Only a few big flakes drifted in the air, which was keen and biting.  But the wind had ceased—­at least, it did not blow here in the cut between the hills—­and it seemed only an ordinary winter day to the two girls from the other side of the Potomac.

Forward they saw a thin stream of smoke rising into the air from the stack of the front locomotive.  The fires in the pusher were banked.  It was not an oil-burner, nor was it anywhere near as large a locomotive as the one that pulled the train.

Rearward they could scarcely mark the roadbed, so drifted over was it.  Fences and other landmarks were completely buried.  The bending telegraph poles, weighted by the pull of snow-laden wires, was all that marked the right of way through the glen.

“What a sight!” gasped Betty.  “Oh, Bobby! did you ever see anything so glorious?”

“I never saw so much snow, if that is what you mean,” admitted the Virginia girl.  “And I am not sure that I really approve of it.”

But Bobby laughed.  She had to admit it was a great sight.  It was now mid-afternoon and all they could see of the sun was a round, hazy ball behind the misty clouds, well down toward the western horizon which they could see through the mouth of this cut, or valley between the hills.  At first they beheld not a moving object on the white waste.

“It is almost solemn,” pursued Betty, who possessed a keen delight in all manifestations of nature.

“It looks mighty solemn, I admit,” agreed Bobby.  “Especially when you remember that anything to eat is three miles away and the drifts are nobody knows how many feet deep.”

Betty laughed.  She was about to say something cheerful in reply when a sudden sound smote upon their ears—­a sound that startled the two girls.  Somewhere from over the verge of the high bank of the cut on their left hand sounded a long-drawn and perfectly blood-curdling howl!

“For goodness’ sake!” gasped Bobby, grabbing her friend by the arm.  “What sort of creature is that?  Hear it?”

“Of course I hear it,” replied Betty, rather sharply.  “Do you think I am deaf?”

Only a very deaf person could have missed hearing that mournful howl.  It drew nearer.

“Is it a dog?” asked Bobby, almost in a whisper, as for a third time the howl sounded.

“A dog barks, doesn’t it?  That doesn’t sound like a dog, Bobby,” said Betty.  “I heard one out West.  I do believe it is one!”

“One what?” cried Bobby, almost shaking her in alarm and impatience.

“A wolf.  It sounds just like a wolf.  Oh, Bobby! suppose there should be a pack of wolves in these hills and that they should attack this train?”

“Wolves!” shrieked Bobby. “Wolves!  Then me for in-doors!  I am not going to stay here and be eaten up by wolves.”

As she turned to dive into the tunnel there was a sharper and more eager yelp, and a shaggy animal came to the edge of the bluff to their left and, without stopping an instant, plunged down through the drifts toward the two girls where they stood on the hard-packed snow at the mouth of the tunnel.