Paul Drez had some interesting notes on fossils that don't belong where they were found. Here are some more paleontological sources of contamination: (1) Quarrying. Sandy shell material from the Sarasota pits is widely used as fill in southern Florida. Well-preserved Pliocene and Pleistocene shells can turn up on driveways, improved dirt roads, harbors, and building lots. (2) Dredging. Modern and fossil shells often turn up in dredged material from rivers and offshore deposits, as collectors are well aware. People flock to gather shells (and shark teeth) whenever offshore sand is pumped onto beaches in South Carolina. (3) Natural erosion occurring today. Rivers and tidal channels can be deep enough in places to erode Miocene and younger shells and mix them with modern shells. This is very common in Florida, Georgia, and South Carolina (USA), for instance. I have also collected Pleistocene shells that were washed up on the beach of Dauphin Island, Alabama, where erosion is taking place on the seafloor. In practice, paleontologists often find rocks and fossils out of place (called "float"), and trace them upstream or upslope back to the source. The famous Burgess Shale was discovered from black shale "float" that had fallen down the slope of a mountain in British Columbia. (4) Natural erosion occurring in ancient times. Storms often mixed ancient and contemporary shells together on the seafloor, so, for instance, shells from the base of the Tertiary often contain an admixture of latest Cretaceous shells. Paleontologists therefore use the youngest fossils from the mix to determine the true age of the deposit, not the oldest ones. Glaciers moved vast quantities of material for hundreds of miles across northern North America, Europe, and elsewhere. Boulders with Cambrian fossils have been moved from Scandinavia to Germany and Poland, for instance. (5) Mixing of shells in collections. A few months ago, Conch-L hosted a discussion on shells that jump from tray to tray when a drawer is jerked or a cabinet is tilted. The owner may not always be aware of this. It's no wonder that many paleontologists prefer to collect their own material when they can. Andrew K. Rindsberg Geological Survey of Alabama Tuscaloosa, Alabama, USA