Each mudstone layer is the result of one such catastrophe.[24] The Greater Phyllopod Bed, a 7 metres (23 ft) thick sequence consisting of Walcott's famous "Phyllopod Bed" plus the 5 metres (16 ft) below that, contains at least 36 layers,[24] deposited over 10 to 100 thousand years, during which the environment was essentially stable.[13]