GRADED SEDIMENT 



gill cover — See operculum. 



glacial — Pertaining to the presence, size, composi- 

 tion, or activity of extensive masses of land ice. 

 (59) 



glacial deposit — See glacial drift. 



glacial drift — (or glacial deposits). Sediments 

 and rock fragments transported by glaciers or 

 icebergs and deposited on land or in the sea. 



glacial epoch — The Pleistocene epoch, the earlier 

 of the two divisions of geologic time included in 

 the Quaternary period; characterized by conti- 

 nental glaciers which covered extensive regions 

 now free from ice. (2) See geologic time 

 scale, 



glacial trough — A U-shaped valley, excavated by 

 a glacier either on land or sea bottom. 



glaciated coast — A coast whose features indicate 

 that it has been covered by continental glaciers 

 of the Pleistocene epoch or a coast covered by 

 glaciers at the present time. ( 2 ) 



glacier — (or land ice) . A mass of land ice, formed 

 by the further recrystallization of firn, flowing 

 slowly (at present or in the past) from an ac- 

 cumulation area to an area of ablation. 



This term covers all such ice accumulations 

 from the extensive continental glaciers of pre- 

 historic ice ages to tiny snowdrift glaciers. (5) 



glacier berg — A mass of glacier ice that has 

 broken away from its parent formation on the 

 coast, and either floats, generally at least 5 

 meters (16.4 feet) above sea level, or is stranded 

 on a shoal. (74) 



glacier ice — ( or lund ice ) . Any ice floating on the 

 sea, such as an iceberg, which originated from a 

 glacier. (74) 



glacier iceberg — An iceberg derived from a 

 glacier as distinguished from tabular icebergs 

 derived from shelf ice. ( 59 ) 



glacier tongue — Projecting seaward extension of 

 a glacier, usually afloat. In the Antarctic, 

 glacier tongues may extend over many tens of 

 kilometers. (74) 



glaciology — The study of snow and ice on the 

 earth's surface, with specific concentration on the 

 regime of active glaciers. See cryology (sense 



3). (5) .... 



gla^on — A fragment of sea ice rangmg ui size 

 from brash ice to a medium ice floe. (59) 



glade — See polynya. 



glare ice — Any highly reflective sheet of ice on 

 water, land, or glacier. ( 5 ) 



glass ice — Rare. See ice rind. 



glass sponge — A sponge in which the internal 

 skeletal elements (spicules) are composed of 

 silicic acid. These sponges are principally in- 

 habitants of deep water to depths as great as 

 about 16,400 feet (5,000 meters) . 



glass worm — See arrow worm. 



glauconite — A gi-een mineral, closely related to 

 the micas and essentially a hydrous potassium 

 iron silicate. Occurs in sediments of marine 



origin and is produced by the alteration of var- 

 ious other mnierals in a marine reducing or 

 anaerobic environment. 



glauconitic sand— /See green sand. 



glaze — A smooth, transparent or translucent coat- 

 ing of ice deposited by a heavy fall of freezing 

 rain. Sometimes popularly called sleet. Called 

 "glaze ice" in British terminology. (68) 



glimmer ice — Ice newly formed in cracks, holes, 

 or puddles on the surface of old ice. (59) 

 Rare. 



glitter — The spots of light reflected from a point 

 source by the surface of the sea. 



Statistical analysis of glitter patterns has 

 revealed relationships from which the roughness 

 of the sea can be determined by the study of 

 photographs of the glitter. (5) 



globe-type luminescence — See glowing-ball 

 luminescence. 



Globigerina — A common form of sediment-pro- 

 ducing f oraminiferan. 



globigerina ooze — A pelagic sediment consisting 

 of more than 30 percent calcium carbonate in the 

 form of foraminiferal tests of which Globiger- 

 ina is the dominant genus. See ooze. 



glowing-ball luminescence — (or glohe-tyfe lu- 

 minescence). A display of biological light ap- 

 pearing as distinct and separate flashes or blobs 

 of light of various diameters, commonly having 

 a disc or globual shape, and originating either at 

 or below the surface of the sea. The organisms 

 responsible for this type of display include jelly- 

 fishes, ctenophores, and tunicates. Glowing- 

 ball type displays are seen inore frequently in 

 warmer waters. See bioluminescence. 



gnomonic projection — A perspective map projec- 

 tion upon a tangent plane, with the point from 

 which the projecting lines are drawn situated at 

 the center of the sphere. The projection is 

 neither conformal nor equal area. It is the only 

 projection on which great circles on the sphere 

 are represented as straight lines. (37) 



goe — A Scottish term for a small sea-cut gorge 

 eroded into a cliffed coast. (48) 



goose barnacle — See stalked barnacle. 



gooseneck barnacle — See stalked barnacle. 



grab — An instrument in which jaws enclose a por- 

 tion of the bottom for retrieval and study. The 

 sample may be unrepresentative in coarse sedi- 

 ments where the jaws may be propped open by 

 gravel or stones permitting part of the sample 

 to wash out. 



graben — See fault block. 



graded bedding — (or diadactic structure). A 

 type of stratification in which each stratum dis- 

 plays a giadation in grain size from coarse below 

 to fine above. (2) 



graded sediment — In geology, a sediment con- 

 sisting principally of grains of the same size 

 range. In engineering, a sediment having a 



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