"Marvelous, anyway, how they use their lightnings to kill," I commented. "Marvelous the way both sides won!" he snapped back. "Doesn't seem to be much left of either of them!" In this statement, however, Clay was mistaken. We were soon to learn that all too much was left of both factions. While the lightnings still leapt and vaulted through space, crossing and criss-crossing the atmosphere with dagger-flames of blue and yellow, there rose a low, regular, distant rumbling--a rumbling too even and continuous for thunder, and yet more ominous-sounding than thunder, since it gained each moment in force and volume and had a monotonous, rhythmical, thudding effect reminding one of the motor of some great machine. "God be merciful, what's this coming?" suddenly cried my companion, pointing far down the cavern. "See, Frank! Can you make out what it is?" At the renewed risk of falling over the edge, I peered in the indicated direction; and, as I did so, I received perhaps the severest shock I had yet had on this day of horrors. "Lord Almighty!" I gasped. "It's a battleship on wheels!" "It's not one of them! It's two!" shouted Clay. And indeed, two monster shapes, each as large as the dreadnoughts of a modern navy, were gliding toward us out of the greenish-yellow glare far to the right. With long, pointed, steel-like prows, thin tapering sterns, and squat funnels belching smoke and steam, they had the shape and appearance of warships, except that they displayed no masts or gun-turrets. But little dark tubes curving from their sides looked very much like guns. "See the wheels," yelled Clay, trying to make himself heard above the increasing uproar of the monsters' approach; and I observed how scores of wheels, each of them twenty or thirty feet across, were arranged all along the sides of the great machines, bearing them forward with the speed of an ocean liner. "Seems to be in a hurry!" I yelled back, as I noticed with what steady roaring haste the vessels pressed forward. But I had no time to wonder what the machines might be, or what incredible people, populating the abysses of the earth, had developed such giant mechanisms. Before I had half recovered from my surprise, I was aware that Clay, no longer able to make his voice heard above the din of the approaching monsters, was nudging my elbow and pointing in great agitation to our left. "See! See there!" I read the unexpressed words on his lips. "Just look at that! Just look! Just look!" Well might he be agitated. From far down the cavern to our left, three more land-battleships were rumbling toward us, shooting out flashes of red and white lightning like a challenge, while hastening to meet the other Titans as though intending a head-on collision. CHAPTER V Separated!