1940 saw the publication of a now classic scientific paper by De Geer, the "Geochronologia Suecica", in which he presented the Swedish Time Scale, a floating varve chronology for ice recession from Skåne to Indalsälven. Ragnar Lidén made the first attempts to link this time scale with the present day. Since then, there have been revisions as new sites are discovered, and old ones reassessed. At present, the Swedish varve chronology is based on thousands of sites, and covers 13,200 varve years.