“You make this assertion very confidently,” he said. “Can you produce any evidence to support it?”
“I can produce perfectly convincing and conclusive evidence,” replied Thorndyke. “A very singular conjunction of circumstances enables us to fix with absolute certainty the place where that button has been lying. Do you happen to be acquainted with the peculiar resonant volcanic rock known as phonolite or clink-stone?”
Rodney shook his head a little impatiently. “No,” he answered, “I have never heard of it before.”
“It is not a very rare rock,” said Thorndyke, “but in the neighbourhood of the British Isles it occurs in only two places. One is inland in the north and may be disregarded. The other is the Wolf Rock.”
Neither of his hearers made any comment on this statement, though it was evident that both were deeply impressed, and he continued:
“This Wolf Rock is a very remarkable structure. It is what is called a ‘volcanic neck’; that is, it is a mass of altered lava that once filled the funnel of a volcano. The volcano has disappeared, but this cast of the funnel remains standing up from the bottom of the sea like a great column. It is a single mass of phonolite, and thus entirely different in composition from the sea bed around or anywhere near these islands. But, of course, immediately at its base, the sea-bottom must be covered with decomposed fragments which have fallen from its sides; and it is with these fragments that our Terebella has built its tube. You remember, Phillip, my pointing out to you as we walked home from the College, that the worm-tube appeared to be built of fragments that were all alike. Now that was a very striking and significant fact. It furnished prima facie evidence that the button had been moored in one place and that it had therefore been attached to some very heavy object. That night I made an exhaustive examination of the material of the tube, and then the further fact emerged that the material was phonolite. This, as I have said, fixed the locality with exactness and certainty. And I may add that, in view of the importance of the matter in an evidential sense, I submitted the fragments yesterday to one of the greatest living authorities on petrology, who recognized them at once as phonolite.”
For some time after Thorndyke had finished speaking, the two brothers sat wrapped in silent reflection. Both were deeply impressed, but each in a markedly different way. To John Rodney, the lawyer, accustomed to sworn testimony and documentary evidence, this scientific demonstration appeared amazingly ingenious, but somewhat fantastic and unconvincing. In the case of Phillip, the doctor, it was quite otherwise. Accustomed to acting on inferences from facts of his own observing, he gave full weight to each item of evidence and his thoughts were already stretching out to the, as yet unstated, corollaries.
John Rodney was the first to speak. “What inference,” he asked, “do you wish us to draw from this very ingenious theory of yours?”
“It is rather more than a theory,” said Thorndyke, “but we will let that pass. The inference I leave to you; but perhaps it would help you if I were to recapitulate the facts.”
“Perhaps it would,” said Rodney.