Não informado. (2001). Bulletin of the Pennsylvania Geological Survey. Pennsylvania Geological Survey.
Chicago-viite (17. p.)Não informado. Bulletin of the Pennsylvania Geological Survey. Harrisburg, Pa: Pennsylvania Geological Survey, 2001.
MLA-viite (8. p.)Não informado. Bulletin of the Pennsylvania Geological Survey. Pennsylvania Geological Survey, 2001.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.