An important feature of many sedimentary rocks is that they are layered, as shown by the sandstone above. Looking at that picture you can visualize that when the parent material (the original sand in this case) was deposited about 4400 years ago during the Biblical worldwide flood. As the floodwaters receded back into the earth at the end of the year, leaving mud and sand in these shapes all over the world to turn in time into Sedimentary rocks.

Layering in sedimentary rocks isn't always as obvious as in the picture. Often the layers are much, much thicker and typically they have been distorted -- squeezed into curves or tilted at crazy angles, for instance. Limestone created by the regularly proceeding chemical precipitation of calcium carbonate onto the ocean floor may not show apparent layering at all.

KINDS OF SEDIMENTARY ROCKS

Here are the most commonly encountered sedimentary rock types:

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  Sandstone: As seen above. Basically sand grains cemented together, which may have been deposited as sand dunes, sand bars, or washed into the sea; that's a genuine sandstone rock as seen above.

• Shale: composed mostly of tiny clay particles of the kind found in mud, much smaller than sand particles, so shale is smoother than sandstone

• Conglomerate: composed mostly of rounded, water-worn, cemented-together pebbles much larger than sand grains; the pebbles are usually of quartz

• Limestone: composed of calcium carbonate (calcite), which may have been chemically precipitated in the sea, or else deposited by living organisms in the sea; often contains fossils of sea life

• Dolomite: like limestone, except that it has more magnesium in it

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  Coal: As you see above, coal is black. It is composed of the remains of plants and animals living before the Biblical world wide flood. Often you can find fossils in coal such as those in the photo. The bottom chunk of coal, as well as showing two long, slender fossils, displays a yellow crust, which is sulfur. Coal, especially that mined in the eastern US, contains so much sulfur that when it is burned the sulfur in the smoke forms sulfuric acid, which, unless removed by scrubbers at the power plant, contributes greatly to acid rain. Three general categories of coal are recognized. From softest to hardest, they are: lignite; bituminous, and; anthracite.

CONCRETIONS

As seen above. Have you ever mixed oil and water, and noticed how droplets of oil joined together to form larger and larger droplets? Something a little like that happens when sand, mud and general muck is deposited, then sits around turning to rock. Sometimes inside the sand, mud or muck certain chemicals come together like oil droplets in water, and as the sand, mud or muck turns to rock, so do the chemical concentrations. The result may be that the chemical concentrations become concretions embedded in the rock, such as those shown above exposed in a rock wall.

Don't forget that fossils are often found in sedimentary rocks. Billions of dead things buried in the mud during the worldwide flood as recorded in the Bible. Quite straightforward really.