• publisher: Urbana, Ill. : State of Illinois, Dept. of Registration and Education, Division of the State Geological Survey
  • creator: Johnson, Robert Britten, 1924- Illinois State Geological Survey
  • contributor: Illinois State Geological Survey.
  • Keyword: Refraction. Fluorspar. Geology Illinois Hardin County. Geology Research.
  • years: 1957.
  • pages: 15 p. :
  • class: QE105
  • download: pdf file