He gazed at it until he was sure that if he ever saw a similar auto tread again he would recognize it.

“That just goes to prove that Dad was right,” said Joe. “Probably I’ve seen auto tires like that often, but I’ve never noticed the markings, and now that I do notice one in particular it seems strange to me. But I wonder what an automobile was doing in here and how it came to get here in the first place!”

However, he gave the matter little further thought and retraced his steps through the woods until he returned to the other boys, who were getting dressed after their swim.

“I thought automobiles weren’t allowed in Willow Grove,” he said casually to Chet Morton.

“Neither they are. You have to park just inside the fence.”

“Well, somebody brought a car right down into the grove.”