If your park is from the 20's and it has not been completely re-done with fill dirt,there is silver.I hunt a lot of NYC parks,some of them,even though they date back to the early 20th Century have mostly filled and yield only a few silver coins,some have not been extensively filled and yield a lot of silver.I'm working a park now that since early Sept. have given up 82 silver coins to me and more to my hunting buddy.I hunt with an Explorer,which I feel is silver magnet.