The Study of the Geometry of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 102

allowing in situ observation of the basal limit of the aquifer and the roof of
the underlying impermeable unit.
￿ Examples of networks whose deepest sections follow the roof of the
underlying impermeable layer: Berger chasm in the Vercors, Pierre-
Saint-Martin network in the French-Spanish Pyrenees, Piagga-Bella
network in the French-Italian Marguareis;
￿ Examples of networks reaching overthrusts in the subalpine units
of the Alpes-Maritimes: Abel chasm on the Saint-Vallier plateau and
Calernaum chasm on the Calern plateau (Figure 51).
Figure 51 Cross-section of the Calernaum chasm, which passes through the Calern plateau
all the way to its impermeable base and then follows the basal overthrust of the unit (Alpes-
Maritimes, Cipières) (from Gilli, 1995).