39Eogan, George, and Eoin Grogan. "Prehistoric and Early Historic Culture Change at Brugh Na Bóinne." Proceedings of the Royal Irish Academy. Section C: Archaeology, Celtic Studies, History, Linguistics, Literature 91C (1991): 110.
The authors state that there may also have been a fourth large site, at Ballincrad (site G), not much survives, but there is evidence that the main mound might have been about 70m (230 ft) in diameter.
Throughout history there have been different accounts of the number of stones in the incomplete "Great Circle" around Newgrange, since some stones have been broken or removed. O'Kelly, however, concluded that there was "very little evidence...in the excavated areas for the original presence of these 'missing' stones...One must be prepared to accept the thesis that the circle may never have been completed." The dating of the monument was made possible because the spaces between the slabs of the roof were caulked with a mixture of burnt soil and sea sand, from which two C14 readings, each of 2500 BCE, could be obtained. (O'Kelly, Michael J., and Claire O'Kelly. Newgrange: Archaeology, Art, and Legend. London: Thames and Hudson, 1982. 79, 22.)