Shell Island, also known as Mochras, is a peninsula lying west of Llanbedr in Gwynedd, Wales. It was formed after the River Artro was diverted by the Earl of Winchelsey in 1819 from its previous course where it entered the sea to the south of Shell Island. Prior to this, access to the ancient settlement on the 'island' would have been through the village of Llandanwg, which is now across the estuary. hand picked from beach drift at Shell Island Shell Island is known for the wide variety of seashells that wash upon the beach, and for its wild flowers. It is said to have been connected to the mythical Cantre'r Gwaelod. Public vehicular access to the 'island' is only possible via a causeway across the estuary of the River Artro when the tide is out. Access on foot is always possible from the adjacent Mochras/Morfa Dyffryn beach, which extends for several kilometres south of Shell Island. Access to emergency vehicles is available at any time through the neighbouring airfield. Shell Island has a popular camp site which offers the opportunity to practise "wild camping" in pitches which are far from the nearest neighbour. Camp fires are allowed on the beach; on the campsite only raised contained fires and barbecues are allowed. The 'island' lies within the Snowdonia National Park, as a result of which the campsite closes from the end of October to the following March. During this period local farmers bring their sheep from the lowlands to graze on the 'island'.
Geology
Mochras is significant for the UKearth sciences. The area consists of a low lying raised beach and it caused a sensation, when the Institute of Geological Sciences drilled a 1938 m deep stratigraphic proving borehole at Mochras Farm between late 1967 and late 1969. Beneath the obscuring recent beach cover, the Mochras Borehole found relatively young Tertiary and Mesozoic rocks, faulted against the ancient Cambrian rocks of the Harlech dome. In 1971, the vertical throw of the fault was judged to be at least 4500 m.
