The Marble Bay deposit is situated within a 13 kilometre long belt of Upper Triassic Quatsino Formation (Vancouver Group) limestone The belt is up to 3 kilometres wide and is preserved along the axis of a broad northwest plunging syncline. The limestone in the vicin- ity of Marble Bay is folded into a smaller open anticline that gently plunges to the southeast. Various quarries are developed in the up- per portion of the middle calcium member some 600 metres above the base of the formation. A few steeply dipping, north to northwest striking faults are evident. The limestone is intruded by a small stock of diorite-gabbro in the vicinity. A few north to northeast trending dykes are exposed in the quarries.

The deposit is composed mostly of fine-grained, black to light grey, calcium and high calcium limestone and some pale brown to greenish grey magnesian limestone with serpentinite and other magnesium silicates. A series of 9 chip samples taken from the east and west ends of the main quarry averaged 51.93 per cent CaO, 3.96 per cent MgO, 1.12 per cent insolubles ,0.39 per cent R2O3, 0.25 per cent Fe2O3, 0.035 per cent MnO, 0.013 per cent P2O5, 0.059 per cent sulphur and 42.41 per cent ignition loss (Bulletin 40, page 73).

Limestone was produced from one large quarry and several smaller quarries on the west shore of Marble Bay by various operators between 1898 and 1962. Most of the limestone was quarried by W.S. Beale between 1946 and 1956.