So we have been fairly thorough in our discussion about coral reefs, which of course are prominent, oceanic features made of hard limestone skeletons produced by tiny coral animals.

我们对珊瑚礁的讨论已经相当深入了；显然，珊瑚礁具有显著的海洋特征，由小型珊瑚动物制造的石灰骨架构成。

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The danger is likely to continue, they say, until the waves reach an inland area of hard rock which will not be eaten as limestone is.

他们说，这种危险可能会持续下去，直到海浪到达内陆坚硬的岩石区域，这些地方的岩石不会像石灰岩那样受到侵蚀。

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Medium hard formation with high compressive strength. Such as hard shale, limestone, sandstone, dolomite, anhydrite and marble.

高抗压强度的中硬地层，如硬页岩。石灰岩。砂岩。白云岩。和硬石膏。大理石。

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The coral turns white when it expels the minute organisms that live within its hard limestone core.

ECONOMIST: Pink coral into grey rubble