 An erosional remnant of the Tasmanian mainland with an elevation of above sea level, the island is estimated to have separated from the Tasmanian mainland at least 15,000 years ago.Eddystone is known for its inaccessibility and distinctive shape, described by Abel Tasman in 1642 as "a tall, obtuse, square tower".A painting from 1823 bears this out, and also shows its proximity to Pedra Branca, to the west.