| Ablation Occurs where more glacial
ice is lost by melting and evaporation each year than is replaced
by the build up of snow. |
 |
| Accretion The build-up of sediment
solely by the action of the forces of nature, e.g. through deposition
by water or wind. |
|
| Aeolian Deposits Sediments made
up of windblown sand or dust |
|
| Alluvial fan A fan-shaped deposit
of sediment left by a fast flowing river or stream that has
lost velocity upon entering a broad, relatively flat valley. |
|
| Ammonite A coiled, chambered
fossil shellfish dominant in the Jurassic and Cretaceous seas
and distantly related to the modern squid and octopus |
|
| Anticline A convex fold in rock,
the central part of which contains the oldest rocks. |
|
| Asthenosphere The uppermost
layer of the mantle, located below the lithosphere. This zone
of soft, easily deformed rock exists at depths of 100 kilometres
to as deep as 700 kilometres. |
|
| Basalt A fine-grained igneous,
extrusive rock dominated by dark-coloured minerals. |
|
| Bedding Parallel layers in a
sedimentary rock. |
|
| Bedrock A general term for the
solid rock that underlies soil and other unconsolidated surface
material. |
|
| Brachiopod A type of shelled
animal with two valves that was common in ancient seas, but
is much rarer today. Sometimes known as a ‘lamp shell’. |
|
| Boulder clay Glacial deposit
consisting of clay containing boulders (of varying size). Boulder
clay is laid down beneath a glacier or ice sheet. Boulder clay
is also know as till. |
|
| Braided river A network of converging
and diverging streams separated from each other by narrow strips
of sand and gravel. |
|
| Breccia A sedimentary rock containing
angular rock fragments which are greater than 2mm across. |
|
| Caledonian Orogeny The mountain-building
event that occurred when England and Scotland collided around
430 million years ago. |
|
| Cambrian A Period of geological
time, dating from about 545 to 495 million years ago. |
|
| Carboniferous A Period of geological
time, dating from about 354 to 290 million years ago. |
|
| Cenozoic (Cainozoic) An Era
of geological time, dating from about 65 million years ago to
present day (comprising the Tertiary and Quaternary Periods). |
|
| Chert A member of a group of
sedimentary rocks that consist primarily of microscopic silica
crystals. |
|
| Clay A very fine grained sediment
that is made up of particles less than 0.004mm in diameter.
Clay typically contains a lot of water and deforms easily when
squeezed. On heating it becomes hardened and is widely used
in the brick making and ceramic industries. |
|
| Coal Typically black in colour
coal is a member of a group of easily combustible, organic sedimentary
rocks composed mostly of plant remains and containing a high
proportion of carbon. |
|
| Conglomerate A sedimentary rock
containing rounded rock fragments greater than 2 mm in diameter. |
|
| Continental drift Movement of
the continents over the Earth’s surface. |
|
| Cretaceous A Period of geological
time, dating from about 142 to 65 million years ago. |
|
| Crinoid A marine invertebrate,
usually possessing a cup-shaped body and five or more feathery
tentacles (often also known as sea-lilies). A few hundred species
presently exist, but thousands of extinct species have been
found as fossils, particularly from the Palaeozoic Era. |
|
| Cross bedding A sedimentary
rock texture characterised by overlapping and cross-cutting
bedding at an angle to the main layers of bedding. Cross bedding
is typical of aeolian sands, beach and deltaic deposits. |
|
| Crust The Earth’s outermost
layer. The continental crust is about 40km thick and consists
mostly of granite; the oceanic crust is about 10km thick and
consists mostly of basalt. |
| |
