Suddenly they were tossed to the ground by a swaying motion, and not far off a great crack opened in the earth.  The roaring, rumbling sound increased in volume.

“An earthquake!  It’s an earthquake!” cried Tom.  “We’re in the midst of an earthquake!”

CHAPTER XIV

A NIGHT IN CAMP

The rumbling and roaring continued for perhaps two minutes, during which time the castaways found it impossible to stand, for the island was shaking under their feet with a sickening motion.  Off to one side there was a great fissure in the earth, and, frightened as he was, Tom looked to see if it was extending in their direction.

If it was, or if a crack opened near them, they might be precipitated into some bottomless abyss, or into the depths of the sea.  But the fissure did not increase in length or breadth, and, presently the rumbling, roaring sound subsided.  The island grew quiet and the airship travelers rose to their feet.

“Bless my very existence!  What happened?” cried Mr. Damon.

“It was an earthquake; wasn’t it, Tom?” asked Mr. Fenwick.

“It sure was,” agreed the young inventor.  “Rather a hard one, too.  I hope we don’t have any more.”

“Do you think there is any likelihood of it?” demanded Mr. Damon.  “Bless my pocketbook!  If I thought so I’d leave at once.”

“Where would you go?” inquired Tom, looking out across the tumbling ocean, which had hardly had a chance to subside from the gale, ere it was again set in a turmoil by the earth-tremor.

“That’s so—­there isn’t a place to escape to,” went on the eccentric man, with something like a groan.  “We are in a bad place—­do you think there’ll be more quakes, Tom?”

“It’s hard to say.  I don’t know where we are, and this island may be something like Japan, subject to quakes, or it may be that this one is merely a spasmodic tremor.  Perhaps the great storm which brought us here was part of the disturbance of nature which ended up with the earthquake.  We may have no more.”

“And there may be one at any time,” added Mr. Fenwick.

“Yes,” assented Tom.

“Then let’s get ready for it,” proposed Mr. Damon.  “Let’s take all the precautions possible.”

“There aren’t any to take,” declared Tom.  “All we can do is to wait until the shocks come—­if any more do come, which I hope won’t happen, and then we must do the best we can.”

“Oh, dear me!  Bless my fingernails!” cried Mr. Damon, wringing his hands.  “This is worse than falling in an airship!  There you do have some chance.  Here you haven’t any.”

“Oh, it may not be so bad,” Tom cried to reassure him.  “This may have been the first shock in a hundred years, and there may never be another.”

But, as he looked around on the island, he noted evidences that it was of volcanic origin, and his heart misgave him, for he knew that such islands, created suddenly by a submarine upheaval, might just as suddenly be destroyed by an earthquake, or by sinking into the ocean.  It was not a pleasant thought—­it was like living over a mine, that might explode at any moment.  But there was no help for it.