Gravel Hill

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“Suppose a to be a gravel hill, and b a strata of clay or rock, impervious to water. The fluid percolating through the gravel would reach the impervious strata, along which it would run until it found an outlet at c at the foot of the hill, where a spring would be formed.” — Wells, 1857


David A. Wells The Science of Common Things; A Familiar Explanation of the First Principles of Physical Science51


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