Hodbarrow Iron Mine (United Kingdom)

One of the largest and best known of the West Cumbrian iron mines. It worked between 1848 and 1968 and produced about 25 million tons of hematite ore.
The mine is on the coast and in order to work the deposit a succesion of three barriers were constructed to keep back the sea. The first was of wood, what remains now as the inner barrier is concrete and the huge outer barrier was constructed from slag faced with concrete blocks on the seaward side.

Bibliography: Cumberland Iron. The Story of Hodbarrow Mine 1855-1968, by A. Harris (1970)