At each
inrush of the wave the air is terribly condensed before it. It seeks
outlet. And so it happens that the air is driven up through some crack
in the rock and the superincumbent earth, one or two hundred feet from
the shore, and a great hole appears in the ground from twenty to
seventy feet deep. Then the water spouts fiercely up and returning
carries back the earth and broken rock into the sea.
No. 3 of the illustrations here given represents such a great
excavation one hundred feet back from the shore. It is one hundred and
fifty feet long by ninety wide and over fifty feet deep. All the
material had been carried out to sea by the refluent wave. On the
natural bridge seen in front the great crowd in Broadway, New York,
might pass or a troop of cavalry could be maneuvered. Through the arch
a ship with masts thirty feet high might enter at high tide. Through
the abutment of the arch where the afternoon sun pours its brightness
the waves have cut other arches not visible in the picture. When the
arches become too many or too wide the natural bridge will fall and be
carried out to sea like many another.
[Illustration: A Natural Bridge, Santa Cruz, Cal.]
But what does the sea do with the harder parts of the cliff? Its waves
wear away the rock on each side and leave one or more long fingers
reaching out into the sea.
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