"The dragon appears in the mythical history and legendary poetry of almost every nation, as the emblem of the destructive and anarchical principle; . . . as misdirected physical force and untamable animal passions. . . . The dragon proceeds openly to work, running on its feet with expanded wings, and head and tail erect, violently and ruthlessly outraging decency and propriety, _spouting fire and fury from both mouth and tail, and wasting and devastating the whole land_."[3] This fiery monster is the comet. [1. Popular Science Monthly," June, 1882, p. 193. 2. Ibid., p. 193. 3. "Chambers's Encyclopaedia," vol. iii, p. 655.] {p. 430} And Milton speaks from the same universal inspiration when he tells us: "A comet burned, That fires the length of Ophiucus huge In th' arctic sky, and _from its horrid hair Shakes pestilence and war_." And in the Shakespeare plays[1] we read: "Hung be the heavens with black, yield day to night! Comets, importing change of times and states, Brandish your crystal tresses in the sky; And with them scourge the bad revolting stars." Man, by an inherited instinct, regards the comet as a great terror and a great foe; and the heart of humanity sits uneasily when one blazes in the sky. Even to the scholar and the scientist they are a puzzle and a fear; they are erratic, unusual, anarchical, monstrous--something let loose, like a tiger of the heavens, athwart an orderly, peaceful, and harmonious world. They may be impalpable and harmless attenuations of gas, or they way be loaded with death and ruin; but in any event man can not contemplate them without terror. [1. 1 Henry VI, 1, 1.] {p. 431} CHAPTER VII. THE EARTH STRUCK BY COMETS MANY TIMES. IF the reader is satisfied, from my reasoning and the facts I have adduced, that the so-called Glacial Age really represents a collision of the earth with one of these wandering luminaries of space, the question can not but occur to him, Was this the first and only occasion, during all the thousands of millions of years that our planet has been revolving on its axis and circling around the sun, that such a catastrophe has occurred? The answer must be in the negative. We find that all through the rocky record of our globe the same phenomena which we have learned to recognize as peculiar to the Drift Age are, at distant intervals, repeated. The long ages of the Palæozoic Time passed with few or no disturbances. The movements of the earth's crust oscillated at a rate not to exceed one foot in a century.[1] It was an age of peace. Then came a tremendous convulsion. It has been styled by the geologists "the epoch of the Appalachian revolution."