It is not alleged for long. Reaching the plateau, they encounter signs of Jurassic life. Finding an enormous three-toed footprint, Professor Summerlee, the sceptic of the quartet, asks whether it belongs to a 'beast'. Challenger gives this short shrift: 'No; a reptile - a dinosaur. Nothing else could have left such a track.'

They are soon up to their necks in iguanodons, pterodactyls, allosauri and megalosauri. Lord Roxton, a big-game hunter, practically faints at the sight of so many heads to add to his collection.

Of course, dinosaur adventures wouldn't be dinosaur adventures without a Tyrannosaurus rex. Malone is tormented by this apex carnivore in one of the story's most vivid passages. Having rashly set out on a midnight jaunt, he is startled by a sound somewhere 'between a snore and a growl, low, deep, and exceedingly menacing ... Something was on my trail, and was closing in upon me every minute'.

Terrifying as dinosaurs can be, they are nothing compared to the ape-men that our intrepid explorers encounter. These are embroiled in constant conflict with a tribe of slightly more evolved humans inhabiting another part of the valley. Having narrowly escaped death at the ape-men's rudimentary hands, Challenger decides it is time to take his leave. Returning to civilisation, his findings are met with derision by the closed-minded souls of the scientists at the Zoological Institute.

This begs the question: exactly which world is the most civilised? The lost or the found? Conan Doyle's combination of fact and near-science fiction has proved influential. It's a clear inspiration for Michael Crichton's Jurassic Park series: part two is even entitled The Lost World.

For the reader today, the novel's appeal might best be summarised by the fictional newspaper report describing the tumultuous finale: 'Apparently the age of romance was not dead, and there was common ground upon which the wildest imaginings of the novelist could meet the scientific investigations of the searcher for truth.'