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- Geographic Subject: Indiana[remove]42
- Topical Subject: Geology15
- Topical Subject: Geology, Stratigraphic12
- Geographic Subject: Illinois8
- Topical Subject: Coal mines and mining8
- Topical Subject: Coal4
- Geographic Subject: Indiana, Northwest3
- Geographic Subject: Michigan3
- Geographic Subject: Ohio3
- Topical Subject: IGS Annual Reports3
- Geographic Subject: Calumet Region (Ill. and Ind.)2
- Geographic Subject: Lake County (Ind.)2
- Topical Subject: Administrative and political divisions2
- Topical Subject: Caves2
- Topical Subject: Clay2
- Topical Subject: Clay industries2
- Topical Subject: Karst2
- Topical Subject: Mines and mineral resources2
- Topical Subject: Shale2
- Topical Subject: Sinkholes2