The thesis is developed that differences in the densities of natural ground waters are sufficient to motivate their circulation in certain cases without the aid of the usual conception of piezometric or artesian head. Such densities are especially likely to be developed in the vicinity of oxidizing ore masses where substantial amounts of heavy salts are taken into solution. These solutions are thus enabled to descend well below the water table producing oxidation, enrichment or solution, since chemical reactions with wall rock tend to replace the heavier elements with equivalent lighter ones. Data for simple chemical solutions and actual mine waters are presented to support this view. The added suggestion is offered that the variations in density of ore-depositing magmatic solutions probably are even greater and more important.