At intervals for many years there has been a small production of fluorite from the vicinity of Madoc, Ontario. During the war some deposits have been developed into mines producing in all several thousand tons of fluorite per annum. The rock formation in the region around Madoc as indicated by Miller and Knight1 consists of Precambrian (Keewatin, Grenville and Hastings), with intrusions of Moira granite, on which lies the Black River limestone. This whole series is cut by veins carrying fluorite, calcite and barite. Many years ago some of the veins were worked for barite, but during the last three years the mines have been worked for fluorite.