"Illinois." . . "Ceramic materials." . . . . "Geology Illinois." . . "Geology." . . "Gravel." . . . . . . . . . . . . . "Short papers on geologic subjects: Areal geology of part of central eastern Illinois, by Howard R. Schwalb ; Prospecting for commercial sand and gravel using electrical earth resistivity, Clinton County, Illinois, by Jerry S. Dobrovolny ; Ceramic materials from magnesium-treated clays, by William D. Johns"@en . . . . . . . . . . . . . . . "Sand." . . "Illinois State Geological Survey." . .