Belle Isle, situated between northern Newfoundland and the southeast coast of Labrador, consists of an uplifted block of Precambrian plutonic rocks intruded by northeast-trending diabase dikes and uncomformably overlain by Lower Cambrian and earlier (?) sedimentary and volcanic rocks. The Precambrian rocks lie along strike and are similar to Grenville gneisses of the Long Range Complex of western Newfoundland. In the southwest part of Belle Isle, the cover rocks are gently dipping basaltic flows and agglomerates that are succeeded conformably by arkosic sandstones and fossiliferous upper Lower Cambrian shales. In the northeast, the basement rocks are overlain by steeply dipping boulder conglomerates and arkosic sandstones, followed conformably by white quartzites.Diabase dikes are inseparable from overlying flows, but do not penetrate higher sedimentary strata of the southwestern Lower Cambrian succession. Toward the northeast, plutonic boulder conglomerates and quartzites are cut by the dikes.The distribution of supracrustal rocks around the periphery of the island, combined with local steeply inclined surfaces of unconformity between basement and cover rocks, indicate a major anticlinal structure produced by Paleozoic deformation. The study also shows that at Belle Isle the established Lower Cambrian succession of southeast Labrador and western Newfoundland is locally underlain by basalts and conglomerates and quartzites that thicken southeastward and northeastward.