sentenced to the garrote. He wondered what that shooting star and the phosphorescent mist could have been? Then he wondered about the skeletons again… about Cesare…
A rifle-shot that sounded like a mere snap in the thin mountain air disturbed his reflections. He looked up and saw a faint wisp of vapor float out of the .30-30 in Cesare's hands. The engineer glanced anxiously to see if the murderer had shot any of his companions. They were all on their mules and all looking at each other and at him. Every one in the crowd had felt instinctively that the desperado had fired at some person—possibly at one of his own party.
“What is it?” cried Standifer.
“A man yonder!” Pablo pointed.
“I don't know whether it was a man or not!” cried Ruano, jumping from his slow mule and setting off down the declivity at a hazardous run.
“Ruano!” shouted M. Demetriovich in horror. “Did you shoot at a human being like that? Drop that rifle, you bloodthirsty fellow. Drop it!”
Extraordinary to say, Cesare did drop his gun and as it struck the stones it fired again. The man plunged on downward at full tilt. It was an amazing flight. He took the boulders like a goat. The party stopped their mounts and sat watching the dash.
“Did you say it was a man?” asked the secretary shakily of Pablo.
“As sure as I am sitting here.” At that moment, the flying Ruano swung in behind a large boulder.
“He was behind that!” cried Pablo sharply. Then he lifted his voice. “Did you get him, Cesare?” he shouted. “Was there any money on him?”
But almost immediately Pethwick glimpsed the murderer again, in fact saw him twice—or he may have caught a flash of two figures, one chasing the other.
Suddenly Pablo began yelling as if on a foxcourse.
A shock of horror went through Pethwick. He knew too well what the convict would do if he caught the man. Nobody could waylay Cesare Ruano, even to look at him, in safety.
“Here, let's get down there!” cried the engineer in urgent tones. “Lord, we ought not to have given that brute a gun!”
“Maybe he hit him!” surmised Pablo in cheerful excitement.
“He's chasing him this minute somewhere behind those boulders.” declared Standifer nervously.
M. Demetriovich dismounted, and from between two boulders recovered Standifer's rifle as they passed it.
Pethwick had screwed up his nerves for some dreadful sight behind the boulder, but there was nothing there. Nothing except a splotch of green liquid on the stones.
Smaller gouts of this green fluid led off down the boulder-field, making from one large boulder to another as if some dripping thing had tried to keep a covert between itself and the party of riders.
Pethwick dismounted and followed this trail perhaps a hundred yards, until it ceased. Then he stood looking about him in the cold sunshine. He could not hear the slightest sound. The blackened valley and the Infernal River lay far below him. High above him, at the end of the trail, the vultures wheeled against the sky.
CHAPTER III.
From his headlong pursuit down the mountain-side Cesare Ruano never returned.
What became of him none of his companions ever discovered. He dropped out of their lives as suddenly and completely as if he had dissolved into thin air.
A dozen possibilities besieged their brains. Perhaps he fell over a cliff. Or was drowned in the river. Or he may have deserted the expedition. Perhaps he was still wandering about, lost or crazed. Perhaps the man he pursued turned and killed him.
All these are pure conjectures, for they had not a clue upon which to base a rational hypothesis. The only hope for a suggestion, the green splotches on the boulders, proved to be a hopeless riddle itself.
The men picked up several of the smaller boulders and when camp was pitched Prof. Demetriovich made a chemical analysis of the stain. Its coloring matter was derived from chlorophyll. If Ruano's shot had penetrated the stomach of some running animal, it was barely possible for such a stain to have resulted—but it was improbable. This stain was free from cellular vegetal structure. In the mixture was no trace of the corpuscles or serum of blood.
On the afternoon of the second day following the incident, the men sat at the dinner-table discussing the matter.
In the tent beside the rude dining-table were cots and another table holding mineral and floral specimens and some insects. Two or three books were scattered on the cots and duffle-bags jammed the tent-corners.
Looking out through the flaps of their tent, the diners could see the eastern peaks and cliffs of the Infernal Valley turning orange under the sunset. M. Demetriovich was talking.
“I consider the chlorophyll an added proof that there is another scientific expedition in this valley.”
“What is your reasoning?” inquired Pethwick.
“Chlorophyll is a substance none but a chemist could, or rather would, procure. It serves no commercial purpose. Therefore it must be used experimentally.”
“Why would a chemist want to experiment in this forsaken place?”
Standifer put in a question—
“Then you think Cesare shot a hole in a canister of chlorophyll solution?”
“When a man has a choice of improbabilities, all he can do is to choose the least improbable,” explained M. Demetriovich friendlily.
“I wonder what Cesare would say about it?” speculated Pethwick.
“The green trail also suggests my theory,” proceeded Prof. Demetriovich. “When Ruano shot the man behind the boulder, his victim evidently did not know that his can of solution had been punctured, for he sat hidden for perhaps a minute while his container leaked a large pool just behind the
