Não informado. (2004). Information Circular. Department of Natural Resources, Division of Geological Survey.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Information Circular. Columbus, Ohio: Department of Natural Resources, Division of Geological Survey, 2004.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Information Circular. Department of Natural Resources, Division of Geological Survey, 2004.
Πρόσοχή: Οι παραπομπές μπορεί να μην είναι 100% ακριβείς.