Part 7 (1/2)

For the sake of the argument, however, we will suppose the northern ice-cap to have been even more imperative in its demands than Mr. Croll has deemed possible, driving some of our warm and cold temperate forms down into the lowlands of Columbia, Venezuela, etc., in the extreme northern portions of South America. But how would these forms have managed, even then, to cross the thermal equator and secure a permanent habitat in the present warm and cold temperate zones of that continent?

Manifestly, this question has never been practically solved, nor is it ever likely to be in our day or generation. It is nevertheless susceptible of solution, as Mr. Darwin thinks, by easy mental processes. We have only to take a bird's eye view of the situation, and mentally follow these forms in their long geographical tramp from the northern to the southern hemisphere.

They must have started, of course, some twenty thousand years or more before the earth reached its last superior limit of eccentricity. At that distant epoch the sub-arctic breezes must have been blowing pretty stiffly in our present temperate lat.i.tudes, and these forms would have been constrained, in due time, to seek a more congenial isotherm. They must accordingly have set out on their expedition, at about the period indicated, with the prospect of a long and tedious journey before them.

Some twenty thousand years must have transpired before they reached the line of the present Gulf states, and it would have taken as many more years for them to deploy to the right and successfully enter the Mexican states. In another twenty thousand years or so they might have doubled Vera Cruz, and headed, in a southeasterly direction, for the Central American states. The thermal equator would by this time have reached a point some thirty degrees south of the geographical equator, while the northern ice-cap would have swept down upon the traditional ”hub of the universe,” or some ten or twelve degrees in excess of Mr. Croll's calculations.

To have accomplished this grand glaciatorial feat the North Pole must have donned some twenty times the amount of ice now about both poles of the earth, and so changed the earth's centre of gravity as to have inundated every foot of land on its habitable surface. But if this terrible catastrophy had been avoided, and some of our extreme northern forms had forced their way through the Isthmus into the lowlands of Columbia, they must have done so at their greatest possible peril, even if they had reached the base of Old Mt. Tolima in advance of the thermal equator, now fleeing in dismay before the southern Ice-monarch, with all his isochimenal hosts in mad pursuit of their invaders. And if these adventurous northern forms had succeeded in ascending Mt. Tolima, they could never have got down again, with the a.s.sistance of forty glaciations.

But we can imagine Mr. Darwin promptly s.n.a.t.c.hing his pen to show the stupidity of these northern forms in not climbing Popocatepetl or some other lofty mountain in Central America or Mexico, on their retreat before the still advancing thermal equator. But how this would have helped them to cross the geographical equator, we fail to see. When Mr. Darwin, and the eminent corps of geologists and physicists accepting his solution of this ”vexed question,” can make a ”warm term” south _succeed_ a ”cold term” north, we shall have no difficulty in solving the problem ourself.

But, unfortunately, the two terms--the cold one north and the warm one south--are simultaneous in occurrence, and the same causes which forced these northern invaders into the tropics, when they followed _after_ the thermal equator, would have driven them ignominously back again _before_ it. The climbing of mountains would only have prolonged their disaster.

For after the glaciation north comes the glaciation south, and unless our cold temperate zone were pushed down beyond the geographical equator, none of its living forms could ever have reached the corresponding zone in the southern hemisphere.

But as this ”migration theory” is one of paramount importance to modern science, and especially to ”Darwinism,” [19] distinctively so called, let us, at the risk of repet.i.tion and tediousness, propose a scientific expedition for the better solution of this problem. To do this, we propose to cut loose from our stupid predecessors, the plants and animals, and invite Mr. Darwin and some of his more distinguished European contemporaries, not omitting Professors Gray, Winch.e.l.l, Yeomans, and some few other American admirers of his, to accompany us on a fresh expedition from the warm and cold temperate zones north to the corresponding zones south, _purely in the interest of science_. To make it certain that the time fixed upon for this ”expedition” to start, will not escape their attention, we will state what many of them already well know, that the present eccentricity of the earth's...o...b..t is very low, being only 0.0168, and that, in the year of our Lord 851,800, it will reach its next superior limit, with a few intervening oscillations of such minimum value as to render it hardly worth our while to start before that time.

We shall be obliged, of course to invite our distinguished European party to join us on this side of the Atlantic, as their own narrow and contracted continent furnishes no proper field for determining the problem in question. We shall insist upon one condition only: ”_That they shall never leave the warm temperate zone in which we shall set out on our expedition, except to pa.s.s halfway into an adjoining zone as is the habit, at times, with plants and animals_.” This condition will have to be rigidly observed, otherwise our expedition would be of no scientific value to future generations. As we shall have plenty of time to provide the necessary outfit, we will appoint Mr. Darwin purveyor-general of the party, and hold him responsible for any misadventure.

We will arrange for the expedition to start in the early autumn of the year of our Lord 831,800, or about twenty thousand years before the earth shall reach its next superior limit of eccentricity,--all of us eager, of course, to brave the climatic vicissitudes of the journey, and to solve the ”great problem of the ages,” which is, to determine how the gigantic elephantoids of the Eocene period managed to cross the thermal equator, and pa.s.s into the present arctic regions of our globe.

As ”the king never dies,” so the old southern Ice-monarch will be succeeded by the young northern one, at about the period named. We shall then have a decided advantage over our predecessors, the plants and animals, in their journey southward, since we shall know the exact route they took, and need only follow it. Presumably they had no such information, nor had they either chart or compa.s.s to guide them,--a circ.u.mstance which Mr. Darwin has not sufficiently taken into account in predicating intelligence of his favorite pedestrians. Besides, these vegetal and animal forms had one difficulty to encounter which we shall not experience. With all the northern forms driven down into the Central American states, they must have been sadly crowded for room, especially near the Isthmus. The social conifers must have monopolized all the more favored sites on the mountain sides and tops, while the humbler denizens of the forest must have contented themselves with still more limited quarters. The more impatient animals, for lack of necessary forage, must have crowded through the Isthmus only to be driven back by the tropical heats to their proper isotherms.

But our warm temperate zone is now moving southward, and our scientific expedition is moving with it. The northern Ice-monarch has resumed absolute sway, and our aphelion distance from the sun has increased some tens millions of miles. We have, in the mean time, moved down to the line of the Gulf states, and are deploying to the right in order to make a triumphant entry into Mexico. Mr. Darwin is daily consulting the isochimenals, and is confident that our northern ice-cap will equal Mr.

Croll's highest expectations. The news finally reaches us that the Gulf stream has turned its course southward, and is now pouring its immense treasures of heat into the South Atlantic, if not turning the African ”horn” and was.h.i.+ng the far-off Australian coast. This fact greatly increases the enthusiasm of our European party, and they hasten forward into the sub-tropical zone, almost ”violating conditions” in their haste to enter the tropics.

At length, we crowd the narrow pa.s.sages of the Isthmus, and the glory of a warm temperate climate bursts upon our view in the Columbian states, of South America. _The expedition promises to be an entire success_. At least, Mr. Darwin thinks so, and he is now the Sir Oracle of our party. We deliberately enter the lowlands of Columbia, and make ready to ascend the sub-tropical mountains--those formerly equatorial--where the ”great scientific problem of the ages” is to be demonstrated. But we are measuring time by almost _Sirius_ distances, and vast geologic periods sweep by without apparent record. The northern ice-cap has been a prodigious one, crowding us nearly down to the geographical equator, with the advantage we have of appropriating some five and half degrees of the sub-tropical zone.

But the year Anno Domini 851,800 finally rolls round, and the maximum of the earth's ice-cap is reached. Old Mt. Tolima looms up in the distance, and we soon ascertain that its height is sufficient for all scientific purposes. Its summit displays a glittering ice-cap, and we are certain to find the proper isotherm by climbing its umbrageous sides. We accordingly make haste to reach its base, and get there not a minute too soon; for the young southern Ice-monarch has stolen a march on the thermal equator, and is driving it irresistibly back to its old quarters. His march northward is a continuous triumph and ovation up to 55A deg., and the heart of Patagonia is made glad by his near approach. True, the white gates of commerce are closed about the Horn; but that is no concern of these wild Patagonians.

The aggressive Britton is driven out of New Zealand, and that is another source of joy to the savage breast. Tasmania would extend a gladder welcome than all to the Ice-crowned monarch, but alas, not a drop of Tasmanian blood runs in human veins! Cape Good Hope has now a sub-arctic climate, and the heart of the wild Kaffir and Zulu rejoices that the sceptre of ”perfidious Albion” is broken.

The thermal equator at length reaches the base of Mt. Tolima, and hastens northward to the Isthmus, and thence to Hondurus and New Guatemala, where, by sheer force of exhaustion, it comes to a halt.

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 pa.s.s into high southern lat.i.tudes, 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 pa.s.sage 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 r.e.t.a.r.d 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...o...b..t. 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 acc.u.mulation of ice about either pole, and the probable s.h.i.+fting 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 acc.u.mulated 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 60A deg.. This acc.u.mulation, 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 _Pre_vision lies behind all possible _pro_vision, 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 a.s.sociation 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 j.a.pan, Mantchooria and Northern China,--_i.e._ Eastern North America with Eastern North Asia--half the earth's circ.u.mference apart, we find an astonis.h.i.+ng similarity.” But why astonis.h.i.+ng? 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-const.i.tuents, and other conditional incidences of this Asiatic region, in the light of all the physiological facts before them, the circ.u.mstance of this great similarity of flora would have been anything but astonis.h.i.+ng. 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 cla.s.ses 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 alt.i.tudes correspondingly varying with the lat.i.tudes 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.