. Oil and gas yielding formations of California. .Upright \ Wells on Inclined Fold. Fig. 17. Wells on Overturned Fold. instances requires the investigation of a wide area in order to obtain asatisfactory solution. Illustration D, Fig. 17, shows mistakes which are qurte likelyto be made by drilling on an overturned fold. If an outcrop of oil-sandhad been discovered at point K, the dip at the outcrop would coincide GEOLOGICAL STRUCTURE PERTAINING TO PETROLEUM. 187 with OM, the axis of the fold. Unless the structure of the formationwere known, it would naturally be supposed
. Oil and gas yielding formations of California. .Upright \ Wells on Inclined Fold. Fig. 17. Wells on Overturned Fold. instances requires the investigation of a wide area in order to obtain asatisfactory solution. Illustration D, Fig. 17, shows mistakes which are qurte likelyto be made by drilling on an overturned fold. If an outcrop of oil-sandhad been discovered at point K, the dip at the outcrop would coincide GEOLOGICAL STRUCTURE PERTAINING TO PETROLEUM. 187 with OM, the axis of the fold. Unless the structure of the formationwere known, it would naturally be supposed that the dip of the oil-sandstratum was fully shown by the exposed rocks at point K. If well Gwere drilled, the oil-sand would be struck at point I, and the oil-sandstratum would be penetrated lengthwise between I and N. This wouldlead to the erroneous conclusion that a very thick stratum of oil-sandhad been penetrated. If well J were drilled with the intention of strik-ing the oil-sand at 0, it is obvious that the oil-sand would be missedaltogether. This illustrates
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