The shooting evidently was taking place at the spot where they had
left Ben to guard the ivory.

Muley-Hassan! was the first thought that shot through Frank's brain.

The next minute, however, he dismissed the idea as absurd. The
Arab, even by the swiftest marching, could not have reached the Moon
Mountains in such record time unless he also had an air-ship, which
Frank knew was impossible.

As the ship soared higher and rushed straight as an arrow through
the air to the ivory cache a strange sight was revealed to the two
young voyagers. High up on the mountain-side they could see Ben
struggling with what appeared to be dozens of naked savages. The
boys could see his gallant resistance as he swung his clubbed rifle
again and again at his savage opponents. Several of them lay dead
on the ground about him, but those that remained were attacking him
with what seemed demoniacal fury.

"Good Lord," gasped Frank, "what on earth can have happened?"

"They're cannibals!" gasped Harry.

"No--no," exclaimed Frank hastily, "they're--give me the glasses
quick, Harry--that's right--I thought so. They're not savages, but
worse almost."

"What do you mean?"