In form they are two submerged plateaux extending from the north-west to the south-east about 169 feet (52 m) apart and separated by a channel of 39–49 feet (12–15 m) depth. The north-west rock is approximately 66 feet (20 m) in diameter, and 16 feet (4.9 m) under water, while the south-east rock is 197 feet (60 m) in diameter and lies only 4 feet (1.2 m) under water.[2]