This was not difficult.
It was well-defined and broad.
For some ways the airship kept on.
Then the volcano and its attendant peaks drew nearer.
To the surprise of all it was seen that the slope of the volcanic mountain were devoid of snow.
What was more, there actually seemed to be vegetation upon it.
But this was probably in the form of Arctic mosses and ferns, which grow in very barren places and even under the snow.
But as the airship now rapidly drew nearer to the volcano a startling discovery was made.
“Look!” cried Jack Wallis, in amazement. “The mountain is hollow!”
Indeed, the appearance of a mighty yawning cavity in its side seemed to warrant this assertion.