Shales are often found with layers of sandstone or limestone. They typically form in environments where muds, silts, and other sediments were deposited by gentle transporting currents and became compacted, as, for example, the deep-ocean floor, basins of shallow seas, river floodplains, and playas.

The most difficult to recognize is the paraconformity where horizontal sedimentary rocks are above and below the contact—there can be scant visible evidence of a hiatus when identical rocks are above and below.

Types

• Disconformity.
• Nonconformity.
• Angular unconformity.
• Paraconformity.
• Buttress unconformity.
• Blended unconformity.

Shale is a fine-grained rock made from compacted mud and clay. The defining characteristic of shale is its ability to break into layers or fissility. Black and gray shale are common, but the rock can occur in any color.

The principal gold-bearing stratum is supposed to be the Benton group, including the Ostrea shales and the Blue Hill shales. It is stated that these rocks over practically the whole of the areas in which they occur contain more or less gold and silver, though the metals may be rather irregularly distributed.

Oil shale is a sedimentary rock. As it reaches its oil window, oil shale releases a liquid known as shale oil. Oil shale is the rock from which shale oil is extracted. Shale oil is similar to petroleum, and can be refined into many different substances, including diesel fuel, gasoline, and liquid petroleum gas (LPG).

Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. Slate is not to be confused with shale, from which it may be formed, or schist.

Another environmental disadvantage to extracting shale oil is the enormous amounts of freshwater required. Water is necessary for drilling, mining, refining, and generating power. Some experts estimate that three litres (. 8 gallon) of water are required to produce just one litre (.

Shale forms in very deep ocean water, lagoons, lakes and swamps where the water is still enough to allow the extremely fine clay and silt particles to settle to the floor. Geologists estimate that shale represents almost ¾ of the sedimentary rock on the Earth’s crust.

In the construction business, shale is an excellent rock to build a foundation on because it’s so strong. Plus, it’s compact enough to endure a structural piling without cracking, unlike clay.