This study focuses on the valley of a small river, the Ysieux, a tributary of the Oise, which delimits the north of the Plain of France. In ancient times it constituted the northern natural limit of the pagus of the Parisii tribe, as well as the later administrative limit of the Gallo-Roman civitas which subsequently coincided with the border of the Parisian Diocese. This valley with more or less steep slopes, especially around the towns of Fosses and Bellefontaine, still marks the limits of Île-de-France and Picardy. The natural topography has led to rich natural subsoil and their exploitation in open air quarries. The colluvial silts of the plateaux of the slopes were exploited to produce tiles, Lutetian limestone layers were widely extracted for local civil and religious construction and potters exploited clay from an extensive (Sparnacian) layer. Rotary querns, in turn, were hewn from a Cuisian sandstone of exceptional quality (Ypresian stage). The intensive field surveys carried out by archaeologists of the JPGF Association since the 1970s in and around this valley identified a large number of rotary quern blancs and aborted roughouts. Subsequently, in 1989, systematic surveys of the northern and southern slopes of the valley pinpointed several extraction sites exploiting Cuisian sandstone. A team led by Christian Garcia and François Boyer of the Groupe Meule has since studied their manufacture and distribution in the area between Chartres, Melun, Amiens and Vendeuil-Caply, Chateaubleau, Senlis, and all the Plain of France. The particular components of the Fosses sandstone, characterised by a combination of black geological (flint) and white elements (feldspar), makes it ideal for provenancing and led to identification of sectors of production at Fosses, Bellefontaine and Luzarches, sources most certainly of the hundreds of rotary querns manufactured and in use since Antiquity.