“This is where they enter,” he said, “and I think our best plan will be to build a fire in the mouth.  We should then have the advantage over them, as we should see them once they came into the reflection.”

They set about collecting wood, when Venning had a thought.

“Which way does the draught set in the tunnel—­away from the cavern or into it?”

“Why?”

“Because, if the current of air blows away from us, we can easily keep them out.”

“It blows from the cave into the tunnel.  I found that out before.”

“Then we have got them, whoever they are.  Make the fire in the passage, pile up blocks of this sulphur on the inner side, and the wind will carry the fumes down into the tunnel.”

“A splendid plan,” said Mr. Hume; and very soon it was carded out, a couple of shots being fired into the dark passage as a warning to the enemy to keep off.  As the flames caught the sulphur, a thick smoke rolled away.  “That will stop them; and now we can wait in peace till the morning.”

The rest of the night passed for them in peace as far as their assailants were concerned, but the chilling damp of the vaults got into their bones, and Venning was pinched and shivering when the first ray of sunshine struck slanting down through the mist-laden atmosphere, bringing with it a message of hope from the bright outer world.

CHAPTER XXIII

THROUGH THE VAULTS

They shared the goats’-milk remaining in the calabash, and at once entered the first exit, that was to lead them, as they ardently hoped, into the warmth and light of the day.  Venning went first, carrying only the strange lantern, and Mr. Hume a foot behind, ready to support the boy with a helping hand if he were again overcome by dizziness.  Their progress was slow, owing to the dark, but the going was easy enough with a gradual ascent.  What pleased them very much was the dwindling of the hubbub made by the waters—­a sign that they were going away from that source of danger.  In silence and in darkness they kept on up to a point where the walls widened out, and where there was a familiar hut-like smell, necessitating a pause for investigation.  Mr. Hume struck a match—­for the fungus-lamp shed no ray—­and holding it up, disclosed a slab of rock with a pile of white ash on it.  Blowing upon this, he started a glow from the still live embers beneath, and placing on a few half-burnt sticks, soon made a fire.  By its light they saw a couple of rush-mats, such as the natives make, on the floor, and these, added to the fire, made a blaze which lit up a cavern bearing evidence of frequent use; for there were other mats on a ledge, together with several calabashes, and an earthen pot of native make.  Seeing where the passage continued, they hurried on, for these human belongings reminded them forcibly of the existence of beings they had no wish to meet in those dark passages.