One of my favorite places from which to collect fossils is a steep, high railway cut in a rural part of southern Kentucky, where a ridge made of limestone sat right across the most efficient route the railway could take. When that cut was first made, professional paleontologists and amateur fossil collectors came by to have a look at the newly exposed rock; but although the fossils could be seen, we could hardly get anything out because they were almost all too firmly locked within the rock. Within just a couple of years, weathering had caused some of the weaker, clay-rich layers to break down a little, yielding loads of fossils. The rock around the fossils broke apart into small grains, and the fossils themselves, skeletal remains of marine animals, could be picked up by the hundreds of thousands: crinoids, blastoids, brachiopods, screw-shaped parts of bryozoans, trilobites, individual cone-shaped corals, strange conical snails, even rare starfish.