National Geographic : 2000 Feb
The Treasure PitThat Nearly Became a Garbage Dump Patches of oil shale are visible among the shrubs that reclaimed the pit after mining was phased out in the 1960s. For 90 years miners took the rock to kilns-where it was burned to pro duce hydrocarbons leaving a crater a thousand yards wide. The rock feels moist; it's 40 percent water and 15 percent de cayed aquatic algae. Dead algae rained to the bottom of the ancient lake after seasonal blooms, creating thin layers in the sediment. Work ers look for fossils by breaking open the layers like pages in a book. Most pages are blank; empty slabs are thrown onto piles (left). If a fossil is found, it's stored in water-the rock crumbles if it dries. To preserve fossils, preparators transfer them to epoxy resin, which makes many specimens look like they're stuck in glycerin soap.