be a productive well, D will be a dry hole. The illusirations accompanying this article show types of geolog- ical structures which have been found favorable to the accumulation of petroleum. The most important of these is the anticline, to which the greater number of the important oil fields of the world may be referred. When there are sufficient rock exposures in a locality the geologist can generally determine the character of the structure but of course it is impossible for him to demonstrate whether or not any particular structure contains an oil pool. He can, however, eliminate many of the risks of prospecting for oil by selecting territory where there are structures favorable to the accumulation of petroleum and where oil yielding horizons may be reached by the Fig. 4—Contour Sketch of Dome. 36. Please note that these images are
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