Returning to the earth, let us consider the products of these violent reactions. The hydrogen and hydrides of boron, silicon, sulphur and carbon, combined with the oxygen of the atmosphere, forming water and boric, silicic, sulphurous and carbonic acids, which in turn acted on the metallic oxides and hydroxides, forming sulphites, carbonates, borates and simple and complex silicates; some quickly, some slowly, some at low temperatures and atmospheric pressure, others at high temperatures in liquid or semi-liquid condition and under the pressure of rock masses above. To determine the relative age of existing rock layers, or the mode of their formation, whether by eruptive action, by surface heat, by deposition of finely divided material under water, or by metamorphic changes of the cooled silicate under subsequent action of water, pressure and heat, is the province of the geologist. The present writer refrains from an opinion whether any of the first formed solid crust could or could not survive to the present day in its primary form, considering the exposure to water, acids, heat and pressure which it suffered. Yet an idea may be formed of the condition of the earth’s surface when it had cooled so far that the more violent chemical action had ceased. It consisted chiefly of silicates, simple and complex; of some of the original binary compounds, which are scarce affected by water or acids, such as the silicide of carbon (carborundum), of stable oxides, chlorides and sulphides, with other compounds in smaller proportion, and free elements in greater proportion than at the present day. Everywhere, from crevices in the surface, hydrocarbons, phosphoretted hydrogen (phosphine) and ammonia were issuing as gases; the atmosphere was heavy with these gases and with carbon dioxide.