A weathered sign in the Minnesota River Valley proudly proclaims: “World’s Oldest Rock.” Erected in 1975, it marks a 3.8-billion-year-old gneiss — or so scientists thought.

It's been a dream of mine for a long while to find Pudding Stones! Pudding stones are a type of sedimentary rock known as conglomerate. These Pudding Stones are conglomerates that have been ...