Among the leading propositions laid down by Arthur Renfrey, Esq., F.R.S. etc., etc., in the able article prepared by him for "The Physical Atlas of Natural Phenomena," by Alexander Keith Johnston, Edinburg Edition, 1856, on "The Geographical Distribution of the most Important Plants Yielding Food," are the following:--

1. "The primary condition of the existence of any species of plant, is its absolute creation, of which we know nothing.

2. "But we assume each species to have been created but once in time and in place, and that its present diffusion is the result of its own law of reproduction under the favorable or restrictive influences of laws external to it.[14]

3. "The most important of external laws are those relating to climate, since any species can flourish only within narrower or wider, but always fixed limits, of temperature, humidity etc.,

4. "The climate depends primarily on latitude, since this indicates distance from the source of heat, and the degree of obliquity of the heating rays."

There are other governing conditions, of course, such as the average rain-fall, distance from the equator, the elevation above the sea level in the various mountain systems of vegetation, etc., including the hygrometric, thermometric, telluric, and other conditions, of the several localities in which the different species of vegetation make their appearance.

But why should this distinguished naturalist insist upon the specific creation of either plants or animals? No scientific work of any paramount value confines the creative power of the universe to such narrow and restricted limits. Nor is there a particle of evidence to be drawn from the Bible that either plants or animals primarily originated in pairs. "Let the earth bring forth" is a command without limitation, or restriction, as to time, place, or number; and there is no reason to doubt that myriads of living forms swarmed everywhere, at first as now, in nature.

The idea, as expressed by Mr. Renfrey, that they were specifically created at one time and place only, whether in pairs, tens, twenties, or hundreds, is neither a rational one, nor has it any experience-argument or scientific authority on which to stand. Take, for instance, an experience-argument directly in point:--When the salt wells were first bored at Syracuse, N.Y., and the salt water was suffered to flow in waste over the low grounds about the salt-works, the small saline plants peculiar to salt-marshes in the warm temperate zone made their appearance, not in pairs, tens or hundreds, but in thousands rather, and have nourished there ever since. They came because conditions favored; because a salt-marsh had been artificially produced hundreds of miles away from the sea coast. This is only one of a large number of cases--more than we have room to specify in this connection--showing that wherever man, artificially or otherwise, produces the necessary conditions of plant-life, nature responds to the germinal law precisely as she did millions of years ago when the first salt-marsh favored the appearance of these saline plants--such as grow under no other conditions or circumstances.

But this idea of plants coming primarily from a single pair of progenitors, and each primordial pair branching off into diversified offspring, as in the case of the cabbage, assumed to be the original ancestor of all the turnips and ruta-bagas, may be an article of botanical faith, but never of experimental proof. "Entia non sunt multiplicanda prÆter necessitatem" is an old and well-approved maxim, applicable alike to the countless myriads of living organisms, as to the innumerable crystalline forms to be found everywhere in nature. Nothing is produced without the necessary conditions on which its production depends. "Necessity," in its primitive signification, is a term of the very widest meaning, and most universal application. It applies as well to the course of nature as to the course of human events--to the laws of vegetable and animal growth as to the inevitable march and order of celestial movements. As applied to any form of life-manifestation it implies a law of development and growth, as well as the physiological conditions without which vital manifestations are impossible. For law, in a physiological sense, is that mode of vital action by which effects are invariably and inevitably produced.[15] And this law is just as dependent on necessary vital conditions as vital manifestations are dependent on a physiological law. There must always be this reciprocal dependence and relationship between conditioning causes and effects. Whenever and wherever the necessary vital conditions exist, the physiological law takes effect, and the requisite vital manifestation is witnessed. And this is no doubt as true of animal as of vegetable life.

The earth's surface has been divided into eight separate zones, each of which is distinguished by its peculiar or characteristic fauna and flora. Their order, measured from the geographical equator, is as follows;

These several zones become sixteen in number when considered with reference to both the northern and southern hemispheres. And a like division of isothermals is made in the case of all our mountain systems, extending in both directions from the equator. In ascending our equatorial, tropical, and sub-tropical mountains, we find, of course, at their several bases, the temperature of the zones in which they respectively lie; from two thousand to three thousand feet, we reach the next higher zone, and so on, at about the same ratio of altitude, until we ascend to the polar zone or the line of perpetual ice and snow. The peak of Teneriffe, for instance, lies in the sub-tropical zone, but, at the elevation named, we meet with the vegetation which characterizes the warm temperate zone. And this holds true of all our mountain systems, in all latitudes, and at all altitudes, in all parts of the globe.

They all present the same or strikingly similar characteristics in plant life, with such variations and modifications only as might be accounted for, were all the influencing conditions and surrounding circumstances, modifying geographical distribution, known to us. From the lowest to the highest regions in which vegetation flourishes, this rule, with slight exceptions only, will be found to obtain, and it is in this direction that the observations of the scientific, as well as practical botanist, should hereafter be extended.

Humboldt noticed this characteristic feature of the earth's vegetation quite early in his explorations, and accordingly divided the tropical mountains, as the earth's surface was then divided, into three separate zones, the tropical, the temperate, and the frigid. But a closer classification now distinguishes them into the same number of zones as are marked, in approximate isotherms, on the earth's surface. Mr. Renfrey gives us further statistics of great value respecting these several plant zones of the globe, all of which fit so admirably into our theory of plant-distribution, that we can hardly see how the most prejudiced mind can resist the force of its application. Among the most important of these statistical facts are tables giving the comparative rain-falls in the different plant zones of the old and new worlds, and the classes of vegetation peculiar to each of them.

The Equatorial zone, for instance, is characterized by extreme luxuriance in growth, owing no doubt to the great heat and abundant moisture therein, and exhibits a vegetation which is peculiar to itself, and which could only thrive under the hygrometric, thermometric, telluric, and other conditions of that extensive zone.

The Tropical zones (those north and south of the equator) are characterized by a more abundant and diversified underwood, and, while retaining some of the equatorial forms, present fewer parasites and less rapid and luxuriant growths. They contain many plants and trees which are peculiar to their own limits, and these are generally the hardiest and most abundant. All equatorial forms disappear in these zones, that is do not pass into the sub-tropical zones. And these characteristics obtain in both the northern and southern tropical zones, as well as in the mountain systems within the equatorial regions.

The Sub-tropical zones, while retaining some of the more marked forms and general features of the tropical zones, such as palms, bananas, etc., exhibit the most striking characteristics of their own, consisting of a greater abundance of forest trees, especially those having broad, leathery and shining leaves, like the magnolias, the different species of laurels, and plants of the myrtle family. The tropical forms all disappear in these zones, as the equatorial do in the tropical zones.

The Warm Temperate zones exhibit the same disposition to retain some of the hardier and more abundant sub-tropical forms that characterize the other zones, in respect to their adjoining isotherms. But the trees and plants peculiar to this zone north, (and the same is no doubt true of the corresponding zone south), are more numerous, and embrace a wider range of deciduous, as well as evergreen growths. Evergreen shrubs, heaths, cistusses, and leguminous plants are everywhere more abundant. The marked characteristic of these zones is that the trees, plants, and arborescent grasses differ more widely in their general character, as well as run more extensively into varieties.

The Cold Temperate zones retain many of the deciduous trees of the warm temperate, but with less conspicuous blossoms, while a stronger tendency is shown toward social conifers, and the trunks of the deciduous trees are more profusely overrun with mosses, lichens, etc. These zones are also abundant in grasses.

The Sub-arctic zone north largely retains its hold upon the social conifers, giving place, northward, on this continent, as well as in Europe and Asia, to birch and alder, alternating with willows where the soil is sufficiently moist. Green pastures are still abundant, and showy flowering herbs abound during the brief spring, summer, and autumn months.

The Arctic zone retains few of the sub-arctic forms and its vegetation generally corresponds to what we call alpine shrubs, grasses, etc.

The North Polar zone shows few signs of vegetation and is thought to be entirely devoid of shrubs. A few small herbacious perennials of the most extreme dwarf habit, with a few lichens and mosses, constitute its entire vegetation.

There are some seeming exceptions to these general statements respecting plant-distribution, but they are hardly exceptions when we consider the elevation at which any one species, as the birches for instance, may appear, as they frequently do, in three several zones.

From these facts, gathered from the highest authorities, and well-attested on all hands, what general conclusions, if any, are to be drawn? Before answering this inquiry, let us proceed to state what conclusions have been drawn. According to all the authorities we have examined on the distribution of plant life; on the migration of plants and animals; on climate and time as affecting the transference of isothermal and isochimenal lines; on glacial and inter-glacial periods (with one important exception only), the assumption maintained is substantially that of Mr. Renfrey, that "each species of plant and animal was created but once in time and place," and that its present diffusion is the result of its "own law of reproduction under the favorable or restrictive influences of laws external to it." In other words, they insist upon original plant-centres, without definitely stating when or where they occurred, and that from these centres both plants and animals have migrated to all parts of the globe where they now appear, even crossing the equatorial zones where they could not live for a single day. This migration theory they attempt to explain in a way that is altogether more ingenious than satisfactory.

The important exception to which we refer is that of Professor Agassiz, as reported by his associate professor of Harvard University, Mr. Asa Gray, in his "Essays and Reviews Pertaining to Darwinism." In this work Professor Gray says of his late distinguished associate, that so far as he was aware, Professor Agassiz was the only leading naturalist "who did not take into his very conception of a species, explicitly or by implication, the notion of a material connection resulting from the descent of the individuals composing it from a common stock, of a local origin."

And Professor Gray adds this further testimony to the closeness of his associate's observations, in considering the very point here under consideration: "Agassiz wholly eliminates community of descent from his idea of species, and even conceives a species to have been as numerous in individuals, and as widely spread over space, or as segregated in discontinuous spaces, from the first to the later periods." And this view is undoubtedly the correct one. At all events, it entirely harmonizes with the facts of the biblical genesis, and obviates the necessity of accounting for the appearance of the same genera and species of plants or animals in the southern as in the northern hemispheres; in fact, their appearance in all parts of the globe, in corresponding isotherms, and under similar conditions of moisture and soil-constituents.

Wherever the hygrometric, thermometric, telluric, and other conditions favor, the class of vegetation indicated by the presence of these conditions makes its appearance, just as the fire-weed makes its appearance in our warm temperate zone, not from the presence of seed, but simply the presence of "conditions"--the provision of man harmonizing with the prevision of nature. In the same way the "Japan clover" made its appearance, as Professor Thurber states, "all over the southern states" during the late civil war, not from the migration of plants, but the presence of natural conditions.[16]

The numerous facts we have already given, and many others that might be arrayed in advocacy of our position, taken in connection with the general facts here presented in regard to plant-distribution, all point directly to climatal and soil conditions as the real cause of dissemination, and not to their migration from continent to continent, and across vast intervening seas and oceans, as the theory of Professor Gray and others would require us to believe. Take the case of the Schizoea pusilla of the New Jersey pine barrens, to which we have already referred, growing in similar barrens in New Zealand, and how are we to account for their antipodal appearance upon the globe? Professor Thurber refers to this plant as a "purely local fern" of New Jersey, and says it was for a long time supposed to be peculiar to that state until it was ascertained that it grew in New Zealand. Whether this plant "travelled" from New Zealand to New Jersey, or journeyed in the opposite direction, none of these "specific-centre" gentlemen can well inform us. Professor Agassiz would have said that it might have appeared, in numerous individuals, in both localities at the same time, or at different times, as conditions favored; and this would have been an exact scientific statement, no doubt, of the fact. Mr. Arthur Renfrey, and those who accept his scientific formulÆ, must insist that this most beautiful of all our ferns was such a "favorite child of nature" that she condescended to create it twice "in time and place," instead of only once. It is a poor rule, they may say, that has no exceptions in phenomenal manifestation.

Professor Gray may insist that such a phenomenon as this requires belief in the supernatural, and that migration by ocean-currents is the more rational theory of the two. But M. Alphonse de Candolle--quite as high authority as we can quote--has come to the conclusion that marine currents, and all other suggested means of distant transportation, "have played only a very small part in the actual dispersion of species," even across narrow channels and the near arms of seas. But why should the appearance of this fern at opposite points of the globe, with thousands of miles of ocean and continent intervening, be any more supernatural than the presence of Bacteria or TorulÆ[17] in different organic infusions? If the vital units of these infusoriÆ, are present in experimental infusion, as Professor Bastian virtually admits, why may not the vital germs or units of this Schizoea pusilla have made their appearance, in developmental forms, both in New Zealand and New Jersey, at the same or different periods of time? If Professor Gray regards the microscopical forms in organic infusions, or the statical forms in inorganic solutions, as supernatural, or as above the powers of nature, then we have no exceptions to make to his position. First, prove that these vital manifestations of nature are above the powers with which she has been endowed, or was originally endowed and we will concede the question of supernaturalness, and drop all exceptions to his line of argument. Whenever a dynamic law, or a statical, is found to be uniformly operative under a given set of conditions, we had supposed the operation not to be above the powers of nature, but in entire accord with them, and hence not supernatural.

But let us see into what an inextricable labyrinth of difficulty we are led by this theory of plant-migration from the equatorial to the sub-arctic zone, and vice-versa, and even beyond the equator to the sub-antarctic zone, and still vice versa. Before proceeding to consider the probable duration of the several geographical epochs, called glacial periods, on which their theory of plant-migration depends, or considering the evidence touching these glacial periods, we will state their position in regard to these possible migrations as briefly and concisely as we know how. Mr. Darwin's solution of this problem is the generally accepted one of the evolutionists, as well as most of the present scientific world. As the truth, or rather the falsity, of his pet theory of evolution depended on the satisfactory solution of this vexed problem, it became necessary for him to give his best and entire mental energies to the gigantic task which was, by universal consent, assigned him. The reader shall see how admirably the thermal equator is crossed by Mr. Darwin, with his vast swarms of flies, mosquitoes, insectivorous and other plants, forest trees, anthropoid apes, and general menagerie of wild animals, such as would gladden the heart of the "great American showman" beyond the most extravagant comparison.

The question, bear in mind, which he was specially called upon to solve, was how the temperate forms north--those, for instance, of the warm and cold temperate zones--managed to cross the thermal equator, and invade the corresponding zones in the southern hemisphere; just as though there was any more necessity of determining this question than the opposite one, of how the southern forms came to invade the northern hemisphere. We will give his solution of this problem in his own language, that we may not be charged with misrepresentation.

He says, in speaking of the glacial periods: "As the cold became more and more intense, we know that arctic forms invaded the temperate regions; and, from the facts just given, there can hardly be a doubt that some of the more vigorous, dominant, and widest-spread temperate forms invaded the equatorial lowlands. The inhabitants (flora and fauna) of these hot lowlands would at the same time have migrated to the tropical and sub-tropical regions of the south; for the southern hemisphere was at this period warmer. On the decline of the glacial period, as both hemispheres gradually recovered their former temperatures, the northern forms living on the lowlands under the equator would have been driven to their former homes or have been destroyed, being replaced by the equatorial forms returning from the south. Some, however, of the northern temperate forms would almost certainly have ascended any adjoining highland, where, if sufficiently lofty, they would have long survived, like the arctic forms on the mountains of Europe.

"In the regular course of events the southern hemisphere would, in its turn, be subject to a severe glacial period, with the northern hemisphere rendered warmer; and then the southern temperate forms would invade the equatorial lowlands. The northern forms which had before been left on the mountains would now descend and mingle with the southern forms. These latter, when the warmth returned, would return to their former homes, leaving some few species on the mountains, and carrying southward with them some of the northern temperate forms, which had descended from their mountain fastnesses. Thus we should have some few species identically the same in the northern and southern temperate zones, and on the mountains of the intermediate tropical regions."

We are sorry to spoil so ingenious a theory as this to account for plant-migration from the temperate zones north to the corresponding zones south. But in spite of all the great names which will frown down upon us in the attempt, we are obliged to demolish this altitudiness structure, even at the risk of its tumbling about our own ears.

But first let us lay down a few undeniable propositions, on the strength of which this ingenious and purely speculative theory of Mr. Darwin must rest:--

1. It is universally conceded by the scientific world that these glacial epochs, however many of them there may have been in the past and however few there may be in the future, depend, for their occurrence, upon the maxima of eccentricity in the earth's orbit about the sun.

2. The actual amount of heat which the earth annually receives from the sun is in no way affected by the eccentricity of its orbit. It is a constant quantity, and only unequally distributed on the earth's surface, being neither increased nor diminished, as our winters occur in aphelion or perihelion.

3. The actual amount of ice-cap accumulated about the two poles of the earth, is also a constant quantity. And to measure the severity of any glacial epoch, we have only to determine the exact amount of ice (not altogether an impossible problem) about the two poles at any given time, and then determine the effect of its entire transference from one pole to the other.

4. It is not probable that the present ice-cap of the south pole extends continuously and permanently much farther north than 80° or 81°. Mt. Erebus, in Victoria Land, lies in about this latitude, and it was only a few years since that the coast line of that island or continent was traversed, by English exploring vessels, from Mt. Erebus to a point some ten or twelve degrees further north. [18]

5. But if we estimate the southern cap as extending continuously to 75°, what would be the effect of its transference at once to the ice-cap of the north pole? Would it extend it, after assuming its proper glacial slope, below 60°, a point falling within the present subarctic zone? The utmost limit to which Mr. Croll, in his great work on "Climate and Time," conceives it possible that it should extend, in any glacial epoch, is to 55°, or about the northern boundary of England.

Now unless the astronomers and physicists are all at sea about the causes of glaciation, the warm temperate zone can never be pushed any further south than the tropical zone, nor the cold temperate any further than the sub-tropical. This would be the extreme limit. Mr. Croll says, in speaking of these glacial periods; "It is, of course, absurd to suppose that an ice-cap could ever actually reach down to the equator. It is probable that the last great ice-cap of the glacial epoch nowhere reached half way to the equator. Our cap (that of Europe) must therefore, terminate at a moderately high latitude." And if the gulf stream flows southward during the glacial period north, as he supposes probable, the cap on this continent would probably terminate at the same moderately high latitude. Assuming that Mr. Croll's estimate is the more probable one, it would only push the cold temperate zone down to the line of the Gulf States; the warm temperate, to the southern line of Mexico; the sub-tropical, to the Central American States, and the tropical to the United States of Columbia, Venezuela, and Guiana.

Suppose, then, that some seven hundred thousand years ago, more or less, when the North Pole had fully donned the earth's ice-cap, with all the isothermal and isochimenal changes thereby effected, what must have been the line of march taken by our northern vegetal and animal forms to escape the cataclysm of ice and snow then impending? Manifestly, they would have flocked, first to the Gulf states, then to Mexico, and afterwards to the Central American states; but none of them could ever have been crowded through the Isthmus of Panama, since at the height of the last glaciation, that portion of the continent must have been the tropical barrier to our northern forms, as it is now the equatorial barrier.

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 latitudes, 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 assistance of forty glaciations.

But we can imagine Mr. Darwin promptly snatching 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 repetition 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, Winchell, 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 orbit 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 pass 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 pass 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 compass to guide them,--a circumstance 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 washing 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 passages 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 55°, 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 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.