This paper is the result of the detailed cartography of an area comprised between Artanavaz and Dora Baltea valley, above Aosta and around Mont Fallère.
Six lithological units are distinguished between the "zone houillère" (external) and the "zone des schistes lustrés" (internal). Three of them (Ruitor, Leverogne and Siviez zones) are old basements composed of polymetamorphic gneisses, micaschists and green schists. The others (Gran Testa zone, Métailler and Mont Fallère units) represent monometamorphic covers of Upper Paleozoic age, constitued by continental clastic metasediments and mafic, then acid magmatic rocks (now prasinites and quartz porphyryies). Two small acid intrusions with probably Permian age appear in the Ruitor zone.
All these lithological units belong to three different tectonic units; from the external to the internal one: Pontis, Siviez-Mischabel and Mont Fort nappes.
This portion of the Alps has been affected first by intense deformations under conditions between green schist and blue schist facies; they are responsible for the main schistosity and isoclinal folds. After that, a general movement toward SE creates open folds and recristallisations under weak green schist facies conditions. A late displacement of all units toward external part of the alpine arc is represented first byopen folds and then by thrust and senestral faults.
A greater tectonic accident ("col de Bard - St-Nicolas accident" wich belongs to the last deformation phase) cut all the units and precedent structures. It is the western segment of the "Aosta valley fault" and is connected to the "Rhône - Simplon line" by relatively recent frontal thrusts. This so defined loop limit the Alpes Pennines block which moves belatedly westward.