A strange change that no one could rightly understand had lately come upon the natural condition of the sulphur mines. The steam that rose from the solfataras had grown less and less week by week and day by day, until in some places it had altogether subsided. This was a grave sign, for in the steam lay the essence of the sulphur, and if it ceased to rise from the pits the sulphur would cease to grow.
Other changes came with this, such as that deep subterranean noises arose from parts of the plain where no fissures had yet been seen, and that footsteps on the earth around these places produced a hollow sound.
From these signs, taken together, the Captain had concluded that the life of the mines, the great infernal fire that raged beneath the surface, was changing ground, leaving the valley, where it had lived for ages, for the mountain heights, where the low grumblings were now heard to come from beneath the earth's crust of lava and basaltic rock.
So, taking counsel of his people, he decided to bore the ground in these new places in the hope of lighting on living solfataras that would stand to him against the loss of the dead ones. And it chanced that he was in the midst of many busy preparations for this work when the report of the warders reached him, and the boring was still uppermost in his mind when he sent back his answer as he came upon the flogging and stopped it.
Thus it happened that the first thought that came to the warders was to send their prisoners to one of the spots that had been marked on the hillside for the test of bore and spade.
So, in less than half-an-hour more, Jason and Sunlocks, lashed together, arm to arm and leg to leg, were being driven up the mountain to the place assigned to them. They found it a hideous and awesome spot. Within a circle of two yards across, the ground was white and yellow and scaly, like a scab on evil flesh. It was hot, so that the hand could not rest upon it, and hollow, so that the foot made it shake, and from unseen depths beneath it a dull thud came up at intervals like nothing else but the knocking of a man buried alive at the sealed door of his tomb.
Beneath this spot the heart of the solfatara was expected to lie, and Jason and Sunlocks were commanded to open it. Obeying gloomily, they took the bore first and pierced the scaly surface, and instantly a sizzling and bubbling sound came up from below. Then they followed with the spades, but scarcely had they lifted the top crust when twenty great fissures seemed to open under their feet, and they could see lurid flames rushing in wild confusion, like rivers of fire in the bowels of the earth.
It was a sight at which the stoutest heart might have quailed, and Jason leapt back to the bank and dragged Sunlocks after him.
"This is not safe," he said.
"In with you," shouted the warders from their own safe footing of four yards away. With a growl from between his clenched teeth, Jason stepped back into the hole, and Sunlocks followed him. But hardly had they got down to the fearsome spot again, when a layer of clay fell in from it, leaving a deep wide gully, and then scarcely a yard of secure footing remained.