The Southern forces, beyond a doubt, would try to shut them in at the western mouth of the valley, and a battle in the night and rain was sure to follow.
The train continued to move slowly forward.

Had Colonel Newcomb dared he would have ordered Canby to increase his speed in order that he might reach the western mouth of the valley before the Southern force had a chance to tear up the rails, but there was no use for the train without the troops and they were already marching as fast as they could.
The gorge was now not more than a quarter of a mile away.

Dick was able to discern it, because the darkness there was not quite so dark as that which lay against the mountains on either side.

He was hopeful that they might yet reach it before the Southern force could close down upon them, but before they went many yards further he heard the beat of horses' feet both to right and left and knew that the enemy was at hand.
"Take the train on through the pass, Canby!" shouted Colonel Newcomb.
"We'll cover its retreat, and join you later--if we can." The train began to rattle and roar, and its speed increased.

Showers of sparks shot from the funnels of the two engines, and gleamed for an instant in the darkness.