The earliest epoch of the Cambrian period in the chronostratigraphic scale, lasting approximately from 542 to 513 Ma ago and comprising the Tommotian, Atdabanian, and Lenian ages. This epoch has also been termed the Comley epoch by some authors and the rocks deposited during this time the Comley series, underlain by the Ediacaran (Precambrian) and overlain by the St David’s.