GeologyRocks

Congelifraction

See frost wedging.

Cretaceous

The final period of the Mesozoic. This period spans 145.5-65.5Ma. The end of the Cretaceous was marked by the KT (now properly called the KP) extinction event, which saw the demise of the dinosaurs as well as several other groups such as ammonites.

Devonian

The fourth period of the Palaeozoic. Spans 409-353Ma. The rocks of this period are referred to as Old Red Sandstone (ORS) as they are often red coloured sandstone. The name originates from the county of Devon in South West England. The colonisation of land was also well under way as shown by the famous Rynie Chert deposit.

Epochs:

• Late Devonian 371-353Ma
• Middle Devonian 380-371Ma
• Early Devonian 409-380Ma

Disconformity

An unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition.

Drumlin

A glacial deposit; an elongate shaped hill. The longest dimension is parallel to the movement of the ice flow (see arrow).

Eustatic Sea Level Change

Sea level change on a global scale. Causes include the switching between ice age and interglacial periods and changes in the global ocean volume due to plate tectonic movement. Combined with the isostatic changes make a relative sea level change.

Flachkarren

See clint.

Formation

A formation is a group of beds used in stratigraphy. This is the smallest unit on a geological map. Formations are grouped together into a group. See also Member.

Fossil

Any remains, trace, or imprint of an organism that has been preserved in the Earth's crust.

Frost Wedging

Also known as congelifraction, frost weathering or frost shattering. When a rock is exposed such that water is liquid during the day, but freezes at night, the expansion of the freezing water can cause stress in the rock such that it can shatter. This is most common in deserts where water in the rock will freeze rapidly during the night.