All these are connected with each other below the surface of the earth in many places by narrow and broader channels, and thus have outlets through which much water flows from one to another as into mixing bowls; huge rivers of both hot and cold water thus flow beneath the earth eternally, much fire and large rivers of fire, and many of wet mud, both more pure and more muddy, such as those flowing in advance of the lava and the stream of lava itself in Sicily.