Bart at that moment led in the cowpony and Calder started to remove the saddle.  He had scarcely done so and hobbled his horse when he was startled by a tremendous snarling and snorting.  He turned to see the stallion plunging hither and thither, striking with his fore-hooves, while around him, darting in and out under the driving feet, sprang the great black wolf, his teeth clashing like steel on steel.  In another moment they might sink in the throat of the horse!  Calder, with an exclamation of horror, whipped out his revolver, but checked himself at the very instant of firing.  The master of the two animals stood with arms folded, actually smiling upon the fight!

“For God’s sake!” cried the marshal.  “Shoot the damned wolf, man, or he’ll have your horse by the throat!”

“Leave ’em be,” said Dan, without turning his head.  “Satan an’ Black Bart ain’t got any other dogs an’ hosses to run around with.  They’s jest playing a little by way of exercise.”

Calder stood agape before what seemed the incarnate fury of the pair.  Then he noticed that those snapping fangs, however close they came, always missed the flesh of the stallion, and the driving hoofs never actually endangered the leaping wolf.

“Stop ’em!” he cried at last.  “It makes me nervous to watch that sort of play.  It isn’t natural!”

“All right,” said Dan.  “Stop it, boys.”

He had not raised his voice, but they ceased their wild gambols instantly, the stallion, with head thrown high and arched tail and heaving sides, while the wolf, with lolling red tongue, strolled calmly towards his master.

The latter paid no further attention to them, but set about kindling a small fire over which to cook supper.  Calder joined him.  The marshal’s mind was too full for speech, but now and again he turned a long glance of wonder upon the stallion or Black Bart.  In the same silence they sat under the last light of the sunset and ate their supper.  Calder, with head bent, pondered over the man of mystery and his two tamed animals.  Tamed?  Not one of the three was tamed, the man least of all.

He saw Dan pause from his eating to stare with wide, vacant eyes among the trees.  The wolf-dog approached, looked up in his master’s face, whined softly, and getting no response went back to his place and lay down, his eyes never moving from Dan.  Still he stared among the trees.  The gloom deepened, and he smiled faintly.  He began to whistle, a low, melancholy strain so soft that it blended with the growing hush of the night.  Calder listened, wholly overawed.  That weird music seemed an interpretation of the vast spaces of the mountains, of the pitiless desert, of the limitless silences, and the whistler was an understanding part of the whole.

He became aware of a black shadow behind the musician.  It was Satan, who rested his nose on the shoulder of the master.  Without ceasing his whistling Dan raised a hand, touched the small muzzle, and Satan went at once to a side of the clearing and lay down.  It was almost as if the two had said good-night!  Calder could stand it no longer.