47O'Kelly, Michael J., and Claire O'Kelly. Newgrange: Archaeology, Art, and Legend. London: Thames and Hudson, 1982. 98.
The "closing stone," was used in an experiment by the excavators to determine how well it would serve to cover the opening of the tomb. They discovered that "with the curved end on the ground and the straight one uppermost it fitted exactly under the overhang of RS1, closing the passage perfectly."