"Perhaps this works like an electric battery," he said. "I'll pull it out."

He did so, and a surprising thing happened. The boat shot forward at enormous speed, and as Jack happened to pull the pin out at a time when the craft was high up, it began to shoot across the water at an angle to the whirlpool. He had solved the problem of how to escape. As he afterward learned, the pin was just for the purpose for which he used it--to cause a sudden increase in speed.

The whirlpool did not give up without a struggle, but the boat was finally successful, and fought its way out to calm water.

"How did you do it?" asked Mark, and Jack told them.

"Well, we'd better start back for the city," proposed Mr.

Roumann. "I guess we've had enough for one day. We'll try again, and take some other route."

"There's no need of that," declared Professor Henderson. "See, we are close to the hills now. We have crossed the whirlpool. Why not go on, and see if we can't find some Cardite? Going back now will be no easier than after we have made an examination. Let's explore the hills."

The boat had shot out on the farther side of the whirlpool, and there was nothing now between it and the sh.o.r.e. After a consultation it was decided to land.

"We can be more careful coming back," said Jack.

Half an hour later they had landed and started up the hills toward the summit. The place seemed to be deserted, but there were evidences that some sort of mining had been going on there, for great holes and shafts were dug in the ground, and there were remains of machinery.

"They must have dug up all the Cardite in this locality," said Professor Henderson, "and they've gone to a new place."

"Which we wish to find," added Mr. Roumann, "and that without being discovered. From the way in which the Martians guard this, it will go hard with us if they see us taking any."

They toiled up to the top of some of the lowest hills. There did not seem to be any of the treasure there, and they went farther.

They were getting tired and hungry, and they sat down to rest and eat some food which they had brought with them.

"Let's try that hill," proposed Mark, pointing to a high one about a mile away. "It looks red from here."

There was a rosy hue about the little mountain, and after a brief rest they headed for the spot.

"There's nothing here!" exclaimed Jack in disgust, as he and Mark, in a final spurt, reached the base of it. "Nothing but ordinary dirt."

Mark looked down. He dug his heel into the sod. Then he uttered a cry of triumph.

"Here it is! Here it is!" he cried. "It's under the gra.s.s!

We've got to dig it up!"

He knelt down, and began to tear away the sod with his hands.

Jack did the same, and when they had lifted aside the tangle of roots and gra.s.s, they saw beneath it a dull gleaming red substance, like clay.

"That's it! That's it!" shouted Mr. Roumann. "We've found it!"

He stooped over, and with his knife began digging some up.

"It's neither warm, nor does it give any light," said Mr.

Henderson in disappointed tones.

"No; it requires special electrical treatment," replied Mr.

Roumann. "I know how to do it, though. Now we shall all be millionaires! There is enough here to make us wealthy for life!"

He began filling his iron boxes, the rest helping him. They were engaged in getting out the Cardite, all working with feverish haste, when Jack, looking up, saw a Martian officer regarding the actions of the world-dwellers with his great, bulging eyes.

CHAPTER XXVIII

THE ATTACK

"They've discovered us!" exclaimed Jack, as he stood up and watched the Martian.

"What?" cried Mr. Roumann. "Oh, it's only one of them," he added, "and he hasn't any of those electrical sticks. Go ahead and take some more of the Cardite."

But the Martian advanced on the travelers, and, by his voice and gestures, seemed to be warning them to stop taking the red material.

"Maybe he's a guard," suggested Mark.

"Very likely," a.s.sented Professor Henderson.

"I'll see if I can't scare him with my gun," remarked Andy.

"I've put in more powder, and a heavier bullet."

He fired in the air, over the Martian's head, but to the surprise of the adventurers the weapon only gave a faint sound, like that of a pop gun, while the bullet rolled from the barrel and dropped at Andy's feet.

"Why, that's worse than ever!" he exclaimed. "I guess the red stuff must have taken all the power out of your gun, Andy," said Mark.

The Martian stood still for a moment. Then he spoke again, more earnestly than before, and waved the strangers away from the red hill.

"We're not going," said Mr. Roumann, and he added a few of the Martian words he had learned, endeavoring to state that they were going to take only a little of the Cardite.

The officer, with a last warning shake of his big head, suddenly turned and ran away.

"I guess he's gone for reinforcements," said Jack.

"No matter," spoke Mr. Roumann. "We'll soon have all we can carry, and then we'll hurry back to the projectile. When we get there we can defy them."

They continued to fill the boxes with the Cardite, and soon had a good supply. Then, taking a look to see if the Martian had summoned any guards, but finding that none was in sight, the adventurers made their way back to their boat, and set it in motion.

"How are we going to escape the whirlpool?" asked Mark.

"I think if we skirt down the sh.o.r.es of the lake for some distance, and then strike across to the city, we'll avoid it,"

replied Professor Henderson. "The pool is not very large, and seems to be only, directly in front of the red hill."

This they found to be the case, and they were soon safely beyond the swirling waters, and on their way back to Martopolis.

"We had better not land at a public dock," suggested Professor Henderson.

"Why not?" asked the German.