Sedimentary rocks are formed when layers upon layers of old sediments from river beds build up. They eventually form a rock. This rock is typically the softest of all the rock types, and therefore the best rock to hold fossils. Igneous rocks are rocks that are formed as a result of volcanic activity. They are created when lava cools. These rocks are unlikely to hold fossils because they are too hard. Metamorphic rocks are rocks that started out life as a different type of rock. They were then subducted under the earths surface where extreme heat and pressure actually changed hem into a different type of rock. Fossils are unlikely in this type of rock because all that heat and pressure has made the rock very hard. Because of this, the most accurate answer would be: sedimentary rock.
