Other
Natural history
History
14
Description and travel
10
Coal mines and mining
3
Hiking
3
Trails
3
Birds
2
Histoire
2
Landscapes
2
Mines and mineral resources
2
Natural areas
2
Natural history museums
2
Nature study
2
Phenology
2
Philadelphia Region (Pa.)
2
Railroads
2
Recreation
2
Sciences naturelles
2
Societies, etc
2
Travel
2
Wilderness areas
2
%SP6
1
Anthracite coal
1
Art
1
Art and science
1
Art et sciences
1
Bucks Co
1
Coal reserves
1
Descriptions et voyages
1
Diaries
1
Genealogy
1
Geological surveys
1
Geology
1
Indians of North America
1
Indiens d'Amérique
1
Intellectual life
1
Kunst
1
Manuscripts
1
Manuscripts, American
1
Museums
1
Natural History
1
Natural history in art
1
Naturwissenschaften
1
Periodicals
1
Pflanzendarstellung
1
Philadelphia museums
1
Quakers
1
Research
1
Scientific expeditions
1
Sources
1
more ...