From librivox.org:

Imagine a strange, tropical place that is almost inaccessible. Time appears to have stood still there. Species of animal and plant life not seen elsewhere on Earth, except in the fossil record, inhabit the place. The lakes heave with the shapes of huge grey bulks moving under the surface. The woods are places where chittering cries move about above your head, as powerful apes move swiftly in the canopy of leaves. Then, a tree splinters nearby, and a dinosaur steps out from his hiding place... and he's eyeing YOU.

Jurassic Park? Not quite. The Lost World was an inspiration for Jurassic Park; in fact, a character in J.P. has the same name as one of the chief characters in The Lost World. It also inspired King Kong. But this is the original! Four adventurers go off to find the place shown in a dead man's sketch book - they find a war between apes and Indians, prowling dinosaurs, a sparkly treasure hidden in the blue clay - they find the Lost World. And because of the treachery of a native guide, their means of escape is destroyed!

From librivox.org:

Three years after the events that took place in The Lost World, Professor Challenger urgently summons his fellow explorers (Professor Summerlee, Lord John Roxton, and reporter E.D. Malone) to a meeting. Oddly, he requires each to bring an oxygen cylinder with him.

What he soon informs them is that from astronomical data and just-received telegraphs of strange accidents on the other side of the world, he has deduced that the Earth is starting to move through a region of space containing something poisonous to humankind.

Shutting themselves tightly up in Challenger's house, they start to consider what may be done. But as their countrymen start to drop, will their oxygen last long enough to determine and implement a solution?