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Fire is the cause assigned by some for earthquakes, but they are not agreed as to its method of action. First among them is Anaxagoras, who is of opinion that pretty much the same cause produces concussion in the earth as in the atmosphere. In the nether parts of earth, air (gas) causes explosions of thick atmosphere massed in clouds with the same violence as on earth clouds are wont to be burst. Fire is struck out by this collision of clouds and by the rush of the atmosphere that is forced out. This fire in seeking an exit meets obstructions and bursts through all obstacles, until it has either found a way of escape to the light through the narrow passages, or has made one for itself by violence and destruction. Other writers who still believe the cause to lie in fire do not suppose that this is its method of action: they think the fire presents itself in more than one place and burns away everything in the vicinity. Then if the parts eaten away fall in at any time, a shock follows in the portions which are deprived of their supports; they first totter and then collapse; nothing encounters them to support their weight. Then chasms and vast gulfs are opened up, or it may be, after hanging a long time in the balance, the ground settles down over what is still left standing. We see the same thing happen ordinarily as often as a part of the city suffers from a fire. The joists are burnt through, or what gave support to the upper part of the buildings is undermined. Then the roofs after tossing about for a long time fall in; their swaying and oscillating continue until they find a resting-place on solid ground.