Columbia subject headings:
Berks County (Pa.)--Maps.
Geology--Pennsylvania--Berks County--Maps.
Geology--Pennsylvania--Lehigh County--Maps.
Lehigh County (Pa.)--Maps.
Maps.
Harvard subject headings:
Berks County (Pa.)--Maps.
Geology--Pennsylvania--Berks County--Maps.
Geology--Pennsylvania--Lehigh County--Maps.
Lehigh County (Pa.)--Maps.
Princeton subject headings: