Columbia subject headings:
Harvard subject headings:
Cairns--Scotland--Orkney.
Megalithic monuments--Scotland--Orkney.
Neolithic period--Scotland--Orkney.
Orkney (Scotland)--Antiquities--History.
Orkney (Scotland)--Antiquities.
Passage Graves culture--Scotland--Orkney.
Tombs--Scotland--Orkney.
Princeton subject headings:
Cairns--Scotland--Orkney.
Neolithic period--Scotland--Orkney.
Orkney (Scotland)--Antiquities.
Scotland--Antiquities.