let us therefore examine the dates of each of these, disregarding the fables invented by the tragedians about the gods; but if man is not eternal then neither is any other animal, so that then neither are the places which receive them, the earth, or the water, or the air; from all which considerations it is plain that this world is liable to destruction.
 But it is necessary to encounter such quibbling arguments as these, lest some persons of too little experience should yield to and be led away by them; and we must begin our refutation of them from the same point from which the Sophists begin their deceit. They say, "There could no longer be any inequalities existing on the earth, if the world were eternal." Why not, my most excellent friends? For other persons will come up and say that the natures of trees are in no respect different from mountains; but just as they at certain seasons lose their leaves, and again at certain seasons recover their verdure again; on which account there is admirable truth in those lines of the poet:—

 "Like leaves on trees the race of man is found, 
 Now green in youth, now withering on the ground; 
 Another race the following spring supplies; 
 They fall successive and successive rise." 

 Homer, II. vi. 147. And so in like manner some portions of the mountains are broken off, and others grow in their stead: but after a long lapse of time the additional growth becomes conspicuous because the trees having a more rapid nature, display their increase with great rapidity; but mountains have a slower character, on which account it happens that the additions which take place in their case are not perceptible by the outward senses except after a long time.
 And these men appear to be ignorant of the manner in which they are produced, since if they had not been, perhaps they would have been silent out of shame; but still there is no reason why we should not teach them; but there is nothing new in what is now said, neither are they our words but the ancient sayings of wise men, by whom nothing which was necessary for knowledge has been left uninvestigated; when the fiery principle which is contained beneath, in the earth, is thrust upwards by the natural power of fire, it proceeds to its own appropriate place; and if it meets with any respite or
 Homer, II. vi. 147. 
 
relaxation, though ever so slight, it draws up with it a large portion of the earthy substance, as much as it can; and when it has emerged from the earth it proceeds more slowly; but the earthy substance being compelled to follow it for a long time, being at last raised to an immense height, is contracted at the top, and at last comes to end on a sharp point imitating the general appearance of the flame of fire;