Columbia subject headings:
Harvard subject headings:
Geological time.
Geology--Germany (West)--Rheinisches Schiefergebirge.
Geology--Germany--Rheinisches Schiefergebirge
Metamorphic rocks.
Potassium-argon dating.
Princeton subject headings:
Metamorphism (Geology)--Germany (West).
Potassium-argon dating.
Schists--Germany (West).