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NATURAL LEVEE: See Levee.

NEAP TIDE: A tide cycle of unusually small amplitude that occurs twice monthly when the lunar and solar tides are opposed-that is, when the gravitational pull of the Sun is at right angles to that of the Moon. (Compare Spring tide.)

NEUTRON: An electrically neutral elementary particle in the atomic nucleus, having the mass of one proton.

NONFOLIATED METAMORPHIC ROCKS: Metamorphic rocks that have no preferred orientation of crystals, or very weak orientation, and thus show little or no slaty cleavage or schistosity.