A Cresset-Stones is a form of medieval lamp. A detailed account of the stone types can be found by Micheal Moore in [The Journal of the Royal Society of Antiquaries of Ireland
Vol. 114 (1984), pp. 98-116](https://www.jstor.org/stable/25508860?Search=yes&resultItemClick=true&searchText=%28Michael&searchText=Moore%29&searchText=AND&searchText=%28Rathcroghan%29&searchUri=%2Faction%2FdoBasicSearch%3FQuery%3D%2528Michael%2BMoore%2529%2BAND%2B%2528Rathcroghan%2529&refreqid=search%3Aac84cd5eafccd29d1f58b6d0bb5a8d00&seq=1#metadata_info_tab_contents)