nts, one might make a guess; but every trace we have found is of
the last inhabitants."

"Well, that ought to do," said Chris.

"But I mean the pumas or jaguars that seem to have here and there turned
the cells into caves, and left their gnawed bones about. They may have
lived here fifty years ago, a hundred years, or five. But there is one
thing evident, and it is this--that the people who lived here chose the
place as being one that they could make into a stronghold, one which
they could fortify so as to defend themselves from their enemies."

"What enemies, sir?" asked Ned sharply.

"Ah, that I can't tell you. The people here must have been to a great
extent civilised, or they would not have been builders; and most likely
their enemies were wild Indian-like tribes who roamed the plains, as
they do to this day. I want to find something left by these builders,
and then perhaps we might learn something."

They had now come to the last of the long range of cells that they had
been making their way through, and further progress was checked by solid
rock which had evidently been neither chipped away nor added to.

They cautiously stepped through the front opening, to stand upon the
rough, crumbled-away terrace, from which they could look down into the
great depression where the ponies and mules were contentedly grazing,
and for about the tenth time looked upward for some means of reaching
the terrace above, one which appeared more time-worn and dangerous than
that upon which they stood; but without ladders it would have been
risking life to make any attempt to reach it.

"Strikes me, sir," said Griggs, "that we've left the way up far behind."

"Why?" said Wilton sharply.

"Because we've seen no way here, and we found one there."

"But _I_ could see nothing likely to lead higher," said Chris.

"We didn't look about much," cried Ned. "We were eager to come along
here."

"Yes, I suppose that was so," said Chris thoughtfully. "Well, there's
the row of cells above us, and there must be a way."

"Unless it has been swept off by some landslip," suggested Bourne.

"Well, we'll turn back now," said the doctor, "for even if we had a
shovel I don't think we should find anything that would help us."

They went back from cell to cell, and twice over found the terrace
outside sufficiently level and secure to allow of their passing along
it, but they soon had to take to the interior again with its low
doorway-like