GLOSSARY
[Abrasion]—erosion of [rock] material by friction of solid particles moved by water, ice, wind, or gravity.
[Absolute time]—[geologic time] measured in years. Compare with relative time.
[Amphibians]—cold-blooded four-footed animals which have gills in youth and lungs in maturity (e.g., frog).
[Anhydrite]—the [mineral] calcium sulfate, CaSO₄. See [Gypsum].
[Anticline]—an arch-like fold in the [rocks], with the beds dipping in opposite directions on the two sides.
[Aquifer]—a water-bearing layer of porous and permeable [rock].
[Aragonite]—a form of calcium carbonate (CaCO₃).
[Archeozoic]—the oldest known geological [era]; early Precambrian.
[Bedding plane]—the plane of demarcation between two individual [rock] layers or [strata].
[Calcite]—a [mineral] composed of calcium carbonate, CaCO₃.
[Caliche]—an accumulation of calcium carbonate, commonly white in color, in the soil profile.
[Cenozoic]—the latest [era] of geologic time, containing the Tertiary and Quaternary [Periods] and continuing to the present time.
[Chert]—dense, hard [rock] of very fine-grained [silica], usually in nodular form. This material is also called flint.
[Concretion]—a concentration, usually spherical, of [mineral] matter in [sedimentary] [rocks], produced by deposits from solution; it is harder than the surrounding rock.
[Conglomerate]—a [sedimentary rock] composed of rounded, water-worn gravel, usually mixed with sand, and cemented together by another [mineral] substance.
[Coprolite]—the fossilized excrement of animals.
[Eolian]—pertaining to the erosion and the deposits resulting from wind action and to [sedimentary rocks] composed of wind-transported material.
[Epoch]—a subdivision of a geologic [period], such as the [Pliocene] [Epoch] of the Tertiary Period.
[Era]—a major division of [geologic time]. All geologic time is divided into five eras: the [Archeozoic], [Proterozoic], [Paleozoic], [Mesozoic], and [Cenozoic] Eras.
[Fluorescence]—luminescence of a [mineral] during exposure to radiation (such as from ultraviolet or X-rays).
[Fluvial deposit]—[sediment] deposited by streams.
[Formation]—a [rock] unit useful for mapping and distinguished primarily on the basis of lithologic character.
[Fossil]—any remains or traces of plants or animals preserved in deposits of a past [geologic age].
[Geode]—a hollow stone, usually lined or filled with [mineral] matter.
[Geologic age]—the age of an object as stated in terms of [geologic time] (e.g., a Pennsylvanian fern, Cretaceous dinosaur).
[Geologic time]—all time which has elapsed since the first known [rocks] were formed and continuing until recent, or modern, times.
[Geologic time scale]—record of the divisions of earth history.
[Gypsum]—a [mineral], hydrated calcium sulfate (CaSO₄·2H₂O). See [Anhydrite].
[Hoodoo]—a form produced by erosion of [rock].
[Ice age]—the [Pleistocene] [Epoch] of the Quaternary [Period], [Cenozoic] [Era]; a time of extensive glaciation.
[Igneous rock]—[rocks] which have solidified from lava or molten rock called magma.
[Joint]—a fracture in a [rock] along which there has been no displacement on opposite sides of the break.
[Joint System]—a series of two or more sets of [joints] passing through a [rock] mass and separating it into blocks of more or less regular pattern.
[Mass-wasting]—erosion caused chiefly by gravity.
[Mesozoic]—the geologic [era] between the [Paleozoic] and [Cenozoic] Eras; the “Age of Reptiles.”
[Metamorphic rock]—[rock] formed from [igneous] or [sedimentary rocks] that have been subjected to great changes in temperature, pressure, or chemical environment.
[Metamorphism]—the process whereby [rocks] are changed physically by heat, pressure, or chemical environment into different kinds.
[Mineral]—a naturally occurring inorganic substance possessing definite chemical and physical properties.
[Nodule]—rounded lump of [rock] or [mineral].
[Outcrop]—the area where a particular [rock] [formation] comes to the surface.
[Paleontology]—the science which deals with the study of [fossils].
[Paleozoic]—that [era] of [geologic time] following the [Proterozoic] and preceding the [Mesozoic].
[Period]—a basic unit of the [geologic time scale] into which the eras are divided, such as the Pennsylvanian [Period] of the [Paleozoic] [Era].
[Permian]—the seventh and last [period] of the [Paleozoic] [Era].
[Pleistocene]—the first of the two epochs of the Quaternary [Period], and that which precedes modern time, known as the Great [Ice Age].
[Pliocene]—last and youngest [epoch] of the Tertiary [Period] of the [Cenozoic] [Era].
[Proterozoic]—youngest [era] of the Precambrian; follows the [Archeozoic] Era and precedes the Cambrian [Period] of the [Paleozoic] Era.
[Red beds]—a general term for red [sandstone], [shales], etc., which appear to characterize arid [periods] in the past.
[Ripple marks]—wave-like corrugations produced in unconsolidated materials by wind or water.
[Rock]—any natural aggregate of [mineral] matter, usually consisting of a mixture of two or more minerals.
[Sandstone]—[sedimentary rock] composed of cemented sand grains, usually quartz.
[Sediment]—material that has been deposited by settling from a transportation agent such as water or air.
[Sedimentary rock]—[rocks] formed by the accumulation of [sediments].
[Shale]—a [sedimentary rock] formed by the hardening of mud and clay and usually tending to split into thin sheets or layers.
[Silica]—an oxide of silicon (SiO₂).
[Siliceous]—containing or pertaining to [silica].
[Silt]—fine muddy [sediment] consisting of particles intermediate in size between clay particles and sand grains.
[Siltstone]—a very fine-grained [sedimentary rock] composed of [silt] grains, and intermediate between [shale] and [sandstone].
[Stratified rocks]—[sedimentary rocks]; those formed in beds, layers, or [strata].
[Stratum]—an individual layer of [rock formation]. (Plural, [strata].)
[Superposition], law of—in an undisturbed sequence of [rocks] younger beds overlie older beds.
[Syncline]—a trough-like fold in the [rocks], with the beds dipping inward on either side. See [Anticline].
[Talus]—a mass of [rock] debris commonly on slopes or at the base of a steep mountain or cliff.
[Topography]—the configuration of a land surface.
[Unconformity]—a break in the sequence of [rock] [formations] which separates younger [strata] from older ones; caused primarily by removal of older rocks by erosion before those of a later sequence were laid down.
[Weathering]—any natural process, mechanical or chemical, whereby [rocks] are disintegrated or decomposed into smaller particles and ultimately into clay and soil.