The captain declared the descent practicable with care, and Mark took the lead, going down with plenty of agility, and closely followed by the little sailor.
At the end of a quarter of an hour they were all on the stony brink of what seemed to be a mud-stream which at some time had flowed down from out of a huge yawning chasm high up above their heads, and perfectly inaccessible from where they stood. According to all appearances, this mud in a thin state must have come down in a perfect cataract till it filled up the space beneath the chasm, which resembled a huge basin, as level as so much water, and when this had become full the stream had begun to form, and down this mud-stream they proposed to go, though how far it extended and would help them on their way experience alone could show.
They stood just at the edge of the pool to find that a walk upon its surface would be dangerous in the extreme, for though the top was elastic a stick was easily driven through, with the result that a jet of steam rushed out with a noise like that of a railway whistle, but the surface of the stream on being tested proved firmer, and they began to descend.
Again the same sense of insecurity was felt, the india-rubber-like film giving way easily and springing up again, while the old muttering and murmuring noises thrilled beneath their feet.
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.”