 Lavas and pelites are seen around Tayvallich in Knapdale, after which area the subgroup is named, where it consists of the Tayvallich Slate and Limestone Formation and the overlying Tayvallich Volcanic Formation..The succession is between 100 and 250m thick but can reach up to 2.5km in the east where the psammites and semipelites occur.The Loch Tay Limestone Formation extends from Campbeltown to Glen Isla.