About halfway to Popsipetel we went ashore and spent two or three days exploring the central part of the island.  Our Indian paddlers took us up into the mountains, very steep and high in this region, overhanging the sea.  And they showed us what they called the Whispering Rocks.

This was a very peculiar and striking piece of scenery.  It was like a great vast basin, or circus, in the mountains, and out of the centre of it there rose a table of rock with an ivory chair upon it.  All around this the mountains went up like stairs, or theatre-seats, to a great height—­ except at one narrow end which was open to a view of the sea.  You could imagine it a council-place or concert-hall for giants, and the rock table in the centre the stage for performers or the stand for the speaker.

We asked our guides why it was called the Whispering Rocks; and they said, “Go down into it and we will show you.”

The great bowl was miles deep and miles wide.  We scrambled down the rocks and they showed us how, even when you stood far, far apart from one another, you merely had to whisper in that great place and every one in the theatre could hear you.  This was, the Doctor said, on account of the echoes which played backwards and forwards between the high walls of rock.

Our guides told us that it was here, in days long gone by when the Popsipetels owned the whole of Spidermonkey Island, that the kings were crowned.  The ivory chair upon the table was the throne in which they sat.  And so great was the big theatre that all the Indians in the island were able to get seats in it to see the ceremony.

They showed us also an enormous hanging stone perched on the edge of a volcano’s crater—­the highest summit in the whole island.  Although it was very far below us, we could see it quite plainly. and it looked wobbly enough to be pushed off its perch with the hand.  There was a legend among the people, they said, that when the greatest of all Popsipetel kings should be crowned in the ivory chair, this hanging stone would tumble into the volcano’s mouth and go straight down to the centre of the earth.

The Doctor said he would like to go and examine it closer.

And when we were come to the lip of the volcano (it took us half a day to get up to it) we found the stone was unbelievably large—­big as a cathedral.  Underneath it we could look right down into a black hole which seemed to have no bottom.  The Doctor explained to us that volcanoes sometimes spurted up fire from these holes in their tops; but that those on floating islands were always cold and dead.

“Stubbins,” he said, looking up at the great stone towering above us, “do you know what would most likely happen if that boulder should fall in?”

“No,” said I, “what?”

“You remember the air-chamber which the porpoises told us lies under the centre of the island?”

“Yes.”

“Well, this stone is heavy enough, if it fell into the volcano, to break through into that air-chamber from above.  And once it did, the air would escape and the floating island would float no more.  It would sink.”