Columbia subject headings:
Geology, Stratigraphic--Permian--Congresses.
Geology, Stratigraphic--Triassic--Congresses.
Geology--Congresses.
Harvard subject headings:
Princeton subject headings:
Geology, Stratigraphic--Permian--Congresses.
Geology, Stratigraphic--Triassic--Congresses.
Geology--Congresses.