A band of limestone, at least 180 metres wide, is exposed at Frederick Point on the south end of Digby Island, 1.5 kilometres southwest of Prince Rupert. The limestone is enclosed in graphitic schist within a broad belt of Permian-Triassic meta-sediments in the Coast Plutonic Complex. The limestone strikes 115 to 130 degrees and dips 35 to 65 degrees northwest.

The deposit is generally composed of white to bluish grey, medium grained, banded limestone containing thin zones of darker, more resistant siliceous limestone that become more numerous towards the margins of the band. Some secondary mica is developed in the limestone.