Note 7 — Chapter XXII
Reading edition
These ebbing and flowing wells are common in parts of the West Indies. The simple fact, that in low islands of small extent, and composed of porous materials, the rain-water can have no tendency to sink lower than the level of the surrounding sea, and must therefore accumulate near the surface, having been overlooked; it has been supposed that sand possesses the power of filtering the salt which is dissolved in the sea-water.