The lost world, as Sir Arthur Conan Doyle imagined it in his 1912 novel of the same name, was a place trapped in time, where dinosaurs clashed with modern man in a hauntingly beautiful, prehistoric setting.

That world, minus the dinosaurs, exists still, in the mountains of South America, the backdrop for Doyle's story. And the clash with modern man in places like Mount Roraima — a spectacular flat-topped mountain on the borders of Venezuela, Brazil and Guyana in northern South America — continues, too, threatening to send parts of Doyle's original lost world the way of the dinosaur.

A prehistoric island in the clouds

Mount Roraima from its peak, surrounded by cloudsMount Roraima may have served as an inspiration for Arthur Conan Doyle's "The Lost World" due to its pristine nature. (Photo: Curioso/Shutterstock)

Mount Roraima is a mesa (tepui in Spanish), part of a mountain range that is among the oldest rock formations on Earth. The range is, by most estimates, some 2 billion years old.

Roraima rises starkly more than 9,000 feet from the savanna below. What makes it and other tepuis in this range so special, though, is not its height, but the dramatic way it gets there. From the slowly climbing foothills surrounding it, Roraima suddenly juts to the sky, sheer 1,300-foot cliffs on all sides. Often ringed by clouds and fog — it rains nearly every day on the summit — Roraima looks like a "remote island in the sky," as National Geographic once put it.

Because of its daily rains — as much as 300 inches a year — because of the cliffs, because there is little vegetation on the top that needs water and little to stop the water's inevitable trip down, Roraima and other tepuis in the region feature some of the highest waterfalls in the world. Some, it has been estimated, have been falling for millions and millions of years.

Unless you're a professional rock climber, there's only one way to Roraima’s summit; an arduous two-day hike up a steep and slippery trail.

But once you get there …

No place like it

Roraima black frog A Roraima black frog clings to a leaf. (Photo: Charles Besancon/Wikimedia Commons)

The summit is truly a world apart. Literally cut off from the rest of the planet, Roraima has its own ecology, with dozens of plants and animals that can be found nowhere else on Earth.

"Around 35 percent of the species on Mt Roraima are endemic […] and 70 percent of those found on South America's tepuis exist only on these plateaus," according to "The World's Great Wonders: How They Were Made & Why They Are Amazing" by Jheri Osman.

Among the plateau's one-offs: the the Roraima black frog, a black, pebbly toad about an inch long with a yellow spotted belly and reportedly makes a sound like a drop in the water.

The top of Roraima is dominated by age-old black rock formations, rich minerals like quartz, moss, low lying plants and some flowers. And water. Lots and lots of water.

Awe-generating views to the horizon can be instantly interrupted by fog and rain. Cold, clear pools of water are everywhere. Visitors can venture to the edge to see waterfalls plunging from the side. It is a place that has attracted adventurers for more than a century.

Doyle's "Lost World" helped popularize it. The book has been the template for many others, and the inspiration for filmmakers from Harry O. Hoyt — his 1925 film, the first to bring Doyle's book to the silver screen, is in the public domain and can be watched in its entirety on The Internet Archive — to Steven Spielberg.

But it's that fascination with the place that threatens it now.

A threat from without

Hikers look out over the Mount Roraim's plateauHikers look out over the Mount Roraima's plateau. Hikers are tourists are contributing to Roraima's deteriorating state. (Photo: Paulo Fassina/Wikimedia Commons)

In 1995 and 1996, the National Parks Institute of Venezuela (INPARQUES) was forced to restrict access to Roraima because of tourists. According to the non-profit ParksWatch, based at Duke University's Center for Tropical Conservation, "[C]onstant hiker presence has damaged tepui vegetation […] There is also garbage accumulation in the most visited places on the tepui … and along the trail. In addition, use of soaps, detergents and shampoo degrades water and soil quality."

Another problem, according to ParksWatch: Tourists, despite warnings not to do so, steal quartz from Crystal Valley on the summit of Roraima.

The International Union for Conservation of Nature has put the Roraima bush toad (Oreophrynella quelchii) on its Red List of Threatened Species under "Vulnerable." One reason is tourists who "frequently" grab the animals. "There is a need for increased education among tourists," the group says, "to make them aware of the importance of not handling these animals in the wild."

In 2003, years after the effects of tourism first were reported, a study found that 3,000 tourists climbed to the top of Roraima every year. That was 12 years ago. Now, with helicopters dropping tourists on the summit and more and more tourists making the climb every year — the nascent tourism industry has been resistant to any restrictions — the damage almost certainly has grown

"I still love it, but there are too many people," Felix Medina, a 59-year-old guide, told the International Business Times earlier this year. "It's chaotic sometimes."

Roraima remains the only tepui in the region where tourists are allowed. So there may well be more lost worlds, still, in South America. But conservationists worry that, unless something is done quickly, one of the originals, Roraima, may be lost forever.

Mount Roraima: 'A remote island in the sky'
This South American mountain is a world onto itself with unique waterfalls and animals.