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Sandstone
As its name implies, sandstone consists of sand grains that have been compressed over time into rock. Sandstone forms wherever deposits of sand are common, including current or former beaches, deserts, deltas and flood plains. Often deposited along with those grains of sand are the remains of animal and plant life. Sandstone, however, usually is too grainy to preserve any but the coarsest of fossil impressions.
Shale
Just mud turned to stone, shale is composed of tiny bits of clay, mica and grit deposited by water and gradually hardened into a rock that is much smoother than sandstone. The tinier particles forming shale more faithfully conform to the hollows and ridges of organic remains and their traces, including animal tracks and burrows, thus preserving a more detailed fossil. Shale sometimes includes fossilized evidence of soft body parts, not just the skeletal remains found in other sedimentary rocks. Some more famous discoveries of fossils preserved in shale include the exceptionally detailed ones found in the Burgess Shale site of Alberta, Canada, and the Green River Shale site in Wyoming and Utah.
Limestone
Although classified as a sedimentary rock, limestone can form chemically from the precipitates of calcium carbonate in fresh and marine waters and from the evaporation of water that produces stalactites and stalagmites in caves; however, the most common type of limestone and the one that contains the most fossils, is sometimes called a "biological" limestone. A hardened composite of tiny bits of algae, coral, shells and fecal matter, biological limestone forms in shallow marine waters. The limestone deposits in Solenhofen, Germany, are famous for exceptionally preserved fossils of life from the Jurassic period.
Coal
Even called a "fossil fuel," the coal burned to produce energy today is composed of the remains of plant life from millions of years ago. Plants died and accumulated in thick layers at the bottom of swamps, where oxygen-deprived waters did not allow normal decay. The plant debris was then buried beneath layers of sediment carried to the swamps, often by flooded streams and rivers. The weight of these burying layers gradually hardened the plant debris into seams of coal. In rock form, coal is mostly sulfur and classified from softest to hardest, as lignite, bituminous and anthracite. Impressions of these long-ago plant life specimens sometimes are fossilized in the rocks.