Ynys Dulas is a small island located off the north-east coast of Anglesey

Anglesey

Anglesey , also known by its Welsh name Ynys Môn , is an island and, as Isle of Anglesey, a county off the north west coast of Wales...

 (Ynys Mon), Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

. It is the most eastern part of the parish

Parish

A parish is a territorial unit historically under the pastoral care and clerical jurisdiction of one parish priest, who might be assisted in his pastoral duties by a curate or curates - also priests but not the parish priest - from a more or less central parish church with its associated organization...

 of Llaneilian.

The island is situated about a mile and a half offshore, within Dulas Bay

Dulas Bay

Dulas Bay is a small bay on the north east coast of Anglesey , north Wales. The bay is bordered by three beaches.- Overview :...

. The size of the island depends on the tide

Tide

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

, with a maximum length of 623 metres and width of 207 metres against a minimum of 184 metres by 35 metres. It has a maximum area of 18.3 acres (74,057.5 m²). The island is mainly rocky, but at low tide sand is exposed, most noticeably on the southern part of the island where it separates the main rock formation from two smaller ones named Garnog (Welsh: Hooves). Seals

Pinniped

Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

 are often spotted living on and around the island (hence it is also known locally as Seal Island), but it is too small for human inhabitation. There is also very little flora

Flora

Flora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...

 on the island owing to its rocky composition. However, on lower lying parts of the island, exposed at low tide, seaweeds and other sea plants live. A smaller rock called Garreg Allan (The Outer, Expelled or Furthest Stone) is found about 100 m behind the island, but is not visible with the naked eye from the shore.

A raised shelf of seabed about 1.5km long reaches out a little beyond Garreg Allan, meaning that the sea around it is no more than 5 metres deep. This is followed by a drop to water much deeper (over 20 metres deep), which indicates that Ynys Dulas may have been part of a recently (geologically speaking) submerged headland. The island also marks the termination of an old limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 headland which geologically separated Dulas Bay from Lligwy Bay

Lligwy Bay

Lligwy Bay is a bay of the Welsh island of Anglesey.It is on the eastward side of the island to the north of the village of Moelfre. It was the site, in October 1859, of the loss of the steam clipper Royal Charter with a loss of life in excess of 450....

 and Red Wharf Bay.

Upon the island is a cylindrical structure with a cone shaped top, built in 1924 by Lady Dorina Neave of Llys Dulas Manor to store food and provide shelter for shipwrecked seamen. There is evidence from a map drawn up in September 1748 by Lewis Morris

Lewis Morris (1701-1765)

Lewis Morris was a Welsh hydrographer, antiquary, poet and lexicographer, the eldest of the Morris brothers of Anglesey....

that the island was once known not as Ynys Dulas but Ynys Gadarn (Strong or Mighty Island).