From the results of certain chemical experiments in the laboratory, it would appear that organic matter is one of the necessary chemical agents for the decomposition of some of the solutions of gold. Therefore, if we assume this hypothesis to have a positive bearing upon this question, the abundance of organic matter occurring in the gravel beds adds to its weight as an argument. Selwyn found in the gold-bearing drifts of Australia quantities of fragments of wood, roots of trees, and other organic _débris_ to serve as nuclei, or as reagents for the reduction of mineral solutions. We may introduce as evidence the formation of iron pyrites in crystalline forms, which is taking place at the present day under the action of sea-water. The metal in these instances replaces the organic structure of wood, or assumes definite forms with a particle of organic matter as a nucleus. The formation of gold nuggets from solutions of the metal is by no means as wonderful or difficult of explanation as some other phenomena witnessed in metallurgy. The strange play of pseudomorphism is well defined in some instances, if not well understood. Here we observe that the peculiarity of form may be rigidly adhered to, while the composition is completely changed. In the waters of certain copper mines, drills, rings, and bars of iron that have accidentally been left have in course of time become transformed into pure copper. The iron of the implements has changed places with the atoms of copper held in solution. In connection with this interesting theory, there are some puzzling facts to be deduced from the phenomena of the auriferous sand beds of some of the rivers of Europe. The gold placers along the coast of the Danube and the Rhine are situated far from the mountains, the supposed sources of the metal, and there are also wide barren districts intervening. The river Tesino affords no gold in its sands until its waters have passed through and beyond Lake Maggiore. From these and other examples, it is quite evident that the gold which appears in these river beds has been derived from the placers through which the rivers have passed, and not from quartz reefs in the distant mountainous regions. The situation of these placers, with the evenness and regularity of their deposits, also the absence of auriferous ledges among the contiguous rocks, permit the observer to indulge in the idea that the gold may have been deposited from solutions and not from the decomposition of crystalline rocks. We certainly have sufficient evidence to object to that final explanation which ascribes all these depositions to aqueous action in distant times, and to the abrasion of primitive mountains, the evidence of whose existence is alone and doubtfully afforded by the _débris_ which form the strata of the gold and diamond placers. The ancients long ago noticed the deposition of gold in the beds of rivers; hence the phrase “The gold-breeding sands of Pactolus.”