A short walk, however, along the track, which was more than ankle-deep in dust, brought them under the sheltering sides of Rakata, up which they soon scrambled to the mouth of their cave.  Here all was found as they had left it, save that the entrance was knee-deep in pumice dust.

And now a new and very strange sensation was felt by each of them, for the loud reports and crackling sounds which had assailed their ears outside were reduced by the thick walls of the cave to a continuous dull groan, as it were, like the soft but thunderous bass notes of a stupendous organ.  To these sounds were added others which seemed to be peculiar to the cave itself.  They appeared to rise from crevices in the floor, and were no doubt due to the action of those pent-up subterranean fires which were imprisoned directly, though it may be very far down, under their feet.  Every now and then there came a sudden increase of the united sounds as if the “swell” of the great organ had been opened, and such out-gushing was always accompanied with more or less of indescribable shocks followed by prolonged tremors of the entire mountain.

If the three friends had been outside to observe what was taking place, they would have seen that these symptoms were simultaneous with occasional and extremely violent outbursts from the crater of Perboewatan and his compeers.  Indeed they guessed as much, and two of them at least were not a little thankful that, awesome as their position was, they had the thick mountain between them and the fiery showers outside.

Of all this the hermit took no notice, but, hastening into the inner cavern, opened a small box, and took therefrom a bundle of papers and a little object which, at a first glance, Nigel supposed to be a book, but which turned out to be a photograph case.  These the hermit put carefully into the breastpocket of his coat and then turned to his companions with a sigh as if of relief.

“I think there is no danger of anything occurring at this part of the island,” he remarked, looking round the cave, “for there is no sign of smoke and no sulphurous smell issuing from any of the crevices in walls or floor.  This, I think, shows that there is no direct communication with Rakata and the active volcano—­at least not at present.”

“Do you then think there is a possibility of an outbreak at some future period?” asked Nigel.

“Who can tell?  People here, who don’t study the nature of volcanoes much, though surrounded by them, will expect things ere long to resume their normal condition.  I can never forget the fact that the greater part of Krakatoa stands, as you know, exactly above the spot where the two great lines of volcanic action cross, and right over the mouth of the immense crater to which Perboewatan and all the other craters serve as mere chimneys or safety-valves.  We cannot tell whether a great eruption similar to that of 1680 may not be in store for us.  The only reason that I can see for the quiescence of this peak of Rakata is, as I said to you once before, that it stands not so much above the old crater as above and on the safe side of its lip.”