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Fossil
purpose is to improve the levels of nitrogen and potassium in a soil. These two elements are vital for plant growth and high crop yields. (See also: Fertile soil.)
Fine-grained rocks
Any rock that is made mainly
of clay-sized particles. Shales and mudstones are the most common sedimentary rocks in the world, making up four-fifths of the sedimentary rock.
Flocculation
The grouping together of clay particles in a soil to make larger clumps that have a size closer to silt or sand.
Calcium is the key element needed for flocculation. It occurs naturally when there is sufficient calcium in a soil. Clay soils without calcium readily become
waterlogged. It is for this reason, rather than to increase fertility, that farmers with clay soils often add lime (calcium hydroxide) to their fields.
Flood basalt
An eruption of basalt that occurs very rarely when a large crack opens in the Earth’s crust. Vast volumes of extremely runny lava stream over the landscape, often extending to cover millions of square kilometres. The largest of them makes up much of the Deccan region of India, but large flood basalts also occur in the Columbia–Snake basin of the northwestern United States.
Foliation
A sheet-like pattern of rock (usually schist) that looks like the pages in a book.
Formation
A collection of related rock layers or beds. A group of related
beds makes a member; a group
of related members makes up a formation. Formations are often given location names, for example, Toroweap Formation (a dominant formation in the Grand Canyon, Arizona). In the case of the Toroweap Formation the members are mainly limestone beds.
Fossil
The remains of living things that have been preserved in rocks. Fossils are used to find out about ancient environments, how rocks formed and what the Earth’s history was like. They are also used to
help find petroleum deposits and have been invaluable in tracing the history of life on Earth.
 Fossil – Fossils are common in rocks. Certain calm conditions allow the almost perfect preservation of large specimens. They are important for the dating of rocks and also to indicate the environmental conditions under which the rocks formed.
The diagram below shows the stages in making a cast or mould of a fossil.
1 – The dead animal is buried by sediment.
2 – The soft parts, and possibly the skeleton as well, are dissolved away, leaving a mould.
3 – Solutions passing through the sediment deposit minerals in the mould to produce a cast of the skeleton (and sometimes also the soft parts) of the original creature. Both mould and cast provide a record of the fossil and may be found in rocks.
Mould
Cast
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