PETROGRAPHY - The systematic description and classification of rocks. 



PHASE - In surface wave motion, a point in the period to which the wave 

 motion has advanced with respect to a given initial reference point. 



PHASE INEQUALITY - Variations in the tides or tidal currents associated 

 with changes in the phase of the moon in relation to the sun. 



PHASE VELOCITY - Propagation velocity of an individual wave as opposed to 

 the velocity of a wave group. 



PHI GRADE SCALE - A logarithmic transformation of the Wentworth grade 

 scale for size classifications of sediment grains based on the 

 negative logarithm to the base 2 of the particle diameter. 

 (j) = -log2d. See SOIL CLASSIFICATION. 



PIER - A structure, usually of open construction, extending out into the 

 water from the shore, to serve as a landing place, a recreational 

 facility, etc., rather than to afford coastal protection. In the 

 Great Lakes, a term sometimes improperly applied to jetties. 



PILE - A long, heavy timber or section of concrete or metal to be 



driven or jetted into the earth or seabed to serve as a support 

 or protection. 



PILE, SHEET - A pile with a generally slender flat cross section to be 



driven into the ground or seabed and meshed or interlocked with like 

 members to form a diaphragm, wall, or bulkhead. 



PILING - A group of piles. 



PLAIN, COASTAL - See COASTAL PLAIN. 



PLANFORM - The outline or shape of a body of water as determined by the 

 Stillwater line. 



PLATEAU - A land area (usually extensive) having a relatively level 

 surface raised sharply above adjacent land on at least one side; 

 table land. A similar undersea feature. 



PLUNGE POINT - (1) For a plunging wave, the point at which the wave curls 

 over and falls. (2) The final breaking point of the waves just 

 before they rush up on the beach. (See Figure A-l.) 



PLUNGING BREAKER - See BREAKER. 



POCKET BEACH - A beach, usually small, in a coastal reentrant or between 

 two littoral barriers. 



POINT - The extreme end of a cape, or the outer end of any land area 

 protruding into the water, usually less prominent than a cape. 



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c 



