In the making of tungsten steels a considerable change has taken place through the increased use of the electric furnace. One considerable producer, the Latrobe Electric Steel Co., makes all of its high-speed tool steel in this way. The Vanadium Alloys Steel Co., one of the larger producers, makes a large part of its steel in the electric furnace, and the Crucible Steel Co. and some other steel companies are understood to make a part or all of their steels thus. The removal of tin, copper and other impurities from ferrotungsten by grinding and chemical treatment has made possible the use of impure ores in the production of high-grade ferrotungsten in the electric furnace. GEOLOGICAL DISTRIBUTION Tungsten, even more than tin, is found almost exclusively with granitic rocks. In a few places tungsten ores are found in volcanic, sedimentary or metamorphic rocks, but as is postulated with certain tin deposits, many of these deposits may be explained on the supposition that they are not far vertically above underlying granite. Among the deposits themselves there is a considerable variety of types, and they may be classed as follows: Segregation deposits, pegmatite dikes, veins, replacement deposits, contact metamorphic deposits and placers. Segregation deposits are few and of little importance and constitute those deposits in which wolframite is segregated in granite, like biotite or hornblende. A closely related type is the occurrence of tungsten minerals in aplitic granite, and this grades almost insensibly into the second type, the pegmatites. The pegmatites are also of comparatively small importance, but do yield certain quantities of tungsten minerals. The pegmatites also grade into the next type, the veins, which have heretofore furnished the greater part of the tungsten minerals of the world. Closely connected with the veins are the fourth type, replacement deposits, in which the country rocks alongside the veins, though the veins may be very small, are replaced by various minerals, including those of tungsten. The only known large examples are the wolframite deposits near Lead, South Dakota, which were considerable producers under the high prices of the Great War. Among the replacement deposits are to be noted also such deposits as those in the Deep Creek Mountains, Utah, in which solutions following cracks in monzonite have replaced the rock with a mass of feldspar, quartz, tourmaline, apatite, scheelite, wolframite (very little), bismuth, copper, and molybdenum minerals, which under other conditions would be unhesitatingly called pegmatite.