Practically the whole of these islands are of volcanic origin, sulphur springs, being strongly in evidence around the shores of Port Megalos, while the water possesses the property of killing and removing in less than thirty-six hours the weeds and barnacles that adhere to a ship. "What do you say to a run ashore, gentlemen?" asked Captain Brookes of several of the officers on the afternoon of their arrival. "I'm told the crater is very interesting." "I, for one, will be very glad of the opportunity, provided I can be spared," replied Sinclair. "And I," exclaimed Gerald, Stockton, Temple, and Slade in chorus. "Very well, only be careful not to go too close to the sulphur springs, and beware of loose stones rolling down the mountain. You will be practically in sight of the ship the whole time, so keep a good look-out in case I have to make a signal for recall." Two hours later, by dint of much exertion and considerable agility, the party of officers gained the edge of the crater. For some time they remained looking at the scene of desolation. "What's that, by Jove!" exclaimed Jack Stockton, pointing to an elongated yellow object swaying in a deep hollow a few hundred yards away. The others looked in the direction indicated. "It's an airship--one of the Zeppelin type," said Gerald. "What on earth is it doing in this part of the globe?" "I wish I'd brought my marine glasses," remarked Sinclair. "This looks like an interesting discovery. She's anchored, I think." "Ay, and there are some men coming this way; they've just descended by a rope ladder. I wonder if they have spotted us?" "I don't think so. Look here, you fellows, they mean mischief! Suppose we take cover and watch their little game?" The only shelter worthy of the name was afforded by a clump of withered thorns. Foliage there was none, but by lying flat on the ground and keeping behind the thick uncovered roots, the officers could follow the movements of the men of the mysterious airship. Evidently the clump was the objective of the strangers, since from it they could command a view of the _Olive Branch_ without appearing on the skyline. The new comers were three tall, bearded men dressed in a brown uniform. One carried a revolver in a pouch, the others were apparently unarmed; all had field-glasses slung over their shoulders. Unsuspectingly they stopped at the clump of thorns, only a few tangled branches separating them from Gerald and his comrades. Out came their glasses, and with them glued to their eyes the chance of detecting the concealed officers was materially lessened. "Yes, there she is," exclaimed one of the strangers, speaking in a guttural tongue that both Gerald and Sinclair were conversant with. "Adolphe was right this time." "Looking at her from here, sir, one would not imagine her to be such a formidable ship."