Edgar Rice Burroughs (1875-1950) was an American novelist most famous for creating the character of Tarzan, yet he also wrote science fiction adventures. As well as stories set on Mars, or Barsoom as its inhabitants know it, and five set on Venus, many more are set in lost worlds that time forgot on Earth. One series of novels is set inside the Earth, which is found to be hollow, in the fantastic land of Pellucidar.

Creation

Edgar Rice Burroughs decided to become a full-time writer in 1911 and began writing the first in the Pellucidar series in January 1913, at a time when he only had three stories serialised in magazines¹ but was struggling to find a publisher interested in two further stories, The Outlaw of Torn and the first Tarzan sequel. His idea, originally titled The Inner World, was set inside the Earth; at the time of writing many scientists believed it was possible for the Earth to be hollow. This idea had first been seriously proposed by Edmond Halley of Halley's Comet fame in 1692, but Marshall B Gardner's A Journey to the Earth's Interior or Have the Poles Really Been Discovered (1913) was a key influence.

Of course there had been numerous myths, legends and novels about underground worlds written prior to Burroughs', of which the most notable are Journey to the Centre of the Earth by Jules Verne (1864) and A Strange Manuscript Found in a Copper Cylinder (1888), originally anonymously published but accepted to be by James de Mille, noted for being the first Canadian science fiction novel.

Pellucidar

The Pellucidar novels are set on the inner surface of Earth's hollow sphere. In the story, the Earth's crust is only 500 miles thick. When the Earth was formed it was a hot, rotating, nebulous mass that cooled and shrank. Centrifugal force hurled out the heaviest elements to form an outer, solid layer that became the Earth's crust – our surface. While the Earth continued to shrink it made a vast hollow interior filled with a breathable atmosphere and at the very centre a small super-heated core that acts as the inner world's sun. Surrounded on all sides by the solid crust, gravity keeps this sun in the very centre of the Earth and it lights every surface of the inner Earth eternally.

Humans and a vast array of other species are perfectly capable of living on the interior of the Earth's surface because gravity pulls them towards the centre of the Earth's crust, rather than the centre of the Earth. The only ways to get to Pellucidar is either by tunnelling through the Earth's crust or by travelling through an entryway at the North Pole.

By some unexplained process, the oceans of Pellucidar are directly under the continents of outer Earth and vice versa, so Pellucidar has the same ratio of land to sea as the outer Earth does sea to land. This means that in terms of land mass, Pellucidar is much larger than outer Earth, with 124,110,000 square miles of land compared to 53,000,000 square miles. Despite this vast area, the main characters frequently unexpectedly bump into each other. If they encounter a stranger on their travels then they are almost certainly either the chief or king of a village themselves or the partner or offspring of a chief or king. Saving them from almost-certain death is the best way to ensure you are welcome in their village, otherwise all tribes on Pellucidar are suspicious of strangers and will put them to death. Every woman met is inevitably a young, single princess about to be married against her will who will inevitably fall in love with a rescuing stranger.

Pellucidar also has its own inner moon, which orbits a mile above Pellucidar's surface. This takes 24 hours to orbit the central core sun, which means that as the Earth itself rotates at the same rate, it always appears above the same part of Pellucidar, named the Land of Awful Shadow. Here the land is bathed in a perpetual eerie twilight, such as that experienced during an eclipse. It is believed that spirits of the dead travel to this moon, which is why it is named the Dead World. The moon itself has mountains, rivers and is believed to also have an atmosphere.

Pellucidar is a world inhabited by prehistoric creatures, such as sabretooth tigers², called 'tarag' in Pellucidar, pterodactyls or 'thipdar', mammoth or 'tandor', dinotherium (prehistoric elephant, the Pellucidar name for which is unknown), phororhacos³ or 'dyal', flying stegosaurus or 'dyrodor', triceratops or 'gyor', a hyaenodon or 'jalok', brontosaurus or 'lidi' and of course the Tyrannosaurus rex, called a 'zarith'.

'Pellucidar' is named after the word pellucid. Like 'Lucid' this word usually means 'transparent' and 'clear and understandable', but originates from the Latin per- meaning 'very' and lucidus meaning 'bright'. The land is therefore called 'very bright' to emphasise the fact that the land has an eternal sun and no night.

The Land that Time Forgot

As there is no day and night, the laws of time no longer apply. This is discovered in the first book At The Earth's Core when at one point two main characters, David Innes and Abner Perry, are separated. Innes escapes their captors, walks across vast distances, explores new lands and islands and eventually returns months later, only for Perry to be convinced that Innes had only been gone an hour. There are even passages in which the main characters awake to be unsure whether or not they have been asleep for a second or a year.

As the sun is always in the same place relative to the surface, in effect this means there are no seasons either and it always appears to be spring. Without a sun rising in the East and setting in the West, compass directions are also unknown.

Since objects fall when dropped even on Pellucidar, we can assume that time does indeed pass, and that it is the human perception of time that is at fault. This is a psychological rather than a physical effect, then. Visitors to Earth's Arctic and Antarctic regions, where the sun never sets in the summer, will vouch for the disorientating effect of the lack of day and night. Perhaps in the absence of any noticeable signs of time passing, the people of Pellucidar have lost their connection with time.

One benefit of the lack of days and nights is that the main heroes no longer seem to age, although they still encounter elderly background characters. How can the lack of ageing of Pellucidar's people be explained? We know that different animal species age at the different rates. Domestic cats appear to age until they are about ten, then can continue for up to two decades with no apparent ageing. Certain species of fish do not appear to age at all and just continue living, growing slowly, until their bodies are too big for them to catch sufficient food. And there is no doubt that mental states can affect the body subtly. So perhaps the people of Pellucidar have developed this agelessness through not believing in time.

As the inner moon called the Dead World itself also fully rotates once every 24 hours, Innes realises that time can be measured by watching the appearance and disappearance of features on its surface. However the people of Pellucidar were uninterested in measuring time and so one of Inne's early edicts as Emperor was to officially abolish time⁴.

Gilaks

In the inner world, humans are called 'Gilaks'. Outwardly identical to us, they have developed a homing instinct like a pigeon which allows them to navigate in a world without stars or a rising and setting sun, although this only works on dry land and they are lost at sea. They often have names consisting of a name and a description, such as Dian the Beautiful, Ghak the Hairy One, Hooja the Sly One and Tanar the Fleet One. The character with the silliest name is undoubtedly 'Old Man whose Name is not Dolly Dorcas'.

Gilaks are extremely tribal. Living in numerous villages, when they encounter someone not from their village they either kill or enslave them if they are male, or enslave or marry them if they are female. The idea of co-operation in the face of the various prehistoric dangers that surround them never seems to occur to them.

The Science of Pellucidar

Burroughs's work was considered 'science fiction' in its day. One of the features of science fiction distinguishing it from fantasy is that anything unusual is explained using science rather than magic. In his Barsoom (Mars) books, for example, Burroughs imagined the thin, natural atmosphere of the planet being augmented by an atmosphere factory - by adding electricity to a type of electromagnetic radiation unknown on Earth, air was produced. Of course, the author's grasp of science is often rather tenuous - such an explanation makes as little sense as invoking magic would.

It can be interesting and amusing to consider the 'scientific' facts and explanations which Burroughs presents as a background to an adventure story.

Gravity

First we'll talk about Gravity. Newton's Law of Universal Gravitation says that everything attracts everything else. Big things exert a bigger pull than small things, but the force is reduced if the thing is far away - if it is twice as far, the force is reduced to one quarter; if it is three times as far, the force is reduced to one ninth.

Every part of the Earth exerts a tiny pull on your body. The bits just under your feet pull on you the strongest, while the bits that are at the other side of the world pull the least. If you are standing in London, then New York's Empire State Building is pulling you towards the southwest, while the Eiffel Tower in Paris is pulling you southeast. The combined effect of all these tiny pulls adds up to a single force pulling you straight down towards the centre of the Earth. This pull is variously known as 'the force of gravity' or just 'your weight'.

If you're standing on the inside of a hollow sphere, with your feet on the surface, the centre of the Earth is directly above your head. Some parts of the sphere are pulling you down (towards your feet) while other are pulling up (towards your head). It's not immediately obvious what the combination of all the different pulls will result in.

Burroughs argued that the bits of the Earth just below your feet are very close to you and pull you away from the centre of the Earth, while the bits of the Earth above your head pulling you towards the centre of the Earth are very far away so their gravitational pull will be small. The resultant force on you will be a pull towards the 'ground' beneath your feet and away from the centre of the Earth. This means that people can walk around on the surface of Pellucidar as if it were the outer surface of a planet.

He acknowledged that the parts of the Earth above your head would have some effect, and said that the force of gravity was slightly less than on the surface, although the effect was not very noticeable - the scientist Perry spotted it but the young David Innes didn't until it was pointed out to him.

Unfortunately it is not that simple. Isaac Newton, who came up with the idea of Gravitation in the first place, also developed the mathematics to study it. If you are inside a hollow sphere and add up all the different pulls, they cancel each other out exactly. You won't feel any force of gravity at any point inside the hollow sphere. With nothing to hold you to the surface, you would drift off into the vast volume of empty space inside the sphere. A practical way to avoid this would be to wear velcro-soled shoes, but the downside is that you would have to cover the entire inner surface of Pellucidar with some sort of looped carpet.

Worse still, the mini-sun sitting at the centre of the Earth would not feel any gravitational pull from the hollow shell around it, so there would be nothing to keep the sun in the centre. Gradually over time it would drift away from the centre and eventually would strike the shell, no doubt knocking a hole in it.

Pellucidar's moon, orbiting its mini-sun once a day so that it matches the rotation of Earth/Pellucidar, is hard to explain. Why is it attracted towards the centre of the planet, when everything else is attracted towards the surface? Perhaps Burroughs felt that it is high enough above the surface to avoid the local pull of the ground and so is attracted to the central sun.

Fusion

According to Innes, the central sun of Pellucidar looks about three times as big as our sun. Since it is only 3,500 miles from the people of Pellucidar, we can calculate that it must have been about 100 miles in diameter. The scientist Perry thought that it must be composed of gas; this presents a problem. A sphere of hydrogen only 100 miles in diameter would not be big enough to support fusion, the nuclear process that powers our sun. At the time Burroughs was writing, it was not known how the Sun works, so he can be forgiven for making this mistake.

But there is another possibility. The central sun may actually be a solid sphere of something dense such as iron, at a very high temperature. If this sphere was heated to 5,500°C, it would glow just like the sun and would be indistinguishable from a small star to the human eye. Geology tells us that in fact parts of the centre of the Earth are even hotter than this, so this not an unreasonable explanation for Pellucidar's sun.

Heat

This brings us to another problem. Innes described the sun as looking much like our sun except that it was 'thrice the size', so we can assume that it is the same colour as our sun. Since the colour of a glowing object depends on its surface temperature, Pellucidar's sun must have a similar surface temperature to that of our sun. If Pellucidar's sun looked a similar size in the sky to ours, then the heat received from it would also be similar.

Unfortunately, we have Innes's statement that it is three times the size. We don't know whether he meant in area or in diameter. If the former, then three times as much heat would be received from it as we receive from our sun at the equator. Worse, if Innes meant three times the diameter, then a person standing on the surface of Pellucidar would feel nine times as much heat coming from the sun as is felt on the equator of Earth. It seems unlikely that life would survive in a world receiving even three times, never mind nine times, as much heat at every point on its surface as the Earth does at its equator.

On the other hand, it is notoriously difficult to judge the size of the Sun in the Earth's sky. An optical illusion makes it look bigger at the horizon than when high in the sky. Who knows what even a tiny sun would look like when directly overhead in a world that has no horizon? Perhaps Innes made a mistake and the apparent size of Pellucidar's sun (and therefore its heating effect) is in fact the same as our own.

The Novels

In common with many of his other stories, Edgar Rice Burroughs presents the Pellucidar novels as true events experienced by others that he is merely publishing. Many of the early novels have elaborate prologues detailing how Burroughs came to learn the tales in order to publish them. These too are included in the summaries below.

1. At the Earth's Core (1914)

This 37,000-word story was written in January to February 1913 with the title The Inner World. It was first published as a serial in All-Story Weekly in four weekly chapters in April 1914 and was published as a novel in 1922. It has also been serialised under the title Lost Inside the Earth.

David Innes has inherited a mining corporation and when his friend Abner Perry invents an 'iron mole' mining machine, they try it out. When it malfunctions, they find themselves travelling 500 miles to the centre of the Earth and emerging in a strange land ruled by Mahars, eight feet tall telepathic pterodactyls who enslave humans and feast on human flesh. Lacking any perception of sound, the Mahars communicate with their servants and slaves by sign language and with each other by 'project[ing] their thoughts into the fourth dimension, when they become appreciable to the sixth sense of their listener.' This ability also allows them to hypnotically control the minds of humans to stop them resisting when they are being eaten. Having webbed feet, Mahars are also at home in water and are as aquatic as penguins. As only females are born they reproduce artificially using what is called 'the Great Secret'.

Captured by the Mahars' gorilla-like servants called the Sagoths, Perry and Innes befriend fellow captives Ghak the Hairy One, ruler of Sari and his niece, Dian the Beautiful One. Dian had fled her home of Amoz as she was being forced to marry Jubal the Ugly One against her wishes. They also encounter Hooja the Sly One. Hooja and Dian disappear while the others are taken to the Mahar capital, Phutra, where they learn the Mahars' great secret. Innes manages to escape and saves the life of Ja, ruler of the island of Anoroc⁵.

Dare David return to Phutra to rescue Ghak and Perry? Will he discover what happened to Dian and persuade her to marry him? Will he return to the surface world? Can Hooja the Sly One be trusted? What impact will the introduction of bows and arrows have on an unsuspecting inner world? Who will be crowned Emperor of all Pellucidar?

The prologue explains that Edgar Rice Burroughs learnt these events after travelling to Africa to hunt lion, where he encountered David Innes and a captive Mahar. This is the story as Innes told it.

At the Earth's Core was adapted into Amicus Productions' penultimate film in 1976.

2. Pellucidar (1915)

Written between November 1914 and January 1915, Pellucidar is a longer, 61,000-word story. It was first published as a five-part serial in All-Story Weekly in May 1915, for which Burroughs was paid $1,522, and it was first published as a novel in 1923. It neatly ties up the loose ends of the story raised in At The Earth's Core.

Innes briefly visited the Earth's surface to gather supplies, including guns, and has returned to Pellucidar, but emerges in an unknown land. Reunited with Perry, he learns that the imperial alliance has been shattered by Hooja the Sly One who has set all the tribes he had united against each other, leading to humans once again being easy prey for the Mahars.

What has happened to Dian? Can they survive a journey across the inner world's sea? Who are the gorilla-sheep people? Will Innes be eaten by a fierce hyaenodon? How will the introduction of gunpowder make Pellucidar a safer place?

Edgar Rice Burroughs learnt this story after David Nestor, who was in Africa hunting a rare antelope, discovered a telegraph box in the Sahara Desert that had been placed there by Innes on his journey back to Pellucidar. The story was dictated along the wire by David Innes in Morse Code.

3. Tanar of Pellucidar (1929)

Written between September and November 1928, 14 years after the previous book. First published serialised in monthly magazine Blue Book between March and August 1929, for which Burroughs was paid $7,500, this 78,000-word story was later published as a novel in 1930.

Tanar the Fleet One is Dian the Beautiful's cousin. He had been sent to investigate reports that a harquebus-armed enemy had assembled an armada to invade the Empire. Captured by the Korsars, a piratical people who have primitive gunpowder weapons and aim to conquer Pellucidar, Tanar is brought on board their leader the Cid's flagship and meets the Cid's beautiful daughter, Stellara. Meanwhile, an unsuccessful rescue mission is led by Innes, who unbeknown to Tanar is also captured.

During a violent storm Tanar and Stellara are stranded on board the damaged vessel when everyone else launches lifeboats, and land on the island of Amiocap. Although famed as the island of love, they are soon condemned to death.

What is Stellara's secret? After the usual round of being captured and kidnapped, separated, reunited and constantly haunted by jealous misunderstandings, will Tanar and Stellara realise their feelings for each other? Can they survive capture by the cannibalistic Buried People and pretty much everyone else they encounter? When Tanar and Innes end up imprisoned in separate underground oubliettes, cut off from daylight and each other with only the snakes in the cell for company, who will escape?

Edgar Rice Burroughs came to learn the story after his neighbour, inventor Jason Gridley, was developing a new form of radio. The Gridley Wave allows radio communication between Earth and Mars and picked up transmissions being broadcast from Perry in Pellucidar.

4. Tarzan at the Earth's Core (1930)

Tarzan at the Earth's Core follows on immediately from Tanar of Pellucidar. Jason Gridley, having learnt that Innes, who he has never met, is still imprisoned in the cells of the Cid, decides to mount a rescue mission. He knows the best man for the job is Tarzan of the Apes, and before you can say 'Me Tarzan, You Jason'⁶, he agrees.

Tarzan's inventor friend Erich von Harben, who had appeared in Tarzan and the Lost Empire, constructs an airship, the O-220⁷, out of a light metal he discovered. The airship is commanded by Tarzan with Jason Gridley second in command and Lieutenant Frederich Wilhelm Eric von Mendeldorf und von Horst, or 'Von' for short, as airship's mate, with ten Waziri warrior friends of Tarzan's as part of the crew. It also carries a lightweight scout aircraft. After travelling to Pellucidar through the polar opening, Tarzan leaves the airship to explore, but is captured by Sagoths. Jason, von Horst and the Waziri search for him, but they are caught in a vast stampede caused by a pack of hundreds of sabretooth tigers hunting, with almost the whole ecosystem trying to escape. They are all separated, with Jason the only one to return to the airship. After trying to search for the others using the scout plane, the aircraft is destroyed by a pteranodon who attacked it thinking it food, and he lands in time to prevent the beautiful Jana, the Red Flower of Zoram, from being captured by four men from a different tribe who want to make her their mate.

Will Jason and Jana reveal their true feelings for each other or will she snub him until the very end of the story? Can a stegosaurus really glide through the air by using its plates as wings and tail as a rudder? Who will be captured by the lizard-people? Is the painfully stereotypical portrayal of Robert Jones the airship's black cook forgivable? When Tarzan meets the Red Flower of Zoram, will he say, 'Me Tarzan, you Jana'?

5. Back to the Stone Age (1937)

Written between January and September 1936 under the title Back to the Stone Age: A Romance of the Inner World⁸, this story was published six years after Tarzan at the Earth's Core. First published in six fortnightly issues of Argosy in January and February 1937, Burroughs was paid $1,000 for the 80,000-word story. In September the same year Burroughs' own publishing company, Edgar Rice Burroughs, Inc printed it as a novel.

This novel begins at the same time as Tarzan at the Earth's Core and follows the adventures of Wilhelm von Horst on the surface of Pellucidar after he is separated from the rest of the airship crew during the mission to rescue Innes. Can he survive being poisoned by pteranodons, captured by cannibals and stalked by sabretooth tigers?

6. Land of Terror (1944)

Land of Terror was written between October 1938 and April 1939. The 60,000-word story was rejected by all the leading magazines of the time and was not published until May 1944, by Edgar Rice Burroughs, Inc and is unique in being the only story not to have appeared in a magazine. It is generally acknowledged in being the weakest in the series.

After travelling far from his empire in an effort to find von Horst, Innes is captured by the bearded warrior women of Oog, who come from a land where men are the weaker sex⁹. After befriending another slave, Zor, they escape only to be captured by the Jukans, a race who are probably the most civilised people on Pellucidar despite all being quite as mad as hatters¹⁰. Innes also learns that the Jukans have captured Dian the Beautiful, who had been leading a rescue expedition to find him but had been attacked by Do-gad, nephew of the king of Suvi, who wished her to be his mate. Befriending slave girl Kleeto, Zor and Innes escape with her, but Dian has disappeared. After befriending a mastodon family, Innes, Zor and Kleeto are captured by man-eating giants.

Will David defeat the Goliath-like Azarians? Will they survive the encounter with giant ants? What are the Floating Islands and why do they move? Will David be reunited with Dian?

7. Savage Pellucidar (1942 & 1963)

Savage Pellucidar consists of four novelettes¹¹, the first three of which were written in late 1940 and were published in magazines in 1942. Burroughs initially planned to publish these three as a novel titled Girl of Pellucidar. The fourth novelette in the collection was written in 1944 and did not appear in print until 1963, following a resurgence in Burroughs' popularity after his death.

1. The Return to Pellucidar
   
   Edgar Rice Burroughs wrote the first story under the title Hodon and O-aa¹², after the two main characters, however it was published in Amazing Stories in February 1942 as The Return to Pellucidar, even though none of the characters have left Pellucidar to return there.

   On the outskirts of Innes' confederated empire lie the tribe-states of Kali and Suvi. Suvi leaves the empire and declares war on Kali. Hodon is dispatched to investigate and meets O-aa, the daughter of the King of Kali, but is unable to warn Innes of the Suvians' betrayal before Innes is captured. They escape but are captured by the sabretooth men, meeting the Old Man whose name is not Dolly Dorcas, a man from the outer world who cannot remember his own name, only that of his ship whaling vessel, the Dolly Dorcas. He fell into Pellucidar through the polar opening many years earlier. Meanwhile Perry invents a gas balloon¹³, but when Dian the Beautiful tests it, the mooring rope is unsecured leaving her to drift out of control.

2. Men of the Bronze Age
   
   First published in Amazing Stories in March 1942, this story continues immediately after The Return to Pellucidar. The balloon carrying Dian lands in a previously unknown continent or large island across the sea, home to Bronze Age city-states. The people of Lolo-Lolo worship Dian as the goddess Noada. Meanwhile O-aa had been kidnapped by an island-dweller but kills him in self-defence shortly before the ship she is on is hit by a severe storm. She is also washed up near where Dian's balloon landed but in the rival city-state of Tanga-Tanga, where she too is worshipped as Noada.

3. Tiger Girl
   
   First published in Amazing Stories in April 1942. After returning to Sari, Innes learns that Dian had been carried away by a balloon and so has Perry build another balloon in the hope it will head in the same direction and lead him to Dian. Meanwhile Hodon heads out to sea hoping to find O-aa while the Old Man whose name is not Dolly Dorcas builds Pellucidar's first clipper ship, the John Tyler, and leads a rescue mission to find them all. Who will find whom only to then be separated by events beyond their control? Who will be surrounded by sabretooth tigers?

4. Savage Pellucidar
   
   The search and rescue missions battle storms, betrayal and dinosaurs while everywhere O-aa and Dian go they encounter tribesmen who wish to take them as their mate. Will everyone finally be reunited and live happily ever after?

   When Burroughs died in 1950 it was assumed that everything he had written had been published. In the early 1960s his novels were released in paperback, leading to a resurgence in his popularity. During this process following the retirement of manager Cyril Rothmund, the Edgar Rice Burroughs, Inc office was reorganised and catalogued and several previously unpublished works were discovered, including Savage Pellucidar. The original ending of 'Tiger Girl' in which everyone was reunited and lived happily ever after had been changed to keep the main characters separate until the very end of this short story.

Review

The Pellucidar novels are highly enjoyable escapism that should not be taken too seriously. They are a product of their time and attitudes have since moved on. For example the novels were written with the Edwardian Boys' Own adventure perspective: though the natives of Pellucidar are noble and brave, David Innes and Abner Perry patronisingly are able to revolutionise and improve their lives. The novels are definitely pro-imperial and in true The Man Who Would Be King style, Innes founds an empire and becomes Emperor.

Similarly, in Pellucidar women are often treated as objects. Marriage is a solemn undertaking that a man can enter into through:

• Kidnapping, such as when Dacor the Strong One stole Canda the Graceful One from her people.
• Placing the largest carcass outside the woman's father's house.
• Defending a woman from another man and then holding her hand. Immediately raising her hand and dropping it indicates she is released, however failure to hold or raise her hand enslaves her.

Although all women are damsels in distress who are prone to being constantly kidnapped and need saving from many different types of savage animal, they are not completely helpless. Most are fierce and proud and more than capable of stabbing potential kidnappers, while the heroes too are always finding themselves imprisoned and imperilled by both men and monsters. Women never reveal their feelings to those they are attracted to, preferring their potential partners to feel the agony of rejection until the very last page, no matter how many times they are rescued from certain doom. Especially if there is a misunderstanding that keeps them apart.

There is no denying that the general assumptions and attitudes of the time in which they were written have influenced the stories. Written in an era in which big game hunters were considered heroes rather than ecological vandals, all animals encountered in Pellucidar are considered fair game to kill without regret. Like most books from the period, there are sentences scattered throughout the series that would be unacceptably racist or sexist if written today, although Burroughs describes both heroes and villains present in almost every race and tribe that the characters encounter on their journey. In 1963 the Pellucidar novels were slightly edited¹⁴. Perhaps the most disturbing sentence in the series is,

Perry was trying to perfect poison gas. He claimed that it would do even more to bring civilisation to the Old Stone Age.

- Land of Terror, Chapter I

Did You Know…?

• Jason Gridley, Tarzan, David Innes, Abner Perry and von Horst are all mentioned as existing on the first two pages of Burroughs' first Venus novel, Pirates of Venus (1932). Jason Gridley's radio system, the Gridley Wave, is also used to communicate with Mars in A Fighting Man of Mars (1930).

• Pellucidar also appears in various Tarzan comic strips, cartoons and live-action episodes.

• Various fan fiction has been written over the decades, including published sequels, the best known of which is Mahars of Pellucidar by John Eric Holmes (1976). Similarly, Lin Carter was inspired by Edgar Rice Burroughs to write the Zanthodon novels.

• Pellucidar really exists! The deepest cave system in the United States is the Lechuguilla Cave in Carlsbad, New Mexico. One of the chambers has been named Pellucidar, with the balcony above named Barsoom.