But, as the equatorial zone extends fifteen degrees both ways from the thermal equator, its southern limit now rests on the geographical equator, and accordingly encircles the base of our "mount of refuge." We are now up this mountain some sixteen thousand feet above the equatorial lowlands, with the sub-tropical, tropical, and equatorial zones between us and the possibility of our further migration southward, without violating the express conditions imposed at the outset of our expedition.
The fact soon stares us in the face that we have been no more successful, in our efforts to cross the thermal equator and pass into high southern latitudes, than the stupid plants and animals before us; and Mr Darwin's faith in high mountains springing from equatorial lowlands, disappears in jest and derision as we all good-humoredly agree "to break conditions," and find our way back to the centres of activity and trade in the Old and New Worlds, leaving the great scientific problem of the ages to solve itself as best it may. We accordingly descend from our mountain fastness, hasten to the coast, and take passage by steamer to Manhattan, the great commercial metropolis of the world. Here we find that the barometer of exchange was long ago taken down in London and hung up in New York. The Old Antiquarian Society rooms are the first object of interest sought by us. On making our way thither we look for a copy of the Herald, of the date of our departure, in which we find an account of the scientific expedition fitted out by us, facetiously termed "The Great Wild-Goose Chase after the Thermal Equator"--presenting one of the most humorous bits of sensational pleasantry ever given to the American public.
But an apology is due the staider reader for the seeming levity of this narrative adventure. The exposition of Mr. Darwin, though widely accepted on both sides of the Atlantic by the scientific world, has seemed to us too trivial for serious reply. If we have leaped over vast periods of time, it makes no difference with the argument. So long as the thermal equator, or more properly the equatorial zone, or any part of it, lies between the warm or cold temperate forms, whether plants or animals, and their point of destination in the southern hemisphere, they can never migrate thither, any more than the right whale of the arctic seas can swim the equatorial oceans. Nothing is gained by going out of the way to climb mountains, except to hopelessly retard the return of both plants and animals to their native zones. If we have not demonstrated this fact to the reader's fullest comprehension, it will be useless for him ever to write a Q.E.D. at the end of any proposition.
It is true that some eminent astronomers and physicists hesitate to accept the theory that these glacial epochs are due to the eccentricity of the earth's orbit. But the argument favoring it is well fortified and ably advanced, and if we add to the astronomical considerations involved, the physical proofs of a change in the earth's centre of gravity, caused by the excessive accumulation of ice about either pole, and the probable shifting of the Gulf stream to a southerly direction during the glacial period north, it is difficult to resist the conviction that the real cause of glaciation has been suggested in this theory. With all the ice now accumulated about the south pole transferred to the north pole, it would make an ice-cap of over thirty miles in thickness at the pole, and one sloping in all directions southward to about 60°. This accumulation, it is claimed, would so change the earth's centre of gravity as to cause all the equatorial warm waters to flow southward instead of northward, as they now do.
This would certainly seem to be a most wonderful provision of nature, as well as one strongly calculated to impress the human mind with the belief that an Infinite Prevision lies behind all possible provision, whether witnessed in the heavens or in the earth, in astronomical or physical phenomena. Everywhere we see infinite perfection, combined with infinite beneficence, in the adaptation of means to ends. Nothing runs to waste--all things are conserved for use.
But in all the outspoken grandeur of the universe, there is nothing so grand, in exhibition at least, as the simple faith of a child, that "He who watereth the hills from his chambers," and "causeth the day-spring to know his place," will watch over the trustful little sleeper during the darkness and silence of the night.
Chapter VI.
The Distribution and Premanence of Species.
Professor Gray, in his address before the American Association for the advancement of science, delivered at Dubuque (Ia.) in 1872, while remarking upon the wide extent of similar flora in the same plant zones, says: "If we now compare, as to their flora generally, the Atlantic United States with Japan, Mantchooria and Northern China,--i.e. Eastern North America with Eastern North Asia--half the earth's circumference apart, we find an astonishing similarity." But why astonishing? Had our distinguished botanical professors, in this country and in Europe, thoroughly informed themselves as to the climatic conditions, the general physical features, geographical characteristics, soil-constituents, and other conditional incidences of this Asiatic region, in the light of all the physiological facts before them, the circumstance of this great similarity of flora would have been anything but astonishing. Indeed, the astonishment, if any, would have been expressed at the want of similarity, had it been found to exist.
Ever since 1862, these distinguished professors have had the great plant-charts of Mr. Arthur Renfrey before them, with the warm temperate zone north accurately laid down in its proper isotherms, as well as the different classes of vegetation peculiar to the two regions referred to, and some general conclusions of value to science might have been drawn therefrom. Besides, the fact of these similar antipodal flora was well known to many of them before this chart was issued. They also knew that all along the higher mountain ranges of this country, as well as in Europe, the same alpine flora was to be found under the same or similar alpine conditions. From Mt. St. Elias, in Alaska, to the Central American States, and thence, through the Isthmus, to the southern extremity of the Andes in South Patagonia, there is one unbroken line of alpine vegetation pressing the sides or summits of the loftier mountain ranges, at altitudes correspondingly varying with the latitudes in which they occur. And the same is true of the Alps in Europe and the Himalaya ranges in Asia, if not of all the mountain systems of the globe.