It was a hard thing to be discreetly silent until their opportunity for thorough search came, and fortunate that they had not long to wait. That very afternoon it rained and most of the boys stayed in camp. Chick-chick was still away on some mysterious errand. Glen and Apple appeared clad in bathing suits and tennis shoes.
With the lighted lanterns they could get a better idea of their surroundings. Page 211
"We don't mind the rain," Apple announced. "We are going out. Look for us when you see us."
They had already cached a couple of lanterns, a pick and two spades near the Ice Box and it was no trick at all to get them into the cave. With the lighted lanterns they could get a better idea of their surroundings. The floor of the cave was waist deep in water which seemed to rush on in a swift current and escape again into the creek through a counter opening a few feet away. The cave was quite long. It did not, as they supposed, have its beginning at the opening where they entered, but extended some distance back into the gloom, and as the current was quite swift back there it was evident that there were other hidden openings. The vault of the cave was high, so high that they could not see the top by the feeble light of their lanterns. But the thing that they could see and that thrust from their minds every other subject was a solid arch of masonry.
"I was right!" shouted Apple. "I was right! That's no natural formation. That has been built up by men's hands years ago. It's sure to be the hiding place of the treasure. What else could it be?"
"It couldn't be anything else," agreed Glen. "We'll mighty soon see. Get up to the top and I'll hand you the things."
"I'm up," said Apple. "Are you coming too?"
"Sure thing. The way to tear this down is a stone at a time beginning at the top."