Reflections from within the Precambrian basement complex were recorded in the vicinity of the Wichita Mountains in southwestern Oklahoma. The reflections of good quality and persistence, depict a section in excess of 20,000 ft. of igneous rocks that appears like a seismic section of sedimentary formations. A well in the area drilled 4,000 ft. of this Precambrian section, encountering alternating layers of silicic and gabbroic igneous rocks exhibiting high contrast in density. Precambrian outcrops of much of the Wichita Mountains, comprising comparable types of rocks, display sheetlike, gently dipping layers, some of which persist for several miles. The seismic reflections are thus produced by the igneous layers of differential acoustic properties. An abrupt change of direction of dip occurring at about mid-depth of the seismic section precludes the possibility that the seismic events are multiple reflections.

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