1. Isobel Smith, Windmill Hill and Avebury: Excavations by Alexander Keiller, 1925–1939 (Clarendon Press, Oxford, 1965).
2. Stuart Piggott, The West Kennet Long Barrow, Excavations 1955–56, Ministry of Works Archaeological Reports no. 4 (HMSO, London, 1962).
3. There are many examples of similar practices at Neolithic tombs, which I discuss (with references) in Britain BC (HarperCollins, London, 2003), chapter 8.