h
the altar, about which such grisly memories clustered, eagerly began to
carry out these orders, while Coyote Pete seated himself on the side of
the summit overlooking the travelers' camp below, and amused himself by
throwing small bits of detached rock down at the unoffending One Spot,
Two Spot and Three Spot.

The base of the altar being duly measured and recorded, Jack, tape in
hand, followed by the others, clambered up its rough sides, which
afforded an easy foothold, for the purpose of ascertaining the
dimensions of the top. To the lad's astonishment, however, there was
no summit. That is to say, the altar was hollow.

The professor exhibited considerable scientific excitement on hearing
this. The man of science had been greatly puzzled over the total
absence of any traces of the human sacrifices he knew must have taken
place there. He now hailed Jack eagerly.

"Are there not some bones or traces of sacrifices inside it, my boy?"
he inquired excitedly.

"Nary a bone," shouted Walter cheerfully.

"Hold on, though," cried Jack. "There are some queer-looking things
down in one corner."

Lowering himself inside the altar, he made for one corner of the
erection, in which he had spied a heap of fragile-looking bones of some
kind.

"Skeletons of snakes!" he cried, holding up one of these for the
inspection of the professor, who had by this time hoisted his bony
frame over the top of the altar and now stood beside them.

"That's right, my boy; they are serpents' skeletons. Doubtless in
their sacrificial ceremonies these people also offered up rattlesnakes,
which seem to have been a sort of sacred reptile among them; much as,
in a sense, the cat was sacred to the ancient Egyptians, and the python
is worshiped in certain parts of India."

"But, professor," protested Jack, "if, as you say, numerous human
sacrifices were offered here in the past, why do we not find any human
remains here?"

"Who can say, my boy? Many of the habits of these pre-historic peoples
are veiled in mystery. We can only surmise and reconstruct. They may
have burned them or disposed of them in some other way."

"Say!" exclaimed Ralph suddenly. "This floor sounds to me as if it was
hollow; maybe there's a chamber or something underneath."

The boy, who had been stamping about with a vague sense of making some
such discovery, hailed them with excited looks.

"Hollow, you say?" asked the professor, with every appearance of deep