A
spring horizon or
spring line is an
impervious layer of rock reaching the surface, along which springs emerge. Since
and impervious
strata often lie on top of one another in horizontal layers, adjacent contact springs often emerge at the same height along a line called the spring horizon.
[Leser, Hartmut et al. Wörterbuch Allgemeine Geographie, dtv, 14th ed., Mar 2010. .]