Fig. 78.—Map showing the principal petroleum and natural gas fields of the United States. (After U. S. Geological Survey.)
Fig. 79.—A vertical (structure) section showing a very common type of oil-bearing structure. In this anticline, water, oil, and gas arranged in order of their specific gravities. Removal of the gas would allow the oil and water to rise higher toward the apex of the porous layer. (After Indiana Geological Survey.)
