The others had gone on and were some distance ahead.  Mark hurried on to join them.  As he got a last glance at the top of the column, over the brow of the hill, he happened to look off to the left.  There was another hill, about the size of the one they had been on.

And, as Mark looked he saw something move.  At first he thought it was another beast.  But, to his terror he saw that the creature had only two legs, and that it stood upright like a man, but such a man as Mark had never seen before, for he was nearly twelve feet tall.

He was about to cry out and warn the others, when the thing, whatever it was, sunk down, apparently behind some tall bushes, and disappeared as if the earth had opened and swallowed it.

“I wonder if I had better tell them,” thought Mark.  “I can’t show them anything.  I wonder if I really saw it, or if it was only a shadow.  I guess I’ll say nothing.  But it is very strange.”

Then he hurried on to join the others.

“What makes you so pale?” asked Jack of his chum.

“Nothing,” said Mark, somewhat confused.  “I guess I’m a little tired, that’s all.”

They reached the ship in safety, and, having dinner started the machinery and took the Mermaid up into the air.

“We’ll travel on and see if we can’t find some human beings,” the professor said.

All that afternoon they sailed, the country below them unfolding like a panorama.  They passed over big lakes, sailing on the surface of some, and over rivers, and vast stretches of forest and dreary plains.  But they never saw a sign of human inhabitants.

It was getting on to five o’clock, the hour when the brilliant lights usually disappeared, when Mark, who was steering in the conning tower, gave a cry.

“What is it?” asked the professor, looking up from a rude map he was making of the land they had just traversed.

“It looks like a town before us,” said the boy.

Mr. Henderson and Jack looked to where Mark pointed.  A few miles ahead and below them were great mounds, not unlike that from which the geyser had spouted.  But they were arranged in regular form, like houses on a street, row after row of them.  And, as they approached nearer, they could see that the mounds had doors and windows to them.  Some of the mounds wer rger than others, and some were of double and triple formation.

“It’s a city!  The first city of the new world!” cried Jack.

“It is a deserted village!” said the professor.  “We have found where the people live, but we have not found them.”  And he was right, for there was not a sign of life about the place, over which the airship was now suspended.

CHAPTER XXIV

 The giants

“Let’s go down and investigate,” suggested Jack.

“Better wait,” counseled the professor.  “It will soon be dark, and, though we will have moonlight, we can not see to advantage.  I think it will be best to keep the ship in the air to-night, and descend in the morning.  Then we can look about and decide on what to do.”