ClipArt ETC
"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

Gravel Hill

"Suppose a to be a gravel hill, and b a strata of clay or rock, impervious to water. The fluid percolating…