That was the one question which occupied, to the momentary exclusion of all others, the mind of every Aerian who was in the caverns. The middle gate was lifted, and every heart stood still as Alan and Alexis strode forward into the dark passage and grasped the levers which actuated the lifting mechanism of the outer one. They took one glance back at the anxious faces which showed so white in the gleam of the electric lamps, and then they pulled. The machinery creaked and groaned as the power was applied. Then came a rending sound and a dull crash. The door lifted a little, quivered and dropped again, and remained immovable. “The machinery has broken down!” said Alan, going back into the gallery. “There must have been a land-slip over the doorway.” “What will you do then?” said Alma. “Surely we have not escaped the conflagration of the world to be buried alive after all!” “No,” he said, looking down at her with a reassuring smile. “It can hardly be as bad as that. Unless a whole mountain has fallen in front of the door, we shall soon find a way out.” The first thing to be done was to get rid of the door, and this Alan accomplished in summary fashion by undermining it with drills, and then, after he had sent everyone into the inner recesses of the caverns, tearing it to fragments with a small quantity of the explosive used in the shells. A mass of earth and stones came rolling into the gallery immediately after the explosion, then an excavating machine was run up on hastily-laid rails and was soon boring its way into the obstructing mass. A distance of ten yards was tunnelled and then there was a rattle and whir in front of the machine, which told that the work was done. There was a cloud of dust from pulverised stones and earth and then came a rush of fresh warm air and a gleam of sunlight through the opening. “Thank God the atmosphere is still there and the sun is still shining!” cried Alan, as he drew the machine back and ran out into the open air. He looked about him for a few moments and then turned and walked back to his companions, who were already crowding towards the opening with faces glad with new hope and drawing deep breaths of the life-giving air, which the mysterious alchemy of Nature had restored unchanged to the earth. He stopped them with a gesture and said-- “Don’t go out yet till we have made the tunnel safe. You will find an awful change out yonder. Aeria is no longer a paradise. It is only a swamp surrounded by naked rocks!” And so they found it to be when they at length passed out through the tunnel and stood upon the black oozy shores of the dreary lake which still half filled what had once been the lovely land of Aeria.