The present Danish-speaking population of Schleswig-Holstein is variously estimated at between 140,000 and 150,000. These subjects of the Kaiser occupy the territory south of the Danish boundary to a line formed by the western section of the Lecker Au, the southern border of the swampy region extending south of Rens and the northern extension of the Angeln hills. Between this line and the area in which German is spoken a zone of the old Frisian tongue of Holland survives along the western coast of the peninsula from the Lecker Au to the Treene river.[72] Frisian is also spoken in the coastal islands. The degree to which linguistic variations adapt themselves to physical configuration is admirably illustrated in this case, by the southerly extension of Danish along the eastern section of the peninsula where persistence of the Baltic ridge appears in the hilly nature of the land. The Low German of the long Baltic plain also continued to spread unimpeded within the low-lying western portion of the narrow peninsula, until its northward extension was arrested by uninhabited heath land. The presence of Frisian along the western coast is undoubtedly connected with the adaptability of Frisians to settle in land areas reclaimed from the sea. The province of Schleswig began to acquire historical prominence as an independent duchy in the twelfth century. Barring few interruptions its union with the Danish crown has been continuous to the time of the Prussian conquest. In 1848 both Schleswig and Holstein were disturbed by a wave of political agitation which expressed itself in demands for the joint incorporation of both states in the German Confederation. To what extent the mass of Danish inhabitants of the duchies took part in this movement is a matter of controversy. Holstein was an ancient fief of the old Germano-Roman Empire. Its population has always been largely German. But the duchy of Schleswig is peopled mainly by Danes. By the terms of the treaty of Prague of August 23, 1866, both Austria and Prussia had agreed to submit final decision on the question of nationality to popular vote.[73] The provisions of the clause dealing with the referendum, however, were not carried out, and on Jan. 12, 1867, Schleswig was definitely annexed by Prussia.[74] Incorporation of the Danish provinces was followed by systematic attempts to Germanize the population[75] through the agency of churches and schools. In addition a number of colonization societies such as the “Ansiedelungs Verein für westliche Nordschleswig,” founded at Rödding in 1891,[76] and the “Deutsche Verein für das nordliche Schleswig” were formed to introduce German ownership of land in the Danish districts. The final years of the nineteenth century in particular constituted a period of strained feeling between Danes and Germans owing to unsettled conditions brought about by duality of language and tradition. [Illustration: