Durdle Door
"They persuaded me to keep on, and at last stranded me on the pebbles, exactly opposite the magnificent arch of Durdle-rock Door. Here I stood and contemplated with astonishment and pleasure this stupendous piece of Nature's work" ..... John O'Keefe, 1792.
The natural arch of Durdle Door has been cut by the sea through the almost vertical Purbeck Caps and the top of the Portland Freestone. From the landward side, as seen here, the Portland Stone is hardly visible and the surfaces which you see here are mainly those of the Purbeck stromatolitic limestones (the Soft Cap), like those of the Fossil Forest. Holes left by late Jurassic trees. Originally there was Kimmeridge Clay seaward of Durdle Door but these relatively soft strata have been easily removed by the sea.
The arch is on the far, western, side and best seen from above the Chalk cliffs to the right. The outlying rocks mark the outcrop of the Portland Stone and basal Purbeck limestone.
The natural arch of Durdle Door is one of the physical features of the area which has retained a name given to it probably more than a 1000 years ago (Arkell, 1947), showing that the coast does not change very rapidly. The name " Durdle " is derived from an Old English word " thirl " , meaning to pierce (as in " nostril ").