North Stack North Stack North Stack (Welsh: Ynys Arw, meaning "rugged island") is a small island situated just off Holy Island on the north-west coast of Anglesey. North Stack can also refer to the headland opposite the island. This is the site of a redundant fog warning station, comprising a number of buildings, including the Trinity House Magazine, built in 1861, where shells for the warning cannon were stored. These buildings now house a bird watching observatory, giving a view of South Stack lighthouse across Gogarth Bay, and the studio of artist Philippa Jacobs. The Precambrian quartzite cliffs of this headland, including
North Solitary Island by the NSW Maritime Parks Authority. Rocks on North Solitary Island consist of mudstone and a light green brittle sillicaceous argillite. The argillite probably formed from volcanic ash falls. The strike of the beds is between 120° and 170° with steep dipping to the west. Some beds show graded bedding. Rocks are frequently folded, and there are also several small faults. Tectonically it is part of the Coffs Harbour Block which in turn is part of the New England Orogen. North Solitary Island North Solitary Island is one of the largest islands found off the New South Wales coast and