our cave, and measure off 50 feet. Stop there. You see, I have
marked the line A and have laid down the slate slab so that this line is
exactly on a line with the one you have measured along the chamber. The
point B, 50 feet from here, which you have just measured, makes an
angle, C. I will now take the slab to the point B, and you may measure
off 50 feet more, and we will call that D. That gives us another angle
line, E. You see, at every point we establish a new base line. C is the
base line for the line E, and so on all through the cave."

[Illustration: _Fig. 32. The Cave, and how it was charted._]

All the measurements were made on the plan outlined, and scratched on
the sooted slab.

"One thing more we must observe. As we are marking the successive
points, you will notice that I took particular care to observe the side
walls of the passageway, so that I could roughly outline them, noting
the distances from the various points, and in a crude way marking out
the irregularities between the points."

The chart interested the boys so intensely that the disappearance of the
light did not again recur to them until they emerged from the mouth of
the cave, when it all came back again, with added wonder and
speculation. How many more mysterious things would present themselves!

CHAPTER XIII

THE EXCITING HUNT IN THE FOREST

They returned to their home with conflicting emotions. It had been an
eventful day. They had a glimpse of the outside world, and an experience
below the surface of the earth. Both were unsatisfying. They could
explain the one far away on the sea; but the other, close at hand, was a
mystery.

"How do you account for the water being so far away from the mouth of
the cave?" was George's inquiry after the evening meal.

"Haven't you noticed that we have had no rain for the past five weeks?"

Such was, indeed, the case. The boys had not been observant, like the
Professor.

"Evidently the water is supplied from rains, and the floor of the cave
permits more or less of the water to leak through, so that, in time, if
we had no rains, the cave would be entirely free of water."

"But how about the animal in there; if it is a water animal, how did it
get in; and if the water ever dries up, how can it live there?"

"There may not be any subterranean connection directly with the sea, and
the animal has been trapped there; or it may be able to reach the sea in
the cave at any time, by some underg