Columbia subject headings:
Geology, Stratigraphic--Quaternary--Congresses.
Volcanic ash, tuff, etc.--Congresses.
Harvard subject headings:
Geology, Stratigraphic--Quaternary--Congresses
Volcanic ash, tuff, etc.--Congresses.
Princeton subject headings:
Geology, Stratigraphic--Quaternary--Congresses.
Volcanic ash, tuff, etc.--Congresses.