The Saint Peter sandstone of Illinois is so well known, as to its general characteristics, that it needs no introduction. The purpose of this paper, therefore, is to call attention to a number of unusual phenomena observed during a State-wide study of the sandstone for the Illinois Geological Survey. Some of the phenomena described have been noted by earlier writers, but their records have been too meager and too generalized to be entirely satisfactory.

Although the Saint Peter underlies almost all of Illinois, it outcrops in a very limited area (figure 1). The principal exposure occurs in the Ottawa-Utica area, in the north-central part of the State. Others in order of importance are in the Oregon-Dixon area, about 40 miles north-west of the Ottawa-Utica district; in the Brookville-Harper area, about 60 miles northwest; and near Shirland, close to the center of the north boundary of the State. In Calhoun . . .

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