The climb down the mountain side was almost more difficult and dangerous than the ascent, but at last all, even the professor, were once more at the side of the Golden Eagle. They were soon on board, and in long spirals, Frank dropped to the earth, landing not far from the edge of one of the small lakes.
"How curiously honeycombed the rocks are," exclaimed Frank, as they got out of the craft.
Indeed the face of the cliff that towered above the lakes did present a singular appearance, there being myriads of holes in its face at a height of a few inches above the surface of the water.
"Doubtless some freak of the volcanic nature of the earth hereabouts," explained the professor; "but they do, indeed, look curious."
The water of the lake, on being tested, was found to be quite fresh and agreeable to the taste though it was warmish and seemed to have an admixture of iron in it. All about them—strangest freak of all—small geysers of hot water bubbled, sending up clouds of steam into the air.
"This is like an enchanted land," was Billy's comment, as he gazed about him. Indeed, what with the towering black mountain above them with its perpetual cloud of smoke hovering above its crest, the green lakes of warm water and the bubbling, steaming geysers, it did seem like another world than ours.
Some time was occupied by a thorough investigation of the small lake and the boys and their scientific companion then advanced on a larger one that lay at some distance.
"Do you think it is wise to go so far from the aeroplane?" asked
Harry.
"Why, there's nothing here that could attack us," the professor was beginning, when he stopped short suddenly with an exclamation.
"Look there!" he exclaimed, pointing down at the ground. "A human track."