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142 "And see, here are some cog-wheels and a lot of old shafting."

"Machinery, and quite some of it, too," murmured Dick. "They must run a regular factory of some sort here."

"I think I have solved the problem!" cried Fred. "I've read of this a number of times. This Sack Todd has a secret process of manufacturing some article and he doesn't want anybody to learn what the process is. So he has established himself here and sworn all his workmen to secrecy."

"I've heard of that myself," said Tom. "A man had a certain process of tanning leather. He kept his secret for years, until a workman got mad at him and gave the thing away."

Dick was inspecting the machinery with care. It was worn out and rusted, and hard to make out just what it was.

"Unless I am mistaken, these are parts of a printing press," said the eldest Rover.

"A printing press?" cried several of the others.

"Yes. But that doesn't solve the mystery of what the press was used for."

It was damp and unwholesome in the cave, and they were glad enough to leave it and come out into the sunlight once more. They walked back to where they had left their horses, and here