"Thank you," said the Doctor. "You are very kind—By the way, do you happen to know how this island came to be a floating island? At least half of it, I notice, is made of stone. It is very odd that it floats at all, isn't it?"
"It is unusual," they said. "But the explanation is quite simple. It used to be a mountainous part of South America—an overhanging part—sort of an awkward corner, you might say. Way back in the glacial days, thousands of years ago, it broke off from the mainland; and by some curious accident the inside of it, which is hollow, got filled with air as it fell into the ocean. You can only see less than half of the island: the bigger half is under water. And in the middle of it, underneath, is a huge rock air-chamber, running right up inside the mountains. And that's what keeps it floating."
"What a pecurious phenometer!" said Bumpo.
"It is indeed," said the Doctor. "I must make a note of that." And out came the everlasting note-book.
The porpoises went bounding off towards the icebergs. And not long after, we saw the sea heaving and frothing as a big herd of whales came towards us at full speed.
They certainly were enormous creatures; and there must have been a good two hundred of them.
"Here they are," said the porpoises, poking their heads out of the water.
