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Now, it will be observed that the principal theories assigned for the Drift go upon the hypothesis that it was produced by extraordinary masses of ice--ice as icebergs, ice as glaciers, or ice in continental sheets. The scientists admit that immediately preceding this Glacial age the climate was mild and equable, and these great formations of ice did not exist. But none of them pretend to say how the ice came or what caused it. Even Agassiz, the great apostle of the ice-origin of Drift, is forced to confess:
"We have, as yet, no clew to the source of this great and sudden change of climate. Various suggestions have been made--among others, that formerly the inclination of the earth's axis was greater, or that a submersion of the continents under water might have produced a decided increase of cold; but none of these explanations are satisfactory, and science has yet to find any cause which accounts for all the phenomena connected with it."
Some have imagined that a change in the position of the earth's axis of rotation, due to the elevation of extensive mountain-tracts between the poles and the equator, might have caused a degree of cold sufficient to produce the phenomena of the Drift; but Geikie says--
"It has been demonstrated that the protuberance of the earth at the equator so vastly exceeds that of any
[1. "Geological Sketches," p. 210.]
possible elevation of mountain-masses between the equator and the poles, that any slight changes which may have resulted from such geological causes could have had only an infinitesimal effect upon the. general climate of the globe."
Let us reason together:--
The ice, say the glacialists, caused the Drift. What caused the ice? Great rains and snows, they say, falling on the face of the land. Granted. What is rain in the first instance? Vapor, clouds. Whence are the clouds derived? From the waters of the earth, principally from the oceans. How is the water in the clouds transferred to the clouds from the seas? By evaporation. What is necessary to evaporation? Heat.
Here, then, is the sequence:
If there is no heat, there is no evaporation; no evaporation, no clouds; no clouds, no rain; no rain, no ice; no ice, no Drift.
But, as the Glacial age meant ice on a stupendous scale, then it must have been preceded by heat on a stupendous scale.
Professor Tyndall asserts that the ancient glaciers indicate the action of heat as much as cold. He says:
"Cold will not produce glaciers. You may have the bitterest northeast winds here in London throughout the winter without a single flake of snow. Cold must have the fitting object to operate upon, and this object--the aqueous vapor of the air--is the direct product of heat. Let us put this glacier question in another form: the latent heat of aqueous vapor, at the temperature of its production in the tropics, is about 1,000° Fahr., for the latent heat augments as the temperature of evaporation descends.
A pound of water thus vaporized at the equator has absorbed one thousand times the quantity of heat which
[1. "The Great Ice Age," p. 98.]
would raise a pound of the liquid one degree in temperature. . . . It is perfectly manifest that by weakening the sun's action, either through a defect of emission or by the steeping of the entire solar system in space of a low temperature, we should be cutting off the glaciers at their source."
Mr. Croll says:
"Heat, to produce evaporation, is just as essential to the accumulation of snow and ice as cold to produce condensation."
Sir John Lubbock says:
"Paradoxical as it may appear, the primary cause of the Glacial epoch may be, after all, an elevation of the temperature in the tropics, causing a greater amount of evaporation in the equatorial regions, and consequently a greater supply of the raw material of snow in the temperate regions during the winter months."
So necessary did it appear that heat must have come from some source to vaporize all this vast quantity of water, that one gentleman, Professor Frankland, suggested that the ocean must have been rendered hot by the internal fires of the earth, and thus the water was sent up in clouds to fall in ice and snow; but Sir John Lubbock disposes of this theory by showing that the fauna of the seas during the Glacial period possessed an Arctic character. We can not conceive of Greenland shells and fish and animals thriving in an ocean nearly at the boiling-point.
A writer in "The Popular Science Monthly" says:
"These evidences of vast accumulations of ice and snow on the borders of the Atlantic have led some theorists
[1. "Heat considered as a Mode of Motion," p. 192.
2. "Climate and Time," p. 74.
3. "Prehistoric Times," p. 401.
4. "Philosophical Magazine," 1864, p. 328.
5. July, 1876, p. 288.]
to suppose that the Ice period was attended, if not in part caused, by a far more abundant evaporation from the surface of the Atlantic than takes place at present; and it has even been conjectured that submarine volcanoes in the tropics might have loaded the atmosphere with an unusual amount of moisture. This speculation seems to me, however, both improbable and superfluous; improbable, because no traces of any such cataclysm have been discovered, and it is more than doubtful whether the generation of steam in the tropics, however large the quantity, would produce glaciation of the polar regions. The ascent of steam and heated air loaded with vapor to the altitude of refrigeration would, as it seems to me, result in the rapid radiation of the heat into space, and the local precipitation of unusual quantities of rain; and the effect of such a catastrophe would be slowly propagated and feebly felt in the Arctic and Antarctic regions.
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
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.
Next: Part II. The Comet.--Chapter I. A Comet Caused the Drift