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Let us ask ourselves, therefore, what it is that stirs the earth to its foundation, what moves a mass of such weight, what it is that is stronger than the earth, and that in its violence can shake such a load. Let us inquire why at one time the earth trembles, at another is loosened and sinks, and again is divided into parts and opens a chasm; or why on some occasions the intervals of destruction are prolonged, on others are suddenly cut short. What is the cause why it now consigns to its depths rivers of renowned greatness, and now causes fresh rivers to issue? why does it sometimes open up springs of hot water, sometimes freeze them with cold? and why at times are fires caused to shoot out through some hitherto unknown opening in mountain or crag, while sometimes well-known fires, that have been famous for centuries, are suppressed? The earthquake produces a thousand strange sights, changing the aspect of the ground, levelling mountains, elevating plains, exalting valleys, raising new islands in the deep. What are the causes that bring these things to pass? That is a subject well worthy our discussion. What, you say, will be the reward of our labour? That reward, I say, which surpasses all others, the knowledge of nature. Among the many serviceable lessons to be derived from such researches, no feature is more commendable than this, that man is thereby made to dwell upon the sight of his own grandeur79; the study is pursued, not in hope of gain, but from the wonder it excites. Let us inquire, therefore, what it is that brings about all this. The inquiry is so fascinating to me that although long ago in my youth I published a volume on earthquakes, I am anxious to make another trial of my powers, and to see whether age has added anything to my knowledge, or, at any rate, to my industry.