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。