1966 Cast Iron Leaping Frog Doorstop Garden Virginia Metalcrafters

this is 8 x 8,weighs more than 4 pounds, (4 pound 2.7 oz) it is marked on bottom 18-21K , VM , also dated with what looks to me to be 1966,but it could possably be 1956, it is mostly a grey green with a touch of black down the center