Back in the Jurassic Period, dinosaurs walked through a faulted rift valley caused by the split of the supercontinent of Pangea. It was warm and often rainy with many streams and lakes. Somewhere along one of the many streams, blocks of hard mud from a former lake bed fell into the rushing water. The mud blocks tumbled, became round, and soft and sticky on their outsides. As they rolled downstream they picked up sand and pebbles from the stream channel. This became the armor.
Now, quick burial (deposition) is needed before the balls dry, crack, and crumble away. These rare sedimentary forms were buried, and eventually turned to stone and preserved in the late Triassic and early Jurassic rock formations exposed in adjacent areas of Turners Falls, Greenfield, and Deerfield, Massachusetts. The pictured AMB is from Turners Falls and is 3 inches long. It is a bit squished by being buried under several thousand feet of sediment before it and its sandy surroundings became a hard rock. The geologic formation is the Turners Falls Sandstone, early Jurassic Period, Mesozoic Era.
Armored mud balls (AMBs) are very rare in the geological record. There are only about 10 sites in the world where lithified (turned to stone) armored mud balls have been found. While quite a number have been seen deposited in stream beds, particularly after floods, these will probably not be preserved in the geological record. They need to be quickly buried and then, over time, lithified. Then, of course, the lithified AMBs have to be exposed by erosion, such as along a river or coastal cliff, or on a hill or mountainside, and next, someone needs to find them.
The only armored mud balls in the world that you can easily see are in Franklin County, western Massachusetts! All others are in rocky outcrops on mountain sides or other remote locations.
Greenfield Community College. GCC has the best collection in the world thanks to the discovery of AMBs in Turners Falls by Prof. Richard Little in the 1970's. His collection from the Connecticut Riverbed outcrops and local quarries consists of large outdoor specimens of conglomerate with AMBs in the Geology Path (S. end of Main Building (brick) plus indoor display cabinets in the geology lab (room N 350) hallway.
Beneski Museum at Amherst College.
Unity Park, Turners Falls.
To discover more consult Prof. Little's "Dinosaurs, Dunes, and Drifting Continents" or "Exploring Franklin County" books. The "Flow of Time" DVD also discusses AMBs. These resources are available on this web site, see Publications Order Form page for details.