The Marble Cove Limestone showing outcrops on the west side of Tzartus Island in Barclay Sound, 45 kilometres southwest of Port Alberni.
A limestone mass of the Upper Triassic Quatsino Formation (Vancouver Group), up to 750 metres wide, extends northeastward from Marble Cove for 1000 metres. The limestone is bounded by volcanics of the Lower Jurassic Bonanza Group to the southeast. The deposit is separated from a body of granodiorite of the Early to Middle Jurassic Island Plutonic Suite to the north by a west trending fault. Bedding strikes 164 degrees and dips 70 degrees northeast.