⁴¹Ó Ríordáin, Sean P., and Marcus P. Ó HEochaidhe. "Trial Excavation at Newgrange." The Journal of the Royal Society of Antiquaries of Ireland 86.1 (1956): 55.
The excavation that first uncovered some of the inscribed kerbstones was done June, 1928 (Praeger and Macalister), and only lasted a couple of weeks.