| St. Peter Sandstone, Illinois Basin
Several authors indicated that the sands within the St. Peter Sandstone are continuous, especially in the middle portions of the unit (Kreutzfeld, 1982; Barnes and others, 1992). The St. Peter Sandstone is partially offset by a number of faults, and these faults can significantly affect sand-body continuity. Therefore, we chose to use the map of Collinson and others (1988), which shows the locations of major faults that offset the St. Peter Sandstone to characterize sand-body continuity, because faulting rather than lithology is the principal factor influencing sand-body continuity of the St. Peter in the central Illinois Basin.

Barnes, D. A., Lundgren, C. E., and Longman, M. W., 1992, Sedimentology and diagenesis of the St. Peter Sandstone, central Michigan Basin, United States: American Association of Petroleum Geologists Bulletin, v. 76, p. 1507–1532.
Collinson, C., Sargent, M. L., and Jennings, J. R., 1988, Chapter 14: Illinois Basin region, in Sloss, L. L., ed., The Geology of North America, v. D-2, Sedimentary Cover—North American Craton: U.S.: Decade of North American Geology: Geological Society of America, p. 383–426.
Kreutzfeld, J. E., 1982, Pore geometry and permeability of the St. Peter Sandstone in the Illinois Basin: University of Toledo, Master's thesis, 353 p.
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