ClipArt ETC
"A sandy stratum, a a, acting as a filter, occupies an inclined position between two other strata impervious to water, such as clay, the water being absorbed by the superficial parts of the strata, as at a a (which may be of very great extent), will penetrate through its whole depth, and, finding no egress below on account of the basin-like form of the stratum, or from its resting at the lower termination upon a compact rock, will accumulate." — Wells, 1857

Sandy Stratum

"A sandy stratum, a a, acting as a filter, occupies an inclined position between two other strata impervious…