1st - Notice this is your very first post - so, Welcome Aboard! You didn't list your state (or country) in your profile. So, you might consider jumping over to Sub-Forums: Select Your Area.... and selecting your state for information (i.e., clubs, hunts, finds, legends, maps, etc.) directly related to your state (or country).
2nd - I moved your post over to here (Forum > Our Discoveries > What Is It?) where it will get more ID traction.
3rd - As other members suggested - it sure does look like King George III coin...