PHILOSOPHICAL JOURNAL.

Geographical Distribution of Animals.

By Professor Louis Agassiz.

The greatest obstacles in the way of investigating the laws of the distribution of organized beings over the surface of our globe, are to be traced to the views generally entertained about their origin. There is a prevailing opinion, which ascribes to all living beings upon earth one common centre of origin, from which it is supposed they, in the course of time, spread over wider and wider areas, till they finally came into their present state of distribution; and what gives this view a higher recommendation, in the opinion of most men, is the circumstance, that such a method of distribution is considered as revealed in our sacred writings. We hope, however, to be able to shew that there is no such statement in the Book of Genesis; that this doctrine of a unique centre of origin, and successive distribution of all animals is of very modern invention; and that it can be traced back for scarcely more than a century in the records of our science.

There is another view to which, more recently, naturalists have seemed to incline; viz., the assuming several centres of origin, from which organized beings were afterwards diffused over wider areas, in the same manner as according to the first theory, the difference being only in the assumption of several centres of dispersion instead of a single one.

We have recently been led to take a very different view of the subject, and shall presently illustrate the facts upon which the view rests. But before we undertake to introduce more directly this subject, there is another point which requires preliminary investigation, which seems to have been entirely lost sight of by all those, without exception, who have studied the geographical distribution of animals, and which seems to us to be the keystone of the whole edifice, whenever we undertake to reconstruct the primitive plan of the geographical distribution of animals and plants. The distribution of organized beings over the surface of our globe in its present condition cannot be considered in itself; and without an investigation, at the same time, of the geographical distribution of those organized beings which have existed in former geological periods, and had become extinct before those of the present creation were called into being. For it is well ascertained now that there is a natural succession in the plan of creation—an intimate connection between all the types of the different periods of the creation from its beginning up to this day; so much so, that the present distribution of animals and plants is the continuation of an order of things which prevailed for a time at an earlier period, but which came to an end before the existing arrangement of things was introduced.

The animal kingdom, as we know it in our days, is therefore engrafted upon its condition in earlier periods; and it is to the distribution of animals in these earlier periods that we must look, if we would trace the plan of the Creator from its commencement to its more advanced development in our own time.

If there is any truth in the view that animals and plants originated from a common centre, it must be at the same time shewn that such an intimate connection between the animals existed at all periods; or, at least, we should, before assuming such a view for the animals living in our days, discover a sufficient reason for ascribing to them another mode of dispersion than to the animals and plants of former periods. But there is such a wonderful harmony in all the great processes of nature, that, at the outset, we should be carefully on our guard against assuming different modes of distribution for the organized beings of former periods, and for those which at present cover the globe. Should it be plain that the animals and plants did not originate from a common centre at the beginning of the creation, and during the different successive geological periods, we have at once a strong indication that neither has such been the case with the animals of the present day; and, on the other hand, if there were satisfactory evidence that the animals and plants now living originated from a common centre, we should consider the matter carefully before trusting to the views derived from geological facts. Let us, therefore, examine first the value of the evidence on both sides.

We have already expressed, and we repeat here, our earnest belief that the view of a unique centre of origin and distribution rests chiefly upon the supposed authority of the Mosaic record; and is in no way sustained by evidence derived from investigations in natural history. On the contrary, wherever we trace the animals in their present distributions, we find them scattered over the surface of our globe in such a manner, according to such laws, and under such special adaptations, that it would baffle the most fanciful imagination to conceive such an arrangement as the mere results of migrations, or of the influence of physical causes over the dispersion of both animals and plants. For we find that all animals and plants of the arctic zones agree in certain respects and are uniform over the three continents which verge towards the northern pole, whilst those of the temperate zone agree also in certain respects, but differ somewhat from each other within definite limits, in the respective continents. And the differences grow more and more prominent as we approach the tropical zone, which has its peculiar Fauna and Flora in each continent; so much so, that it is impossible for us to conceive such a normal arrangement, unless it be the result of a premeditated plan, carried out voluntarily according to predetermined laws.

The opinion which is considered as the Biblical view of the case, and according to which all animals have originated in a common centre, would leave us at a loss for any cause by which to account for the special dispersion of animals and plants beyond the mere necessity of removing from the crowded ground to assume wider limits, as their increased number made it constantly more and more necessary and imperative. According to this view, the animals of the arctic zone as well as those of the tropics,—those of America as well as those of New Holland,—have been first created upon the high lands of Iran, and have taken their course in all directions, to settle where they are now found to be strictly limited. It does not appear how such migrations of polar animals could have taken place over the warmer tracts of land which they had to cross, and in which they cannot even be kept alive, in our days, with the utmost precautions: nor how the terrestrial animals of New Holland, which have no analogies in the main continents, could have reached that large island, nor why they should have all moved thither. And, indeed, it is impossible, with such a theory, to account, either for the special adaptation of types to particular districts of the earth's surface, or for the limited distribution of so many species which are found only over narrow districts in their present arrangement. It is inconsistent with the structure, habits, and natural instincts of most animals, even to suppose that they could have migrated over any great distances. It is in complete contradiction with the laws of nature, and all we know of the changes our globe has undergone, to imagine that the animals have actually adapted themselves to their various circumstances during their migration, as this would be ascribing to physical influences as much power as to the Creator himself.

And, again, the regular distribution, requiring precise laws, as we find it does, cannot be attributed either to the voluntary migration of animals, or to the influence of physical causes, when we see so plainly that this distribution is in accordance with the geographical distribution of animals and plants in former geological periods. But about this presently. We will only add, that we cannot discover in the Mosaic account anything to sustain such a view, nor even hints leading to such a construction. What is said of animals and plants in the first chapter of Genesis, what is mentioned of the preservation of these animals and plants at the time of the deluge, relates chiefly to organized beings placed about Adam and Eve, and those which their progeny had domesticated, and which lived with them in closer connection.

Let us now look at the results of geological investigations respecting the origin of earlier races of animals and plants. It is satisfactorily ascertained at present, that there have been many distinct successive periods, during each of which large numbers of animals and plants have been introduced upon the surface of our globe, to live and multiply for a time, then to disappear and be replaced by other kinds. Of such distinct periods, such successive creations, we now know at least about a dozen, and there are ample indications that the inhabitants of our globe have been successively changed at more epochs than are yet fully ascertained. But whether the number of these distinct successive creations be twelve or twenty, the fact stands in full light and evidence, that animals and plants which lived during the first period disappeared, either gradually or successively, to make room for others, and this at often-repeated intervals; and that the existence of animals and plants which live now is of but recent origin, is equally well ascertained.

There is another series of phenomena, not less satisfactorily established, which go to shew that the extent of dry land rising above the surface of the ocean has neither been equally extensive at all times, nor has it had the same outline at all periods. On the contrary, we know that, early in the history of our globe, there has been a period, when but few low groups of islands existed above the surface of the ocean, which, through successive elevation and depression, have gradually enlarged and modified the extent and form of the mainland.

Again, in examining the remains of organized beings preserved in the different strata constituting the solid crust of our globe, we find that at each period, animals and plants were distributed in the ocean and over the mainland in a particular manner, characteristic of every great epoch. A closer uniformity in their distribution is found in the earlier deposits, so much so that the oldest fossils discovered in the southern extremity of Africa, on the eastern and southern shores of New Holland, and in Van Diemen's Land, in North America, or in various parts of Europe, are almost identical, or at least so nearly related, that they resemble each other much more than the animals and plants which at present live in the same countries; shewing that uniformity in the aspect of the surface of the globe, as well as in the nature of animals and plants, was at first the prevailing rule, and that, whatever was the primitive region of these animals and plants, their types occupied much more extensive districts than any race of living beings during later periods. Are we to infer from this fact, that, at that period, these animals and plants originated from one common centre, and were distributed equally all over the globe? By no means. Though slight, we find nevertheless such differences among them in distant parts of the world as would rather sustain the view of an adaptation in the earliest creations to more uniform circumstances, than that of one centre of origin for all animals and plants of those days. During later periods, indeed, we find from geological evidence that large islands had been formed, more extensive tracts of land elevated above the surface of the ocean, and the remains both of the animals and plants derived from these different regions present already marked differences when we compare them with each other,—varieties similar to those which exist between the respective continents at present, though perhaps less marked. Shall we here again assume that animals and plants originated from another centre, or from the same centre as those of former periods, to migrate over those different parts of the world, through the sea as well as over land? It is impossible to arrive at such a conclusion, when we consider the distribution of fossil remains in the more recent geological deposits, or in those strata which were formed during the latest geological periods, immediately before the present creation. For we find in these comparatively modern beds a distribution of fossil remains which agrees in a most remarkable manner with the present geographical arrangement of animals and plants. For instance, the fossils of modern geological periods in New Holland are of the same types as most of the animals now living there. Again, the recent fossils of Brazil belong to the same families as those prevailing at present in Brazil; though, in both cases, fossil species are distinct from living ones. If, therefore, the organized beings of the recent geological periods had arisen from one central point of distribution, to be dispersed and finally to become confined to those countries where their remains are found in a fossil condition, and if the animals now living had also spread from a common origin over the same districts, and had then been circumscribed within equally distinct limits, we should be led to the unnatural supposition, that animals of two distinct creations, differing specifically throughout, had taken the same lines of migration, had assumed finally the same distribution, and had become permanent in the same regions, without any other inducement for their removal and final settlement than the mere necessity of covering more extensive ground after they had become too numerous to remain any longer together in one and the same district. This were to ascribe to the animals themselves, or to the physical agents under which they live, and by which they may be influenced, as much wisdom, as much providential forethought, as is evinced throughout nature, both in the distribution of animals, and in their special adaptation to particular portions of the globe in which they are closely circumscribed at present, and to which they were limited under similar circumstances during those periods which preceded immediately the present arrangement of things. Now these facts in themselves leave not the shadow of a doubt in our mind, that animals were primitively created all over the world, within those districts which they were naturally to inhabit for a certain time. The next question is—were these organized beings created in pairs, as is generally thought and believed? The opinion, that all animals must be[N1] referred to one single, primitive pair, is derived from evidence worthy of consideration, no doubt, but the value of which may fairly be questioned by naturalists; since this point, at least if we except Adam and Eve, is entirely of human construction, and only assumed because it is thought to shew a wise economy of means in the established order of things which exists. It is supposed, that, if one pair were sufficient, there is no reason why the Creator should have introduced at one time a greater number of each kind, as economy of means is always considered an indication of high wisdom. But are not these human considerations? And if they are, and if we are entitled to question their value, let us see how they answer the object which was intended, namely, the peopling of the whole world with various races of organized beings.

Whenever we consider the economy of nature, we observe great varieties in the habits of different animals. There are, indeed, some which live constantly in pairs, and which by nature are designed to perpetuate their races in that way, and to spread generation after generation over their natural boundaries, thus mated. But there are others to which it is equally natural to live in herds or shoals, and which we never find isolated. The idea of a pair of herrings, or of a pair of buffaloes, is as contrary to the nature and habits of those animals[N2], as it is contrary to the nature of pines and birches to grow singly, and to form forests in their isolation.

But we can go further. There are animals in which the number of individuals of different sexes is naturally unequal, and among which there are either constantly more males or constantly more females born, as the result of their peculiar nature and habits in the creation. A bee-hive never consists of a pair of bees; and never could such a pair preserve the species, with their habits. For them it is natural to have one female and many males devoted to it, and thousands of neutral bees working for them. And this is the natural original mode of existence among that species of animals, which it would be utterly contrary to the laws of nature to consider as derived from a single pair. There are a number of birds, on the contrary, in which only a few males are universally found with many females, living together in companies, such as the pheasants, and our domesticated fowls. It were easy to multiply examples in order to shew that a creation of all animals in pairs would have been contrary to their very nature, as we observe it in all. To assume that they have changed this nature would be to fall back upon the necessity of ascribing to physical influences a power which they do not possess,—that of producing changes in the very nature of organized beings, and of modifying the primitive plan of the Creator.

Again, there are animals which, by nature, are impelled to feed upon other animals. Was the primitive pair of lions to abstain from food until the gazelles and other antelopes had sufficiently multiplied to preserve their races from the persecution of these ferocious beasts? Were all animals, and the innumerable tribes of ferocious fishes which live upon smaller ones, to abstain from food till these had been multiplied to a sufficient extent to secure their preservation? Or were, perhaps, the carnivorous animals created only at a later period? But we find them everywhere together. They constitute natural, harmonious groups with the herbivorous tribes, both in the waters and on land, preserving among each other such proportions as will maintain for ages an undisturbed harmony in the creation.

Again, we find animals and plants occurring in distinct districts, unconnected with each other, in such ways that it would seem almost impossible for either to migrate from any point of their natural circle of distribution over its whole surface. Have, for instance, such animals as are found identical both in America and Europe been created either in Europe or in America, and wandered from one of the continents over to the other? Have those species which occur only in the far north, and upon the higher summits of the Alps, been created either in the Alps or in the north, and wandered from one place to the other? We are at a loss for substantial arguments for believing that either one or the other place has been the primitive location of such animals, or for denying their simultaneous creation in both.

Evidence could be accumulated to shew, we will not say the improbability only, but even the impossibility, of supposing that animals and plants were created in single pairs, and assumed afterwards their present distribution. But the facts mentioned will be sufficient to introduce our argument, and from all we know of the laws of nature and of the distribution of animals, we conclude that they could neither originate from a single pair, nor upon a single spot. And as for plants, we would ask naturalists whether it were not superfluous to create more than a single stalk of most plants, as vegetables, with a few exceptions, may multiply extensively from a single stem. But if it is granted that animals could not originate from a single pair, nor upon a single spot, what is the more natural view to take of the subject?

Without entering fully into this question, we may as well state that we have been gradually led to the conclusion, that most animals and plants must have originated primitively over the whole extent of their natural distribution. We mean to say that, for instance, lions, which occur over almost the whole of Africa, over extensive parts of Southern Asia, and were formerly found even over Asia-Minor and Greece, must have originated primitively over the whole range of these limits of their distribution. We are led to these conclusions by the very fact, that the lions of the East Indies differ somewhat from those of Northern Africa; these, again, differ from those of Senegal. It seems more natural to suppose that they were thus distributed over such wide districts, and endowed with particular characteristics in each, than to assume that they constituted as many species; or to believe that, created anywhere in this circle of distribution, they have gradually been modified to their present differences in consequence of their migration. We admit these differences to be primitive and contemporaneous, from the fact, that there are other animals of different genera extending over the same tracts of land which have different representatives in each, circumscribed within narrower bounds, and this particular combination in each special district of the wider circle covered by the lion, seems, in our opinion, the strongest argument in favour of the view, that the particular districts of distribution have been primitively ascribed, with definite limits, to each species. Why should the antelopes north of the Cape of Good Hope differ from those of Arabia, or those of the Senegal, or those of the Atlas, or those of the East Indies, if they were not primitively adapted with their special modifications to those districts, when we see the lion cover the whole range? And why should the varieties we notice among the lions within these boundaries not be primitive, though not constituting distinct species, when we see the herbivorous species of the same genus differ from one district to another? And why should the differences in that one species of lion be the result of changes in its primitive character, arising from its distribution into new districts, when we see that the antelopes are at once fixed as distinct species over the same ground?

This argument cannot be fully appreciated by those who are not extensively acquainted with natural history, but we may, perhaps, make it plainer by alluding to some other similar facts. Our fresh waters teem everywhere with animals and plants. Fishes and mollusca are among the most prominent of their animals. Let us compare for a moment the different species which occur in the Danube, in the Rhine, and in the Rhone, three hydrographic basins entirely unconnected with each other throughout their whole extent. They spring from the same mountain chain, as we may take the Inn as the source of the Danube. These three great rivers rise within a few miles of each other. Nevertheless, most of their fishes differ, but there are some which are common to the three. We find the pickerel,—the European pickerel, in the three basins. The eel is also common to them all. One kind of trout occurs in the three. But how strange the distribution of some others!—for instance, the perches. In the Rhine we find Perca fluviatilis, and Acerina cernua; in the Rhone, Perca fluviatilis, and Aspro vulgaris; in the Danube, Perca vulgaris, Lucio-perca Sandra, Acerina cernua, A. Schraitzer, Aspro vulgaris, and A. Zingel. If these animals had not originated in these rivers separately, why should not such closely-allied species, some of which occur in the three basins, have all spread equally into them? and if they originated in the separate basins, we have within close limits a multiple origin of the same species.

And that this multiple origin must be admitted as a fact is shewn by the following further evidence. Among the carpes we find, for instance, Barbus, Gobio, Carpio, common to the three. But the Danube has three Gobios, whilst the others have but one, one of the Danube being identical with the one of the other two rivers. The most striking fact, however, occurs in the genus Leuciscus. Leuciscus dobula is common to the three; but in addition to it, the Danube has several species which occur neither in the Rhine nor in the Rhone. The basin of the Rhone, again, has several species which occur neither in the Danube nor in the Rhine; and in the Rhine, there are species which belong neither to the Rhone nor to the Danube. Now, we ask, could all these species of Leuciscus have been created in one of the basins,—in the Danube for instance,—and have migrated in such a way, that a certain number of the species should remain solely in the Danube, while some others left the Danube altogether to settle finally only in the Rhone, and others to settle only in the Rhine; that one accompanying those species peculiar to the Rhone, remained in the Danube with those species peculiar to it, and settled also in the Rhone, with those species peculiar to that river, and also in the Rhine with the species peculiar to the Rhine? And whether we assume the Rhone as the primitive centre, instead of the Danube or the Rhine, the argument holds equally good. We have one species common to the three rivers, and several species peculiar to each, which could never have migrated (if migration took place) in such a manner as to assume their present combinations. But if, on the contrary, we suppose that all the species originated in the rivers where they occur, then we have again a multiple origin of that species which is common to the three, for it were wonderful if that one alone had migrated, when they are all so closely allied. Here, again, we arrive at the conclusion, that the same species can have a multiple origin, in the same manner as, from the considerations alluded to before, we have decided that species do not originate from single pairs, but in their natural proportion with the other species with which they live simultaneously over the whole ground which they cover. And this is the view which we take of the natural distribution of animals, that they originated primitively over the whole extent of their natural distribution; that they originated there, not in pairs, but in large numbers, in such proportions as suits their natural mode of living, and the preservation of species; and that the same species may have originated in different unconnected parts of the more extensive circle of their distribution. We are well aware that there are very many species which are known to have spread beyond what we would call their natural limits; species which did not occur in North America before the settlement of the whites, that are now abundant here over very extensive tracts of country; other species which have been introduced from America into Europe, and also into other parts of the world, in different ways. But these are exceptional facts; and, what is more important, these changes in the primitive distribution of organised beings, both animals and plants, have taken place under the influence of man,—under the influence of a being acting not merely from natural impulses, or under the pressure of physical causes, but moved by a higher will. So that these apparent exceptions to the rule would only go to confirm it; as, within the limits of these secondary changes, we see a will acting, just as we consider that the primitive distribution of all organized beings has been the result of the decrees of the Creator, and not the result of mere natural influences.

Having thus led the way to what we would consider as a fairer ground for investigating the natural geographical distribution of animals and plants, let us now examine the natural lines which seem to regulate this distribution. Nothing can be more striking to the observer than the fact, that animals, though endowed with the power of locomotion, remain within fixed bounds in their geographical distribution, although an unbounded field for migration is open to them in all directions, over land, through the air, and through the waters. And no stronger argument can be introduced to shew that living beings are endowed with their power of locomotion to keep within general boundaries, rather than to spread extensively. There is another fact which shews that animals are made to remain within these natural limits. We would allude especially to the difficulty we experience whenever we attempt to transport animals from their native country into other countries, even if we secure for them as nearly as can be the same conditions in which they used to live. Again, observe the changes which animals undergo when they are once acclimatized to countries different from their native land. There can be no more striking evidence of this than the endless variety of our domestic animals, and there is no subject which more requires a renewed and careful investigation than this. We do not, however, feel competent to introduce this point more fully to the notice of our readers. Some facts bearing upon the question may best be mentioned in a reference to the different animals which man has thus made subservient to his social condition. We shall here allude only to the laws of distribution of wild animals in their natural condition.

It has already been stated, that the present distribution of animals agrees with the distribution of extinct types belonging to earlier geological periods, so that the laws which regulate the geographical distribution of animals seem to have been the same at all times, though modified in accordance with the successive changes which the animal kingdom has undergone from the earliest period of its creation to the present day. The universal law is, that all animals are circumscribed within definite limits. There is not one species which is uniformly spread all over the globe, either among the aquatic races or among the terrestrial ones. Of the special distribution of man, who alone is found everywhere, we shall speak hereafter. The special adaptation of animals to certain districts is not merely limited to the individual species. We observe a similar adaptation among genera, entire families, and even whole classes. For instance, all Polypi, Medusæ, and Echinoderms, that is to say all Radiata, without exception, are aquatic.[1] That large group of animals has not a single terrestrial representative upon any point of the surface of the globe; and during all periods of the history of our earth, we find that they have always been limited to the liquid element. And they are not only aquatic, they are chiefly marine, as but exceedingly few of them are found in fresh waters. Among Mollusca we find almost the same adaptation. Their element also is the sea. The number of fresh-water species is small, compared with that of marine types; and we find terrestrial species in only one of their classes. In former periods, also, Mollusca were chiefly marine; fluviatile and terrestrial types occurring only in more recent periods.

With the Articulata, we find another state of things. Two of their classes, the worms and Crustacea, are chiefly marine, or at least aquatic, as we have a number of fresh-water worms, and some fresh-water Crustacea. But insects are, for the most part, chiefly terrestrial, feeding upon terrestrial plants, at least in their full-grown condition; though a large number of these animals are fluviatile, and even some marine, during their earlier periods of life. In the Vertebrata, the adaptations are more diversified. Only one class of these animals is entirely aquatic—the fishes; and the number of the marine species is far greater than that of the fresh-water kinds. Among reptiles there are many which are aquatic, either throughout life, or through the earlier period of their existence. But, as if animal life rose to higher organization, as it leaves the ocean to inhabit dry land or fresh waters, we find that the greater number of the aquatic reptiles are fluviatile, and but a few marine. This fact agrees wonderfully with the natural gradation of the classes already mentioned. The lower type of animals, the Radiata, is almost exclusively marine. Among Mollusca, we have a greater number of marine types, a large number of fluviatile species, and fewer terrestrial, and these are the highest in their class. Again, among Articulata, the lower classes, worms and Crustacea, are marine, or at least fluviatile, whilst the highest class, that of insects, is chiefly terrestrial or fluviatile, during the earlier periods of their growth. Among the Vertebrata we see the lowest form, that of fishes, entirely aquatic, and the same rule applies partially to the reptiles; but as the class rises, the number of the fluviatile species is greater than that of the marine types. Next, among birds, which by their structure are exclusively adapted to live in the atmospheric air, we find the larger number to be terrestrial, and only the lower ones to live upon water, or dive occasionally into it, always seeking the surface, however, to breathe and to perform their most important vital functions. It is, nevertheless, not a little strange, that this class should by nature be adapted to rise into the air, just as if the first tendency towards liberating them from the aquatic element had been carried to an excess, and gave them a relation to the earth which no other class, as a whole, holds to that degree, except, perhaps, the insects, which are placed among the Articulata in the same relation to the lower classes and the natural element, which the class of birds maintains among Vertebrata. The highest class of Vertebrata affords us examples of these three modes of adaptation, the lowest of these being entirely aquatic, and even absolutely marine; next, we have fluviatile types of the large terrestrial mammalia, in the family of Manatees, again, a swimming family among Carnivora, another flying, most of them however walking upon their four extremities on solid ground, but at the head of all, man, standing upright, to look freely upwards, and to contemplate the whole universe.

This wonderful adaptation of the whole range of animals, as it exists at present, shews the most intimate connection with the order of succession of animals in former geological periods. The four great types, Radiata, Mollusca, Articulata, and Vertebrata, were introduced at the beginning simultaneously. However, the earliest representatives of these great types were all aquatic. We find in the lowest beds which contain fossils, Polypi, together with star-fishes, bivalve shells, univalves, chambered shells, cases of worms, and Crustacea, being representatives of at least seven out of nine classes of invertebrate animals, if we are not allowed to suppose that Medusæ existed also, and if insects were still wanting for a time. But, in addition to these, fishes among Vertebrata are introduced, but fishes only, all of which are exclusively marine. At a somewhat later period insects come in. We find next reptiles in addition to fishes—the lower classes, or invertebrates, continuing to be represented through all subsequent epochs, but by species changing gradually at each period, as all classes do after they have been once introduced. The first representatives among reptiles are marine, next huge terrestrial ones, some, perhaps, flying types, and with them, and perhaps even before them, birds, allied to the wading tribes: still later, Mammalia, beginning again with marine and huge terrestrial types, followed by the higher quadrupeds; and, last only, Man,—at the head of the creation, in time as well as in eminence, by structure, intelligence, and moral endowments.

Besides the general adaptation of animals to the surrounding media, there is a more special adaptation, which seems not less important, though it is perhaps less striking. Animals, as well as plants, do not live equally at all depths of the ocean, or at all heights above its surface. There must be a deep influence upon the geographical distribution of animals in a vertical direction derived from atmospheric pressure above the surface of the waters, and from the pressure of the water itself at greater and greater depths,—the level of the ocean, or a small elevation above its surface, or a shallow depth under its surface, being the field of the most extensive and intensive development of animal life. And it is not a little remarkable that in the same classes we should find lower types at greater depths in the ocean, and also lower types at greater heights above. We will quote a few examples, to shew how much we may expect from investigations pursued in this direction, for at present we have but little information which can aid us in ascertaining the relationship between atmospheric and hydrostatic pressure and the energies of animal life.

Among Polypi, the higher forms, such as Actiniæ, are more abundant in shallow water than the lower coral-forming types. Among Medusæ, the young are either attached to the bottom, or grow from the depth, while the perfect free forms of these animals come to the surface. Among Echinoderms, the Crinoids are deep-water forms; free star-fishes and Echini, and, above all Holothuriæ, living nearer the surface. Among Mollusca, the Acephala, which are lowest, have their lower types,—the Brachiopods, entirely confined to deep waters; the Monomyarians appear next, and, above them, the Dimyarians; among these latter, the highest family, the Nayades, rises above the level of the ocean into the fresh waters, and extends even to considerable heights above the sea, in lakes and rivers. A number of examples of all classes should be mentioned, to shew that this is the universal case; as, for instance, among Crustacea the Macrura are, in general species of deeper water than the true crabs, of which some come even upon dry land. Again, on the slopes of our mountains, the highest forms among Mammalia which remain numerous are the Ruminants and Rodents. There are no Carnivora living in high regions. Among birds of prey, we have the vultures, rising above the highest summits of mountains, while eagles and falcons hover over the woods and plains, by the water sides, and along the sea-shores. Among reptiles, salamanders, frogs, and toads occur higher than any turtles, lizards, &c. But the same adaptation may be traced with reference to the latitudes under which animals are found. Those of the higher latitudes, the arctic and antarctic species, resemble both the animals of high, prominent mountain chains, and those of the deep sea-waters, which there meet in the most unexpected combinations (and it is surprising to see how extensively this is the case); while, in lower latitudes, towards the tropics, we find everywhere the higher representatives of the same families. For instance, among Mammalia we observe monkeys only in warm latitudes, and they die out in the warmer parts of the temperate zone. The great development of Digitigrades—lions, tigers, &c., takes place within the tropics, smaller species, like wolves and foxes, weasels, &c., occurring in the north, whilst the Plantigrades, which come nearer and nearer to the seal, follow an inverse progression, the largest and most powerful of them being the arctic ice bear, which meets there his family relations, the Pinnipedia, that are so numerous in the polar regions. Again, the families of Ruminants and Pachyderms seem to form an exception, for though belonging to the lower types of Mammalia, they prevail in the tropical zone; but let us remember that they were among the earlier inhabitants of our globe, and the fact of their occurring more extensively in warm climates is rather a reminiscence of the plan of creation in older times, than an adaptation to the law regulating at present the distribution of organized beings. The gradation of animals among birds being less satisfactorily ascertained, we do not venture to say anything respecting their geographical distribution, in relation to climates. But among reptiles, we cannot overlook the fact, that the crocodiles, which are the highest in structure, are altogether[N3] tropical, and the Batrachians, which rank lowest, especially the salamandroid forms, are rather types of the colder temperate zone than of the warm, &c. From these facts it is plain, that the geographical distribution of all groups has a direct reference to atmospheric and hydrostatic pressure on one side, and also to the intensity of light and heat over the surface of the globe.

The special adaptation of minor groups begins very early in the history of our globe, and extends at present all over its surface. In the same manner as animals are adapted to natural limits in their large primitive groups which we call classes, we find also the minor divisions more closely adapted to particular circumstances of the physical condition of all parts of the globe. Among Mammalia, the great type of Marsupialia is placed in New Holland, and extends little beyond that continent into the adjacent islands. A very few representatives of that family are found in America. Asia, Africa, the colder parts of North America, and its southern extremity, are entirely deprived of this type. The family of Edentata, again, has its centre of development in South America, where the sloth, dasypus, ant-eaters, &c., form characteristic types, of which a few analogues occur in Africa, along its southern extremity and western coast. Now it is a fact upon which we cannot insist too strongly, that the same districts of New Holland and South America were, during an earlier geological period comparatively recent, the seat of an equally wide development of the same animals in the same extensive proportion as at present. We need only refer to the beautiful investigations of Dr Lund, upon the fossil mammalia of Brazil, and to those, no less important, of Professor Owen, upon the fossil remains of mammalia of New Holland, to leave not a shadow of doubt upon this adaptation, which indicates distinctly these two regions, at two distinct periods remote from each other, as the points of development of two distinct families, which have never spread over other parts of the globe at any period since the time of their existence, indicating at least two distinct foci of creation, with the same characters, at two successive epochs; a fact which, in our opinion, can never be reconciled to the idea of a unique centre of origin of the animals now living. But though other families have never been and are not now localized in so special a manner, we nevertheless find them circumscribed within certain limits, in particular districts, or, at least, in particular zones.

As already mentioned, the monkeys are entirely tropical. But here, again, we notice a very intimate adaptation of their types to the particular continents, as the monkeys of tropical America constitute a family altogether distinct from the monkeys of the Old World, there being not one species of any of the genera of Quadrumana, so numerous on this continent, found either in Africa or in Asia. The monkeys of the Old World, again, constitute a natural family by themselves, extending equally over Africa and Asia; but the species of Africa differ from those of Asia; and there is even a close representative analogy between those of different parts of these two continents; the orangs of Africa, the chimpanzee and gorilla, corresponding to the red orang of Sumatra and Borneo, and the smaller long armed species of continental Asia. And what is not a little remarkable is the fact, that the black orang occurs upon that continent which is inhabited by the black human race, whilst the brown orang inhabits those parts of Asia over which the chocolate-coloured Malays have been developed. There is again a peculiar family of Quadrumana confined to the Island of Madagascar—the makis—which are entirely peculiar to that island, and the eastern coast of Africa opposite to it, and to one spot on the western shore of Africa. But in New Holland, and the adjacent islands, there are no monkeys at all, though the climatic conditions seem not to exclude their existence any more than those of the large Asiatic islands, upon which such high types of this order are found. And these facts more than any other, would indicate that the special adaptation of animals to particular districts of the surface of our globe is neither accidental, nor dependent upon physical conditions, but is implied in the primitive plan of the creation itself. Whatever classes we may take into consideration, we shall find similar adaptations, and though, perhaps, the greater uniformity of some families renders the difference of the types in various parts of the world less striking, they are none the less real. The Carnivora of tropical Asia are not the same as those of tropical Africa, or those of tropical America. Their birds and reptiles present similar differences. The want of an ostrich in Asia, when we have one, the largest of the family, in Africa, and two distinct species in Southern America, and two cassowaries, one in New Holland, and another in the Sunda Islands, shews this constant process of analogous or representative species repeated over different parts of the world to be the principle regulating the distribution of animals, and the fact that these analogous species are different, again, cannot be reconciled to the idea of a common origin, as each type is peculiar to the country where it is now found. These differences are more striking in tropical regions than anywhere else. The rhinoceros of the Sunda Islands differs from those of Africa, and there is none in America. The elephant of Asia differs from that of Africa, and there is none in America. One tapir is found in the Sunda Islands, there is none in Africa, but we find one in South America, &c. Everywhere special adaptation, particular forms in each continent, an omission of some allied type here, when in the next group it occurs all over the zone.

As we ascend into the temperate zone, we find, however, the similarity greatly increased. The difference between the species of the same family in temperate Asia, temperate Europe, and temperate America is much less than between the corresponding animals of the tropical zone, and no doubt it is to this great assemblage of more uniform animals, living originally within the main seat of human civilization, that we must ascribe the idea of their common origin, which has so long prevailed and been so serious an obstacle to a real insight into these natural phenomena. What, indeed, could be more natural for man, when for the first time reflecting upon nature around him,—when seeing, as far as he could extend his investigations, all things alike,—than to imagine that every thing arose from a common centre, and spread with him over the world, as it has been the fate of the white race, and of that only, to extend all over the globe, and that, influenced by the phenomena of the zone in which he lived and wandered, and from which he extended farther, he took it for granted that all animals followed the same laws. But now that we know the whole surface of our globe so satisfactorily, there can no longer be a question about the difference between animals and plants in the lower latitudes in all continents. Besides, we see them equally striking in the southernmost extremities of the three great continents, so that there can no longer be any doubt about the primitive adaptation of these various types to the continents where they live, as we do not find a single one naturally diffused everywhere over all continents. Notwithstanding, therefore, the slighter differences we notice between the animals of different continents in the temperate zone, we are thus led step by step to ascribe to them also a special origin upon those continents where they now occur.

But as soon as we rise to the highest latitudes, the uniformity becomes so close, that there is no longer any marked difference noticed between the animals about the arctic regions, either in America, Europe, or Asia; and we are naturally led to restrict the idea of a common centre of origin, or at least of a narrow circle of primitive development, to those animals which spread equally over the icy fields extending around the northern pole upon the three continents which meet in the north. The phenomena of geographical distribution which we observe there among the terrestrial animals are repeated in the same manner among the aquatic ones. The fishes in the arctic seas do not materially differ on the shores of Europe, Asia, and America, and through the northern Atlantic and through Behring's Straits they extend more or less towards the colder temperate zone, or migrate into it at particular seasons of the year, as do most birds of the arctic regions also. But in the temperate zone we begin to find more and more marked differences between the inhabitants of different continents, and even between those of the opposite shores of the same ocean; as, for instance, the fishes of Europe (some of the northern species excepted) are not identical with those of the temperate shores of North America, notwithstanding the very open field left for their uniform distribution across the Atlantic. Such is also the case between the fishes of Western Africa and those of Central America, and between those of the southern extremities of these continents. The fishes of the Indian Ocean, and the fishes of the Pacific vary greatly, and, though some families have a wider range, there are many which are circumscribed within the narrowest limits. It is one of the most striking phenomena[N4] in the geographical distribution of aquatic animals, to find entire families of fishes completely circumscribed within particular groups of islands, such, for instance, as the Labyrinthici, which are peculiar to the Sunda Islands, and the family of Goniodonts, which are found only in the rivers of South America.

A similar narrow limitation occurs also among the terrestrial animals, as the family of Colubris is entirely circumscribed within the boundaries of the warmer parts of the American continent. The appearance during the warmer season of the year of a few species of that family in the Northern States, does not make this case less strong. Examples might be multiplied without end to shew everywhere special adaptation, narrow circumscription, or representative adaptation of species in different parts of the world; but those mentioned will be sufficient to sustain the argument that animals are naturally antochthones wherever they are found, and have been so at all geological periods; that in northern regions they are most uniform; that their diversity goes on increasing through the temperate zone till it reaches its maximum in the tropics; that this diversity is again reduced in the aquatic[N5] animals towards the antarctic pole, though the physical difference between the southernmost extremities of America, Africa, and New Holland, seems to have called for an increased difference between their terrestrial animals.

We are thus led to distinguish special provinces in the natural distribution of animals, and we may adopt the following division as the most natural: First, the arctic province, with prevailing uniformity. Second, the temperate zone, with at least three distinct zoological provinces—the European temperate zone, west of the Ural Mountains, the Asiatic temperate zone east of the Ural Mountains, and the American temperate zone, which may be subdivided into two, the eastern and the western—for the animals east and west of the Rocky Mountains differ sufficiently to constitute two distinct zoological provinces. Next, the tropical zone, containing the African zoological province, which extends over the main part of the African continent, including all the country south of the Atlas and north of the Cape Colonies; the tropical Asiatic province, south of the great Himalayan chain, and including the Sunda Islands, whose Fauna has quite a continental character, and differs entirely from that of the Islands of the Pacific, as well as from that of New Holland; the American tropical province, including Central America, the West Indies, and tropical South America. New Holland constitutes in itself a special province, notwithstanding the great differences of its northern and southern climate, the animals of the whole continent preserving throughout their peculiar typical character. But it were a mistake to conceive that the Faunæ or natural groups of animals are to be limited according to the boundaries of the mainland. On the contrary we may trace their natural limits into the ocean, and refer to the temperate European Fauna the eastern shores of the Atlantic, as we refer its western shores to the American temperate Fauna. Again, the eastern shores of the Pacific belong to the western American Fauna, as the western Pacific shores belong to the Asiatic Fauna. In the Atlantic Ocean there is no purely oceanic Fauna to be distinguished, but in the Pacific we have such a Fauna, entirely marine in its main character, though interspread with innumerable islands extending east of the Sunda Islands and New Holland to the western shores of tropical America. The islands west of this continent seem, indeed, to have very slight relations in their zoological character with the western parts of the mainland. South of the tropical zone we have the South American temperate Fauna, and that of the Cape of Good Hope, as other distinct zoological provinces. Van Diemen's Land, however, does not constitute a zoological province in itself, but belongs to the province of New Holland, by its zoological character. Finally, the antarctic circle encloses a special zoological province, including the antarctic Fauna, which, in a great measure, corresponds to the arctic Fauna in its uniformity, though it differs from it in having chiefly a maritime character, while the arctic Fauna has an almost entirely continental aspect.

The fact that the principal races of man, in their natural distribution, cover the same extent of ground as the great zoological provinces, would go far to shew that the differences which we notice between them are also primitive; but for the present we shall abstain from further details upon a subject involving so difficult problems as the question of the unity or plurality of origin of the human family, satisfied as we are to have shewn that animals, at least, did not originate from a common centre, nor from single pairs, but according to the laws which at present still regulate their existence.

Additional Illustrations of the Geographical Distribution of Animals.

I.—Geographical Distribution of Sturgeons.[2]

The sturgeons are generally large fishes, which live at the bottom of the water, feeding with their toothless mouths upon decomposed organized substances. Their movements are rather sluggish, resembling somewhat those of the cod-fish.

Their geographical distribution is quite peculiar, and constitutes one of their prominent peculiarities. Located as they are, in the colder portions of the temperate zone, they inhabit either the fresh waters or the seas exclusively, or alternately both these elements,—remaining during the larger part of the year in the sea, and ascending the rivers in the spawning season. Although adapted to the cold regions of the temperate, they do not seem to extend into the arctic zone, and I am not aware that they have been observed in any of the waters of the warmer half of the temperate zone. The great basin of salt-water lakes or seas which extends east of the Mediterranean, seems to be their principal abode in the Old World, or at least the region in which the greater number of species occur; and each species takes a wide range, extending up the Danube and its tributaries, and all the Russian rivers emptying into the Black Sea. From the Caspian they ascend the Wolga in immense shoals, and are found further east in the lakes of Central Asia, even as far as the borders of China. The great Canadian lakes constitute another centre of distribution of these fishes in the New World, but here they are not so numerous, nor do they ever occur in contact with salt water in this basin.

Northwards, there is another great zone of distribution of sturgeons, which inhabit all the great northern rivers emptying into the Arctic Sea, in Asia as well as in America. They occur equally in the intervening seas, being found on the shores of Norway and Sweden, in the Baltic and North Seas, as well as in the Atlantic Ocean, from which they ascend the northern rivers of Germany, as well as those of Holland, France, and Great Britain. Even the Mediterranean and the Adriatic have their sturgeons, though few in number. There are also some on the Atlantic shores of North America, along the British possessions as well as the northern and middle United States. They seem to be exceedingly numerous in the Northern Pacific, being found everywhere from Behring's Straits and Japan to the northern shores of China, and on the north-west coast of America, as far south as the Columbia River. Again, the so-called western waters of the United States have their own species, from the Ohio down to the lower portion of the Mississippi, but it does not appear that these species ascend the rivers from the Gulf of Mexico. I suppose them to be rather entirely fluviatile, like those of the great Canadian lakes.

Beyond the above limits southwards there are nowhere sturgeons to be found, not even in the Nile, though emptying into a sea in which they occur; and as for the great rivers of Southern Asia and of tropical Africa, not only the sturgeons, but another family is wanting there,—I mean the family of Goniodonts, which in Central and Southern America takes the place of the sturgeons of the north. Again, all the species in different parts of the world are different.

It is a most extraordinary fact, which will hereafter throw much light upon the laws of geographical distribution of animals and their mode of association, viz., that certain families are entirely circumscribed within comparatively narrow limits, and that their special location has an unquestionable reference to the location of other animals; or, in other words, that natural families, apparently little related to each other, are confined to different parts of the world, but are linked together by some intermediate form, which itself is located in the intermediate track between the two extremes. In the case now before us, we have the sturgeons extending all around the world in the northern temperate hemisphere, in its seas as well as in its fresh waters, all closely related to each other. Neither in Asia nor in Africa is there an aberrant form of that type, or any representative type in the warmer zones; but in North America we have the genus Scaphirhynhus, which occurs in the Ohio and Mississippi, and which forms a most natural link with the family of Goniodonts, all the species of which are confined exclusively to the fresh waters of Central and South America. The closeness of this connection will be at once perceived by attempting to compare the species of true Sonicariæ with the Scaphirhynhus. I know very well, that the affinities of Goniodonts and Siluroids with sturgeons are denied, but I still strongly insist upon their close relationship, which I hope to establish satisfactorily in a special paper, as I continued to insist upon the relation between sturgeons and gar-pikes, at one time positively contradicted and even ridiculed. I trust then to be able to shew, that the remarkable form of the brains of Siluridæ comes nearer to that of sturgeons and Lepidostei than to that of any other family of fishes. This being the case, it is obvious that there must be in the physical condition of the continent of America some inducement not yet understood, for adaptations so special and so different from what we observe in the Old World. Indeed, such analogies between the organized beings almost from one pole to another, occur from man down to the plants in America only, among its native products; while, in the Old World, plants as well as animals have more circumscribed homes, and more closely characterized features, in the various continents, at different latitudes.

As for the species of sturgeons which occur in the Canadian lakes, I know only three from personal examination, one of which was obtained in Lake Superior, at Michipicotin, another at the Pic, and the third at the Sault; though I know that they occur in all other Canadian lakes, yet it remains to be ascertained how the species said to be so common in Lake Huron, compared with those of Lake Superior, and with those in the other great lakes and the St Lawrence itself. As for the Atlantic species, ascending the rivers of the United States west and south of Cape Cod, I know them to differ from those of the lakes, at least from those which I possess from Lake Superior. The number of species of this interesting family which occur in the United States is, at all events, far greater than would be supposed from an examination of the published records. Upon close comparison of the specimens[N6] in my collection from different parts of the country, and in different museums, as those of the Natural History Society of Boston, of Salem, of the Lyceum of New York, my assistant, Mr Charles Giran, and myself, have discovered several species not described. For this comparison I was the better prepared, as I had an opportunity in former years of studying almost all the European species in a fresh condition, during a prolonged visit in Vienna.

II.—Fishes of Lake Superior compared with those of the other great Canadian Lakes.

Besides the interest there is everywhere in studying the living animals of a new country, there is a particular interest to a naturalist in ascertaining their peculiar geographical distribution, and their true affinities with those of other countries. It is only by following such a course, that we can hope to arrive at any exact results as to their origin. In this respect the fresh-water animals have a peculiar interest, as from the element they inhabit, they are placed under exceptional circumstances.

Marine animals, as well as those inhabiting dry land, seem to have a boundless opportunity before them to spread over large parts of the earth's surface, and their locomotive powers would generally be sufficient to carry them almost anywhere; but they do not avail themselves of the possibility; notwithstanding their facilities for locomotion, they for the most part remain within very narrow limits, using their liberty rather to keep within certain definite bounds. This tendency of the higher animals especially, to keep within well-ascertained limits, is perhaps the strongest evidence that there is a natural connection between the external world and the organised beings living upon the present surface of our globe. The laws which regulate these relations, and those of geographical distribution in particular, have already been ascertained to a certain extent, and will receive additional evidence from the facts recorded during our journey.

The fresh-water animals are placed in somewhat different circumstances. Their abode being circumscribed by dry land, within limits which are often reduced to a narrow current of water, and being further, for the most part, prevented by structural peculiarities from passing from the rivers into the ocean, they are confined within narrower limits than either terrestrial or marine types. Within these limits again they are still further restricted; the shells and fishes of the head waters of large rivers, for instance, being scarcely ever the same as those of their middle or lower course, few species extending all over any fresh-water basin from one extreme of its boundary to the other; thus forming at various heights above the level of the sea, isolated groups of fresh-water animals in the midst of those which inhabit the dry land. These groups are very similar in their circumscription to the islands and coral reefs of the ocean; like them, they are either large or small, isolated and far apart, or close together in various modes of association. In every respect they form upon the continents, as it were, a counterpart of the Archipelagos.

From their circumscription, these groups of lakes present at once a peculiar feature in the animal kingdom, their inhabitants being entirely unconnected with any of the other living beings which swarm around them. What, for instance, is there apparently in common between the fishes of our lakes and rivers, and the quadrupeds which inhabit their shores, or the birds perching on the branches which overshadow their waters? Or what connection is there between the few hermit-like terrestrial animals that live upon the low islands of the Pacific and the fishes which play among the corals, or in the sand and mud of their shores? And nevertheless there is but one plan in the creation; fresh-water animals under similar latitudes are as uniform as the corresponding vegetation, and however isolated and apparently unconnected the tropical islands may seem, their inhabitants agree in their most important traits.

The best evidence that in the plan of creation animals are intended to be located within circumscribed boundaries, is further derived from their regular migrations. Although the arctic birds wander during winter into temperate countries, and some reach even the warmer zones; although there are many which, from the colder temperate climates, extend quite into the tropics, there is nevertheless not one of these species which passes from the northern to the southern hemispheres; not one which does not return at regular epochs to the countries whence it came from. And the more minutely we trace this geographical distribution, the more we are impressed with the conviction that it must be primitive; that is to say, that animals must have originated where they live, and have remained almost precisely within the same limits ever since they were created, except in a few cases, where, under the influence of man, those limits have been extended over large areas. To express this view still more distinctly, I should say the question to be settled is, whether for instance the wild animals which live in America originated in this continent, or migrated into it from other parts of the world; whether the black bear was created in the forests of New England and the northern states, or whether it is derived from some European bear, which by some means found its way to this continent, and being under the influence of a new climate, produced a new race; whether the many peculiar birds of North America which live in forests composed of trees different from those which occur either in Europe or Asia, whether these birds, which themselves are not identical with those of any other country, were or were not created where they live; whether the snapping turtle, the alligator, the rattlesnake, and other reptiles which are found only in America, have become extinct in the Old World after migrating over the Atlantic, to be preserved in this continent; whether the fishes of the great Canadian lakes made their appearance first in those waters, or migrated thither from somewhere else? These are questions which such an inquiry into the geographical distribution of animals involves; it is the great question of the unity or plurality of creations; it is not less the question of the origin of animals from single pairs or in large numbers; and, strange to say, a thorough examination of the fishes of Lake Superior, compared with those of the adjacent waters, is likely to throw more light upon such questions, than all traditions, however ancient, however near in point of time to the epoch of creation itself.

In order to proceed methodically in this investigation, our first step must be to examine minutely, whether the fishes of Lake Superior are the same as those of other lakes, in this or any other country; and, if not, how they differ. To satisfy ourselves in this respect, we shall successively examine all the families of fishes, which have representatives in those great fresh-water seas. (Agassiz on Lake Superior, p. 246.) Professor Agassiz, after admirable histories of the fishes of Lake Superior, concludes with the following excellent observations:—[3]

III.—General Observations; all Fresh-water Fishes of North America different from those of Europe—Lake Superior and the Lakes north of it constitute a distinct Zoological District—These Fishes have been created where they now live—Deductions from this fact.

Such a critical revision of the fishes of Lake Superior, and the other great Canadian lakes, was the first necessary step in the investigation I am tracing, in order to ascertain the natural primitive relations between them and the region which they inhabit. Before drawing the conclusions which follow directly from these facts, I should introduce a similar list of the fishes living in similar latitudes, or under similar circumstances, in other parts of the world; and more particularly of the species of Northern Europe. But such a list, to be of any use, should be throughout based upon a critical comparative investigation of all the species of that continent, which would lead to too great a digression. The comparison of the fresh-water fishes of Europe, which correspond to those of North America, has been carried so far, that I feel justified in assuming, what is really the fact, that all the species of North America, without a single exception, differ from those of Europe, if we limit ourselves strictly to fishes which are exclusively the inhabitants of fresh water.

I am well aware that the salmon which runs up the rivers of Northern and Central Europe, also occurs on the eastern shores of the northern part of North America, and runs up the rivers emptying into the Atlantic. But this fish is one of the marine arctic fishes, which migrates with many others, annually further south, and which migratory species is common to both continents. Those species, however, which never leave the fresh waters, are, without exception, different on the two continents. Again, on each of the continents, they differ in various latitudes; some, however, taking a wider range than others in their natural geographical distribution.

The fresh-water fishes of North America, which form a part of its temperate fauna, extend over very considerable ground; for there is no reason to subdivide into distinct faunæ the extensive tracts of lands between the arctics and the Middle States of the Union. We notice over these, considerable uniformity in the character of the fresh-water fishes. Nevertheless, a minute investigation of all their species has shewn that Lake Superior proper, and the fresh waters north of it, constitute in many respects a special zoological district, sufficiently different from that of the lower lakes and the northern United States, to form a natural division in the great fauna of the fresh-water fishes of the temperate zone of this continent.

We have shewn that there are types, occurring in all the lower lakes, which never occur in Lake Superior and northwards, and that most of the species found in Lake Superior are peculiar to it; the Salmonidæ only taking a wider range, and some of them covering almost the whole extent of that fauna, while others appear circumscribed within very narrow limits.

Now, such differences in the range which the isolated species take in the faunæ, is a universal character of the distribution of animals; some species of certain families covering, without distinction, extensive grounds, which are occupied by several species of other families, limited to particular districts of the same zone.

But after making due allowance for such variations, and taking a general view of the subject, we arrive, nevertheless, at this conclusion; that all the fresh-water fishes of the district under examination are peculiar to that district, and occur nowhere else in any other part of the world.

They have their analogues in other continents, but nowhere beyond the limits of the American continent do we find any fishes identical with those of the district, the fauna of which we have been recently surveying. The lamprey eels of the lake district have very close representatives in Europe, but they cannot be identified. The sturgeons of this continent are neither identical with those of Europe nor with those of Asia. The cat-fishes are equally different. We find a similar analogy and similar differences between the perches, pickerels, eelpouts, salmons, and carps. In all the families which occur throughout the temperate zone, there are near relatives on the two continents, but they do not belong to the same stock. And in addition to these, there are also types which are either entirely peculiar to the American continent, such as Lepidosteus and Percopsis, or belong to genera which have not simultaneous representatives in the two worlds, and are therefore more or less remote from those which have such close analogues. The family of Percoids, for instance, has several genera in Europe, which have no representatives in America; and several genera in America which have no representatives in Europe, besides genera which are represented on both continents, though by representatives specifically distinct.

Such facts have an important bearing upon the history of creation; and it would be very unphilosophical to adhere to any view respecting its plan, which would not embrace these facts, and grant them their full meaning. If we face the fundamental question which is at the bottom of this particular distribution of animals, and ask ourselves, where have all these fishes been created, there can be but one answer given which will not be in conflict and direct contradiction with the facts themselves, and the laws that regulate animal life. The fishes, and all other fresh-water animals of the region of the great lakes, must have been created where they live. They are circumscribed within boundaries over which they cannot pass, and to which there is no natural access from other quarters. There is no trace of their having extended further in their geographical distribution at any former period, nor of their having been limited within narrower boundaries.

It cannot be rational to suppose that they were created in some other part of the world, and were transferred to this continent, to die away in the region where they are supposed to have originated, and to multiply in the region where they are found. There is no reason why we should not take the present evidence in their distribution as the natural fact respecting their origin, and that they are, and were from the beginning, best suited for the country where they are now found.

Moreover, they bear to the species which inhabit similar regions, and live under similar circumstances in Europe and Asia, and the Pacific side of this continent, such relations, that they appear to the philosophical observer as belonging to a plan which has been carried out in its details with reference to the general arrangement. The species of Europe, Asia, and the Pacific side of this continent, correspond in their general combination to the species of the eastern and northern parts of the American continent, all over which the same general types are extended. They correspond to each other on the whole, but differ as to species.

And again, this temperate fauna has such reference to the fauna of the arctic, and to that of the warmer zones, that any transposition of isolated members of the whole plan would disturb the harmony which is evidently maintained throughout the natural distribution of organized beings all over the world. This internal evidence of an intentional arrangement, having direct reference to the present geographical distribution of the animals, dispersed over the whole surface of our globe, shews most conclusively, that they have been created where they are now found. Denying this position were equivalent to denying that the creation has been made according to a wise plan. It were denying to the Creator the intention of establishing well-regulated natural relations between the beings he has called into existence. It were denying him the wisdom which is exemplified in nature, to ascribe it to the creatures themselves,—to ascribe it even to those creatures in which we hardly see evidence of consciousness, or, worse than all, to ascribe this wonderful order to physical influence or mere chance.

As soon as this general conclusion is granted, there are, however, some further adaptations which follow as a matter of course. Each type, being created within the limits of the natural area which it is to inhabit, must have been placed there under circumstances favourable to its preservation and reproduction, and adapted to the fulfilment of the purposes for which it was created. There are in animals peculiar adaptations which are characteristic of their species, and which cannot be supposed to have arisen from subordinate influences. Those which live in shoals cannot be supposed to have been created in single pairs. Those which are made to be the food of others cannot have been created in the same proportions as those which feed upon them. Those which are everywhere found in innumerable specimens, must have been introduced in numbers capable of maintaining their normal proportions to those which live isolated, and are comparatively and constantly fewer. For we know that this harmony in the numerical proportions between animals is one of the great laws of nature. The circumstance that species occur within definite limits where no obstacles prevent their wider distribution, leads to the further inference that these limits were assigned to them from the beginning and so we would come to the final conclusion, that the order which prevails throughout the creation is intentional,—that it is regulated by the limits marked out on the first day of creation,—and that it has been maintained unchanged through ages, with no other modifications than those which the higher intellectual powers of man enable him to impose upon some of the few animals more closely connected with him, and in reference to those very limited changes which he is able to produce artificially upon the surface of our globe.[4]

On the Geography and Geology of the Peninsula of Mount Sinai, and the adjacent Countries.

By John Hogg, M.A., F.R.S., F.L.S.; Honorary Secretary of the Royal Geographical Society, &c. Communicated by the Author.

(Continued from page 219.)

This town is named in Scripture Elath or Eloth; in the Septuagint Αἰλὰθ, and Αἰλὼν; Αἰλὰς, Ἀειλὰ, or Aila by the Greeks; Ælana by the Romans; and Ailah by the Arabians: it is described in 1 Kings ix. 26, as on the shore of the Red Sea in the land of Edom; and in 2 Chron. viii. 17, at the sea-side in the land of Idumea. From Procopius, in the 6th century, we learn the following exact account,[5] which agrees very well with the site of those mounds—the eastern limits of Palæstina (including of course that part of the peninsula which he elsewhere relates[6] was called Palæstina Tertia), reach along the Red Sea. On the shore is placed the town Aïlas, where, the sea ending, it is contracted into a very narrow bay.

Edrisi, in the 12th century, terms the steep descent from the Desert El Tyh by El Nakb to Akaba—Akaba Ailah—i.e., the Descent of Ailah; and Makrisi, in the 14th century, as cited by Burckhardt (p. 511), speaks of the Akaba, or steep mountain before Aila. Consequently, I take it to be correct that these mounds indicate the former position of Elath,[7] on the shore of the Sea of Edom or Idumea—an arm of the Red Sea.

At a short distance from them, but westward, a large space, like a marsh, seemed to be impregnated with nitre, which is left incrusted in some spots upon their surface. From hence, going up the extensive valley El Araba, it is found to be full of sand drifts, with here and there a few trees scattered about; the torrents, after rain, flow along the west side, and their waters, which are not absorbed by the sand, enter the sea at the north-west angle. The width of this part of the Wadi is near 5 miles, but in advancing farther to the north it becomes wider. The mountains on the east are high—from 2000 to 2500 feet; being of granitic, or rather porphyritic formation, they are highly picturesque, and have fine, lofty, jagged peaks: but those on the west, which are sandstone and chalk, are lower; rising to about a level with the desert El Tyh, they do not exceed 1500, or in places 1800 feet in elevation.

Not far from Wadi Ghadyan,[8] towards the west side, a great marsh-like tract, apparently impregnated with nitre, exhibits an incrustation on its surface. And the water in the spring itself is, according to M. De Bertou, strong of sulphur.

Passing the opening of Wadi Beianeh, and still ascending, the most elevated table-land or small plateau of the Wadi-El-Araba is reached at about the line of 30° north latitude, and 35° 15' east longitude nearly, which is very near 500 feet higher than the level of the Gulf of Akaba, according to Herr Schubert. About that point the water-shed occurs; some of the waters of the Araba flow south into the sea of Akaba, but most are carried off north by the tributaries of the Wadi-el-Jeib into the Dead Sea.

The same traveller (Schubert) found the depression of the bed of that deep Wadi at about 4 miles south of El Weibeh (hole with water,) to be 91 Paris feet, or 97 English feet below the level of the Red Sea; the commencement, or most southern limit of that depression taking place at about 15 miles northward of Gebel Harun in Wadi-el-Araba. Consequently, the Dead Sea, Asphaltic Lake (Bahr Lut)—the Sea of Lot—must lie considerably lower than the level of the Gulf of Akaba; indeed, Herr Schubert gives the level of the Dead Sea as being 598 Paris feet, and M. Russegger even more than 1300 English feet below that of the Mediterranean.

These geographical facts then afford, as some authors have supposed, sufficient evidence that the River Jordan, although taking its source at an elevation of 1800 feet in the north Syrian mountains—has not flowed through the entire valley El Araba into the Gulf of Akaba; or rather, into the Red Sea, beyond what is now the Strait of Tiran. And certainly these facts are decisive that it never has done so—if the natural conformation of this region has always been the same, as it now exists with regard to depth and height. But against its having continued the same, ab initio, up to the present time, much reasonable hypothesis, and several remarkable appearances may be fairly advanced.

Of the latter, some are the volcanic phenomena apparent around the Dead Sea and El Ghor,[9] on the north; in the basaltic cliffs and creeks nearly opposite the Isle of Kureiyeh; the frequent displacements of strata and rocks in many places on the north-west side of the Gulf of Akaba; the coincidences exhibited by the strata in the Isle of Tiran, with those of the Arabian and Sinaic shores; and the volcanic remains and crater-like hills between them and Sherm on the south. Moreover, it may be collected from Scripture, that certain changes had actually been effected in the vicinity of the Dead Sea (Gen. xix. 25); and that they were caused by fire (Ibid. xxiv. 28); if then, at that period, the southern part of the valley of the Jordan, the plain of the Dead Sea, and El Ghor had, through igneous, or volcanic, or other agency, sunk much below their former levels, it is possible that a corresponding elevation of the land in Wadi-el-Araba might have taken place at the same (or perhaps at another) time, by the same (or by a subsequent similar) agency.

Again, it seems probable from Scripture, that the Dead Sea and Wadi-el-Araba had been once continued, or more connected in their levels; because in Joshua iii. 16, and xii. 3, the former is called the sea of the plain (even) the Salt Sea; and in Deut. iv. 49, only the sea of the plain; the original Hebrew expression in all three verses is, Yam ha Arabah; that is, the Sea of the Araba; and the Septuagint renders it ἡ θάλασσα Ἄραβα. Ha Arabah, in Hebrew, signifies the same as El Arabah in Arabic—a desert-plain, or a plain. So, likewise, we find in Deut. ii. 8, the children of Edom described as dwelling in Seir, through the way of the Plain from Elath, and from Eziongaber; the Hebrew and Greek words for the plain are here also the same, viz., Arabah. Consequently, these passages from Scripture, shewing that both extremes, north and south, of this great plain or Wadi, bore the same appellation, prove that it was esteemed one entire valley in its whole extent, from the Dead, or Salt Sea, to Elath and Eziongaber on the Red Sea, or Ælanitic Gulf, in the land of Edom (1 Kings ix. 26, and 2 Chron. viii. 17.) And, indeed, according to Dr Robertson, no such division of it, as M. De Bertou and some other travellers assert, into Wadi-el-Akaba, and Wadi-el-Araba,[10] at this day exists.

After having attained the highest point, or short table-land of the Wadi-el-Araba, the descent in fact begins in a direct line nearly due north to the Dead Sea; it is in places more elevated, rougher, and more sandy than in others; and its width also becomes greater. Gebel-el-Beianeh appears the loftiest of the chain on the west; but this is scarcely two-thirds as high as the east range, Gebel-el-Shera (Mount Seir); the former is entirely sterile and arid, whilst the latter is covered with herbs and occasional trees, and seems to have a sufficiency of rain. The east Wadis also, which are numerous, are filled with trees, shrubs, and flowers; and their eastern and higher portions, being well cultivated, yield good crops. So Strabo, calling the district Nabathæa, states it abounded in pastures; ἡ Ναβαταία πολύανδρος οὖσα ἡ χώρα καὶ ἔυβοτος;[11] and being the country of Esau, it was of the fatness of the earth, and of the dew of heaven from above.—Gen. xxvii. 39.

The range of Mount Seir, Gebel-el-Shera, i.e., the mountains of a region or tract, under which I have only included those mountains, commencing with Mount Seir itself on the north, and extending to Gebel-el-Ithm on the south. On the eastern side is now sandstone, veined with oxide of iron; and those mountains still further to the east, forming a part of the Nabathæan chain, are limestone with flints, of the same cretaceous series as that of the Sinaic Peninsula; they present many varied forms and shapes.

El Araba, in the approach to Wadi Gharandel, is more covered with shifting sands, broken by innumerable undulations, and low hills; into these sands the waters of Wadi Gharandel, which, according to Burckhardt, have a sulphureous taste, lose themselves. In the ascent of this Wadi (Gharandel) towards Gebel Kula, a mountain is climbed which is composed of calcareous rocks, sandstone and flints, lying over each other in horizontal layers. Gebel Kula is covered on its summit, with a chalky surface. But in Wadi Dalegheh the mountains are calcareous, with some flints, and perfectly bare.

East of these valleys, and distant about six miles, are said to be the vestiges of a Roman road, which probably led near Usdaka—the Szadeke of Burckhardt—to Petra. Near that place is a hill with some considerable ruins, very possibly the remains of what the Peutingerian Table calls Zadagasta; which word seems to have been corrupted into Zadeka, and Sudaka, or Usdaka. A fine spring, or Ain, is there much noted. Also, further north five or six miles, at Ain Mefrak, some ruins are visible. And the same traveller noticed, a few miles north of the present picturesque village of Eljy—situate a little east of Petra, in a more fertile spot—the substructions of walls and paved roads, all constructed of flints. The present road, traversed by the Hadj, or pilgrims, from Syria to Mecca, passes about five miles more eastwards, through Maan (Maon, Judges x. 12), placed in a rocky district. This town is divided by two hills, on each of which stands a portion of it. The fruits, especially pomegranates, peaches, apricots, and grapes, are there excellent, and are much sought after by the Syrian pilgrims. Burckhardt (p. 436), says here, are several springs, to which the town owes its origin; and I presume the word itself, Ma'an, is abbreviated by use from Mayan, signifying a fountain.

Fourthly.—Petra, the Greek appellation of the capital of the ancient Nabathæa, or territory of the Nabathæi, and the Edom of Scripture, was called in Hebrew, Sela; both words meaning a rock, and the first of which gave its name to the country—Arabia Petræa. It is also called Joktheel, in 2 Kings xiv. 7. Strabo has distinctly recorded that Petra was the capital of the Nabathæans who were Idumæans. (Lib. xvi.) The former appellation having been bestowed upon this people as descendants of Nebaioth, (1 Chron. i. 29), or Nebajoth (Gen. xxv. 13), who was Abraham and Hagar's grandson, and Ishmael's first-born son. Petra is correctly described by the same Greek geographer, as well as by the Roman naturalist. The short account of the last I here transcribe: Nabatæi oppidum includunt Petram nomine in convalle, paulo minus duum mill. passuum amplitudinis, circumdatum montibus inaccessis amne interfluente.[12] I will not add here any description of the very magnificent remains of this remarkable city, the city of the Rock—or rather excavated and carved out of the natural rock—whose dwellings are said to have been in the clefts of the rock, (Obadiah 3), since they are now so well known.

Coming to Petra from Eljy, on the east, the body of the regular mountain on that side is limestone, and higher than the red sandstone, where the tombs in Wadi Mousa are excavated. The cliffs at Petra are of red sandstone, which is soft and easily cut, causing the sculptures to decay quickly, unless where they may have been protected from the weather. This formation extends far to the north and south, and rests on the lower masses of porphyry.

The colour of the sandstone rocks in Wadi Mousa is not a dull monotonous red, but a variety of bright hues, from the deepest crimson, as Dr Robinson writes (vol. ii., p. 531), to the softest pink; verging also sometimes to orange and yellow. These varying shades are often distinctly marked by waving lines, imparting to the surface of the rock a succession of brilliant and changing tints, like the hues of watered silk, and adding greatly to the imposing effect of the sculptured monuments.

The site of Petra, in the high ravine, is called by the Arabs, Wadi Mousa; most likely corrupted from Moseroth, or Mosera (Deut. x. 6), where Aaron died and was buried. It is extremely interesting, and is well watered by a flowing stream—the El Syk of Burckhardt. The sandstone rocks, with their craggy and precipitous sides, have their summits resembling rounded peaks; peaks, probably owing to the softness of the stone, rounded by the effects of weather. The height of this Wadi is estimated at near 2200 feet above the adjoining Wadi-el-Araba. To the west of Petra, Mount Hor, Gebel Harun constitutes the loftiest point of this sandstone tract. It stands out conspicuously, and is a cone irregularly truncated with three rugged peaks, of which that to the NE. is the highest, and has upon it the Mahommetan Wely; or the tomb of Aaron, called Neby Harun. This peak rises to about 2700 feet above Wadi Mousa, or to 5300 feet above the sea.

Captains Irby and Mangles, the first Europeans who ascended Gebel Harun, thus describe the view from the summit. It is extremely extensive in every direction; but the eye rests on few objects which it can clearly distinguish, and give a name to, although an excellent idea is obtained of the general face and features of the country. The chain of Idumean mountains, which form the western shore of the Dead Sea, seem to run on to the south, though losing considerably in their height. They appear in this point of view, barren and desolate. Below them is spread out a white sandy plain, seamed with the beds of occasional torrents, and presenting much the same features as the most desert parts of the Ghor. Where this desert expanse approaches the foot of Mount Hor, there arise out of it, like islands, several lower peaks and ridges, of a purple colour, probably composed of the same kind of sandstone as that of Mount Hor itself, which, variegated as it is in its hues, presents in the distance one uniform mass of dark purple. Towards the Egyptian side there is an expanse of country without features or limit, and lost in the distance. The lofty district which we had quitted in our descent to Wadi Mousa, shuts up the prospect on the south-east side; but there is no part of the landscape which the eye wanders over with more curiosity and delight than the crags of Mount Hor itself, which stand up on every side, in the most rugged and fantastic forms, sometimes strangely piled one on the other, and sometimes as strangely yawning in clefts of a frightful depth.

Under the term Nabathæan Chain, or the chain of the mountains of Edom, I have restricted those mountains beginning north of 30° N. Lat., and which then tend round northward, by the east of Petra. They are the loftiest on the east, attaining probably to an altitude of 3000 feet above the Wadi-el-Araba. This chain presents to the view, on the east, long elevated ranges of limestone, sometimes with flints, but of more easy slopes, without precipices, being smooth and rounded. Further still to the east, the high plateau of the Great Eastern Desert—of which El Nejd is a portion—stretches out to an almost indefinite extent. To the west and north, and around Mount Hor, lofty party-coloured sandstone ridges and cliffs prevail; then succeed high masses of porphyry, constituting the body of the mountains, but lower than the sandstone. And, lastly, more northwards, the chain sinks down into low hills of argillaceous rock, or of limestone.

The entire breadth of the Seir range seems not to exceed eighteen English miles, between Wadi-el-Araba and the Eastern Desert; whilst that of the more northern, or Nabathæan chain, does not exceed twenty-two miles between those districts.

Going west from Petra, the valley of the Araba is again entered, where the deeper Wadi-el-Jeib is seen to wind along, very near the middle of it, from the south, then sweeping off NW., it meets the Wadi-el-Jerafah, which comes in from the SW. Afterwards, it is called only Wadi-el-Jeib; and being a deep valley within a larger valley, it forms the chief water-course of the greater portion of the Araba, and carries down to the Dead Sea, in the wet season, an immense body of water.

El Araba, more to the north of Gebel Harun, is much wider; in parts of it there are gravel hills; and here and there, masses of porphyry lie about in the sand, having been washed down by the torrents. Eleven or twelve miles north of that Mount (Hor), occurs the pass of Nemela among low hills of limestone, or rather a yellowish argillaceous rock, the dark steep mass of the mountain being porphyry, as before described; thence the Wadi ascends between the porphyry and limestone formations; and on the top is a little basin of yellow sandstone capping the porphyry.

Coming back southward through the Wadi-el-Araba, as far as the embouchure of the valley of the Jerafah—meaning gullying,—which is about a mile wide, the mountains on this west side are found to be composed of chalk and limestone; and, in many places, with large pieces of black flint.