BUREAU OF GEOLOGY


is presently in the process of revising this classification; the above term
will no longer be used.

ion An atom or group of atoms with an electric charge.

isopach map A map that shows the thickness of a bed, formation, sill
or other tabular body throughout a geographic area, based on a variety of
types of data.

karst A type of topography that is formed by the dissolution of lime-
stone, dolomite or gypsum rock by rainwater or rivers. The topography is
characterized by closed depressions, sinkholes, caves and underground
drainages.

ketone Any of a class of organic compounds containing a carbonyl
group, e.g., C = O, attached to two organic groups, such as CH3COCH3.

lagoon A shallow stretch of seawater, such as a sound, channel, bay,
or saltwater lake, near or communicating with the sea and partly or
completely separated from it by a low, narrow, elongate strip of land,
such as a reef, barrier island, sandbank or spit. It often extends roughly
parallel to the coast, and it may be stagnant.

lignin An organic substance somewhat similar to carbohydrates in
composition that occurs with cellulose in woody plants.

lignite A brownish-black coal that is intermediate in coalification
between peat and bituminous coal; consolidated coal with a calorific
value less than 8300 BTU/pound, on a moist, mineral-matter-free basis.
Cf: brown coal.

marine environment Areas directly influenced by normal salinity sea-
water (approximately 35 parts per thousand).

marl An old term loosely applied to a variety of materials most of
which occur as soft, loose, earthy and semifriable or crumbling unconsol-
idated deposits consisting chiefly of an intimate mixture of clay and
calcium carbonate in varying proportions, formed under either marine or
freshwater conditions.

marsh A water saturated, poorly drained area, intermittently or per-
manently water-covered, having aquatic and grasslike vegetation. Cf:
swamp; bog.

megawatt A unit of power equal to 1 million watts.

metamorphism The mineralogical and structural adjustment of solid
rocks to physical and chemical conditions which have been imposed at
depth below the surface zones of weathering and cementation and


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