background Cornish cornwall cracked England english geology gray Great Britain grey lines natural nature rock sedimentary texture worn yellow birds cliff coastline crack danger fissure guillemots Pembrokeshire razorbills sea stack united kingdom wales water welsh cave cavern hole ocean shore waves boulders Catalan catalonia Catalunya coastal conifers costa brava eroded mediterranean pines precarious rocks Spain spanish summer trees unstable beach cloud horizon Lofoten Islands norway norwegian sky stones wild blocks chalk face gap gulley gully kent landscape passage ravine white Balanus barnacles covered pool seaweed speckled stone erosion layers silver