THE CONSTRUCTION OF THE FIRST ‘GEOGNOSTIC’ MAP OF DENMARK IN 1835: FROM THE SEARCH FOR COAL TO STRATIGRAPHY OF THE NORTHERN EUROPEAN BASIN

In 1835, the chemist and geologist Johan Georg Forchhammer published a booklet on the ‘geognostic’ relationships in Denmark, the result of intensive search for mineral resources. Attached to the last page, a folded colored map presented the geological formations observable in Denmark, similar to maps already published in England and France. This first geognostic map of Denmark was the result of an original approach since, concerning the north-eastern half of the map, surface formations were not represented, but rather the underlying formations were depicted as they were hidden by superficial deposits. Indeed, in the absence of outcrops, Forchhammer actually put forward in 1820 the hypothesis that the Jurassic and Cretaceous formations had been deposited in a large basin in Northern Europe, bordered by ‘Primitive mountains’. As in England and France, the Jurassic and Cretaceous formations should therefore appear as extensive belts parallel to Primitive mountains. He attempted to validate his hypothesis by field campaigns which met with partial success and resulted in the present 1835 map and its accompanying memoir. This inferential mapping marked a turning point towards modern Danish geology.