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The authors want to underline that present-day research cannot be detached from a long tradition. Two centuries of observations made by field geologists, and new methods helped to attain our present level of knowledge. In this sense, the different sections recall the evolution of ideas accompanied by a growing sophistication of methods.

(1984). Chronology of a core sample in the Col du Dome (Mont Blanc massif) La Houille Blanche: Vol. 70, No. 6-7, pp. 491-498.

Foreland-propagating external thrust belts may be considered as essentially plane strain phenomena so that displacements can be correlated throughout their linked, three-dimensional fault geometry. This approach has been applied to part of the northwest external French-Swiss Alps, around the Mont Blanc basement massif. Imbricates of basement and cover sequences on the SW margin of this massif restore to a width in excess of 77 km with an implicit shortening of at least 67 km. These displacements can be correlated with those in the neighbouring Helvetic nappes by transferring movements, via lateral branch lines, onto the Mont Blanc thrust. By reappraising thrust geometries, the Helvetic/Ultrahelvetic nappe complex has been restored to a width of 114 km to the ESE of the Aiguilles Rouges basement massif. Displacements on the internal (SE) margin of the Mont Blanc massif, estimated by balanced sections and a restoration of the Ultrahelvetic klippen in the sub-alps, exceed 59 km. Thrust continuity, incorporating the restorations of nappes and imbricate geometries around the Mont Blanc massif, is illustrated on a crude, restored branch-line map which also serves as a preliminary palaeogeographic reconstruction. External thrust systems, to the east of the external Belledonne/Aiguilles Rouges massif, restore to a width of at least 140 km in the footwall to the Frontal Pennine thrust.

In 1980 and 1981 mercury was determined in the filtered air (0.45 μm filter pore size) over the Ligurian coast from Diano Marina to Genoa and over Tuscany from Florence to Rosignano Solvay after air sampling using an airship. From 1980 to 1982 air sampling was also performed 1–2 m over the ground in Genoa and Rosignano Solvay, in Fiascherino/La Spezia, in the ventilated air of the mercury mine of Abbadia San Salvatore (Mt. Amiata/ Tuscany), in the surroundings of the geothermal hydroelectric power plants in Larderello as well as in Piancastagnaio and Bagnore (Mt. Amiata region), at one small fumarole of Vesuvius, at high altitudes of the Mont Blanc massif and some other sites. Air samples were taken using gold and silver adsorbers for the mercury collection. Determinations of the electrothermally desorbed mercury were carried out by atomic adsorption spectrometry. Different local conditions resulted in a wide concentration range of total or prevailing elemental mercury (about 1–1200 ng/m3, STP). The background levels (1–6 ng/m3, STP) were lower over the sea than over land. A geochemical anomaly (Mt. Amiata) and civilization accounted for the regional enhancement of atmospheric mercury levels; industrial activities influenced only even more limited areas. As a rule several hundred meters away from the point sources the air was almost unpolluted by mercury.

Three generations of mylonites occur in the Mont Blanc Massif :— the first one has produced mylonitic schists trending N20°E, of regional extension; the late Variscan Mont Blanc granite intruded these mylonites;— the second one has affected large areas in the Mont Blanc granite, with the same N20°E direction;— the third one is located along rather narrow bands N45°E, in the granite as well as in the older mylonitic schists.All theses mylonites have been generated under (Bi) - greenschist facies conditions. They exhibit steeply plunging schistosity and lineation. They are all ante-Alpine; paradoxically, Alpine structures within the massif do not exhibit a striking appearence.

Observations in the upper Bon Nant valley in the southwest part of the Mont Blanc massif show that klippes are more numerous than hitherto supposed. They indicate that dislocation at the base of the Tre-la-Tete and Mont-Tondu massifs involved faulting, during which tectonic slices were superposed on each other from east to west, and that large vertical faults are probably absent.

Field observations and microscope analyses of crystalline rocks of the Mont Blanc massif (France) lend support to the concept that Alpine deformation was continuous in space and regional in scale. The Mont Blanc and Aiguilles Rouges massifs are both part of the same Prealpine basement, which became separated by Alpine deformation. The general structural trend of the Aiguilles Rouges massif is north-south, but that of the Mont Blanc massif more closely corresponds to the Alpine trend. This change in orientation is directly related to mylonization of schistose crystalline basement rocks, under Alpine stresses.

Presents arguments in support of the concept that dynamometamorphic processes (recrystallization by mechanical deformation during which no material is added from sources outside the rock mass being deformed) and regional metamorphism (rock alteration accompanied by the additionof material from adjacent terrain or from depth) are parts of a same process and not distinct independent processes. The concordance exhibited by a differentially metamorphosed mass of Liassic limestones wedged in crystalline rocks of the Mont Blanc massif, exposed in a gorge near the tongue of the Tre-la-Tete glacier, France, is cited as an example of recrystallization which took place during the regional metamorphism associated with Alpine crustal movements.

Results of in situ stress measurements performed in bore-holes from the road tunnel between Chamonix and Courmayeur are given.

The Arp Nouva peat bog located in the upper Ferret Valley in the Mont Blanc massif was critically evaluated since published radiocarbon dates have led to controversial conclusions on the formation of this swamp. Radiocarbon dating of woody fragments from three pits of up to 1 m depth was used to discuss the question of whether the historically documented rock avalanche occurring in 1717 CE overran the peat bog or settled prior to its formation. For the deepest samples in the pits, calibrated radiocarbon ages between 1,652 and 1950 CE (95.4%; confidence level) were obtained, which fit very well into the time frame of the historical documented 1717 CE rock avalanche event. It can, therefore, be concluded that the Arp Nouva peat bog was formed by blockage of the Bella Combe torrent by the rock avalanche deposits. Furthermore, careful sample preparation with consequent separation of woody fragments from the bulk peat sample has shown that the problem of too old14C ages can be circumvented. This work demonstrates that a combined geomorphological and geochronological approach is the most reliable way to reconstruct landscape evolution. The key to successful14C dating is careful sample selection and the identification of the material that might not be ideal for chronological reconstructions.

Growth curves spanning the last two and a half centuries have been constructed for Rhizocarpon geographicum s.l. and Aspicilia cinerea, two ubiquitous lichen species that grow on granitic substrate...