EditorialGears map of the district of Clausthal and Zellerfeld, Map of the shafts, passages and tunnels of the mines in the Clausthal-Zellerfeld region (Harz), pl. 1, after p. 240, 1846, Am?d?e Burat; Carl Hartmann: Theorie der Erzlagerst?tten, begr?ndet auf di...