During this interval their eyes gradually became accustomed to
the lamp-lit darkness, so that they could see much better than at first.

In a few minutes their young guide returned, leading Harry Mule, whose
swinging collar-lamp and wondering expression struck Miss Nellie as so
comical that she could not help laughing at him.

"Haw! he-haw, he-haw, he-haw!" brayed Harry Mule, in answer to the
unaccustomed sound; and at this greeting the girl laughed more heartily
than ever.

The mule was hitched to the car, Derrick sprang in front, cracked the
whip that had hung about his neck, and they started on what, to two of
them at least, was the most novel ride they had ever undertaken.

When they reached his stable Harry Mule stopped short and refused to go
on.

"What is the matter?" asked Miss Nellie.

"I expect he wants us to go in and see his house," answered Derrick.

"Why, I never heard of such a funny mule. Do you suppose he knows we are
visitors?"

"Of course he does," answered the boy, gravely; "and he knows that
visitors always want to see the mine stable."

So they all went in to look at it. In the long, low, narrow chamber,
hewn from solid rock, were thirty stalls. Several of them were occupied
by spare mules, who turned an inquiring gaze at the visitors, and
blinked in the light of their lanterns. At one end were bales of hay and
bags of oats, while just outside the door stood a long water-trough,
which, as mine water is unfit for use, was supplied from above-ground
through iron pipes brought down the slope. In spite of living in a
continual midnight, so far from pastures and the light of day, which
some of them did not see from one year's end to another, these mine
mules were fat and sleek, and appeared perfectly contented with their
lot.

Apparently satisfied that justice had been done to his place of abode,
Harry Mule offered no further objection to moving on, when they again
got into the car, and the stable was quickly left behind.

By-and-by Derrick called out "Door!"

As it opened for them to pass, and Paul Evert recognized his friend, he
cried, "Oh, Derrick, Socrates--" Then seeing the visitors, he stopped
abruptly, and stared at them in confusion.

"Never mind, Polly; we'll be back pretty soon," shouted Derrick, as the
car rolled on, "and then you can tell us all about it."

"What did he say?" inquired Mrs. Halford.

"I didn't quite understand," replied Derrick; "but, if you don't mind,
we'