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Neogene
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The Neogene period is the interval of geological time from 24 to 1.8 million years ago. Neogene is derived from the Greek word for recent.
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nappe
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A large body of rock that has been moved by gravity, thrust faulting, or any other mechansm some distance from its place of origin.
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native metal
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A natural deposit of a metallic element in pure metallic form, neither oxidized nor combined with sulfur or other elements.
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neap tide
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A tide cycle of unusually small amplitude, which 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.
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nebula
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An immense, diffuse body of interstellar gas and dust that has not condensed into a star.
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nebular hypothesis
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A theory of the formation of the planets that states that a rotating nebula contracted and was then torn into fragments by centrifugal forces, with planets condensing from the fragments.
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neoglaciation
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Neoglaciation refers to the advances made by mountain glacier since the great Pleistocene ice age. In the Cascades the advances have occurred since 6,600 years before present.
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neutron
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An electrically neutral elementary particle in the atomic nucleus having the mass of one proton.
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neutron-activation analysis
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A method of identifying isotope of an element by bombarding them with neutron and observing the characteristic radioactive decay products emitted.
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nonconformity
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An type of unconformity in which young sedimentary rocks lie on top of older metamorphic or intrusive igneous rocks.
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nonsilicate minerals
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A mineral without silicon (Si).
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norite
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An igneous rock with mafic composition.
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normal fault
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A dip-slip fault in which the block above the fault has moved downward relative to the block below.
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normal polarity
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Geomagnetic polarity that is the same as the present polarity.
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nunatak
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Islands of mountain tops that pertrude above glacier.
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nuée ardente
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"A French term applied to a highly heated mass of gas-charged ash which is expelled with explosive force down the mountainide; a significant volcanic hazard."
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