From a topological point of view, the Thommen mining area is very homogeneous, since the mining areas did not develop depending on the epoch, but the mining centers remained topologically the same over the entire funding period. The origins of Thommen slate mining can be found in the area of the Sattelberg. At least since the end of the 17th century, two main mining areas were important for Thommen slate mining. On the one hand the districts "Heckenberg" and "Hesselnbüsch" bordering on the district "Sattelberg" and the adjacent district "An der Köpp", on the other hand the actual "Thomerberg" with the adjacent district "Brasilienberg". Until the commercial restructuring of mining in 1863, these areas remained the main mining areas. After 1863, Thommen slate mining concentrated almost exclusively on the "Thomerberg" and the adjoining "Brasilienberg" with the various large mines. Little changed in this constellation until shortly before the First World War. The most productive pits by far, such as the pits "Mertesnaf I", "Mertesnaf II", "Neue Mertesnaf", "Mertesnafergraben" and "Alte Graebenkaul" were located on the natural border between Thommerberg and Brazil Mountain, the so-called "Mertesnafgraben". .