Columbia subject headings:
Geology--Delaware.
Geology--White Clay Creek Valley (Pa. and Del.)--Guidebooks.
Petrology--Delaware.
Petrology--White Clay Creek Valley (Pa. and Del.)--Guidebooks.
Piedmonts (Geology)--Delaware.
Piedmonts (Geology)--White Clay Creek Valley (Pa. and Del.)--Guidebooks.
White Clay Creek Valley (Pa. and Del.)--Guidebooks.
Harvard subject headings:
Princeton subject headings:
Geology--Delaware.
Piedmonts (Geology)--Delaware.