88. But, if the intensity of volcanic heat be such as is here stated, it will be found very difficult to account for a fire of such activity, and of such long continuance in the same spot, by any decomposition of mineral substances near the surface. In the place where this combustion is supposed to exist, it must be remembered, that there is no fresh supply of materials to replace those that have been consumed, and that, therefore, the original accumulation of these materials in one spot, must have been very unlike any thing that has ever been observed concerning the disposition of minerals in the bowels of the earth. 89. If, on the other hand, we ascribe the phenomena of volcanoes to the central heat, the account that may be given of them is simple, and consistent with itself. According to all the appearances from which the existence of such heat has been inferred above, it is of a nature so far different from ordinary fire, that it may require no circulation of air, and no supply of combustible materials to support it. It is not accompanied with inflammation or combustion, the great pressure preventing any separation of parts in the substances on which it acts, and the absence of that elastic fluid without which heat seems to have no power to decompose bodies, even the most combustible, contributing to the unalterable nature of all the substances in the mineral regions. There, of consequence, the only effects of heat are fusion and expansion; and that which forms the nucleus of the globe may therefore be a fluid mass, melted, but unchanged by the action of heat.