During the English industrial revolution, tin was considered valuable enough to go tunneling under the sea off Cornwall to find it... as technology advanced, bigger and more powerful steam engines made it possible to mine further under the sea... until the price of tin dropped... or the roof caved in
Andrew, I'm making an assumption that this is more PS work. The sky appears unnatural somehow, it's kind of disturbing, but ... I don't know I kind of like it in a strange sort of way.