Carbonate rocks were studied from the Middle Cambrian Drake Icefall Formation and the Middle to Upper Cambrian Minaret Formation. Additionally, carbonate clasts from the Middle Cambrian Union Glacier Formation and the Permo-Carboniferous Whiteout Conglomerate were examined. No in situ Lower Cambrian carbonate rocks are known to crop out in the Ellsworth Mountains; only reworked clasts of such rocks are found in the Heritage Group and the Whiteout Conglomerate. These clasts suggest that during Early (and Middle?) Cambrian time, a wide carbonate platform developed in or close to the Ellsworth Mountains. This was the site of skeletal algae and archaeocyathid boundstones...