But while a train may go two or three miles in a few minutes it takes troops marching in the darkness over uncertain ground a long time to cover the same distance.

They marched a full half hour and then Dick suppressed a cry.

The light, burning as intensely red as before, appeared again on the mountain to the right, but further toward the west, seeming to have moved parallel to the Northern troops.
As Dick looked it began to flash swiftly from side to side and that chill and weird feeling again ran down his spine.

He looked toward the south and there was the second signal, red and intense, replying to the first.
Dick heard a deep "Ah!" run along the line of young troops, and he knew now that they understood as much as he or any of the officers did.

He now knew, too, that they would not pass out of the valley without a combat.