With the supply of 4 figures and 24 closely interpreted dialectometrical maps, this paper analyses the linguistic change of the geolinguistic deep structures in Northern France (Domaine d'Oïl) between 1300 and 1900. As a matter of fact, the result will show - with some well explainable exceptions - the great stability of these deep structures. The two empirical bases are, on the one hand, the scripta-atlas of the Amsterdam Romanist Anthonij Dees of Northern France (published in 1980) and the "Atlas linguistique de la France" (ALF) of Jules Gilliéron and Edmond Edmont (1902-1910). Whereas the Dees-atlas is based on the philological exploitation of 3300 medieval non literary documents (charters) and therefore refers to written materials, the ALF contains oral materials which have been collected by field work and standardized interviews with competent dialect speakers. For to comparison of the two empirical levels (scripturality and orality) we use well experienced methods of the "Salzburg School of Dialectometry" like similarity maps, parameter maps, interpoint maps, correlation maps and trees.