When we consider the magnitude of the ice-sheets which, it is claimed by the glacialists, covered the continents during the Drift age, it becomes evident that a vast proportion of the waters of the ocean must have been evaporated and carried into the air, and thence cast down as snow and rain. Mr. Thomas Belt, in a recent number of the "Quarterly Journal of Science," argues that the formation of ice-sheets at the poles _must have lowered the level of the oceans of the world two thousand-feet!_ The mathematician can figure it out for himself: Take the area of the continents down to, say, latitude 40°, on both sides of the equator; suppose this area to be covered by an ice-sheet averaging, say, two miles in thickness; reduce this mass of ice to cubic feet of water, and estimate what proportion of the ocean would be required to be vaporized to create it. Calculated upon any basis, and it follows that the level of the ocean must have been greatly lowered. What a vast, inconceivable accession of _heat_ to our {p. 62} atmosphere was necessary to lift this gigantic layer of ocean-water out of its bed and into the clouds! The ice, then, was not the cause of the cataclysm; it was simply one of the secondary consequences. We must look, then, behind the ice-age for some cause that would prodigiously increase the _heat_ of our atmosphere, and, when we have found _that_, we shall have discovered the cause of the drift-deposits as well as of the ice. The solution of the whole stupendous problem is, therefore, heat, not cold. {p. 63} PART II. The Comet. CHAPTER I. A COMET CAUSED THE DRIFT. Now, good reader, we have reasoned together up to this point. To be sure, I have done most of the talking, while you have indulged in what the Rev. Sydney Smith called, speaking of Lord Macaulay, "brilliant flashes of silence." But I trust we agree thus far that neither water nor ice caused the Drift. Water and ice were doubtless associated with it, but neither produced it. What, now, are the elements of the problem to be solved? First, we are to find something that instantaneously increased to a vast extent the heat of our planet, vaporized the seas, and furnished material for deluges of rain, and great storms of snow, and accumulations of ice north and south of the equator and in the high mountains. Secondly, we are to find something that, _coming from above_, smashed, pounded, and crushed "as with a maul," and rooted up as with a plow, the gigantic rocks of the surface, and scattered them for hundreds of miles from their original location. {p. 64} Thirdly, we are to find something which brought to the planet vast, incalculable masses of clay and gravel, which did not contain any of the earth's fossils; which, like the witches of Macbeth, Look not like th' inhabitants of earth, And yet are on it; "