The Burgess Shale

You cannot walk up to this one. Access is by guided hike with Parks Canada, to one of three Burgess Shale sites across Yoho and Kootenay national parks, and places are reserved in advance through the Parks Canada reservation service. That restriction is the point: collecting here became politically difficult from the mid-1970s once Parks Canada and UNESCO recognised what the deposit was, and the ground is now protected accordingly.

Charles Walcott found it on 30 August 1909, near the end of the season's fieldwork. He came back in 1910 with his wife, sons and daughter and opened a quarry on the flank of Fossil Ridge, and he returned almost every year until 1924. By then he was 74 and had taken out more than 65,000 specimens, and he was still describing them when he died in 1927.

It is also a cautionary tale. Walcott, following the scientific consensus of his day, tried to file every fossil into a living group. Sorted that way they looked like curiosities, and for decades that is what they were taken for. Alberto Simonetta reopened the material first-hand in 1962, and it became clear Walcott had barely scratched the surface. Harry Whittington restarted excavation with the Geological Survey of Canada, opened the Raymond Quarry about twenty metres higher up the ridge, and with his research students Derek Briggs and Simon Conway Morris reassessed the whole fauna. What emerged did not fit the modern groups at all: Opabinia with five eyes and a snout like a vacuum hose, and Hallucigenia, which was first reconstructed upside down and walking on its spines.

The rock is black shale about 505 million years old, cropping out near Field in Yoho and again in Kootenay 42 kilometres to the south. Soft parts survive here, down to eyes, guts and traces of brains, which is why a middle Cambrian sea floor in the Rockies can still start arguments.