The yaks were yoked, and a good luncheon put up, prepared for a day's jaunt, the trip being planned for the day of the week which had been set apart for exploration purposes. Within an hour the team was tethered at the spot where Harry and George put up the team when they started out on their former tour of investigation.

"Now, George, we shall have to depend on you to lead the way."

"When I left Harry we were on the little hill beyond that clump of bushes."

"We must have been much farther away," was Harry's opinion.

"Let us go over at any rate, and we can probably get our bearings from there."

The spot pointed out was just as much a mystery after reaching it as before. It was suggested that, as neither knew how to determine the direction of the "hole" from that point, time might be saved by each taking a different direction, with the understanding that if anything was discovered a shot should be fired as a signal.

After carefully noting the two large trees where the team was located, they separated, Harry going to the north, George to the northwest and the Professor directly west. The ridge on which they were ran north and south, and to the west was a decline. It was considerably south of the trail taken on their former trips, so it was really undiscovered territory.

The Professor pa.s.sed down the long incline, carefully noting every set of bush, such as George declared he had pa.s.sed through at the time he was deposited in the "hole." When the bottom of the ravine was reached he turned to the right, working his way diagonally up the hill.

George, on the other hand, made for some bush ahead of him, which looked familiar, but in this he was disappointed, and going to the left, considerably farther down the hill, was rewarded by the rediscovery of the "hole." Without waiting he fired a shot, and to his surprise found the Professor within a hundred feet.

"I have found it. See, that is the place I went through."

Harry was not far away, and he rushed up out of breath. The bushes were swept aside and George went in, followed by the Professor and Harry. He had not gone five feet when he stopped.

[Ill.u.s.tration: _Fig. 19. Fig. 20. Luxurious vegetation around stone and hole._]

"This isn't the place. There is a big rock here; not a hole."

This was indeed the case.

George's countenance was a study. The Professor and Harry had a good laugh at the discomfiture of George.

"So you think you fell into a hole? It must have been a pretty solid hole." The rock was about ten feet across, and flat on top, and the bush grew all around it, thus entirely screening it from observation.

"Well, we must try again."

"I would like to know why vegetation acc.u.mulates around a stone, or around a hole, and gets so much larger than at other places?"

"It is accounted for by the little germs we talked about the other day.

Did you ever notice the musty smell that comes up from an overturned stone?"

"Yes, and I have often wondered what it was."

"There is always more or less moisture under the stone, so that the germs are readily bred, and as they form carbonic and nitrogenous gases, which the plant must have, you can readily see why vegetation thrives around the stones."

"But where there is a hole it is drier, and the same thing occurs there?"

"That is a good observation. Two things are required to cultivate the germs, aside from the food. One is moisture and the other is heat. The earth is full of bacteria from which plants get their food; some places the bacteria go down only one or two feet; at other places, where it is warm, as in the tropics, they have been found five or six feet below the surface. When a hole is made, and the sun strikes it, the bottom of the hole gets warm, and thus facilitates the growth of the germs around the hole, so that the plants in the immediate vicinity get an extra supply of nitrogen."

"But where do they get the moisture?"

"That is another one of nature's great surprises, and shows how every contingency seems to be provided for. I suppose you have both cultivated corn--that is, have gone between the rows with a cultivator, and stirred up the earth. You did this, as you were told, to keep down the weeds.

That was one reason, but it is not the princ.i.p.al one. A dry crust forms over the surface of the ground, owing to the heat of the sun. When the cultivator breaks up the crust the heat from the sun draws up the moisture from below, and you are therefore watering your corn, and what is more, you are breeding bacteria so as to supply food for the plants."

"After learning this I am glad we discovered the stone."

A more persistent search was now made, and George's "hole" was really found to exist. It was just as he described it. Everywhere along the hillside were rocks projecting out from the surface, but here was a depression, or hole, fully fifteen feet square, with rocky sides, the wall on the upper side of the hill being fully fifteen feet high, whereas the lower margin of the hole had a wall not over four feet high, so that it will be seen George had no difficulty in getting out after he had recovered from his fall.

The Professor was in the hole in an instant. The growth about the depression was so dense that it made the hole dark, but there was an unmistakable odor of asphaltum. Some of the overhanging branches were trimmed off, and every portion of the walls examined.

"What do you think made this? Was it washed out?"

"Some one dug this hole," was the Professor's response.

"What makes you think it was dug out?"

"There is plenty of evidence to show that. Look at the marks of tools on the walls all about you."

"Do you suppose it was made to get oil?"

"No; but to get metals."

"What kinds, do you think?"

"Gold or silver; most likely silver."

"Do you think we have silver here?"

"Unquestionably; we have some samples of it at the Cataract now."

"When did you get it?"

"At the time we found the lead ore. Silver is usually a partner of lead, and from my examination of the samples we have it is rich in silver. It is likely that the indications of lead and silver all along this ridge attracted the attention of a mining engineer, and this was a test hole in prospecting for the ore."

"But if this hole was dug out, as you say, where did they put the dirt and rock which came out of it?"

"Examine below and you will see."

Below the hole the side was rather steep, but when the surface of the hill was examined there was no longer any doubt of the human agency which made it.

It was with a certain sense of joy that the boys heard this news. The island had been explored by white people; it might again be visited by some wanderers on the sea. This was a comforting a.s.surance. It had the effect of giving new courage, as no other event had, since they reached the rocky sh.o.r.e during that tempestuous night, nearly eight months before.

"Don't you think we can get kerosene here?" was George's inquiry.

"I do not think it is likely. What we see here is a mere trace of surface oozing, found in many places, and it generally indicates petroleum at some depth, but whether in sufficient quant.i.ties to pay cannot be determined without boring."

George's hope of a better light faded.

Under the direction of the Professor the balance of the day was spent in gathering samples of minerals, and George, in one of his searches, brought a sample of very peculiar greenish ore, interlaid with patches of brown substance. The Professor was much delighted with this.

"You have found a fine sample of zinc, and if you direct us to the place we must take a quant.i.ty of it. I have been specially looking out for samples of this."