The Precambrian Holyrood granite of southeastern Newfoundland is of particular geological interest, because of its tectonic position on the easternmost exposed flank of the Appalachian mobile belt. Although previously considered to have been emplaced during the Grenville orogeny, this granite yields a Rb/Sr isochron age of 574 ± 11 million years (m.y.). Tectonic and sedimentary events that followed the granite emplacement, and that preceded the deposition of nonconformably overlying fossiliferous Lower Cambrian strata, are believed to have required at least 15 m.y. Consequently, a tentative maximum age of 560 ± 11 m.y. is proposed for the base of the Cambrian in this region.