Still as death he lay waiting, wondering why the fearsome brute did not at once attack him, instead of hovering there in mid-air. His curiosity was quickly satisfied. Like a flash a second vampire swooped into view and hurled itself upon Wilson’s ghoulish guardian. In an instant the twain were fighting tooth and nail, their mighty wings raising a deafening clamour. Not a move dared the lad make, fearing that the great bats might unite forces against him did they see him stirring. Round and round the brutes circled, rocking, reeling in their frenzied efforts to destroy each other. Now they sank until they were whirling but a few feet above Wilson’s head; anon, they would soar into the gloom far beyond his sight. For an hour the duel raged, the creatures’ efforts growing feebler as the time went on, while the crimson rain which sprinkled down over the engineer bore grim testimony to the sanguinary nature of the struggle. Suddenly, with a shrill scream, one of the vampires pitched heavily earthward. Its adversary swayed unsteadily for a moment, then fluttered to the ground beside it. In a second Tom was upon his feet. Knife in hand, he moved towards his foes. One was already dead, and the other, too exhausted to move and bleeding from a score of wounds, fell an easy prey to the engineer’s weapon. Feeling deeply thankful for his escape from a terrible death, the lad stood looking down on the carcases for a few moments; then, striding forward over the moss, he plunged through the encircling fungi. As he emerged from the glistening growths a startled cry escaped him. The ground before him was thickly covered with bones! At the sight of the ghastly relics his already overstrained nerves almost gave way, but, exerting all his self-control, he pulled himself together and strode down the valley, hoping ere long to regain the coast. CHAPTER XVIII. THE SINKING POOL. FOR some time Wilson plodded on, his one idea being to escape from the ghostly valley. The weirdness of the place, enclosed as it was on every side by towering cliffs, its unnatural stillness, and, above all, the grim remains with which the ground was littered, sent an uncanny thrill through the engineer; and, despite his resolution, he found himself continually glancing backward, to make certain that no spectral form was dogging his steps. All unconsciously he was moving in exactly the opposite direction to that he wished to take, straying farther at each step into the interior of the underworld. The valley seemed to be endless, and the lonely traveller grew tired after awhile of the eternal monotony of the scene around. More, he grew afraid; afraid that he would never find his way out of these ghostly wilds, where reigned an everlasting silence--afraid that he would never again see the _Seal_ or the comrade from whom he had been snatched so suddenly.