In the essentially continuous late Precambrian – Early Paleozoic succession of eastern Newfoundland, abundantly fossiliferous Cambrian shales are separated in most places from underlying strata by a quartzite-siltstone unit. This unit has been referred to the Random Formation in the Avalon-Bonavista area (east) and to the Blue Pinion Formation in the Fortune Bay area (west), and its age and significance in defining a Cambrian-Precambrian boundary have been in doubt for some time. An erosional disconformity at the top of the Random Formation has been interpreted as the base of the Cambrian by most authors. Recent stratigraphic studies indicate that both the Random and Blue Pinion Formations are parts of a laterally continuous lithologic unit and that the upper contact of this unit is gradational and conformable in central parts of its outcrop area. New fossil discoveries both within and beneath the Blue Pinion Formation indicate that the quartzite-siltstone unit is diachronous, and that its westernmost exposures are of Cambrian age.