Columbia subject headings:
Geochemistry--Congresses.
Geology, Stratigraphic--Precambrian--Congresses.
Ore deposits--Congresses.
Volcanic ash, tuff, etc.--Congresses.
Harvard subject headings:
Princeton subject headings:
Geochemistry--Congresses.
Geology, Stratigraphic--Proterozoic--Congresses.
Ore deposits--Congresses.
Volcanic ash, tuff, etc.--Congresses.