When I was a kid, I got my hands on a copy of C.B. Colby's book of "hair raisers and incredible happenings," called Strangely Enough. I believed every story in it about "oddities in science and nature," "buried treasure on land and sea," and "high adventures and impossible escapes."
The most memorable story was about a fellow who had spent the day exploring a cave near the beach on an island in the Caribbean while on vacation. He found a bunch of clay balls in stashed in the back of the cave. Some were pea sized, and others were the size of golf balls. He filled his pockets with the balls, and then left the cave and started walking along the beach. For fun, he tossed all the balls into the ocean. When he arrived back home in United States, he discovered that one of the clay balls was still in his pants pocket. He broke open the ball and discovered a precious jewel inside. (I haven't read the story for decades, so I probably screwed up some of the details.)
Of course, looking back, I realize that the stories are just recycled urban legends. However, Colby has a fan base of people like me who enjoyed his books when they were growing up. The website Artifacts and Talismans has an appreciation of C.B. Colby and his writing.
Paperback copies of Strangely Enough can be had for 1 cent on Amazon.