Besides these contemporaneous deposits, veins or lodes carrying the ores of various metals are found cutting rocks of all ages, and are probably even now in process of formation. - The question of eruptive or exotic rocks has already been briefly alluded to, but from its intimate connection with volcanic phenomena, from which it cannot well be separated, it is proposed to consider the whole subject in the article Volcano, in which connection the various theories with regard to the nature of the earth's interior, the sources of subterranean heat and of ancient and modern eruptive rocks, as well as of the gaseous products of volcanic eruptions, will be discussed. (See also Granite.) Under the head of Mountain will be considered some of the most important questions of geological dynamics, namely, those relating to the elevation of continents, the phenomena of denudation, and the origin of mountains. The chemical history of the globe, or what may be called chemical geology, will be discussed under the titles Rocks and Water.