work with — tectonic squeezing of the beds produced a vertical cleavage that fractures the rocks, so they split perpendicular to the fossils. The Walcott quarry produced such spectacular fossils because it was so close the Stephen formation — indeed the quarry has now been excavated to the very edge of the Cambrian cliff. Both the thick and thin Stephen formation were deposited below wave base. It was originally thought that the Burgess Shale was deposited in anoxic conditions, but mounting research shows that oxygen was continually present in the sediment. The anoxic setting had been thought to not only protect the newly dead organisms from decay, but it also created chemical conditions allowing the preservation of the soft parts of the organisms. Further, it reduced the abundance of burrowing organisms — burrows and trackways are found in beds containing soft-bodied organisms, but they are rare and generally of limited vertical extent. Subdivisions The formation is made up of the Kicking Horse member, which includes the Alalcomenaeus–Sanctacaris beds; this underlies and interdigitates with the unfossiliferous Yoho River member. These two are truncated by an unconformity and covered by the Campsite Cliff member, which contains the Ogygopsis beds. The Wash member, which contains many shelly but no soft-bodied fossils, interrupts this sequence in places, and directly underlies the Phyllopod beds, which mark the base of the Walcott Quarry member. This underlies the Wapta member, which is unconformably overlain by 'Tokumm'. The Wapta member has been redefined into the Raymond Quarry member, Emerald Lake member, Odaray member, Paradox member and Marpole member. The thin Stephen grades conformably into the overlying Eldon formation. Fossiliferous collection sites Of the dozen-plus fossiliferous sites in the Stephen formation, the Walcott Quarry is the most famous, bearing the Phyllopod beds. This lies at the base of the Walcott Quarry member, and three other quarries – the Raymond, UE and EZ – lie above it. The UE and EZ quarries herald from the Upper Ehmaniella Zone and Ehmaniella Zone, respectively, and belong to the Emerald Lake member. The Campsite Cliff member contains the Ogygopsis-bearing Mount Stephen trilobite beds (both on Mount Stephen), while the Collins Quarry (containing the Sanctacaris beds) is situated in the Kicking Horse member. The S7 locality on Mount Stephen has been attributed both to the Campsite Cliff member and the Kicking Horse member. The Trilobite Beds, the first Burgess Shale locality to be discovered,