there ought to be lava according to your
ideas. How shall we prove it?"

"If I am right," said the captain, "we shall find that this stream ends
all at once, just as the lava hardened when the flow ceased, for there
was no stream of volcanic matter right down to the shore."

"And there is no stream of mud any further," said Mark laughing; "for
there's the end."

Mark was quite right, for about a couple of hundred yards below them the
mighty walls of verdure suddenly came together and blocked out further
progress, while, when they reached the spot, it was to find that the
bituminous mud spread out here into a pool, further progress being, as
it were, stopped by a dam of blackish rock which resembled so much
solidified sponge, so full was it of air-holes and bubble-like cells.

"I am no geologist," said the major, "so I give in to you, Strong. You
must be right."

"I think I am," said the captain, quietly examining the rocky dam and
the surface of the mud. "Yes, I should say that here is the explanation
of this curious stream."

"Then all I can say is," said the major wiping his forehead, "that I
wish the eruption had been a little bigger, and the lava stream had
ended on the sands exactly one hundred yards from camp."

"And the mud had flowed over it and made our road?" said Mark laughing.

"That goes without saying," cried the major. "Now, then, I propose a
halt and food."

There was plenty of shade close at hand, but unfortunately no water.
Still, a good rest and a hearty meal proved most grateful, and as soon
as it was done the major lit a cigar, the captain, Small, and two of the
men seemed to be dozing, and Mark and Billy Widgeon looked at them and
then at each other.

"Going to do a bit o' hammock work, Mr Mark, sir?" said Billy.

"I'm not sleepy."

"More am I, sir. Let's see if we can't get some fruit."

"All right!" cried Mark, jumping up.

"Don't go far, my boy," said the captain; and Mark started, for he had
thought his father was asleep, while on looking at him he still lay back
in the same position with his eyes closed.

"No, father, I won't go far," he said.

"Keep within range of a shout--well within range, for it's very easy to
get lost in one of these jungles, and we shall be too tired to hunt for
you now."

"I won't go far," said Mark; and he and Billy Widgeon began to walk
slowly back along the stream, looking to left and right for a way
between the trees into the jungle.

"