Passage: The fossil-bearing deposits of the Burgess Shale correlate to the Stephen Formation, a collection of slightly calcareous dark mudstones, about 508 million years old. The beds were deposited at the base of a cliff about 160 m tall, below the depth agitated by waves during storms. The vertical cliff was composed of the calcareous reefs of the Cathedral Formation, which formed shortly before the deposition of the Burgess Shale. The precise formation mechanism is not known for certain, but the most widely accepted hypothesis suggests that the edge of the Cathedral Formation cliff became detached from the rest of the reef, slumping and being transported some distance <unk> kilometers <unk> anopendicularly away from the reef. The beds were deposited at the base of a cliff about 160 m tall, below the depth agitated by waves during storms. The vertical cliff was composed of the calcareous reefs of the Cathedral Formation, which formed shortly before the deposition of the Burgess Shale Shale. The
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