About 50 years ago I found 2 clay marbles that actually have clearly viable finger prints in them. I don't have a clue on how to date these things and I still have them in an old jewelers box. I do know that the area I found them in was a well used Native American camp site close to the Monongahela River in Allegheny County.
my grandfather dug footers for garages for around 35 years. i have some money for sure in the thousands of marbles he found and gave me. i will never forget him coming home from work and me always waiting with my hands out.
i had a jewelry shop go through just one box and told me he would give me 800 for the entire box but he was really only interested in 4 of them. they were bigger marbles.
i did some research and put them on ebay and they sold for 1100.