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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. 3 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 WAL

LACE, F.L.S., &c. 2 Vols. London. 1869.

5. Contributions to the Theory of Natural tion. By ALFRED WALLACE, F.L.S. 1870.

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 As most of our readers are aware, ages. 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 apSelec-plied to the stony science. It has existed 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

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.

8. Migrations Vegetales, in "Revue des Deux | imosity and ridicule. Gaining strength by Mondes." By M. MARTINS. 1870.

9. Recherches sur le climat et la végétation du pays Tertiare. By Professor HEER. Paris. 1861. 10. The Geological Relations of the Existing Fauna and Flora of the British Islands. By Pro

fessor EDWARD FORBES. London. 1846.

11. The Atlantis Hypothesis in its Botanical Aspect. By Professor OLIVER, in Nat. Hist. Re

view." 1862.

12. New Holland in Europe. By Professor UNGER. Translation in Seemann's Journal of Bot

any. 1865.

13. The Principles of Geology. By Sir CHARLES LYELL, Bart., F.R.S., &c. Tenth Edition. 2 Vols.

London. 1868.

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of facts, it had subsequently to grasp 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

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 tion of animals and plants. Not many number is every year becoming fewer. years ago this was their besetting diffiThe natural corollary from this idea is that culty. Even the gigantic intellect of Humthe present creation of animals and plants boldt had to be content with guessing at a is also special, and the result of a separate truth which has only been made known and distinct act of creative power. It will since his death. The occurrence of anibe 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 whole secret of their geographical distrifauna and flora, will equally include the bution and isolation, apart from the laws faunas and floras of every period of the of natural selection which have been in earth's past history. This proves that the operation, is to be found in an intimate plan of their construction, at least, has never knowledge of the geological changes which been altered. In numerous instances ex- have impressed themselves on physical tinct forms have enabled the naturalist to geography. render this classification more complete,

It is well known that the farther we go by filling up the gaps which before ex- back in time, to study the different aniisted, and thus drawing the various orders mals and plants, the more are we struck and classes nearer to each other. Recent with their unlikeness to anything now livresearches 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 bistory; 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, the whole lifeto understand many a problem which be- I history of our planet, is that the farther 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 Archæopteryx) 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 elapsed since they were blood relations ! of the known instances of the geological Another illustration from the more ancient antiquity of certain groups. The Nautilus, formations, and then we will proceed to Terebratula, Rhynconella, Lingula, &c., have notice how the lineage of existing forms had a continuous range of existence ever becomes clearer as we come to the Tertiary since Silurian times at the least. During epoch. That many of the Secondary genera the Primary epoch, the commonest and of shells are still in existence, is well known, most widely distributed fishes were the among which the commonest are, T'ellina, Ganoids, an order distinguished by being (which then first appeared), Cardium, Carcovered with enamelled bony plates, in- dita, Mya, Solen, Trochus, Pecten (which had stead of horny scales. This dominant appeared in the Primary epoch), and a mulgroup gradually' dwindled during the titude of others. But one illustration we latter stages of the Secondary epoch, and cannot forego. In the upper English chalk was replaced by other orders, which are strata we meet with a species of brachiopod now as cosmopolitan as the Ganoids once (Terebratula lineata) which the best palæonwere. But 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

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- Itaceous facies of the Abysmal fauna.

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As just remarked, when we come to localities of existing species is good evistudy the relations of the Tertiary fauna dence of their antiquity. If the latter and flora to those now in existence, the rule be good, the philosophical student lineage becomes so striking that in many would apply it to every case, whether of instances it appears almost like that of fa- animals or plants, even though their rether and child. This rule holds good, also, mains had not been met with in the fossil in that we find the relationship to be condition. As Darwin has shown, the nearer in proportion as we approach the fossil evidence is extremely fragmentary, human epoch. The earlier stages of the nor would the most sanguine of geologists Tertiary age are most interesting on ac-expect the whole fauna and flora of every count of the distribution of animals over geological period to be perfectly preserved European latitudes whose natural home in the rocks, seeing that the preservation we have been in the habit of supposing of the forms he meets with is due wholly was far away. The commonest of mam- to accidental causes. A glance at such malian species peculiar to this era are the books as Loudon's Hortus Britannicus” Tapir-like animals first made known to the will show that certain genera include scientific world by the genius of Cuvier. species whose geographical localities are This group is now limited to such widely as far asunder in distance as they possibly severed and isolated areas as parts of can be. In our opinion, such cases speak South America and the Malayan archipel- very plainly of their antiquity. A short ago, two species being met with in the time ago it was imagined that true woody former region, and one in the latter. The trees, except the coniferæ, did not appear tapiroid animals had as cosmopolitan a before the Tertiary epoch, when they were distribution during the early Tertiary, regarded as fit associates for the great or Eocene period, as the marsupials number of new forms of mammalia then above mentioned, enjoyed during Second-introduced. But the discovery of such ary times. Their present limited areas of well known forms as the Oak, Fig, Myrtle, occupation are due to the numerous physi- Walnut, Banksia, Dryandra, &c., in the cal changes which have passed over those upper cretaceous deposits of Aix-la-Chacountries where their bones are found in pelle, has shown how great is the antiquity the fossil condition, so that their geogra- of these now almost cosmopolitan genera. phical isolation is a good index to what has Time and space forbid us to do more than taken place in this respect since the Tapir glance at the tropical character of the family was domiciled in Europe. It is early Tertiary fauna and flora. If we more than probable that, since then, the could lay one land surface over another two great continents of India and America the condition in which the Hibernian have been disjoined. The high grounds affirmed his rightful inheritance to be — of this submerged area are still occupied and place a slice of Borneo or Sumatra so by the Pacific islands and coral reefs, the as to overlie merrie England, we should very existence of the latter being, accord- have as near an approximation to Eocene ing to Darwin, sufficient evidence that the conditions in this country as we could imdepression is still going on. Even such agine! apparently insignificant animals as land The middle period in the Tertiary epoch snails have been subjected to the same that commonly known to geologists as geographical changes as larger and more the Miocene, bears out our argument still important groups. A common snail in the further. Here it is that we first meet with United States (Helix labyrinthica) is abun- the most abundant evidence of the direct dantly found in the fossil state in certain ancestry of our living animals and plants, Eocene beds in Hampshire a sure proof which since then have been distributed of its having once lived in that county as over the entire surface of the earth. Of it is now living in America, and an equally all the fossils of this important period eloquent testimony to the physical changes the vegetable organisms are the most comwhich have narrowed its distribution to its plete, and it is from them that we can depresent localities. The fossil plants of the rive our most important and correct genearly Tertiary epoch speak to the same eralizations. First of all, they point to a effect as the fossil animals. Unger has much warmer climate placed by Professhown that the Eocene beds of Europe sor Heer as sixteen degrees higher than contain one hundred and seventy-three the present -existing over Europe. This species closely analogous to forms now temperature, however, was not so elevated growing so far away as New Holland, and as during the previous Eocene period, as is the southern hemisphere generally — an- very evident when we compare the fossil other illustration that widely dissevered floras of the two eras. Beds of lignite, of

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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 fora 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 fora 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 fora 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-Asiastic types in the Caucasus and Asia ous.

Minor generally. Camphor trees, now When we come to analyze what may be such very characteristic objects in Japantermed the Geographical character of this ese scenery, abound in the fossil state in Miocene flora - no matter what part of these strata even as far north as Iceland, Europe may be selected for the purpose Greenland, and Spitzbergen! we are at once struck with its peculiari- The only deposits of the age we are now ties. It is not a European flora, so much considering, to be found in England, are at as one now more or less distributed all Bovey Tracey, in Devonshire, where the over the globe. The percentages of the Lignite, or “ Brown coal,” as it is also called, fossil plants enable us even to point out is worked for the purpose of baking coarse the routes which the vegetable migrations pottery. In this very limited area fifty subsequently took, whilst geological pro- species of fossil plants have been met with, cesses explain the means by which they twenty of which are common to the abovebecame limited to the regions they now mentioned Swiss deposits. These fifty occupy. The large number of species we species include evergreen Oaks, Fig-trees, have to deduce from almost wholly pre- Vines, Laurels, Dryandras, &c. cludes the possibility of a mistake. Thus In the Isle of Mull we meet with strata in Switzerland alone the Miocene beds of the same age, and again at Antrim, in have yielded upwards of eight hundred Ireland; but their floral yield has hitherto species of true flower-bearing, or phaenoga- been small. In fact, these beds are mainly mous plants alone, besides mosses, ferns, interesting on account of their possessing &c. The total number of fossil plants cat- evidence of the last active volcanoes in the alogued from these beds, cryptogamous as British isles. The Greenland beds have well as phænogamous, is upwards of three yielded several hundred species to the thousand. It is the latter on which most zeal of Mr. Whymper, and their general reliance can be placed for the purposes we teaching is pretty much the same as those seek, and we shall therefore leave the of Switzerland, allowing for difference in 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 twenty-bers four hundred and twenty-six species seven species, or nearly one half, were of true flower-bearing plants, exclusive of evergreens. Since this gorgeous flora was others. Amongst this great number are decidedly European, it has become more such woody types as the Birch, Willow, or less cosmopolitan, and been scattered Juniper, Rose, Oak, Maple, Plane-trees, by geological agencies nearly all over the Vines, Walnuts, &c., all of them now charworld. The majority of the species have acteristic of genial temperate conditions. migrated to America; next we find genera The geology of the Aleutian islands — that remained European. Afterwards, in which more or less connect the Old World the order in which they are represented in with the New - indicates a connection of the fossil state, we find other species which these two great continents during the Mi

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