In Western Switzerland, the Middle Penninic subdomain comprises units located between the Sion-Courmayeur Nappe and the Tsaté and Zermatt-Saas nappes. These units were first grouped together within the “Grand St-Bernard Nappe” (Argand 1911), which was then subdivided into several nappes.

The Middle Penninic units are thought to be derived from the Briançonnais Terrane, which consisted of a polycyclic crystalline basement cut by Late Cambrian (ca. 500 Ma) and Permian (ca. 270 Ma) granitic intrusions, Permo-Carboniferous sediments that filled narrow basins and a characteristic Mesozoic – Paleogene sedimentary cover. Much of this Briançonnais cover was detached at the level of the Triassic evaporites to form some of the nappes in the Prealps.

In eastern Switzerland, the internal part of the Middle Penninic is represented by the Tambo and Suretta basement-cover nappes and, additionally, by detached sedimentary nappes. Structurally, the Suretta Nappe occupies the core of the very large-scale north facing Niemet-Beverin Backfold that postdates nappe stacking and can be followed all the way into the Prättigau Half-Window. The sedimentary Schams Nappe Complex and the upper part of the Lower Penninic Tomül Nappe are wrapped around the Suretta Nappe in this mega-fold and backthrust to the southeast in an overturned position over the top of the Suretta Nappe and of the Upper Penninic Avers Nappe. The Mesozoic strata in all these Middle Penninic units can definitely be attributed to the Briançonnais paleogeographic realm.