"There may be fissures in the earth, or portions less dense than others which, by the general disarrangements of the adjacent parts, and by the enormous pressure exerted by the force of gravity, are contracted, and the movement causes such friction and intense heat as to liquefy the rock. In doing so a large amount of gas is evolved, the movement of which causes the disturbance of the earth's crust, which manifests itself to us in the form of earthquakes. At the same time the confined gases seek an outlet, which they find at the weakest part, and the volcanoes spout forth the lava, flame, and gases. There is an undoubted connection between earthquakes and volcanic eruptions. Earthquakes usually precede volcanic action. This internal combustion is going on at all times, and is only more violent at some period than at others. The lava in the Crater of Stromboli has been in a liquid state for more than two thousand years."

"Before we left home I saw in a paper that some scientist described the kind of rock and other matter which was seven miles down in the earth."

"Was anyone ever down as far as that?"

"No; a little over a mile is as far as man has actually penetrated the earth."

"Then, I should like to know how geologists can tell with any certainty what the rock is like several miles down?"

"That is known just as positively as though a hole had been dug down that distance."

"I don't see how that is possible."

"I am going to make you a sketch which you can examine at leisure, that will show how he knows. a.s.suming that the earth has a crust--that is, the outside or cooled part, let the first sketch (Figure 10) represent this crust, before the mountains and valleys were formed. The slightly curved horizontal lines merely represent the different layers of the crust, such as rock, clay, coal, slate, and the like. When the cooling process took place the earth grew smaller within, so that the crust was forced together.

[Ill.u.s.tration: _Fig. 10. NORMAL CRUST OF THE EARTH_]

"The second sketch (Figure 11) shows this crust forced together, so that when the upheaval took place, two mountain ranges, A and B, were formed, with a valley (C) between them, and the broken lines (D), where the crust separated, were exposed, and by that means examinations can be readily made way down into the crust, without ever leaving the surface of the earth."

As it was understood that the boys should take at least a day each week for hunting, particularly since such sport would develop expertness in the use of their weapons, an early start was made on the day selected, which was within a week of the time they returned home.

Ever since the disappearance of the boat left at the falls in South River, there was some anxiety on that score. It was a frequent topic of conversation, and after they left home it was by a mutual impulse that they wended their way south, taking a trail which was now familiar to them.

"See here, Harry, I should like to go to the place where I discovered South River, and where I had the experience with the snake and the strange animal, which frightened me so."

[Ill.u.s.tration: _Fig. 11. MOUNTAIN UPHEAVAL_]

"Then we must go to the left, because, you remember, you came up between these hills, and crossed the stream where I found you."

It was about three miles across from the Cataract house, but less from their original home. When they reached the river the surroundings were very much unlike anything George had seen before, and he could not identify the place where the ramie plant had been found.

The ocean could be seen plainly from their position, and George thought they were too far east, which proved to be the case.

"Here it is, Harry; here is a low place, and you can see the ramie plant all about here. I am sure of it."

"Is this the place you lost the hatchet?"

"So I did: I'll show you the place." But he failed to find the hatchet.

Subsequently Harry stumbled across it, but it was found some distance from the place where George declared he lost it.

"Let us try to cross the river. We can do it if we find a couple of logs."

At a bend of the river they found a lot of driftwood caught in the roots of a tree, and after some work a number of pieces were cut and laid crosswise on each other.

After the experiences of several expeditions of this kind, to say nothing of the exploring trips, the need of the bolo and ropes impressed itself on their minds. They were never without them.

The river at this point was fully one hundred feet wide, but by the aid of long poles the raft was not long in making the trip. After properly securing it they took up their weapons and at once made a dive for the interior.

The trees were fairly thick, and before going very far Harry checked George with the statement that there was game ahead, as he had heard rustling sounds in the leaves.

Both were now looking forward intently, expecting and hoping that some game worthy of attention would appear. Whenever they stopped, the animal, or what it was, would stop, to resume its motion whenever they moved. This was getting to be decidedly interesting, and at the same time trying to the hunters. The distance was fully a mile from the river. The noise which came from the slight rustling of the leaves and the occasional breaking of a twig was growing acute.

"Are we hunting or being hunted?" said George, under breath.

Not forgetting the Professor's story of the hunter's careful scrutiny of leaves, they adopted that plan, but it gave them no clue. Whatever it was, it was in front of them, but they were unable to get a glimpse of it.

Once, by agreement, they stopped and were silent for several minutes.

The silence was just as profound and continued as their own. It was getting tense, when George hit upon a plan.

"Let us be quiet for a minute or so, and then suddenly bound forward and give a whoop. I think that will frighten him, and enable us to sight him."

"Before doing that get the guns ready for a shot, and don't fire too soon. Don't get excited. Remember the Professor's warning; a shot close at hand, deliberately aimed, is more positive than a dozen shots excitedly fired at a distance."

When all was ready Harry whispered, "Now!"

With a whoop both started forwardly on a run as fast as the dense underbrush would permit. Before they had gone twenty feet a large leopard-like animal sprang transversely across their path, then, seeing the boys, crouched for a spring. The guns were c.o.c.ked and ready, and it is a wonder that in the excitement there was not a premature shot.

"Now, steady," said Harry. "Aim, fire!" and the moment both shots rang out. Harry cried excitedly, "Now for the other guns!"

The other guns were not necessary then. The animal gave a savage growl and bounded to the left, and after they had time to recover, both moved toward the spot.

"We have hit him, sure," was George's exultant shout. "See the blood on the leaves. My! he was as big as a lion!"

"Let's follow him," was Harry's determination. And off they started, the blood tracks plainly showing the way. Not a further view was obtainable of the animal, and in less than a quarter of a mile all blood traces disappeared, to the chagrin of both.

They directed their steps toward the river, but within two hundred feet of the spot where they had last stopped, George stepped back and cried: "There he is now, right ahead of us."

"Let us be careful now; he may be angry." There was no alternative but to fire. The shots were almost at the same instant, and to their great relief the animal, after a single leap, fell down without a groan.

The approach was cautious, because experience had not taught them whether it was safe immediately to make an examination of the body.

After some hesitation they went up closer, and when all doubts as to his death had been dispelled a careful examination was made.

They found only a single shot wound between the shoulders.

Here was a dilemma, surely enough. The river fully a half mile away, if not more, and the brute too large to carry, made them hesitate about attempting to skin it in the absence of the Professor.

"I wish we knew what kind of an animal it is. We had better go home and bring the Professor back with us in the morning."

So taking note of the surroundings, to familiarize themselves with the location, they hurried back to the river, and rafted themselves over.

The Cataract home was reached about four o'clock, after one of the most adventurous days spent on the island, although, in some respects, not as exciting as their earlier experiences. They had begun to be veterans.

They were not merely boys.

Naturally, the Professor heard a stirring tale, and when it was all told over and over again, he told them he thought that undoubtedly the region beyond the river would turn out to be their hunting preserves, a statement which the boys did not forget to profit by, as we shall see later on.

"I wonder why we haven't seen more animals north of the South River?

There have been very few in this section," was George's observation.

"Undoubtedly the mountain region affords them safer retreats, and it is one of the things which indicate to me that we shall find that section very wild, and when we are in shape to do so may be able to have some interesting and exciting times in that part of our domain," was the Professor's response.