This photograph was taken here on September 19th 1895 during an expedition to Sisteron by the Geological Society of France. The presence of renowned geologists such as Wilfrid Kilian and Emile Haug is a good indication of the interest that the scientific community already had in the geology of our region. Alongside these eminent scientists, and other members of the Geological Society of France, certain prominent locals with a passion for earth-sciences such as Gustave Tardieu, a pharmacist, and Saint-Marcel Eysseric, a lawyer and photographer, took part in this field-trip.
At that time, it was already known that the glaciers had arrived on the doorstep of Sisteron in the Quaternary period, but it was not possible to precisely pin-point the last moments of their presence here. Indeed, the radiation process, which today allows us to precisely date elements, was only discovered in 1896 by the French physicist Henri Becquerel.
The discovery of a fragment of fossilised juniper wood in a glacial moraine (sediments left behind as the glacier retreated) made it possible to carry out a precise-dating analysis (carbon-dating), thanks to the carbon 14 contained in this fragment, and to estimate the last major advancement of the Würm glacier (the last glaciation in the Alpine chronology) at 18,000 years BC. The moraines closest to Sisteron are located at Plan Roman, 4km north of the town, the maximum point of the glacier's extension. Stages of its retreat can also be seen at Le Poët and Rourebeau, about 10km further up-slope.