“We must get him,” said Dick.
The man with the mules started to return along the way he had come. They saw at once that the path he was taking would bring him close to them.
With the mules unloaded the man evidently had no intention of walking. He mounted one of the animals and rode towards them at a fast trot.
He was within twenty yards when Dick aimed his revolver and fired. The mule the man was riding bolted, throwing its rider heavily. Before he could recover himself he was bound and helpless. The other three mules stampeded wildly and were soon out of sight.
Carried to the camp the man soon recovered. But he resolutely refused to say a word.
“Well,” said Dick. “We must try to get into the cave. Perhaps the tunnel out of which the brook runs will lead us to it.”
They were soon at the mouth of the strange tunnel. There was no sign of the molten matter of the previous night. The stream, thick with mud, flowed sluggishly, but the water was cool, and the ground, which the night before had been too hot to walk upon, was now not more than uncomfortably warm.
With Dick leading, Scott and Yvette next in order, and Jules bringing up the rear they entered the mouth of the tunnel. There was, they found, just room for them to pass, stooping low and walking knee deep in the little stream. They were, of course, in total darkness, for Dick was afraid to show a light for fear of betraying their presence.
For a hundred yards Dick groped his way onward. Then his outstretched hands struck something soft. It was a kind of curtain hung across the stream, thick and heavy.
Cautiously he slightly raised one corner and peered through. The sight that struck his eyes filled them with amazement.