319 CHAP. XVIII. On Volcanoes and Earthquakes. The history of Volcanoes forms one of the most popular and the most interesting branches of Gco- logy. If the splendour and the consequences of their eruptions attract the ordinary spectator, the Geologist finds, in their phenomena, difficulties which it is his duty to explain, and analogies widely con nected with other departments of his pursuit. While they are the great sources of the rocks that are formed in our own times, they throw light on the history of the unstratified substances : in the power by which they elevate and derange the surface of the earth, they afford a clue to the nature of the far greater changes which it has formerly undergone: and, in reflecting on their seats and causes, we are led to form conjectures respecting the interior parts of the globe. If, in history as in nature, we find the memorials of countries destroyed, of mountains formed and de molished, of cities overwhelmed, of rivers that have changed their courses, of lakes swallowed up, or generated, so, in compensation of all this evil, the land is raised above the level of the waters and new islands emerge from the ocean. The most delightful parts of Italy have suffered from volcanic fires; the history of the Subapennine hills even proves that vast tracts of this country have been raised into ex istence by their power. And, however terrific may be the phenomena of volcanoes, they are less inte resting than these records of antient eruptions ; which connect the present appearances with others, of a far