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The weathering on this old bridge gives testimony to the extent of the tidal fluctuations on the marsh. The still damp area from the water level up to the the bottom of the white band is the range of the twice daily low and high tides caused by the earth's daily rotation.
     The dry band bleached white by salt is indicative of the additional tidal range caused by the twice monthly alignment of the earth, moon and sun.
     The brown and green top portion of the bridge is above the range of either of the periodic tides.
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