fabric — The relative size, shape, and spatial 

 arrangement of grains or crystals in a sediment 

 deposit or a rock. (2) 



f acies — Areally segregated parts of a sedimentary 

 deposit which differ in mineral composition, 

 bedding, fossils, etc. but belong to any geneti- 

 cally related body of sedimentary deposits. (2) 



Fahrenheit temperature scale — (abbreviated 

 F). A temperature scale with the freezing 

 point at 32 degrees and tlie boiling point of water 

 at 212 degrees at standard atmosphere pressure. 



fair tide — See beam tide. 



Falkland Current — A current flowing northward 

 along the Argentine coast. The Falkland Cur- 

 rent originates from part of the West Wind 

 Drift. At about 35°S it is joined by the Brazil 

 Current where both turn to flow east across the 

 South Atlantic. 



falling tide — (sometimes called ehh tide). The 

 portion of the tide cycle between high water and 

 the following low water. (5) 



falloff — In underwater sound, the decrease in 

 acoustic energy as it travels away from the sound 

 source. 



fallout — The radioactive debris, usually from a 

 nuclear detonation, which has been deposited on 

 the earth after being airborne. Special forms 

 of fallout are "dry fallout", "rainout", and 

 "snowout". (70) 



false anticline — A structure resembling an anti- 

 cline produced by compaction of sediment over 

 a resistant mass such as a buried hill or reef. 



(2) 



false bottom — See deep scattering layer. 



false ice foot — Ice formed along a beach terrace 

 just above high water mark, derived from snow 

 melting above the beach terrace. (59) Rare. 

 See ice foot, quar ice. 



family — See classification of organisms. 



fan — A gently sloping, fan-shaped feature nor- 

 mally located near the lower termination of a 

 canyon. (62) 



fan shooting — See arc shooting. 



faro — A small atoll-shaped reef or coral knoll with 

 lagoons a few to about 100 feet (30 meters) deep, 

 forming part of a barrier or atoll rim. (2) 



fast ice — 1. Sea ice that generally remains in the 

 position where originally formed and may attain 

 a considerable thickness. It is formed along 

 coasts where it is attached to the shore or over 

 shoals where it may be held in position by is- 

 lands, grounded icebergs, or grounded polar ice. 



(Preferred definition) (74) 



2. (also called land fast ice). Any type of 

 sea ice attached to the shore (ice foot, ice shelf), 

 beached (shore ice), stranded in shallow water, 

 or frozen to the bottom of shallow waters (an- 

 chor ice). (5) 



fast ice belt — See ice foot. 



Fata Morgana — A complex mirage that is charac- 

 terized by multiple distortions of images, gen- 

 erally in the vertical, so that such objects as 

 cliffs and cottages are distorted and magnified 

 into fantastic castles. 



An unusual density stratification is required to 

 produce this mirage, namely the joint occur- 

 rence, in vertically adjacent layers, of density 

 gradients that would give an inferior mirage 

 and a superior mirage. A strong inversion over 

 a relatively warm sea may satisfy this require- 

 ment. The instability of the air layer lying 

 immediately over the sea in the mirage charac- 

 teristics, a circumstance that suggests the fairy- 

 like features of the mirage forms. ( 5 ) 



fathogram^ — 1. The graphic presentation of the 

 bottom profile determined by a Fathometer*. 

 2. Often erroneously applied to any echo- 

 gram. 



fathom — The common unit of depth in the ocean 

 for countries using the English system of units, 

 equal to 6 feet (1.83 meters). It is also some- 

 times used in expressing horizontal distances, in 

 which case 120 fathoms make one cable or very 

 nearly 1-tenth nautical mile. 



fathom curve — See isobath. 



Fathometer* — Copyrighted trade name for a 

 type of echo sounder. Often incorrectly used 

 for any sonic submarine depth measuring 

 system. 



fault — A fracture or fracture zone in rock along 

 which one side has been displaced relative to 

 the other side. The intersection of the fault 

 surface with any designated surface, such as the 

 sea bottom, is called a fault line. If a fault is 

 not a single clean fracture but a wide zone 

 (hundreds or thousands of feet) with small 

 interlacing faults and filled with breccia, it is 

 called a fault zone. 



fault block — A rock body bounded on at least two 

 opposite sides by faults. It usually is longer 

 than it is wide ; when it is depressed relative to 

 the adjacent regions it is called a graben, fault 

 embayment, fault trough, or rift valley, and 

 when it is elevated it is called a horst. Mozam- 



61 



