Ender in Exile (Ender's Saga 1.20)

"I have to know what they were doing here. Certainly not farming--there's no trace of their crops gone wild here. No orchards. No middens, either--this wasn't a great settlement. And yet there was so much traffic, along that single path."

"Mining?" asked Po.

"Can you think of any other purpose? There's something in those tunnels that the formics thought was worth the trouble of digging out. In large quantities. For a long time."

"Not such large quantities," said Po.

"No?" said Sel.

"It's like steel-making back on Earth. Even though the purpose was smelting iron to make steel, and they mined coal only to fire their smelters and foundries, they didn't carry the coal to the iron, they carried the iron to the coal--because it took far more coal than iron to make steel."

"You must have gotten very good marks in geography."

"My parents and I were born here, but I'm human. Earth is still my home."

"So you're saying that whatever they took out of these tunnels, it wasn't in such large quantities that it was worth building a city here."

"They put their cities where the food was, or the fuel. Whatever they got here, they took little enough of it that it was more economical to carry it to their cities, instead of building a city here to process it."

"You may grow up to amount to something, Po."

"I'm already grown up, sir," said Po. "And I already amount to something. Just not enough to get any girl to marry me."

"And knowing the principles of Earth's economic history will attract a mate?"

"As surely as that bunny-toad's antlers, sir."

"Horns," said Sel.

"So we're going in?"

Sel mounted one of the little oil lamps into the flared top of his walking stick.

"And here I thought that opening at the top of your stick was decoration," said Po.

"It was decorative," said Sel. "It was also the way the tree grew out of the ground."

Sel rolled up his blankets and put half the remaining food into his pack, along with their testing equipment.

"Are you planning to spend the night down there?"

"What if we find something wonderful, and then have to climb back out of the tunnels before we get a chance to explore?"

Dutifully, Po packed up. "I don't think we'll need the tent in there."

"I doubt there'll be much rain," Sel agreed.

"Then again, caves can be drippy."

"We'll pick a dry spot."

"What can live in there? It's not a natural cave. I don't think we'll find fish."

"There are birds and other creatures that like the dark. Or that find it safer and warmer indoors. And maybe a species of some chordate or insect or worm or fungus we haven't seen yet."

At the entrance, Po sighed. "If only the tunnels were higher."

"It's not my fault you grew so tall." Sel lit the lamp, fueled by the oils of a fruit Sel had found in the wild. He called it "olive" after the oily fruit on Earth, though in no other attribute were they alike. Certainly not flavor or nutrition.