At the incitation of Prof. Dr. B. G. Escher I undertook, in the springs of 1925 and 1926 the geological investigation of the Northern part of the Luganese Porphyry-district. I thus mapped one of the parts of this district, which remained to be revised, since T. Harada in 1883 published his thesis on the petrography of these regions. The investigated area is bounded to the North by the Tresa river, at the same time part of the Swiss-Italian frontier, and running from Ponte Tresa on the Lago di Lugano to Luino on the Lago Maggiore; on the West by the shore of the last mentioned lake between Luino and Porto Valtravaglia. The southern border is given by the broken line: Ponte Tresa-Marchirolo-Cugliate-Cunardo-Ferrera-Mesenzana-San Michele-Porto Valtravaglia.