PEiU-i/lFROST - Permnnently frozen subsoil, 



PERMANENT CURRENTo - A current that runs contliiuously independent of 



the tidBB and temporary causes , Perraenent currents include the fresh 

 water discharge of a river and the currents that form the general 

 circulatory systems of the oceans. 



PERi»IEABLE GROIN - See under GROIN, 



FETRGGRArhT - The description and systematic classification of rocks. 



PIER - A structure., extending out into the -water from the shore j to 

 serve as a landing place ^ a recreational facility, etc., rather 

 than to afford coastal protection, 



PILE - A long, slender piece of wood, concrete, or metal to be driven 

 or jetted into the earth or sea bed to serve as a support or 

 protection. 



PILING - A group of piles. 



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

 into the ground or sea bed and meshed or interlocked with like 

 members to form a diaphragm, wall, or bulkhead, 



PINNAGIE - A tall, slender, pointed., rocky mass. See also REEF PINNACLE, 



PLAIN - An extent of Level or nearly level land, 



PLAIN, COASTAL - A plain fronting the coast and generally representing 

 a strip of recently emerged sea bottom, 



PLAi\fF0Ri4 = The outline or shape of a body of water as determined by 

 the still water line. 



PLATEAU - An elevated plain, table land, or flat-topped region of con- 

 siderable extent. 



PLUNGE POINT - (See Figure A-l) (l) For a plunging wave, the point at 

 which the Xiiave curls over and falls; (2) The final beraking point 

 of the waves just before they rush up on the beach. 



PLUNGING BREAKER - See under BREAKER „ 



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

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



A-23 



