At last his superior intelligence asserted itself.  His brain became clearer, recovered its power of analysis.  He began to criticize, reflect, and this is the theory he evolved—­

Some one, long ago, had discovered valuable minerals in the volcanic rock.  Mining operations were in full blast when the extinct volcano took its revenge upon the human ants gnawing at its vitals and smothered them by a deadly outpouring of carbonic acid gas, the bottled-up poison of the ages.  A horde of pigs, running wild over the island—­placed there, no doubt, by Chinese fishers—­had met the same fate whilst intent on dreadful orgy.

Then there came a European, who knew how the anhydrate gas, being heavier than the surrounding air, settled like water in that terrible hollow.  He, too, had striven to wrest the treasure from the stone by driving a tunnel into the cliff.  He had partly succeeded and had gone away, perhaps to obtain help, after crudely registering his knowledge on the lid of a tin canister.  This, again, probably fell into the hands of another man, who, curious but unconvinced, caused himself to be set ashore on this desolate spot, with a few inadequate stores.  Possibly he had arranged to be taken off within a fixed time.

But a sampan, laden with Dyak pirates, came first, and the intrepid explorer’s bones rested near the well, whilst his head had gone to decorate the hut of some fierce village chief.  The murderers, after burying their own dead—­for the white man fought hard, witness the empty cartridges—­searched the island.  Some of them, ignorantly inquisitive, descended into the hollow.  They remained there.  The others, superstitious barbarians, fled for their lives, embarking so hastily that they took from the cave neither tools nor oil, though they would greatly prize these articles.

Such was the tragic web he spun, a compound of fact and fancy.  It explained all perplexities save one.  What did “32 divided by 1” mean?  Was there yet another fearsome riddle awaiting solution?

And then his thoughts flew to Iris.  Happen what might, her bright picture was seldom absent from his brain.  Suppose, egg-hunting, she had stumbled across this Valley of Death!  How could he hope to keep it hidden from her?  Was not the ghastly knowledge better than the horror of a chance ramble through the wood and the shock of discovery, nay, indeed, the risk of a catastrophe?

He was a man who relieved his surcharged feelings with strong language—­a habit of recent acquisition.  He indulged in it now and felt better.  He rushed back through the trees until he caught sight of Iris industriously kneading the sago pith in one of those most useful dish-covers.

He called to her, led her wondering to the track, and pointed out the fatal quarry, but in such wise that she could not look inside it.

“You remember that round hole we saw from the summit rock?” he said.  “Well, it is full of carbonic acid gas, to breathe which means unconsciousness and death.  It gives no warning to the inexperienced.  It is rather pleasant than otherwise.  Promise me you will never come near this place again.”