walking slowly, did not prove very
difficult, for the water had cut the bed in which it ran so straight
down through the lava that there was quite a well-marked angle, which he
could run his right foot along and make his way without stooping, save
at rare intervals.

As he went on with his eyeballs aching from the strong natural effort to
see through the darkness, his mind would keep wandering away to the
glory of the sunshine without, and how beautiful were light and life,
and how little appreciated till a person was shut off from their
enjoyment.

Travelling slowly on in this way for how long a time he could not tell,
he at last became conscious of the fact that he must be nearing the
place where they had turned off nearly at right angles and plunged from
silence into the deafening roar of echoes formed by the noise of falling
waters. For there it all was plainly on the ear, but as it were in
miniature, and Oliver stopped short, thinking.

"Shall I be doing wisely in going forward after all?" he said to
himself, and he hesitated as he thought of one of the main objects of
his being there--to try and let poor Wriggs know that he was not
forsaken and that help would soon be at hand.

"My voice can never be heard in all that din," he said to himself, and
before going farther he uttered a loud shout, and listened to the
echoes, one of which struck him as being so peculiar that he shouted
again with the repetition sounding even more peculiar.

His heart began to throb and his hopes to rise, for he felt convinced
that the "ahoy" was an answer to his call, and in a wild fit of
excitement and joy he said to himself,--

"It must be. Now, let's try if it is after all only an Irish echo."

"Ahoy!" he cried. "Where are you?"

There was utter silence for a few moments, and then he heard a cry
sounding so wild and strange that it seemed to freeze the very marrow in
his bones.

CHAPTER FORTY TWO.

A LONELY VIGIL.

Oliver was too much startled for a few moments to move or speak. Then
making an effort to master his dread, "It's an Irish echo," he said.
"Poor Wriggs, he is making his way towards me. Ahoy! this way."

"Comin' sir," came plainly enough now, but directly after every echo
seemed again blurred and confused like a picture reflected in agitated
water. But the sound was certainly very near, and each shout and answer
came closer, till at last the man's steps were plainly heard in a slow
shuffling fashi