Pontis Nappe and the zone Houillère

Pontis Nappe: the dolomitic cliffs at the entrance of Val d’Hérens between Sion and Vex, associated with Triassic series, is actually part of the Zone Houillère.

The Zone Houillère: covering the Rhone Valley this zone contains detritic rocks such as quartzite with mica (transformed sandstone).  'Houille' means coal in French, and the old mines in Bramois at the entrance of the Val d’Hérens testify to the abundance of this combustible rock, associated with Carboniferous volcanic rocks. The rest of the Triassic to Tertiary series is in the Prealps Plastiques Nappe.

NB: The Mt Fort, Siviez-Mischabel and Pontis Nappes were previously grouped in a larger Grand Saint-Bernard Nappe. Together with the Houillère Zone, and the Mt Rose and Gran Paradiso Nappes, this area represents the paleographic Briançonnais domain largely developed in France and Italy. Between the upper Jurassic and the Tertiary this domain formed a micro-continent separated from Europe by the Sion-Courmayeur zone.