. Bulletin of the Department of Geology. Geology. 1916] Umpleby: Ore on the Limestone Side of Garnet Zones 35 ore-bodies occur in the limestone close to or adjoining the granite, but ore also occurs in the granite, "often at considerable distance from the limestone." "The constituent minerals, and general character of the ore-bodies in the two formations, are very similar.'' The principal copper minerals are bornite and chalcopyrite, which are associated either with magnetite and hematite or with garnet, augite and tremo- lite. "All the ore-bodies of this (the latter) class

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. Bulletin of the Department of Geology. Geology. 1916] Umpleby: Ore on the Limestone Side of Garnet Zones 35 ore-bodies occur in the limestone close to or adjoining the granite, but ore also occurs in the granite, "often at considerable distance from the limestone." "The constituent minerals, and general character of the ore-bodies in the two formations, are very similar.'' The principal copper minerals are bornite and chalcopyrite, which are associated either with magnetite and hematite or with garnet, augite and tremo- lite. "All the ore-bodies of this (the latter) class, so far discovered, occur in the limestone, close to the granite, and are often separated from the granite by a zone of more or less completely replaced lime-. Fig. 10. Section through Alberta Mine, Mackay, Idaho, showing occurrence of ore in the central part of a garnet-diopside mass. stone."18 This relationship is clearly brought out by the geologic maps of the Grafter Mine and the Best Chance ore-body. Endo- morphism has resulted in a considerable development of garnet, pyroxene and epidote in the granitic mass. Interpretation The extent to which the occurrence of ore on the limestone side of garnet zones, as illustrated in the seven well known districts cited above, represents a general law cannot be definitely stated at present. Indeed, the object of this paper is merely to set it forth as a working hypothesis in the hope of arousing discussion and stimulating obser- vation. It is highly probable, however, that there are many more examples of the relationship. In papers on four of the districts cited one writer has clearly stated or illustrated the relationship, but in the writing of another on the same deposit I have been unable to find a quotable statement. The occurrence of ore on the limestone side of garnet zones, whether it be a constant relationship or not, must be explained for is ibid., p. 22.. Please note that these images are extracted from scanned page im