Injun knew about these.  “Him shoot,” he said.

The startled expression on Whitey’s face gradually gave way to one of understanding and disgust.  “They came from the water tank,” he said.  “Don’t you see?  We’re late, and what I heard was the train going the other way.  Then it stopped, and they’re holding it up.”  And Whitey sat down on one of the rails, thoroughly disgusted.

For a while nothing was said.  The disappointment was too great for words.  The boys’ chance for heroism had melted in the fog, which the mist had now become.  Injun slowly put on his shirt.  It was nothing but a garment now, no heroic rescue signal.

“I’ll bet that clock at the ranch was wrong.  It always is.  I might have known it,” Whitey said dejectedly.  The thought of the loss of the gold was forgotten in his disappointment at failure.  “I hope no one was hurt—­I mean none of the trainmen or passengers,” he added.  “But I guess not.  Those bandits had the drop on them, and they couldn’t have put up much of a fight.  How do you suppose we heard those shots?  We must be at least a mile from the tank.

“Him fog,” Injun answered.  “Hear plain.”  And it is true that fog has a way of conveying sound.

An idea brought Whitey to his feet with a leap.  “What fools we are to be sitting here!” he cried.  “We’ll follow those robbers.  The people on the train won’t do that.  They’ve no horses.”

Here, indeed, was a brilliant thought.  The boys could track the bandits to their hiding-place, and possibly recover the ore.  At least, they could return and report where the men had gone.  There was a chance to distinguish themselves yet.  In a moment they were mounted and dashing down along the track, toward the water tank.

Presently a shrill whistle was followed by the faint rumbling of the train as it resumed its way.  “See?” yelled Whitey.  “The train’s just starting.  We won’t be very late, and the men’s tracks will be plain.  Gee!  I hope it doesn’t rain.”

A few minutes’ ride brought the boys to the deserted water tank.  They dismounted to pick up the trail of the robbers.  Near the tank, where the express car must have stood, were the traces of many feet.  There were others leading from the cars in the rear.  Noting these, Whitey said:  “Mebbe they held up the passengers, too.  It’s likely that they would.”

But, singularly enough, most of these tracks led on toward the high bridge which spanned the gully.  The boys followed them curiously, and when they reached the bridge Injun stopped.

“Huh!  Go back again, too,” he muttered.  And sure enough in the maze of footprints many seemed to lead back toward the water tank.

“Why do you s’pose they went to the bridge?  Prob’ly to see if it was safe; that the robbers hadn’t damaged it,” Whitey said.

“Mebbe,” said Injun, who was figuring things out in his own way and seldom spoke until he had them figured.