From The Westminster Review. THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS AND PLANTS, GEOLOGICALLY CONSIDERED.* THE subject we have chosen for treatment in the present article is one of the deepest interest to naturalists. As yet, however, it is surrounded by much that is vague and disconnected. The facts of which it treats have only fallen into their harmonious arrangement since the publication of the "Origin of Species." Darwin may well claim that only from his point of view can the subject of the Geographical Distribution of animals and plants be scientifically treated. The manner in which this question has been taken up by naturalists all over the world shows the influence which a great mind has over its fellows. Natural history has received a similar impetus under the Darwinian theory that astronomy did under the older Copernican. It is our purpose, in the following pages, to briefly review the subject of the distribution of existing animals and plants, in the light of paleontology, as well as of those geological phenomena which have 1. The Geographical Distribution of Mammals. By ANDREW MURRAY. London. 1866. 2. The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races, in the Struggle for Life. By CHARLES DARWIN, M.A., F.R.S., &c. Second Edition. London. 1860. 8 The Descent of Man, and Selection in Relation to Sex. By CHARLES DARWIN, M.A., F.R.S., &c. 2 Vols. London. 1871. 4. The Malayan Archipelago By ALFRED WALLACE, F.L.S., &c. 2 Vols. London. 1869. produced such enormous physical changes on the surface of our earth. In doing so it will be plainly seen that the relations of the existing fauna and flora are more intimate as we approach the present epoch. Indeed there is no fact in modern geology so generally admitted as the impossibility of severing the various groups of existing animals and plants from those of bygone ages. As most of our readers are aware, these ages are usually grouped under three great divisions, relatively termed the Primary, Secondary, and Tertiary. These names indicate their relative antiquity. Each division is provisionally subdivided into epochs, and thus the geological nomenclature is made up. But even before Darwin advanced his views, the principal naturalists had been forced to see that the life-systems of these various stages were related to each other, and together formed one grand total which might be regarded as the biological history of our planet. Of these systems the existing one is the last, and bound to the rest by lines of descent. These lines can be traced far away to the dim Laurentian age, but are strongest as the geological student ascends the geological scale towards the present time. The most stubborn of anti-Darwinists has to confess that the tertiary species of animals and plants, relatively few though they be, are nearly related to their present representatives. Geology has passed through many social phases in its brief history. The classification of Comte is certainly correct when ap 5. Contributions to the Theory of Natural Selec-plied to the stony science. It has existed tion. By ALFRED WALLACE, F.L.S. London. 1870. 6. The Naturalist on the Amazons. By HENRY BATES. 2 Vols. London, 1863. 7. The Student's Flora of the British Islands. By Dr. HOOKER, F.R.S. London. 1870. simply as a catalogue of lusus naturæ, just as astronomy was hidden under the form of astrology. Then it emerged into daylight, only to be the butt of theological an 8. Migrations Vegetales, in "Revue des Deux | imosity and ridicule. Gaining strength by Mondes." By M. MARTINS. 1870. its grasp of facts, it had subsequently to be ill-treated at the hands of its friends under the form of "Reconciliation" theories, until, like the infant Hercules, it has strangled the snakes in its cradle, and has arisen to impress its indelible influence on almost every phase of modern thought. Unfortunately, the idea that the various geological periods were marked by distinct life-forms - the product of the earlier French school of geological thought tion of animals and plants. Not many years ago this was their besetting difficulty. Even the gigantic intellect of Humboldt had to be content with guessing at a truth which has only been made known since his death. The occurrence of ani which were successively created and de-fore was incomprehensible. Its latest act stroyed, has not yet completely died away. of filial gratitude is to assist naturalists in There are not wanting eminent naturalists accounting for the geographical distribuwho still cling to this idea, although their number is every year becoming fewer. The natural corollary from this idea is that the present creation of animals and plants is also special, and the result of a separate and distinct act of creative power. It will be our aim to show the fallacy of this no-mals and plants so unlike each other, in tion, and to bring to bear upon it the most districts where the physical and geographrecent investigations in natural science. ical conditions were so similar, might well In doing so we shall be obliged also to prove a hard nut for non-geological natudeal with another and equally gross mis- ralists to crack. It has been the necessity take — viz., that the earth's crust contains of seeking the lineal ancestry of existing no "missing links." To no science is geol- species in the geological epochs which apogy more indebted than to zoology. Only proached most nearly to our own, that has by its aid have geologists been able to un- caused us to see what perils and migraderstand the exact relations of extinct to tions they have undergone through the living forms of life. Numerous though slowly changing physical conditions. Inthese fossil species are, the rocks of Great stead of regarding the present animal and Britian alone having yielded nearly four-vegetable populations of the globe as a teen thousand, we arrive at the striking distinct and synchronous creation, sepadiscovery that they are all reducible to the rated from any that went before, we are same orders and classes as their modern compelled by the sheer weight of facts, to representatives. The natural history clas-regard them as the direct results. The sification, intended to embrace the recent fauna and flora, will equally include the faunas and floras of every period of the earth's past history. This proves that the plan of their construction, at least, has never been altered. In numerous instances extinct forms have enabled the naturalist to render this classification more complete, by filling up the gaps which before existed, and thus drawing the various orders and classes nearer to each other. Recent researches in palæontology and natural ing. The primeval forms have been thrust history have been travelling towards the aside by others better fitted to take a leadsame goal from opposite points. The ing position in the great battle of life. former has been multiplying the list of ex- Analogous functions have been performed isting species found in the fossil state, and by successive and distinct groups; a few the latter has been bringing to light the types, however, have stood the heat and fact that many so-called extinct forms are burden of the fight, and to these we will still living in abysmal and unexplored devote a sentence or two of notice. They depths of the sea. We stated the great bear much the same relation to existing benefits which zoology has conferred on forms that the Celtic words in our langeological science, especially in the earlier guage do to the Saxon, Danish, and Noryears of the latter's history; geology has man, which subsequently overlaid them. now arrived at a maturity and strength One geographical peculiarity is always which enables it to repay its foster-mother true of these ancient groups - they exist the debt it owes. By the knowledge of its in widely severed latitudes. The most organic remains it has enabled zoologists striking fact, perhaps, in the whole lifeto understand many a problem which be-l history of our planet, is that the farther whole secret of their geographical distribution and isolation, apart from the laws of natural selection which have been in operation, is to be found in an intimate knowledge of the geological changes which have impressed themselves on physical geography. It is well known that the farther we go back in time, to study the different animals and plants, the more are we struck with their unlikeness to anything now liv we go back in time, the more lowly or- | count its former widely diffused condition, ganized is the sum total of species, whether is it not evident that the isolated areas it of animals or plants. Now it is exactly now occupies are mainly to be ascribed to these forms which have had the greatest geological causes? Again, so far as is yet geological antiquity. Whilst one type of known, the only warm-blooded animals specialized organism after another has which lived during the entire Secondary passed away, the humbler forms have epoch (with the exception of such rare maintained their ground unchanged, or forms as the Archaeopteryx) were Marnearly so, in organization. It is the moral supials. They became extinct in Europe of the oak and the reed: the storm which during the Mid-tertiary, or Miocene period, felled the former has simply beat the although we still find them living in lands latter to the ground, to spring to its as far apart from each other as North original position after the blast has passed America and Australia. There is every away. These lowly organized types have reason for believing that the latter country now the most cosmopolitan distribution, has been dry land since the close of the so that, in this respect, they resemble Secondary age, at the least, so that its higher forms, which also have a great characteristic modern mammalia may be antiquity. Among the lichens brought by traced thus far back in time. The AusSir James Ross from the high latitudes of tralian cave breccias yield gigantic extinct the southern hemisphere, the greater por- forms of the same order and no other. In tion were found to be specifically identical America, the opossums represent this with those growing in Europe. Professor group, and their peculiar features, when Owen mentions one species of Foraminifera compared with those of their Australian (Webbina rugosa) which has continued in representatives, only too surely indicate existence since the Liassic period. We the immense period of time which has give the following as the most remarkable of the known instances of the geological antiquity of certain groups. The Nautilus, Terebratula, Rhynconella, Lingula, &c., have had a continuous range of existence ever since Silurian times at the least. During the Primary epoch, the commonest and most widely distributed fishes were the Ganoids, an order distinguished by being covered with enamelled bony plates, instead of horny scales. This dominant group gradually' dwindled during the latter stages of the Secondary epoch, and was replaced by other orders, which are now as cosmopolitan as the Ganoids once elapsed since they were blood relations! Another illustration from the more ancient formations, and then we will proceed to notice how the lineage of existing forms becomes clearer as we come to the Tertiary epoch. That many of the Secondary genera of shells are still in existence, is well known, among which the commonest are, Tellina, (which then first appeared), Cardium, Cardita, Mya, Solen, Trochus, Pecten (which had appeared in the Primary epoch), and a multitude of others. But one illustration we cannot forego. In the upper English chalk strata we meet with a species of brachiopod (Terebratula lineata) which the best palæonBut there still exists what we may tologists recognize as identical with the term "outliers" of this ancient fish-fauna, existing Rhynconella caput-serpentis. The in the Bony Pike of North American lakes antiquity of the latter species might have and rivers, in the Polypterus of South been guessed at from its peculiar geographAfrica, and in the recently discovered and ical distribution. It is common to both rare "Mud Fishes" (Ceratodus), of Aus- sides the Atlantic, as well as to the South tralia. Our common Sturgeon is nearly African and Chinese seas. This wide related to this interesting group. Gün- severance of the areas from each other, ther says that these Ganoids now form it cannot be too firmly insisted upon, is in only three and a half per cent. of known every case illustrative of the antiquity of species of fish. The widely isolated char- a species. Dr. Carpenter and Prof. Wyacter of this fauna plainly enough indi- ville-Thomson believe we are still living in cates its antiquity, and as surely foretells a Cretaceous epoch, owing to the creits ultimate extinction. Taking into ac-taceous facies of the Abysmal fauna. were. As just remarked, when we come to study the relations of the Tertiary fauna and flora to those now in existence, the lineage becomes so striking that in many instances it appears almost like that of father and child. This rule holds good, also, in that we find the relationship to be nearer in proportion as we approach the human epoch. The earlier stages of the Tertiary age are most interesting on account of the distribution of animals over European latitudes whose natural home we have been in the habit of supposing was far away. The commonest of mammalian species peculiar to this era are the Tapir-like animals first made known to the scientific world by the genius of Cuvier. This group is now limited to such widely severed and isolated areas as parts of South America and the Malayan archipelago, two species being met with in the former region, and one in the latter. The tapiroid animals had as cosmopolitan a distribution during the early Tertiary, or Eocene period, as the marsupials above mentioned, enjoyed during Secondary times. Their present limited areas of occupation are due to the numerous physical changes which have passed over those countries where their bones are found in the fossil condition, so that their geographical isolation is a good index to what has taken place in this respect since the Tapir family was domiciled in Europe. It is more than probable that, since then, the two great continents of India and America have been disjoined. The high grounds of this submerged area are still occupied by the Pacific islands and coral reefs, the very existence of the latter being, according to Darwin, sufficient evidence that the depression is still going on. Even such apparently insignificant animals as land snails have been subjected to the same geographical changes as larger and more important groups. A common snail in the United States (Helix labyrinthica) is abundantly found in the fossil state in certain Eocene beds in Hampshire - a sure proof of its having once lived in that county as it is now living in America, and an equally eloquent testimony to the physical changes which have narrowed its distribution to its present localities. The fossil plants of the early Tertiary epoch speak to the same effect as the fossil animals. Unger has shown that the Eocene beds of Europe contain one hundred and seventy-three species closely analogous to forms now growing so far away as New Holland, and the southern hemisphere generally-another illustration that widely dissevered localities of existing species is good evidence of their antiquity. If the latter rule be good, the philosophical student would apply it to every case, whether of animals or plants, even though their remains had not been met with in the fossil condition. As Darwin has shown, the fossil evidence is extremely fragmentary, nor would the most sanguine of geologists expect the whole fauna and flora of every geological period to be perfectly preserved in the rocks, seeing that the preservation of the forms he meets with is due wholly to accidental causes. A glance at such books as Loudon's "Hortus Britannicus will show that certain genera include species whose geographical localities are as far asunder in distance as they possibly can be. In our opinion, such cases speak very plainly of their antiquity. A short time ago it was imagined that true woody trees, except the conifera, did not appear before the Tertiary epoch, when they were regarded as fit associates for the great number of new forms of mammalia then introduced. But the discovery of such well known forms as the Oak, Fig, Myrtle, Walnut, Banksia, Dryandra, &c., in the upper cretaceous deposits of Aix-la-Chapelle, has shown how great is the antiquity of these now almost cosmopolitan genera. Time and space forbid us to do more than glance at the tropical character of the early Tertiary fauna and flora. If we could lay one land surface over another — the condition in which the Hibernian affirmed his rightful inheritance to beand place a slice of Borneo or Sumatra so as to overlie merrie England, we should have as near an approximation to Eocene conditions in this country as we could imagine! Of The middle period in the Tertiary epoch that commonly known to geologists as the Miocene, bears out our argument still further. Here it is that we first meet with the most abundant evidence of the direct ancestry of our living animals and plants, which since then have been distributed over the entire surface of the earth. all the fossils of this important period the vegetable organisms are the most complete, and it is from them that we can derive our most important and correct generalizations. First of all, they point to a much warmer climate placed by Professor Heer as sixteen degrees higher than the present existing over Europe. This temperature, however, was not so elevated as during the previous Eocene period, as is very evident when we compare the fossil floras of the two eras. Beds of lignite, of Miocene age, rich in fossil plants, are met have been transferred to Asia, Africa, and with in Switzerland, Germany, Scotland, even to Australia. The American types Ireland, Devonshire, Iceland, Greenland, are in the largest proportion. This is the and Spitzbergen. The high northern char- most persistent feature of the Miocene acter of the last mentioned localities shows flora wherever we study it in the Old us that when these plants grew there, in World. Their analogues now grow in the consequence of the mean elevation of tem- forests of Virginia, North and South Caroperature, it is probable that no, ice-cap ex- lina, and Florida. They include such isted at the North Pole, to the extreme of familiar examples as Magnolias, Tulipwhich this gorgeous flora may have ex- trees, Evergreen Oaks, Maples, Planetended. For it must be recollected that trees, Robinias, Sequoias, &c. The higher these fossil plants afford every evidence of climature of the mid-Tertiary period is their having grown on or near the spots further corroborated by the testimony of where they are now found, and that they the fossil plants now growing elsewhere were not floated or drifted thither. We than in America. Professor Oliver, who find the petals, stamens, pistils, and even so skilfully laid down the relations of the the pollen of the flowers preserved. Many Miocene flora to existing forms, in the of the leaves have their backs covered Natural History Review for 1864, has there with "bunt" and "rust-fungi which shown that we must seek for the Euroaffected them as they attack their repre- pean species of the Miocene beds by the sentatives at the present day! This alone shores of the Mediterranean; and the is strong evidence that the flora is indigen ous. Asiastic types in the Caucasus and Asia Minor generally. Camphor trees, now such very characteristic objects in Japanese scenery, abound in the fossil state in these strata even as far north as Iceland, Greenland, and Spitzbergen! The only deposits of the age we are now considering, to be found in England, are at Bovey Tracey, in Devonshire, where the Lignite, or "Brown coal," as it is also called, is worked for the purpose of baking coarse pottery. In this very limited area fifty species of fossil plants have been met with, twenty of which are common to the abovementioned Swiss deposits. These fifty species include evergreen Oaks, Fig-trees, Vines, Laurels, Dryandras, &c. When we come to analyze what may be termed the Geographical character of this Miocene flora-no matter what part of Europe may be selected for the purpose we are at once struck with its peculiarities. It is not a European flora, so much as one now more or less distributed all over the globe. The percentages of the fossil plants enable us even to point out the routes which the vegetable migrations subsequently took, whilst geological processes explain the means by which they became limited to the regions they now occupy. The large number of species we have to deduce from almost wholly precludes the possibility of a mistake. Thus in Switzerland alone the Miocene beds have yielded upwards of eight hundred species of true flower-bearing, or phænogamous plants alone, besides mosses, ferns, &c. The total number of fossil plants catalogued from these beds, cryptogamous as well as phænogamous, is upwards of three thousand. It is the latter on which most reliance can be placed for the purposes we seek, and we shall therefore leave the former more or less out of our calcula-latitude. tions. Among this large number of flower- The fossil Miocene flora of Iceland numbearing plants, three hundred and twentyseven species, or nearly one half, were evergreens. Since this gorgeous flora was decidedly European, it has become more or less cosmopolitan, and been scattered by geological agencies nearly all over the world. The majority of the species have migrated to America; next we find genera that remained European. Afterwards, in the order in which they are represented in the fossil state, we find other species which In the Isle of Mull we meet with strata of the same age, and again at Antrim, in Ireland; but their floral yield has hitherto been small. In fact, these beds are mainly interesting on account of their possessing evidence of the last active volcanoes in the British isles. The Greenland beds have yielded several hundred species to the zeal of Mr. Whymper, and their general teaching is pretty much the same as those of Switzerland, allowing for difference in bers four hundred and twenty-six species of true flower-bearing plants, exclusive of others. Amongst this great number are such woody types as the Birch, Willow, Juniper, Rose, Oak, Maple, Plane-trees, Vines, Walnuts, &c., all of them now characteristic of genial temperate conditions. The geology of the Aleutian islands — which more or less connect the Old World with the New - indicates a connection of these two great continents during the Mi |