Coral reef A fringing reef forms around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast
Two Water Mills with an Open Sluice Two Water Mills with an Open Sluice Two Water Mills with an Open Sluice, also known as Two Watermills and an Open Sluice, Two Undershot Water Mills with an Open Sluice is a 1653 painting by the Dutch Golden Age painter Jacob van Ruisdael. It is in the collection of the Getty Museum in Los Angeles. The painting shows two working undershot water mills, with the major one being half-timbered with a cob-facade construction, tie beams, and vertical plank gable. This is characteristic of the water mills in the Bentheim area in Germany, to where Ruisdael had travelled in the