It was not a stopping train and it was only necessary to watch that the signals were shown for clear at the few stations that came at infrequent intervals along the line.
Joe Halkett appeared to be working very well. He had got the train adjusted to its gait, and the cars were thumping over the frogs and switches at a reasonable pace, labouring, panting, and grunting when mounting a steep gradient, but settling down again when there was a stretch of good running ground ahead. It was mostly cultivated prairie land, but now and again the track was through gloomy pine forests or deep mountain defiles.
Dusk had already deepened into darkness when they were rattling along the track across the Piegan Indian Reservation, and Halkett had somehow worked up his engine to such easy going that Sergeant Silk began to believe that he had exaggerated the disabilities of both locomotive and engineer, and that he might just as well have been enjoying the greater comfort of one of the passenger cars, or been seated luxuriously in the private Pullman spinning yarns with the Colonel and Sir George.
In the darkness Silk did not perceive the change that had come upon Halkett's face. It was only when Joe chanced to lean over into the light from the open fire-box that he saw the look of terror that had come into it. It was a look like that of a man who had got some terrible secret on his soul and was driven half mad by it.
"Joe? What's the matter?" Silk cried, starting to his feet. He glanced round at the fireman.
Dick had just come back from the water tank.
"Say, Sergeant," he gasped, "the water's runnin' low, an' we've passed the plug. We've got ter go back!"
Silk was alarmed. He knew well that one of the important things for an engine-driver to do is to figure out at what plugs he can fill his tank most advantageously, and that it is a high crime to run short of water.
"Are you certain sure we've passed it?" he asked sharply. He had leapt to the lever to stop the train, and whistle for brakes.
The fireman nodded.