The known facts on the distribution of the silica in and associated with many ore deposits suggest that only a small proportion of this oxide is imported into the ore zone from distances measured in thousands of feet or more. Most of it appears to be derived from the desilication of alumino-silicate walls and transported for distances often measured in inches, and rarely more than hundreds of feet.This belief suggests a unique approach to the theory of the character of the ore-forming fluids, and further, following Knopf, that the "magma" need not be called upon to supply much of the silica and perhaps none at all for many ore deposits.Speculation on the nature of the ore-making fluids leads to the further suggestion that they are similar to volcanic emanations. The original environment of the ore body could be a mass of structurally open ground of one form or another that is the site of a pool or reservoir of condensate, connate, meteoric or sea water. This is activated by the "volcanic emanations." The alumino-silicate walls are attacked particularly by hot water and carbonic acid and the silicates broken down to form lower silica species and other minerals. The excess silica is moved to the more open ground. In the form of quartz, chalcedony, etc., it is progressively fractured and forms the channel and locus of deposition for most of the sulphides.The most active agents and/or elements in the genesis of ore deposits are those among the most active and conspicuous in vulcanism and the solar system. Particularly these are H, O, C and S and Cl usually encountered as H 2 O, CO 2 , H 2 S and simple chlorine compounds.