Subject
Geology
66
History
21
Coal mining
17
Mines
17
Maps
15
Coal fields
11
Economic geology
11
Forests and forestry
11
Geologic maps
11
Coal
10
Mineralogy
10
Coal mines and mining
9
Mining
9
Stratigraphy
9
Atlas
8
Field notes
8
Gold mining
8
Gold ores
8
Mines and mineral resources
8
Field trips
7
Geologic history
7
Iron ores
7
Coal deposits
6
Coal mines
6
Coal seams
6
Forest management
6
Mineral resources
6
Mining industry
6
Description and travel
5
Economic conditions
5
Gold
5
Mineral Resources
5
Paleontology
5
Production
5
Age
4
Botany
4
Building stone
4
Buildings
4
Coal Mines
4
Fieldwork
4
Fisheries
4
Gold mines and mining
4
Metallic minerals
4
Mineral exploration
4
Natural resources
4
Oil shale
4
Quarries
4
Statistics
4
Stone
4
Economic aspects
3
more ...