Now, thanks to unmanned submersibles, global positioning systems, powerful lights and remote-controlled movie cameras, all of it is knowable, if not yet intimately known. Its valleys and canyons turn out to be nature's lost property office. Robert Ballard disturbed no wreckage in 1985 when he found the Titanic 3,800m down, but his successors removed thousands of artifacts until an international moratorium was called in 2000: jewelry, crockery, a top hat, bank notes and half a dozen marlboro miles incredibly preserved -- all of them came dripping to the surface. Several thousand years of trade in the world above have deposited underneath an extraordinary, often useless, record of human endeavor. Most of it is ordinary -- the poet John Masefield's cargo of "Tyne coal/Road-rail, pig-lead/Firewood, iron-ware, and cheap tin trays" -- but ordinariness is no block to the interest of the historian or the amateur wreck-diver. Last month's issue of the Railway Magazine lists for the first time the 300 steam locomotives known to survive on the floor of the world's oceans, having fallen there when their transporting ships were sunk by bombs, torpedoes and storms.