The chief effect of volcanic eruptions on the Geological structure of our Globe consists in the accumulation of cinders and molten rock, either upon the Surface of the Earth, or in the crevices and caverns that abound within its solid Crust. Sometimes, indeed, the operations of an active Volcano are accompanied by a movement of upheaval or of subsidence. Thus for instance, we have seen that a portion of the Italian coast was elevated when Monte Nuovo was thrown up, that the town of Tomboro was submerged on the occasion of the eruption of Sumbawa, and that the bottom of the sea was notably upheaved by the last outbreak of the volcanic fires of Santorini. Nevertheless it appears to be generally the case that when the Crust of the Earth is once burst open, and a means of escape thus afforded to the fiery agent below,--in other words, when the active volcano is established,--the process of upheaval gives place to that of eruption. But when, as is often the case, no such safety-valve is offered to the surplus energies of the subterranean fires, then the giant power of heat, in its struggle to escape, shakes the foundation of the hills, and uplifts the superincumbent mass of solid rocks. This theory which ascribes the phenomena of Earthquakes and Volcanos to the same common cause, acting under different circumstances, is now almost universally adopted by Geologists; and it may be briefly enforced by the following considerations. First, though Earthquakes have sometimes occurred far away from any known volcanic region, yet they are more frequent in the neighborhood of active or extinct Volcanos. Secondly, almost all volcanic eruptions are preceded by Earthquakes; and the Earthquakes generally cease, or, at least become less violent, when the subterranean fire breaks out in the form of a Volcano. And, Thirdly, it is plain that the condensed steam which is generated by internal heat, and the expansive power of the heat itself, must, of necessity, when pent up in the caverns of the Earth, tend to produce those very phenomena by which Earthquakes are distinguished. Let it be observed, however, that while we explain the phenomena in question by the agency of subterranean heat, this doctrine is by no means necessary for the main purpose of our present argument. Whatever may be the cause from which the Earthquake shock proceeds, it is enough for us to show that the Crust of the Earth has been from time to time upraised, and dislocated, and rent asunder in modern times, just as it is supposed in Geological theory, to have been upraised, and dislocated, and rent asunder from time to time in by-gone ages. We will set down a few out of the many examples observed and recorded during the last hundred and twenty years.