“On a little farther,” Dr. Rander said, urging the mules to ascend the difficult slope.
At last they came to a place where a high rock protruded far over the river. Here the old explorer called a halt and pointed up the side of a mountain.
“In that little notch up there is the entrance to the treasure,” he said. “As I said before, there is a huge cave that occupies the entire mountain. There we will find the treasure, if there is any.”
The youths’ hearts beat rapidly. They could hardly believe that at last they were nearing the great secret.
“But,” hesitated Bob Holton, “how are we going to get across this roaring river?”
“That,” the old explorer returned, “will be the most difficult part of our entire journey. Come. Let me show you.”
They followed him to the edge of a high rock that protruded far out over the seething rapids.
“Look there,” he said, pointing to something.
Stretching from the rock across the river to another protruding crag was a heavy metal wire, which, strange to say, showed not the slightest trace of rust.
“That cable was put there by the Incas,” Dr. Rander said. “It is hundreds of years old, but still looks as if it had been built but yesterday. It is coated with some secret preservative, which prevents it from rusting through.”