Ceollach the second bishop of the Mercian Church, was a Scot by birth. He was appointed bishop by Oswy before the end of the year.658, and was consecrated by Finan. His episcopate was very short; immediately, as it would seem, on the evacuation of Mercia by Oswy, he retired to Iona, about 659. In the Scotch calendars he appears as Colochtus, Colathus, Ceolla, and Colace (Forbes, Kal. Scottish Saints, p. 237, 299, 302), and elsewhere as Cellah (Malmesbury, Gestce Pontif. ed. Hamilton, p. 307).