Natural England - Geology glossary (D to F)
Geology glossary (D to F)
This page of the glossary covers D to F. You can navigate to the next section from the links at the bottom of this page.
| Delta An accumulation of sediment where a river enters a lake or ocean and where, due to a reduction in velocity, it sheds its sediment load. |
| Devensian A geological time period (between 115,000 and 10,000 years ago). This period includes the most recent ice sheet glaciation of northern Britain. |
| Devonian A period of geological time, dating from about 417 to 354 million years ago. |
| Dolomite A carbonate sedimentary rock consisting chiefly (more than 50% by weight) of the mineral dolomite (MgCO3.CaCO3). |
| Drift A general term applied to material (clay, sand, silt, boulders) transported by a glacier and deposited directly by or from the ice, or by glacier melt water streams. Generally applies to Pleistocene glacial deposits but can be broadly used to describe all superficial deposits. |
| Dyke A sheet-like body of igneous rock which cuts across the bedding or structural planes of the host (older) rock. |
| Earthquake A movement within the Earth's crust or mantle, caused by the sudden rupture or repositioning of underground rocks as they release stress. Earthquakes are often associated with areas of active faulting and mountain building. |
| Epicentre The point on the Earth's surface immediately above the origin of an earthquake. |
| Erosion The process by which particles of rock and soil are loosened, through weathering, and then transported elsewhere, through the action of wind, water, ice, or gravity. |
| Erratic A rock fragment carried by glacial ice, or by floating ice, and subsequently deposited at some distance from the outcrop from which it was derived. |
| Esker A ridge of sediment (often winding) made up of sand and gravel deposited by glacial meltwater. An esker may vary from several 10s of metres to more than 500 kilometres long, and may be anywhere from 3 to over 300 metres high. |
| Evaporite An inorganic rock or sediment formed by the evaporation of saline water such as sea water. |
| Extrusive Igneous rocks that are erupted at the Earth’s surface (also known as volcanic rocks). |
| Fault A fracture in rock along which movement has occurred. Faults occur when rocks are squeezed or pulled apart and the movement can range from several millimetres to several hundred kilometres. |
| Flint Granular microcrystalline silica, usually dull and dark that often occurs as lumps or nodules in calcareous rocks such as the Cretaceous Chalk of southern England. |
| Floodplain The low land that surrounds a river and becomes submerged when the river overflows its banks. |
| Fluvial Of or related to rivers; produced by river action. |
| Fold A bend formed in a layer of rock, usually caused when rocks are squeezed. |
| Fossil Mineralised remains or traces of an organism. |
