the case, but the broken up character of the sides and floor
prevented them from readily grasping the formation. After making a jog
the cave again turned into the cliff, practically on a line with the
opening section or mouth of the cave. It was dark at first, but now, for
some peculiar reason, it grew lighter as they advanced, and finally
George stopped.

"What makes that peculiar light?"

"It is not a light; it is merely white walls and ceilings."

"What causes it?"

"Carbonate of lime, or chalk, which is caused by lime water coming from
above and trickling down through to openings or crevices, and leaving
the deposits there. It is not an uncommon thing in caves, and I
foreshadowed it in the cave when I stated that the rocks were of
limestone formation. You will remember we made lime from this kind of
rock."

A loud splash and a groan-like noise put further conversation at an end.
"What was that?" asked George, as he retreated. In doing so he tripped,
and, in falling, the light he carried was extinguished as it flew from
his hand.

Clearly there was water ahead. "Let us go forward, a little closer,"
said the Professor. "You might get your guns ready, in case of
necessity."

Within thirty feet of them was the edge of water, and the light threw a
beam beyond for a hundred feet or more.

"It seems as though we have reached the end of our explorations here."
As they looked, the water was agitated, and it was plain that some
aquatic animal was within the cave.

To return was the only thing to do, and as they went back the sides of
the cavern were examined, and the Professor took a number of samples, as
he said: "Don't lose the candle until we get where we can see daylight.
Although we are not more than two hundred feet from the mouth of the
cave, the remarkable bend or jog near the mouth of the cave makes it as
dark as though we were in a thousand feet."

"What sort of animal do you suppose that was?"

"Possibly a sea lion, or a seal."

After the open air was reached the Professor said: "I do not see how
this cave would account for the phenomena that George saw the other
day."

"Why not?"

"The cave is too deep. It is not a true air pocket, and----"

"What is this? Here is another one, still larger, and lower down. Here,
hold the candle." Harry was down in an instant.

"Probably this is what George saw."

True enough; it was an air pocket which extended in about fifty feet,
and had no passageway be