Descriptionary

deposition an accumulation of material, such as silt, seashells, minerals, or the process of accumulation.

diagenesis the changes that occur to a fossil after burial.

dike a long formation of igneous rock intruded into the fissure of another rock.

dome an upfold of rock forming the shape of an inverted cup.

drill core a tube-shaped or elongated shaft of mud, rock, sediment, or ice extracted from the Earth for laboratory study.

drumlin an elongated hill, 8 to 60 meters high and 0.5 to 1 kilometer in length, consisting of rocks and gravel deposited by a glacier.

eon the longest division of geological time, some­times denoting two or more eras. Sometimes used to denote a span of 1 billion years.

epoch a subdivision of geological time denoting a portion of a period.

era a major division of geological time comprising one or more periods.

erosion the wearing away of a surface or geological feature by wind, rain, river flow, etc.

erratic a boulder that is out of place in its environ­ment, having been transported over long distances by a glacier.

escarpment a cliff.

esker a winding ridge of stratified glacial deposits, stretching from a few meters to as long as 160 kilo­meters.

eustatic change worldwide change of sea level pro­duced by an increase or decrease in amount of ocean water.

evaporite any salt deposit left behind when seawa- ter evaporates.

extrusive rock rock solidified from magma that has flowed out of the earth and onto the surface.

fault a fracture in strata or, on a larger scale, the Earth's crust.

floodplain an area bordering a stream that periodi­cally floods.

fold bend or wrinkle in rock formed when rock was in a plastic state.

fold mountain a mountain consisting of sedimen­tary rocks that have been folded over and elevated.

fossil fuels underground deposits of hydrocarbons, including petroleum, methane, coal, and natural gas, formed from the fossilized remains of millions of tons of prehistoric plants and animals, with phy- toplanktons and zooplanktons transforming largely into petroleum and terrestrial plants and organisms transforming largely into coal.

frost action erosional process caused by the expan­sion of water through repeated cycles of freezing and thawing.

geocentric pertaining to the center of the Earth.

geochronology the history of the Earth as marked by geological events.

geodesy the science of the measuring of Earth's size, shape, and weight.

geomorphology the study of land forms.

geosyncline a basin in which thousands of meters of sediments have accumulated and which may ultimately become compressed into a mountain system.

Gondwanaland hypothetical Southern Hemisphere continent thought to have broken up in the Mesozoic era and now the continents of Africa, India, Austra­lia, South America, and Antarctica.

guyot flat-topped mountain under the sea.

igneous rock rock formed from the cooling and solidification of magma.

inselberg a vestigial mountain reduced by erosion to a rocky nubbin or isolated "island," found in ancient desert areas.

intrusive rock rock that has solidified from magma after intruding into or between other rocks.

island-arc deeps deep sea trenches bordering some continents; some reach depths of 9,000 meters.

kame a steep hill of stratified glacial drift.

karst topography an area characterized by numer­ous sinkholes and caverns, due to limestone erosion.

Kerguelen-Gaussberg Ridge a mountain range under the Indian Ocean between India and Antarctica.

kettle a depression in a large accumulation of gla­cial drift caused by an ice block melting and later forming a lake.

koppie pile of boulders formed by the weathering and breakdown of inselbergs.

lava extruded from a volcano, any molten rock or molten rock that has cooled and hardened.

lithosphere the outermost layer of the Earth, com­prising the crust and the upper mantle.

loess an accumulation of loose silt, deposited by wind as dust.

lowland any land at or slightly above sea level.

magma molten rock beneath the surface of the Earth.

magnetic reversal a complete shift of Earth's mag­netic field, which, if occurring today, would make a compass needle point south instead of north. Such reversals have taken place several times throughout the Earth's history.

magnetostratigraphy the study of magnetized rocks to determine magnetic reversals in the Earth's past.

mantle the layer of Earth between the crust and the core.

marl forming in a water environment, a loose deposit of clay and calcium carbonate.

melange different types of rocks grouped together.