The vast north-west European plain expands north of the Paris Basin,. Belonging to this morphological entity, the lower areas of northern France have distinct physical characteristics: low plains (at about 20 m of altitude) and width (several kilometers) disproportionately small compared to the size of the tributaries that drain them (Lys, Deûle, Scarpe...). Quaternary sedimentary cover is continuous and locally thick (up to more than 20 m). The ante-quaternary substratum at the outcrop in the lower area is devoid of hard rock likely to feed alluvial gravels. Also most deposits at the bottom of the valley of the lower country are composed of sand and silt, possibly enriched with a local supply of chalk gravels. Finally although juxtaposed with the Paris Basin, the lower country has a very different morphostratigraphic system: undulating valleys, gradual transitions between slopes and valley bottoms, few coarse deposits and wind deposit (loess, sand) valley bottoms at the end of the Last Glacial Maximum. This morphostratigraphic configuration has important consequences for the conservation and detection of archaeological sites prior to loess deposits. The old deposits can be very well preserved at the bottom of valleys (for example Eemien in Waziers) or at the bottom of slopes. But the detection of this potential is limited by two factors: - deposit depths (more than 3 m at Waziers, and potentially much more in some valley areas), – the similarity of chronologically indistinguishable deposits prior to the end of the Weichselien glaciation does not allow the establishment of reference points in testing. The associated archaeological potential is difficult to estimate quantitatively but important qualitatively. The difficulty of highlighting archaeological deposits in such a context requires consideration of our methods.