Have you ever heard of the buried silver with this stamp in fayette county pennsylvania?
okay I work with a lot of silver so send me a few pounds of it so I can let you know if it is worth that much!
Take it to a reputable coin dealer -- he should be able to research it. Unless it's extremely rare it's probably only worth its melt value or a bit more, but you never know.
Do you not have Google? Punch in about half the words of your question and you'll likely have an answer.
I wouldn't worry too much about the history. Most Gold and silver in existence has been melted down hundreds of time over the past 5,000 years (really). What you really need to know is the actual silver content ratio. It doesn't matter if the purity is stamped on the side as 0.9999% pure. The purchaser has ways of determining actual purity very quickly and they will always check it.