The writer proposes an alternative explanation of the sharply contrasted lithologic character of the Paleozoic sediments (Ordovician to Lower Mississippian) in the Arbuckle Mountains and the Ouachita Mountains, respectively. Although only 12 miles separate the two facies, the former is a normal sedimentary series, the latter is characteristically siliceous (cherts, siliceous limestone, novaculites, et cetera). Van der Gracht and Ulrich proposed thrust faulting of great magnitude bringing into proximity sediments from different geosynclines; the writer rejects this in favor of minor faulting, and essential identity of both series, with a single geosynclinal deposition.

A large part of the paper consists in showing that lithologically and paleontologically the two series can be closely matched. Petrological evidence is given of the secondary character of the silicification of the Ouachita facies.

The excessive silicification is explained by H2O-SiO2 solutions being stable under conditions of high temperature and pressure, unstable under low. Release of internal pressure by faulting will cause SiO2 to precipitate. In support of this view, it is shown that various sediments show marked silicification in the vicinity of faults.

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