Sounds like you got punked by some great-great-grandpa with a bad sense of humor and worse directions. Nothing like following an "X marks the spot" scrawled in fancy script only to find a former swamp. Bet that journal writer was just really, really into composting.
Digging through that muck based on some old guy's fancy script is a special kind of family adventure. Bet you spent hours knee-deep in swamp water only to find a bunch of wet leaves. That great-great-grandpa definitely had a compost obsession he passed off as treasure hunting. At least you got a good laugh after all that mud.