He sat down on the ore-heap and thought.
He was pretty sure that the latter plan of the goblins was to inundate the mine by breaking outlets for the water accumulated in the natural reservoirs of the mountain, as well as running through portions of it.
While the part hollowed by the miners remained shut off from that inhabited by the goblins, they had had no opportunity of injuring them thus; but now that a passage was broken through, and the goblins' part proved the higher in the mountain, it was clear to Curdie that the mine could be destroyed in an hour.

Water was always the chief danger to which the miners were exposed.

They met with a little choke-damp sometimes, but never with the explosive firedamp so common in coal-mines.

Hence they were careful as soon as they saw any appearance of water.

As the result of his reflections while the goblins were busy in their old home, it seemed to Curdie that it would be best to build up the whole of this gang, filling it with stone, and clay or lie, so that there should be no smallest channel for the water to get into.
There was not, however, any immediate danger, for the execution of the goblins' plan was contingent upon the failure of that unknown design which was to take precedence of it; and he was most anxious to keep the door of communication open, that he might if possible discover what the former plan was.