The lithological repertory of the western basin of the river Somme has been tested through a study of Hallencourt (Somme) silex mine situated on an outlier of the Campanian period , and of surrounding excavations of surface sites. A geo-archaeological method describes how silex scatters according to the shape and dimensions of the sites, and duggests a complementary linkage beetween the economies of raw materials and fragmentation. This leads to a surface mapping of mining sites, showing their extracting structures and their silex-splitting facilities, the sequences of operations on axes, the great structure based on a mining area hardly lived in, with its internal organization and peripheral dwellings enjoying access to the site.