et.

But so long as it would hold it proved to be a capital road, for while
there was a wall of dense verdure on either side, not so much as a scrap
of moss had taken root on the surface of the smooth slope, which wound
in and out with the ravine, acting in fact as a stream of water does
which runs down some mountain scar, save that here there was no
progress. The mud had once been hot and fluid, and doubtless was still
so, to some extent, below; but, after filling up every inequality, it
kept to one regular level, forming what Mark at once dubbed Gutta-percha
Lane.

It was now long past mid-day, and as they walked steadily on, growing
more confident as the toughness of the bituminous mud, for such it
proved to be, proved itself worthy of the trust it was called upon to
bear, the question arose where the stream would end.

As far as the captain could make out, in spite of its zigzagging and
abrupt curves, the course of the stream was decidedly towards the camp,
but as they descended lower one thing was very plain, and that was that
they were getting into thicker jungle, which grew taller and darker with
every hundred feet of descent.

"How do you account for it?" Captain Strong said at last to the major,
as they now found themselves walking down a winding road some fifteen to
twenty feet wide, and with dense walls of verdure rising fully two
hundred feet in height.

"I think there must have been a stream here, and at some time there has
been an eruption and the mud has flowed down it and filled it up."

"If there had been a stream," the captain said, "we should have seen
some sign of its outlet near the camp."

"Then you have a theory of your own?"

"Yes," said the captain; "it seems to me that first of all this was
merely a jagged ravine, running from the mountain's shoulder right down
to the sea."

"That's what I thought. With a stream at the bottom."

"No stream," said the captain. "Nothing but vegetation. Down this a
stream of red-hot lava must have flowed and burned the vegetation clean
away, leaving a place for the mud to come down and harden as you have it
now. It may have been a year after the eruption--twenty, fifty, or a
hundred years, but there it is."

"If you are right, we should see traces of the burning on the trees,"
said the major.

"That does not follow. These trees may have sprung up since, right to
the very edge of the stream, but no farther."

"Then under this mud or bitumen