Why are there more fossils in some rocks than others?
Igneous rocks are formed from molten magma so almost never contain fossils (occasional trees have been found) and metamorphic rocks have been heated and buried so fossils are destroyed. So fossils are essentially confined to sedimentary rocks. But they vary in fossil content as well. Why? Some areas have more life — limestones formed in shallow warm seas full of shells and corals and . . . can be almost completely composed of fossils. Shales formed from muds near the coast can also have lots of fossils. Greywackes formed by deposition from rapidly moving currents in deeper water have few fossils. Desert sediments have fewer sediments. Then there is the influence of preservation. Sediments at the bottom of the Black Sea have incredible preservation because the water is without oxygen so not only does nothing oxidize, there are no scavengers down there. Organic remains in muds are also preserved because there is no flow of water through the mud. Such matter in sands may be destroyed as
