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Subject
- Agriculture2
- Bicycles2
- Bituminous coal--Pennsylvania--Maps4
- Canals2
- Cities and towns1
- City planning1
- Coal3
- Coal mines and mining1
- College campuses1
- Counties1
- Drift2
- Floods1
- Gas fields1
- Gas reservoirs1
- Gas wells--Pennsylvania--Maps4
- Geology35
- Geology, Stratigraphic7
- Geology, Structural21
- Geomorphology2
- Glacial landforms4