EOLIAN SANDS 



perature, salinity, light conditions, current 

 velocity, etc., but usually excluding biotic fac- 

 tors. 



eolian sands — (or aeolian sands, Mown sands). 

 Sediments of sand size or smaller which have 

 been transported by winds. They may be recog- 

 nized in marine deposits off desert coasts by the 

 greater angularity of the grains compared with 

 waterborne particles. 



Eotvos effect — The east-west component of the 

 movement of the ship, including the effect of 

 marine currents, modifies the centrifugal force 

 of the earth's rotation. It is a vertical force 

 experienced by a body moving in an east-west 

 direction on the rotating earth. In gravity 

 measurements a positive correction is applied if 

 moving eastward and a negative correction ap- 

 plied in moving westward. 



epeiric seas — Shallow inland seas with restricted 

 communication with the open ocean and having 

 depths less than 250 meters (137 fathoms). 

 Hudson Bay is an example. (2) See inland 

 seas, epicontinental seas. 



epeirogenic movement — See epeirogeny. 



epeirogeny — (or epeirogenic movement^. The 

 broad uplift and subsidence of the whole or large 

 portions of continental areas or oceanic basins. 



(2) 



Ephemeris — A publication giving the computed 

 places of the celestial bodies for each day of the 

 year, or for other regular intervals. (63) 



epicenter — The point on the earth's surface di- 

 rectly above the focus of an earthquake. 



epicontinental marginal sea — A subdivision of 

 the ocean, generally less than 7,500 feet deep, 

 overlying a continental shelf and part of a 

 continental slope, which is partly enclosed by 

 extensions of the land, shallow banks, or islands 

 (such as Laptev Sea) . 



epicontinental sea(s) — Shallow seas which oc- 

 cupy wide portions of a continental shelf or lie 

 in the interior of a continent. See epeiric seas, 

 inland seas, shelf seas. 



epilimnion — The layer of water above the thermo- 

 cline in a fresh water lake or pool ; distinguished 

 from hypolimnion, the layer below the thermo- 

 cline. In the ocean, the equivalent is the mixed 

 layer. (5) 



epipelagic — The upper portion of the oceanic pro- 

 vince, extending from the surface to a depth 

 of about 100 fathoms (200 meters) . {See figure 

 for classification of marine environments.) 



epiphytic — Growing attached to another plant. 



epoch — 1. A particular instant for which certain 

 data are given. ( 68 ) 



2. A given period of time during which a 

 series of related acts or events takes place. ( 68 ) 



3. (or tidal epoch, phase lag, phase differ- 

 ence). Angular retardation of the maximum 

 of a constituent of the observed tide behind the 



corresponding maximum of the same constitu- 

 ent of the hypothetical equilibrim tide. (68) 

 4. A division of geologic time. 



equal area projection — (also called authalic pro- 

 jection). A map projection on which a con- 

 stant ratio of areas is preserved; that is, any 

 given part of the map on an equal area pro- 

 jection bears the same relation to the area on 

 the reference surface which it represents. 



equation of continuity — (or continuity equation) . 

 A hydrodynamical equation which expresses the 

 principle of the conservation of mass in a fluid. 

 It equates the increase in mass in a hypothetical 

 fluid volume to the net flow of mass into the 

 volume. (5) 



equation of motion — The Newtonian law of mo- 

 tion states that the product of the mass of an 

 elemental volume of fluid and acceleration equal? 

 the vector sum of the forces acting on the volume. 

 In meteorological and oceanographic use, both 

 sides of the equation of motion are divided by 

 mass to give force per unit mass. 



The forces considered in ocean currents are 

 gravity, coriolis force, pressure gradient force, 

 and frictional forces. 



equatorial air — According to some authors, the 

 air of the doldrums of the equatorial trough, to 

 be distinguished somewhat vaguely from the 

 tropical air of the trade- wind zones. Tropical 

 air becomes equatorial air when the former en- 

 ters the equatorial zone and stagnates. There 

 is no significant distinction between the physical 

 properties of these two types of air in the lower 

 troposphere. (5) 



equatorial calms — See doldrums. 



Equatorial Convergence — The zone along which 

 waters from the Northern and Southern Hem- 

 ispheres converge. This zone generally lies in 

 the Northern Hemisphere, except in the Indian 

 Ocean. 



Equatorial Convergence line — See Equatorial 

 Convergence. 



Equatorial Convergence zone — See Equatorial 

 Convergence. 



Equatorial Countercurrent — An ocean current 

 flowing eastward near the Equator. 



In the Atlantic Ocean, it flows east between 

 the North and South Equatorial Currents across 

 the full width of the ocean in northern sum- 

 mer, and across the eastern half of the ocean in 

 northern winter. It eventually becomes the 

 Guinea Current. 



In the Pacific Ocean, it flows east across the 

 ocean between 3°N and 10°N. East of the 

 Philippines it is joined by the southern part of 

 the North Equatorial Current. 



In the Indian Ocean, it flows to the east be- 

 tween the monsoon drift and the South Equa- 

 torial Current ; unlike the Equatorial Counter- 

 currents of the Atlantic and Pacific Oceans, it 

 is located south of the Equator. In northern 



58 



