TY  - RPRT
TI  - Map showing high-purity silica sand of Middle Ordovician age in the Midwestern states
AU  - Keith B. Ketner
PY  - 1979
DO  - 10.3133/mf1097
UR  - https://pubs.usgs.gov/publication/mf1097
ID  - mf1097
ER  -