The soft-bodied organisms for which the Burgess Shale is famous are fossilized in the mudstone layers, which are between 2 and 170 millimetres (0.079 and 6.693 in) thick, averaging 30 millimetres (1.2 in),[13] and have well-defined bases.[24] Opinions vary about how the mudstone layers were produced: perhaps by mudslides from the top of the "Cathedral" limestone platform, when its edge collapsed occasionally; or possibly by storms that created back-currents that abruptly washed large volumes of mud off the platform.