An example bearing on our present subject may serve to illustrate this.

In the latter part of the Upper Silurian period (the Lower Helderberg

age), vast areas of the American continent[EV] were covered with an

ocean in which were deposited organic limestones whose fossils show

that this great interior sea was pervaded by equatorial waters bringing

food and warmth, while the incipient ranges of the Appalachians on the

east, and the Cordilleras on the west, and the Laurentian axis on the

north, fenced off from it the colder arctic waters. How different must

the climate of America and of the region north of it have been in these

circumstances from that which prevails at present, or from that which

prevailed in certain other periods, when it was open to the incursions

of the arctic ice-laden currents, bearing loads of fine sediment![EW] It

was in these circumstances, and in the similar circumstances in which the

great Corniferous limestone of the Devonian was deposited--a limestone

showing in its rich coral fauna even warmer waters than those of the

Lower Helderberg--that the Devonian flora took its origin in the north

and advanced southward over new lands in process of emergence from the

sea. The somewhat similar condition evidenced by the Lower Carboniferous

limestone preceded the advent of the great and rich flora of the

coal-formation.

[EV] See a memoir and map by Prof. Hall, "Reports of the Regents of New

York," 1874-'75.

[EW] It seems certain that the faunæ of the old limestones, like the

Trenton, Niagara, Lower Helderberg, and Corniferous, belong to warm and

sheltered sea areas, and that those rich in graptolites and trilobites,

enclosed in muddy sediments, belong to the colder arctic waters. Such

arctic faunæ are those of the Quebec group and of the Utica shale, and to

some extent that of the Hamilton group.

Lyell's theory on this subject has, I think, in some recent publications,

been somewhat misapprehended. It is true that he stated hypothetically

two contrasted conditions of distribution, in one of which all the land

was equatorial, in another all polar; but he did not suppose that these

conditions had actually occurred; and even in his earlier editions,

before the recent discoveries and discussions as to ocean currents,

he was always careful to attach due value to these in connection with

subsidences and elevations.[EX] In his later editions he introduced more

full references to current action, and also stated Croll's theory, but

still maintained the validity of his original conclusions.

[EX] See "Principles of Geology," edition of 1840, chapter vii.

The sufficiency of this Lyellian theory to account for the facts, in so

far as plants are concerned, may, I think, be inferred from the course

of the isothermal lines at present. The south end of Greenland is on

the latitude of Christiania in Norway on the one hand, and of Fort

Liard in the Peace River region on the other; and while Greenland is

clad in ice and snow, wheat and other grains, and the ordinary trees

of temperate climates, grow at the latter places,[EY] It is evident,

therefore, that only exceptionally unfavourable circumstances prevent

the Greenland area from still possessing a temperate flora, and these

unfavourable circumstances possibly tell even on the localities with

which we have compared it. Further, the mouth of the McKenzie River is in

the same latitude with Disco, near which are some of the most celebrated

localities of fossil Cretaceous and Tertiary plants. Yet the mouth of

the McKenzie River enjoys a much more favourable climate and has a much

more abundant flora than Disco. If north Greenland were submerged, and

low land reaching to the south terminated at Disco, and if from any cause

either the cold currents of Baffin's Bay were arrested, or additional

warm water thrown into the North Atlantic by the Gulf Stream, there is

nothing to prevent a mean temperature of 45° Fahr. from prevailing at

Disco; and the estimate ordinarily formed of the requirements of its

extinct floras is 50°,[EZ] which is probably above rather than below the

actual temperature required.

[EY] See "Macoun's Report," "Geological Survey of Canada," and

Richardson's "Boat Voyage."

[EZ] Heer. See, also, papers by Prof. Haughton and by Gardner in "Nature"

for 1878.

Since, then, geological facts assure us of mutations of the continents

much greater than those apparently required to account for the changes of

climate implied in the existence of the ancient arctic floras, it does

not seem absolutely necessary to invoke any others.[FA] If, however,

there are other true causes which might either aid or counteract those

above referred to, it may be well to consider them.

[FA] Sir William Thomson, "Transactions of the Geological Society of

Glasgow," February 22, 1878.

Mr. Croll has, in his valuable work "Climate and Time" and in various

memoirs, brought forward an ingenious astronomical theory to account

for changes of climate. This theory, as stated by himself in a recent

paper,[FB] is that when the eccentricity of the earth's orbit is at a

high value, and the northern winter solstice is in perihelion, agencies

are brought into operation which make the southeast trade-winds stronger

than the northeast, and compel them to blow over upon the northern

hemisphere as far as the Tropic of Cancer. The result is that all the

great equatorial currents of the ocean are impelled into the northern

hemisphere, which thus, in consequence of the immense accumulation of

warm water, has its temperature raised, so that ice and snow must to a

great extent disappear from the arctic regions. In the prevalence of

the converse conditions, the arctic zone becomes clad in ice, and the

southern has its temperature raised.

[FB] "Cataclysmic Theories of Geological Climate," "Geological Magazine,"

May, 1878.

At the same time, according to Croll's calculations, the accumulation

of ice on either pole would tend, by shifting the earth's centre of

gravity, to raise the level of the ocean and submerge the land on the

colder hemisphere. Thus a submergence of land would coincide with a cold

condition, and emergence with increasing warmth. Facts already referred

to, however, show that this has not always been the case, but that in

many cases submergence was accompanied with the influx of warm equatorial

waters and a raised temperature, this apparently depending on the

question of local distribution of land and water; and this in its turn

being regulated not always by mere shifting of the centre of gravity,

but by foldings occasioned by contraction, by equatorial subsidences

resulting from the retardation of the earth's rotation, and by the excess

of material abstracted by ice and frost from the arctic regions, and

drifted southward along the lines of arctic currents. This drifting must

in all geological times have greatly exceeded, as it certainly does at

present, the denudation caused by atmospheric action at the equator,

and must have tended to increase the disposition to equatorial collapse

occasioned by retardation of rotation.[FC]

[FC] Croll, in "Climate and Time," and in a note read before the British

Association in 1876, takes an opposite view; but this is clearly contrary

to the facts of sedimentation, which show a steady movement of _débris_

toward the south and southwest.

While such considerations as those above referred to tend to reduce

the practical importance of Mr. Croll's theory., on the other hand

they tend to remove one of the greatest objections against it--namely,

that founded on the necessity of supposing that glacial periods recur

with astronomical regularity in geological time. They cannot do so if

dependent on other causes inherent in the earth itself, and producing

important movements of its crust.

The third great cause of warmer climates in the past is the larger

proportion of carbon dioxide, or carbonic-acid gas, in the atmosphere in

early geological times, as proved by the immense amount of carbon now

sealed up in limestone and coal, and which must at one time have been in

the air. It has been shown that a very small additional quantity of this

substance would so obstruct radiation of heat from the earth as to act

almost like a glass roof. If, however, the quantity of carbonic acid,

great at first, was slowly and regularly removed, even if, as suggested

by Hunt, small additional supplies were gradually added from space, this

cause could have affected only the very oldest floras. But it is known

that some comets and meteorites contain carbonaceous matter, and this

allows us to suppose that accessions of carbon may have been communicated

at irregular intervals. If so, there may have been cycles of greater

and less abundance of this substance, and an atmosphere rich in carbon

dioxide might at one and the same time afford warmth and abundance of

food to plants.

It thus appears that the causes of ancient vicissitudes of climate are

somewhat complex, and when two or more of them happened to coincide very

extreme changes might result, having most important bearings on the

distribution of plants.

This may help us to deal with the peculiarities of the great Glacial age,

which may have been rendered exceptionally severe by the combination of

several of the causes of refrigeration. We must not suppose, however,

that the views of those extreme glacialists who suppose continental

ice-caps reaching half way to the equator are borne out by facts. In

truth, the ice accumulating round the pole must have been surrounded by

water, and there must have been tree-clad islands in the midst of the icy

seas, even in the time of greatest refrigeration. This is proved by the

fact that, in the Leda clay of eastern Canada, which belongs to the time

of greatest submergence, and whose fossil shells show sea-water almost

at the freezing-point, there are leaves of poplars and other plants

which must have been drifted from neighbouring shores. Similar remains

occur in clays of like origin in the basin of the great lakes and in the

West. These have been called "interglacial," but there is no evidence to

prove that they are not truly glacial. Thus, while we need not suppose

that plants existed within the Arctic circle in the Glacial age, we have

evidence that those of the cold temperate and sub-arctic zones continued

to exist pretty far north. At the same time the warm temperate flora

would be driven to the south, except where sustained in insular spots

warmed by the equatorial currents. It would return northward on the

re-elevation of the land and the renewal of warmth.

If, however, our modern flora is thus one that has returned from the

south, this would account for its poverty in species as compared with

those of the early Tertiary. Groups of plants descending from the north

have been rich and varied. Returning from the south they are like the

shattered remains of a beaten army. This, at least, has been the case

with such retreating floras as those of the Lower Carboniferous, the

Permian, and the Jurassic, and possibly that of the Lower Eocene of

Europe.

The question of the supply of light to an arctic flora is much less

difficult than some have imagined. The long summer day is in this respect

a good substitute for a longer season of growth, while a copious covering

of winter snow not only protects evergreen plants from those sudden

alternations of temperature which are more destructive than intense

frost, and prevents the frost from penetrating to their roots, but, by

the ammonia which it absorbs, preserves their greenness. According to

Dr. Brown, the Danish ladies of Disco long ago solved this problem.[FD]

He informs us that they cultivate in their houses most of our garden

flowers--as roses, fuchsias, and geraniums--showing that it is merely

warmth and not light that is required to enable a sub-tropical flora to

thrive in Greenland. Even in Canada, which has a flora richer in some

respects than that of temperate Europe, growth is effectually arrested

by cold for nearly six months, and though there is ample sunlight there

is no vegetation. It is, indeed, not impossible that in the plans of the

Creator the continuous summer sun of the arctic regions may have been

made the means for the introduction, or at least for the rapid growth and

multiplication, of new and more varied types of plants.

[FD] "Florula Discoana," Botanical Society of Edinburgh, 1868.

Much, of course, remains to be known of the history of the old floras,

whose fortunes I have endeavoured to sketch, and which seem to have been

driven like shuttle-cocks from north to south, and from south to north,

especially on the American continent, whose meridional extension seems to

have given a field specially suited for such operations.

This great stretch of the western continent, from north to south, is also

connected with the interesting fact that, when new floras are entering

from the arctic regions, they appear earlier in America than in Europe,

and that in times when old floras are retreating from the south old

genera and species linger longer in America. Thus, in the Devonian and

Cretaceous new forms of those periods appear in America long before they

are recognized in Europe, and in the modern epoch forms that would be

regarded in Europe as Miocene still exist. Much confusion in reasoning

as to the geological ages of the fossil floras has arisen from want of

attention to this circumstance.

What we have learned respecting this wonderful history has served

strangely to change some of our preconceived ideas. We must now be

prepared to admit that an Eden can be planted even in Spitzbergen, that

there are possibilities in this old earth of ours which its present

condition does not reveal to us; that the present state of the world is

by no means the best possible in relation to climate and vegetation; that

there have been and might be again conditions which could convert the

ice-clad arctic regions into blooming paradises, and which at the same

time would moderate the fervent heat of the tropics. We are accustomed to

say that nothing is impossible with God; but how little have we known of

the gigantic possibilities which lie hidden under some of the most common

of his natural laws!

These facts have naturally been made the occasion of speculations as

to the spontaneous development of plants by processes of varietal

derivation. It would, from this point of view, be a nice question to

calculate how many revolutions of climate would suffice to evolve the

first land-plant; what are the chances that such plant would be so

dealt with by physical changes as to be preserved and nursed into a

meagre flora like that of the Upper Silurian or the Jurassic; how many

transportations to Greenland would suffice to promote such meagre flora

into the rich and abundant forests of the Upper Cretaceous, and to

people the earth with the exuberant vegetation of the early Tertiary.

Such problems we may never be able to solve. Probably they admit of no

solution, unless we invoke the action of an Almighty mind, operating

through long ages, and correlating with boundless power and wisdom

all the energies inherent in inorganic and organic nature. Even then

we shall perhaps be able to comprehend only the means by which, after

specific types have been created, they may, by the culture of their

Maker, be "sported" into new varieties or subspecies, and thus fitted

to exist under different conditions or to occupy higher places in the

economy of nature.

Before venturing on such extreme speculations as some now current on

questions of this kind, we would require to know the successive extinct

floras as perfectly as those of the modern world, and to be able to

ascertain to what extent each species can change either spontaneously

or under the influence of struggle for existence or expansion under

favourable conditions, and under arctic semi-annual days and nights, or

the shorter days of the tropics. Such knowledge, if ever acquired, it may

take ages of investigation to accumulate.

As to the origin and mode of introduction of successive floras, I am, for

the reasons above stated, not disposed to dogmatise, or to adopt as final

any existing theory of the development of the vegetable kingdom. Still,

some laws regulating the progress of vegetable life may be recognised,

and I propose to state these in connection with the Palæozoic floras, to

which my own studies have chiefly related.

Fossil plants are almost proverbially uncertain with reference to their

accurate determination, and have been regarded as of comparatively little

utility in the decision of general questions of palæontology. This

results principally from the fragmentary condition in which they have

been studied, and from the fact that fragments of animal structures are

more definite and instructive than corresponding portions of plants.

It is to be observed, however, that our knowledge of fossil plants

becomes accurate in proportion to the extent to which we can carry the

study of specimens in the beds in which they are preserved, so as to

examine more perfect examples than those usually to be found in museums.

When structures are taken into the account, as well as external forms, we

can also depend more confidently on our results. Further, the abundance

of specimens to be obtained in particular beds often goes far to make up

for their individual imperfection. The writer of these pages has been

enabled to avail himself very fully of these advantages; and on this

account, if on no other, feels entitled to speak with some authority on

theoretical questions.

It is an additional encouragement to pursue the subject, that, when

we can obtain definite information as to the successive floras of any

region, we thereby learn much as to climate and vicissitudes in regard to

the extent of land and water; and that, with reference to such points,

the evidence of fossil plants, when properly studied, is, from the close

relation of plants to those stations and climates, even more valuable

than that of animal fossils.

It is necessary, however, that in pursuing such inquiries we should have

some definite views as to the nature and permanence of specific forms,

whether with reference to a single geological period or to successive

periods; and I may be excused for stating here some general principles,

which I think important for our guidance.

1. Botanists proceed on the assumption, vindicated by experience, that,

within the period of human observation, species have not materially

varied or passed into each other. We may make, for practical purposes,

the same assumption with regard to any given geological period, and may

hold that for each such period there are specific types which, for the

time at least, are invariable.

2. When we inquire what constitutes a good species for any given period,

we have reason to believe that many names in our lists represent merely

varietal forms or erroneous determinations. This is the case even in the

modern flora; and in fossil floras, through the poverty of specimens,

their fragmentary condition, and various states of preservation, it

is still more likely to occur. Every revision of any group of fossils

detects numerous synonyms, and of these many are incapable of detection

without the comparison of large suites of specimens.

3. We may select from the flora of any geological period certain

forms, which I shall call _specific types_, which may for such period

be regarded as unchanging. Having settled such types, we may compare

them with similar forms in other periods, and such comparisons will

not be vitiated by the uncertainty which arises from the comparison of

so-called species which may, in many cases, be mere varietal forms, as

distinguished from specific types. Our types may be founded on mere

fragments, provided that these are of such a nature as to prove that they

belong to distinct forms which cannot pass into each other, at least

within the limits of one geological period.

4. When we compare the specific types of one period with those of another

immediately precedent or subsequent, we shall find that some continue

unchanged through long intervals of geological time, that others are

represented by allied forms regarded either as varietal or specific, and

as derived or otherwise, according to the view which we may entertain as

to the permanence of species. On the other hand, we also find new types

not rationally deducible on any theory of derivation from those known

in other periods. Further, in comparing the types of a poor period with

those of one rich in species, we may account for the appearance of new

types in the latter by the deficiency of information as to the former;

where many new types appear in the poorer period this conclusion seems

less probable. For example, new types appearing in poor formations, like

the Lower Erian and Lower Carboniferous, have greater significance than

if they appeared in the Middle Erian or in the Coal Measures.

5. When specific types disappear without any known successors, under

circumstances in which it seems unlikely that we should have failed to

discover their continuance, we may fairly assume that they have become

extinct, at least locally; and where the field of observation is very

extensive, as in the great coal-fields of Europe and America, we may

esteem such extinction as practically general, at least for the northern

hemisphere. When many specific types become extinct together, or in close

succession, we may suppose that such extinction resulted from physical

changes; but where single types disappear, under circumstances in which

others of similar habit continue, we may not unreasonably conjecture

that, as Pictet has argued in the case of animals, such types may have

been in their own nature limited in duration, and may have died out

without any external cause.

6. With regard to the _introduction_ of specific types we have not as

yet a sufficient amount of information. Even if we freely admit that

ordinary specific forms, as well as mere varieties, may result from

derivation, this by no means excludes the idea of primitive specific

types originating in some other way. Just as the chemist, after analysing

all compounds and ascertaining all allotropic forms, arrives at length at

certain elements not mutually transmutable or derivable, so the botanist

and zoölogist must expect sooner or later to arrive at elementary

specific types, which, if to be accounted for at all, must be explained

on some principle distinct from that of derivation. The position of

many modern biologists, in presence of this question, may be logically

the same with that of the ancient alchemists with reference to the

chemical elements, though the fallacy in the case of fossils may be of

more difficult detection. Our business at present, in the prosecution of

palæobotany, is to discover, if possible, what are elementary or original

types, and, having found these, to enquire as to the law of their

creation.

7. In prosecuting such questions geographical relations must be carefully

considered. When the floras of two successive periods have existed in

the same region, and under circumstances that render it probable that

plants have continued to grow on the same or adjoining areas throughout

these periods, the comparison becomes direct, and this is the case with

the Erian and Carboniferous floras in northeastern America. But, when

the areas of the two formations are widely separated in space as well

as in time, any resemblances of facies that we may observe may have no

connection whatever with an unbroken continuity of specific types.

I desire, however, under this head, to affirm my conviction that,

with reference to the Erian and Carboniferous floras of North America

and of Europe, the doctrine of "homotaxis," as distinct from actual

contemporaneity, has no place. The succession of formations in the

Palæozoic period evidences a similar series of physical phenomena on the

grandest scale throughout the northern hemisphere. The succession of

marine animals implies the continuity of the sea-bottoms on which they

lived. The headquarters of the Erian flora in America and Europe must

have been in connected or adjoining areas in the North Atlantic. The

similarity of the Carboniferous flora on the two sides of the Atlantic,

and the great number of identical species, proves a still closer

connection in that period. These coincidences are too extensive and too

frequently repeated to be the result of any accident of similar sequence

at different times, and this more especially as they extend to the more

minute differences in the features of each period, as, for instance, the

floras of the Lower and Upper Devonian, and of the Lower, Middle, and

Upper Carboniferous.

8. Another geographical question is that which relates to centres of

dispersion. In times of slow subsidence of extensive areas, the plants

inhabiting such areas must be narrowed in their range and often separated

from one another in detached spots, while, at the same time, important

climatal changes must also occur. On the re-emergence of the land such

of these species as remained would again extend themselves over their

former areas of distribution, in so far as the new climatal and other

conditions would permit. We would naturally suppose that the first of

the above processes would tend to the elimination of varieties, the

second, to their increase; but, on the other I hand, the breaking up of a

continental flora into that of distinct islets, and the crowding together

of many forms, might be a process fertile in the production of some

varieties if fatal to others.

Further, it is possible that these changes of subsidence may have some

connection with the introduction, as well as with the extinction, even of

specific types. It is certain, at least, in the case of land-plants, that

such types come in most plentifully immediately after elevation, though

they are most abundantly preserved in periods of slow subsidence. I do

not mean, however, that this connection is one of cause and effect; there

are, indeed, indications that it is not so. One of these is, that in some

cases the enlargement of the area of the land seems to be as injurious to

terrestrial species as its diminution.

9. Another point on which I have already insisted, and which has been

found to apply to the Tertiary as well as to the Palæozoic floras, is the

appearance of new types within the arctic and boreal areas, and their

migration southward. Periods in which the existence of northern land

coincided with a general warm temperature of the northern hemisphere seem

to have been those most favourable to the introduction of new forms of

land-plants. Hence, there has been throughout geological time a general

movement of new floras from the Palæarctic and Nearctic regions to the

southward.

Applying the above considerations to the Erian and Carboniferous floras

of North America, we obtain some data which may guide us in arriving at

general conclusions. The Erian flora is comparatively poor, and its

types are in the main similar to those of the Carboniferous. Of these

types a few only reappear in the middle coal-formation under identical

forms; a great number appear under allied forms; some altogether

disappear. The Erian flora of New Brunswick and Maine occurs side by

side with the Carboniferous of the same region; so does the Erian of New

York and Pennsylvania with the Carboniferous of those States. Thus we

have data for the comparison of successive floras in the same region. In

the Canadian region we have, indeed, in direct sequence, the floras of

the Upper Silurian, the Lower, Middle, and Upper Erian, and the Lower,

Middle, and Upper Carboniferous, all more or less distinct from each

other, and affording an admirable series for comparison in a region whose

geographical features are very broadly marked. All these floras are

composed in great part of similar types, and probably do not indicate

very dissimilar general physical conditions, but they are separated from

each other by the great subsidences of the Corniferous limestone and the

Lower Carboniferous limestone, and by the local but intense subterranean

action which has altered and disturbed the Erian beds toward the close

of that period. Still, these changes were not universal. The Corniferous

limestone is absent in Gaspé, and probably in New Brunswick, where,

consequently, the Erian flora could continue undisturbed during that long

period. The Carboniferous limestone is absent from the slopes of the

Appalachians in Pennsylvania, where a retreat may have been afforded to

the Upper Erian and Lower Carboniferous floras. The disturbances at the

close of the Erian were limited to those eastern regions where the great

limestone-producing subsidences were unfelt, and, on the other hand, are

absent in Ohio, where the subsidences and marine conditions were almost

at a maximum.

Bearing in mind these peculiarities of the area in question, we may now

group in a tabular form the distinct specific types recognised in the

Erian system, indicating, at the same time, those which are represented

by identical species in the Carboniferous, those represented by similar

species of the same general type, and those not represented at all.

For example, _Calamites cannæformis_ extends as a species into the

Carboniferous; _Asterophyllites latifolia_ does not so extend, but is

represented by closely allied species of the same type; _Nematophyton_

disappears altogether before we reach the Carboniferous.

_Table of Erian and Carboniferous Specific Types._

Erian types. Represented in By identical By related

Carboniferous-- types. forms.

1. Syringoxylon mirabile ?

2. Nematoxylon

3. Nematophyton

4. Aporoxylon

5. Ormoxylon

6. Dadoxylon *

7. Sigillaria Vanuxemii *

8. S. palpebra *

9. Didymophyllum

10. Calamodendron *

11. Calamites transitionis *

12. C. cannæformis *

13. Asterophyllites scutigera *

14. A. latifolia

15. Annularia laxa

16. Sphenophyllum antiquum *

17. Cyclostigma

18. Arthrostigma

19. Lepidodendron Gaspianum *

20. L. corrugatum *

21. Lycopodites Matthewi *

22. L. Richardsoni

23. Ptilophyton Vanuxemii

24. Lepidophloios antiquus *

25. Psilophyton princeps

26. P. robustius

27. Cordaites Robbii *

28. C. angustifolia

29. Archæopteris Jacksoni

30. Aneimites obtusa *

31. Platyphyllum Brownii

32. Cyclopteris varia *

33. C. obtusa

34. Neuropteris polymorpha *

35. N. serrulata *

36. N. retorquata *

37. N. resecta

38. Megalopteris Dawsoni.

39. Sphenopteris Hoeninghausi *

40. S. Harttii *

41. Hymenophyllites curtilobus

42. H. obtusilobus *

43. Alethopteris discrepans *

44. Pecopteris serrulata *

45. P. preciosa

46. Trichomanites *

47. Callipteris *

48. Cardiocarpum *

49. C. Crampii

50. Antholithes *

51. Trigonocarpum *

Of the above forms, fifty-one in all, found in the Erian of eastern

America, all, except the last four, are certainly distinct specific

types. Of these only four reappear in the Carboniferous under identical

species, but no less than twenty-six reappear under representative or

allied forms, some at least of which a derivationist might claim as

modified descendants. On the other hand, nearly one half of the Devonian

types are unknown in the Carboniferous, while there remain a very large

number of Carboniferous types not accounted for by anything known in

the Devonian. Further, a very poor flora, including only two or three

types, is the predecessor of the Erian flora in the Upper Silurian,

and the flora again becomes poor in the Upper Devonian and Lower

Carboniferous. Every new species discovered must more or less modify the

above statements, and the whole Erian flora of America, as well as the

Carboniferous, requires a thorough comparison with that of Europe before

general conclusions can be safely drawn. In the mean time I may indicate

the direction in which the facts seem to point by the following general

statements:

1. Some of the forms reckoned as specific in the Devonian and

Carboniferous may be really derivative races. There are indications that

such races may have originated in one or more of the following ways: (1)

By a natural tendency in synthetic types to become specialised in the

direction of one or other of their constituent elements. In this way

such plants as _Arthrostigma_ and _Psilophyton_ may have assumed new

varietal forms. (2) By embryonic retardation or acceleration,[FE] whereby

certain species may have had their maturity advanced or postponed, thus

giving them various grades of perfection in reproduction and complexity

of structure. The fact that so many Erian and Carboniferous plants seem

to be on the confines of the groups of Acrogens and Gymnosperms may be

supposed favourable to such exchanges. (3) The contraction and breaking

up of floras, as occurred in the Middle Erian and Lower Carboniferous,

may have been eminently favourable to the production of such varietal

forms as would result from what has been called the "struggle for

existence." (4) The elevation of a great expanse of new land at the

close of the Middle Erian and the beginning of the coal period would, by

permitting the extension of species over wide areas and fertile soils,

and by removing the pressure previously existing, be eminently favourable

to the production of new, and especially of improved, varieties.

[FE] In the manner illustrated by Hyatt and Cope.

2. Whatever importance we may attach to the above supposed causes of

change, we still require to account for the origin of our specific

types. This may forever elude our observation, but we may at least hope

to ascertain the external conditions favourable to their production. In

order to attain even to this it will be necessary to inquire critically,

with reference to every acknowledged species, what its claims to

distinctness are, so that we may be enabled to distinguish specific types

from mere varieties. Having attained to some certainty in this, we may be

prepared to inquire whether the conditions favourable to the appearance

of new varieties were also those favourable to the creation of new types,

or the reverse--whether these conditions were those of compression

or expansion, or to what extent the appearance of new types may be

independent of any external conditions, other than those absolutely

necessary for their existence. I am not without hope that the further

study of fossil plants may enable us thus to approach to a comprehension

of the laws of the creation, as distinguished from those of the continued

existence of species.

3. In the present state of our knowledge we have no good ground either

to limit the number of specific types beyond what a fair study of

our material may warrant, or to infer that such primitive types must

necessarily have been of low grade, or that progress in varietal

forms has always been upward. The occurrence of such an advanced and

specialised type as that of _Dadoxylon_ in the Middle Devonian should

guard us against these errors. The creative process may have been

applicable to the highest as well as to the lowest forms, and subsequent

deviations must have included degradation as well as elevation. I can

conceive nothing more unreasonable than the statement sometimes made that

it is illogical or even absurd to suppose that highly organised beings

could have been produced except by derivation from previously existing

organisms. This is begging the whole question at issue, depriving science

of a noble department of inquiry on which it has as yet barely entered,

and anticipating by unwarranted assertions conclusions which may perhaps

suddenly dawn upon us through the inspiration of some great intellect,

or may for generations to come baffle the united exertions of all the

earnest promoters of natural science. Our present attitude should not be

that of dogmatists, but that of patient workers content to labour for a

harvest of grand generalisations which may not come till we have passed

away, but which, if we are earnest and true to Nature and its Creator,

may reward even some of us.

Within the human period great changes of distribution of plants have

occurred, chiefly through the agency of man himself, and we have

had ample evidence that plants are able to establish themselves and

prosper in climates and conditions to which unaided they could not have

transported themselves, as, for instance, in the case of European weeds

naturalised in Australia and New Zealand. There is, however, no reason

to believe that any specific change has occurred to any plant within the

Pleistocene or modern period.

In a recent address, delivered to the biological section of the British

Association, Mr. Carruthers has discussed this question, and has shown

that the earliest vegetable specimens described by Dr. Schweinfurth from

the Egyptian tombs present no appearance of change. This fact appears

also in the leaves and other organs of plants preserved in the nodules

in the Pleistocene clays of the Ottawa, and in specimens of similar age

found in various places in Britain and the continent of Europe.[FF]

[FF] "Proceedings British Association," 1886, "Pleistocene Plants of

Canada," Canadian Naturalist, 1866.

The difficulties attending the ordinary theories of evolution as applied

to plants have been well set forth by the same able botanist in his

"Presidential Address to the Geological Association in 1877," a paper

which deserves careful study. One of his illustrations is that ancient

willow, _Salix polaris_, referred to in a previous chapter, which now

lives in the arctic regions, and is found fossil in the Pleistocene beds

at Cromer and at Bovey Tracey.

He notes the fact that the genus _Salix_ is a very variable one,

including 19 subgeneric groups and 160 species, with no less than 222

varieties and 70 hybrids. _Salix polaris_ belongs to a subgeneric group

containing 29 species, which are arranged in four sections, that to which

_S. polaris_ belongs containing six species. Now it is easy to construct

a theoretical phylogeny of the derivation of the willows from a supposed

ancestral source, but when we take our little _S. polaris_ we find

that this one twig of our ancestral tree takes us back without change

to the Glacial period. The six species would take us still farther,

and the sections, sub-genera, and genus at the same rate would require

an incalculable amount of past time. He concludes the inquiry in the

following terms:

"But when we have reached the branch representing the generic form we

have made but little progress in the phylogenesis of _Salix_. With

_Populus_ this genus forms a small order, Salicineæ, The two genera are

closely allied, yet separated by well-marked characters; it is not,

however, difficult to conceive of both having sprung from a generalised

form. But there is no record of such a form. The two genera appear

together among the earliest known dicotyledons, the willows being

represented by six and the poplars by nine species. The ordinal form, if

it ever existed, must necessarily be much older than the period of the

Upper Cretaceous rocks, that is, than the period to which the earliest

known dicotyledons belong.

"The Salicineæ are related to five other natural orders, in all of which

the apetalous flowers are arranged in catkins. These different though

allied orders must be led up by small modifications to a generalised

amentiferous type, and thereafter the various groups of apetalous

plants by innumerable eliminations of differentiating characters until

the primitive form of the apetalous plant is reached. Beyond this the

uncurbed imagination will have more active work in bridging over the gap

between Angiosperms and Gymnosperms, in finding the intermediate forms

that led up to the vascular cryptogams, and on through the cellular

plants to the primordial germ. Every step in this phylogenetic tree

must be imagined. The earliest dicotyledon takes us not a step farther

back in the phylogenetic history of _Salix_ than that supplied by

existing vegetation. All beyond the testimony of our living willows is

pure imagination, unsupported by a single fact. So that here, also, the

evidence is against evolution, and there is none in favour of it."

It is easy to see that similar difficulties beset every attempt to trace

the development of plants on the principle of slow and gradual evolution,

and we are driven back on the theory of periods of rapid origin, as we

have already seen suggested by Saporta in the case of the Cretaceous

dicotyledons. Such abrupt and plentiful introduction of species over

large areas at the same time, by whatever cause effected--and we are

at present quite ignorant of any secondary causes--becomes in effect

something not unlike the old and familiar idea of creation. Science

must indeed always be baffled by questions of ultimate origin, and,

however far it may be able to trace the chain of secondary causation

and development, must at length find itself in the presence of the

great Creative Mind, who is "before all things and in whom all things

consist."

APPENDIX.

I.--COMPARATIVE VIEW OF THE SUCCESSIVE PALÆOZOIC

FLORAS OF NORTHEASTERN AMERICA AND

GREAT BRITAIN.

In eastern Canada there is a very complete series of fossil plants,

extending from the Silurian to the Permian, and intermediate in its

species between the floras of interior America and of Europe. I may

use this succession, mainly worked out by myself,[FG] to summarise the

various Palæozoic floras and sub-floras, in order to give a condensed

view of this portion of the history of the vegetable kingdom, and to

direct attention to the important fact, too often overlooked, that there

is a definite succession of fossil plants as well as of animals, and

that this is important as a means of determining geological horizons.

A British list for comparison has been kindly prepared for me by Mr.

R. Kidston, F. Gr. S. For lists referring to the western and southern

portions of America, I may refer to the reports of Lesquereux and

Fontaine and White.[FH]

[FG] "Acadian Geology," "Reports on Fossil Plants of Canada," Geological

Survey of Canada.

[FH] "Geological Surveys of Pennsylvania, Ohio, and Illinois."

In this connection I am reminded, by an excellent little paper of M.

Zeiller,[FI] on Carboniferous plants from the region of the Zambesi,

in Africa, that the flora which in the Carboniferous period extended

over the temperate portions of the northern hemisphere and far into the

arctic, also passed across the equator and prevailed in the southern

hemisphere. Of eleven species brought from the Zambesi by M. Lapierre

and examined by M. Zeiller, all were identical with European species

of the upper coal-formation, and the same fact has been observed in the

coal flora of the Cape Colony.[FJ] These facts bear testimony to the

remarkable uniformity of climate and vegetation in the coal period, and

I perfectly agree with Zeiller that they show, when taken in connection

with other parallelisms in fossils, an actual contemporaneousness of the

coal flora over the whole world.

[FI] Paris, 1883.

[FJ] Grey, "Journal of the Geological Society," vol. xxvii.

1. Carboniferous Flora.

(1) _Permo-Carboniferous Sub-Flora_:

This occurs in the upper member of the Carboniferous system of Nova

Scotia and Prince Edward Island, originally named by the writer the

Newer Coal-formation, and more recently the Permo-Carboniferous, and

the upper beds of which may not improbably be contemporaneous with the

Lower Permian or Lower Dyas of Europe. In this formation there is a

predominance of red sandstones and shales, and it contains no productive

beds of coal. Its fossil plants are for the most part of species found

in the Middle or Productive Coal-formation, but are less numerous, and

there are a few new forms akin to those of the European Permian. The most

characteristic species of the upper portion of the formation, which has

the most decidedly Permian aspect, are the following:

_Dadoxylon materiarium_, Dawson.

* _Walchia_ (_Araucarites_) _robusta_, Dn.

* _W._ (_A._) _gracilis_, Dn.

* _W. imbricatula_, Dn.

_Calamites Suckovii_, Brongt.

_C. Cistii_, Brongt.

* _C. gigas_, Brongt.

_Neuropteris rarinervis_, Bunbury.

_Alethopteris nervosa_, Brongt.

_Pecopteris arborescens_, Brongt.

* _P. rigida_, Dn.

_P. oreopteroides_, Brongt.

* _Cordaites simplex_, Dn.

Of these species, those marked with an asterisk have not yet been found

in the middle or lower members of the Carboniferous system. They will

be found described, and several of them figured, in my "Report on the

Geology of Prince Edward Island."[FK] The others are common and widely

diffused Carboniferous species, some of which have extended to the

Permian period in Europe as well. From the upper beds, characterised by

these and a few other species, there is a gradual passage downward into

the productive coal-measures, and a gradually increasing number of true

coal-formation species.

[FK] 1871.

It is worthy of remark here that the association in the

Permo-Carboniferous of numerous trunks of _Dadoxylon_ with the branches

of _Walchia_ and with fruits of the character of _Trigonocarpa_, seems to

show that these were parts of one and the same plant.

This formation represents the Upper Barren Measures of West Virginia,

which are well described by Fontaine and White,[FL] and the reasons

which these authors adduce for considering the latter equivalent to the

European Permian will apply to the more northern and eastern deposits

as well, though these have afforded fewer species of plants, and are

apparently less fully developed.

[FL] "Report on the Permian Flora of Western Virginia and South

Pennsylvania," 1880.

(2) _Coal-formation Sub-Flora_:

The Middle or Productive Coal-formation, containing all the beds of coal

which are mined in Nova Scotia and Cape Breton, is the headquarters of

the Carboniferous flora. From this formation I have catalogued[FM] one

hundred and thirty-five species of plants; but, as several of these are

founded on imperfect specimens, the number of actual species may be

estimated at one hundred and twenty. Of these more than one half are

species common to Europe and America. No less than nineteen species

are _Sigillariæ_, and about the same number are _Lepidodendra_. About

fifty are ferns and thirteen are _Calamites_, _Asterophyllites_, and

_Sphenophylla_. The great abundance and number of species of Sigillariæ,

Lepidodendra, and ferns are characteristic of this sub-flora; and among

the ferns certain species of _Neuropteris_, _Pecopteris_, _Alethopteris_,

and _Sphenopteris_ greatly preponderate.

[FM] "Acadian Geology," and "Report on Flora of Lower Carboniferous,"

1873.

These beds are the equivalents of the Middle Coal-measures, or Productive

Coal-measures of Pennsylvania, Ohio, &c., and of the coal-formation

proper of various European countries. Very many of the species are common

to Nova Scotia and Pennsylvania; but in proceeding westward the number of

identical species seems to diminish.

(3) _The Millstone Grit Sub-Flora_:

In this formation the abundance of plants and the number of species

are greatly diminished.[FN] Trunks of coniferous trees of the species

_Dadoxylon Acadianum_, having wide wood-cells with three or more series

of discs and complex medullary rays, become characteristic. _Calamites

undulatum_ is abundant and seems to replace _C. Suckovii_, though _C.

cannæformis_ and _C. cistii_ continue. _Sigillariæ_ become very rare,

and the species of Lepidodendron are few, and mostly those with large

leaf-bases. _Lepidophloios_ still continues, and _Cordaites_ abounds in

some beds. The ferns are greatly reduced, though a few characteristic

coal-formation species occur, and the genus _Cardiopteris_ appears. Beds

of coal are rare in this formation; but where they occur there is in

connection with them a remarkable anticipation of the rich coal-formation

flora, which would thus seem to have existed locally in the Millstone

Grit period, but to have found itself limited by generally unfavorable

conditions. In America, as in Europe, it is in the north that this

earlier development of the coal-flora occurs, while in the south there

is a lingering of old forms in the newer beds. In Newfoundland and Cape

Breton, for instance, as well as in Scotland, productive coal-beds and a

greater variety of species of plants occur in this formation.

[FN] "Report on Fossil Plants of the Lower Carboniferous and Millstone

Grit of Canada," 1873.

The following would appear to be the equivalents of this formation, in

flora and geological position:

1. The Seral Conglomerate of Rogers in Pennsylvania, &c.

2. The Lower Coal-formation Conglomerate and Chester groups of Illinois

(Worthen).

3. The Lower Carboniferous Sandstone of Kentucky, Alabama, and Virginia.

4. The Millstone Grit and Yoredale rocks of northern England, and the

Culmiferous of Devonshire.

5. The Moor rock and Lower Coal-measures of Scotland.

6. Flagstones and Lower Shales of the south of Ireland, and Millstone

Grit of the north of Ireland.

7. The Jüngste Grauwacke of the Hartz, Saxony, and Silesia.

(4) _The Carboniferous Limestone Series_:

This affords few fossil plants in eastern America, and in so far as known

they are similar to those of the next group. In Scotland it is richer

in plants, but, according to Mr. Kidston, these are largely similar

to those of the underlying beds, though with some species which extend

upward into the Millstone Grit. In Scotland the alga named _Spirophyton_

and _Archæocalamites radiatus_--which in America are Erian--appear in

this formation.

(5) _The Lower Carboniferous Sub-Flora_:

This group of plants is best seen in the shales of the Horton series,

under the Lower Carboniferous marine limestones. It is small and

peculiar. The most characteristic species are the following:

_Dadoxylon_ (_Palæoxylon_) _antiquius_, Dn.--A species with large

medullary rays of three or more series of cells.

_Lepidodendron corrugatum_, Dn.--A species closely allied to _L.

Veltheimianum_ of Europe, and which is its American representative.

This is perhaps the most characteristic plant of the formation. It is

very abundant, and presents very protean appearances, in its old stems,

branches, twigs, and _Knorria_ forms. It had well-characterised stigmaria

roots, and constitutes the oldest erect forest known in Nova Scotia.

_Lepidodendron tetragonum_, Sternberg.

_L. obovatum_, Sternb.

_L. aculeatum_, Sternb.

_L. dichotomum_, Sternb.

The four species last mentioned are comparatively rare, and the specimens

are usually too imperfect to render their identification certain, but

Lepidodendra are especially characteristic trees of this horizon.

_Cyclopteris_ (_Aneimites_) _Acadica_, Dn.--A very characteristic

fern, allied in the form of its fronds to _C. tenuifolia_ of Goeppert,

to _C. nana_ of Eichwald, and to _Adiantites antiquus_ of Stur. Its

fructification, however, is nearer to that of _Aneimia_ than to that of

_Adiantum_.

Ferns of the genera Cardiopteris and _Hymenophyllites_ also occur, though

rarely.

_Ptilophyton plumula_, Dn.--This is the latest appearance of this Erian

genus, which also occurs in the Lower Carboniferous of Europe and of the

United States.

_Cordaites borassifolia_, Brongt.

On the whole, this small flora is markedly distinct from that of the

Millstone Grit and true coal-formation, from which it is separated by the

great length of time required for the deposition of the marine limestones

and their associated beds, in which no land-plants have been found; nor

is this gap filled up by the conglomerates and coarse arenaceous beds

which, as I have explained in "Acadian Geology," in some localities take

the place of the limestones, as they do also in the Appalachian region

farther south.

The palæobotanical and stratigraphical equivalents of this series abroad

would seem to be the following:

1. The Vespertine group of Rogers in Pennsylvania.

2. The Kinderhook group of Worthen in Illinois.

3. The Marshall group of Winchell in Michigan.

4. The Waverley sandstone (in part) of Ohio.

5. The Lower or False Coal-measures of Virginia.

6. The Calciferous sandstones of McLaren, or Tweedian group of Tate in

Scotland.

7. The Lower Carboniferous slate and Coomhala grits of Jukes in Ireland.

8. The Culm and Culm Grauwacke of Germany.

9. The Graywacke or Lower Coal-measures of the Vosges, as described by

Schimper.

10. The Older Coal-formation of the Ural, as described by Eichwald.

11. The so-called "Ursa Stage" of Heer includes this, but he has united

it with Devonian beds, so that the name cannot be used except for

the local development of these beds at Bear Island, Spitsbergen. The

Carboniferous plants of arctic America, Melville Island, &c., as well as

those of Spitzbergen, appear all to be Lower Carboniferous.[FO]

[FO] "Notes on Geological Map of the Northern Portion of the Dominion of

Canada," by Dr. G. M. Dawson, 1887.

All of the above groups of rocks are characterised by the prevalence of

_Lepidodendra_ of the type of _L. corrugatum_, _L. Veltheimianum_, and

_L. Glincanum_; pines of the sub-genus _Pitus_ of Witham, _Palæoxylon_

of Brongniart, and peculiar ferns of the genera _Cyclopteris_,

_Cardiopteris_, _Triphyllopteris_, and _Sphenopteris_. In all the regions

above referred to they form the natural base of the great Carboniferous

system.

In Virginia, according to Fontaine and White, types, such as

Archæopteris, which in the north are Upper Erian, occur in this group.

Unless there have been some errors in fixing the lower limit of the

Vespertine, this would indicate a longer continuance of old forms in the

south.

2. Erian Flora.

(1) _Upper Erian Sub-Flora_:

This corresponds to the Catskill and Chemung of the New York series, and

to the Upper Devonian of Europe.

The flora of this formation, which consists mostly of sandstones, is not

rich. Its most distinctive species on both sides of the Atlantic seem to

be the ferns of the genus _Archæopteris_, along with species referred to

the genus _Cyclopteris_, but which, in so far as their barren fronds are

concerned, for the most part resemble _Archæopteris_.

The characteristic American species are _Archæopteris Jacksoni_,

_A. Rogersi_, and _A. Gaspiensis_. _Cyclopteris obtusa_ and _C._

(_Platyphyllum_) _Brownii_ are also very characteristic species. In

Europe, _Archæopteris Hibernica_ is a prevalent species.

_Leptophleum rhombicum_ and fragments of _Psilophyton_ are also found in

the Upper Erian. There is evidence of the existence of vast numbers of

_Rhizocarps_ in this period, in the deposits of spore-cases (_Sporangites

Huronensis_) in the shales of Kettle Point, Lake Huron; and in deposits

of similar character in Ohio and elsewhere in the West.

The Upper Erian flora is thus very distinct from that of the Lower

Carboniferous, and the unconformable relation of the beds in the

Northeast may perhaps indicate a considerable lapse of time. Still,

even in localities where there appears to be a transition from the

Carboniferous into the Devonian, as in the Western States and in Ireland,

the characteristic flora of each formation may be distinguished, though,

as already stated, there is apparently some mixture in the South.

(2) _Middle Erian Sub-Flora_:

Both in Canada and the United States that part of the great Erian system

which may be regarded as its middle division, the Hamilton and Marcellus

shales of New York, the Cordaites shales of St. John, New Brunswick, and

the middle shales and sandstones of the Gaspé series, presents conditions

more favourable to the abundant growth of land-plants than either the

upper or lower member. In the St. John beds, in particular, there is a

rich fern flora, comparable with that of the coal-formation, and numerous

stipes of ferns and trunks of tree-ferns have been found in the Hamilton

and Corniferous series in the West, as well as trunks of _Dadoxylon_. It

is, however, distinguished by a prevalence of small and delicate species,

and by such forms as _Hymenophyllites_ and the smaller Sphenopterids, and

also by some peculiar ferns, as _Archæopteris_ and _Megalopteris_. In

addition to ferns, it has small _Lepidodendra_, of which _L. Gaspianum_

is the chief. _Calamiteæ_ occur, _Archæocalamites radiatus_ being the

dominant species. This plant, which in Europe appears to reach up into

the Lower Carboniferous, is so far strictly Erian in northeast America.

_Sigillariæ_ scarcely appear, but _Cordaites_ is abundant, and the

earliest known species of _Dadoxylon_ appear, while the Psilophyton, so

characteristic of the Lower Erian, still continues, and the remarkable

aquatic plants of the genus _Ptilophyton_ are locally abundant.

(3) _Lower Erian Sub-Flora_:

This belongs to the Lower Devonian sandstones and shales, and is

best seen in that formation at Gaspé and the Bay des Chaleurs. It is

equivalent to the Oriskany sandstone, so far as its animal fossils and

mineral character are concerned. It is characterised by the absence

of true ferns, _Calamites_ and _Sigillariæ_, and by the presence

of such forms as _Psilophyton_, _Arthrostigma_, _Leptophleum_, and

_Nematophyton_. _Lepidodendron Gaspianum_ and _Leptophleum_ already

occur, though not nearly so abundant as Psilophyton.

The Lower Erian plants have an antique and generalised aspect which would

lead us to infer that they are near the beginning of the land-flora, or

perhaps in part belong to the close of an earlier flora still in great

part unknown and few indications of land-plants have been found earlier.

At Campbellton and Scaumenac Bay, on the Bay des Chaleurs, fossil fishes

of genera characteristic of the Lower and Upper Devonian horizons

respectively, occur in association with fossil plants of these horizons,

and have been described by Mr. Whiteaves.[FP]

[FP] "Transactions of the Royal Society of Canada."

It is interesting to note that, as Fontaine and White have observed,

certain forms which are Erian in the northeast are found in the Lower

members of the Carboniferous in West Virginia, indicating the southward

march of species in these periods.

3. The Silurian Flora and still Earlier Indications of Plants.

In the upper beds of the Silurian, those of the Helderberg series, we

still find _Psilophyton_ and _Nematophyton_; but below these we know no

land-plants in Canada. In the United States, Lesquereux and Claypole have

described remains which may indicate the existence of lycopodiaceous and

annularian types as far back as the beginning of the Upper Silurian, or

even as low as the Hudson River group, and Hicks has found _Nematophyton_

and _Psilophyton_ in beds about as old in Wales, along with the uncertain

stems named _Berwynia_. In the Lower Silurian the _Protannularia_ of

the Skiddaw series in England may represent a land-plant, but this is

uncertain, and no similar species has been found in Canada.

The Cambrian rocks are so far barren of land-plants; the so-called

_Eophyton_ being evidently nothing but markings, probably produced by

crustaceans and other aquatic animals. In the still older Laurentian the

abundant beds of graphite probably indicate the existence of plants, but

whether aquatic or terrestrial it is impossible to decide at present.

It would thus appear that our certain knowledge of land-vegetation begins

with the Upper Silurian or the Silurio-Cambrian, and that its earliest

forms were Acrogens allied to Lycopods, and prototypal trees, forerunners

of the Acrogens or the gymnosperms. In the Lower Devonian little advance

is made. In the Middle Devonian this meagre flora had been replaced by

one rivalling that of the Carboniferous, and including pines, tree-ferns,

and arboreal forms of Lycopods and of equisetaceous plants, as well as

numerous herbaceous plants. At the close of the Erian the flora again

became meagre, and continued so in the Lower Carboniferous. It again

became rich and varied in the Middle Carboniferous, to decay in the

succeeding Permian.

II.--HEER'S LATEST RESULTS IN THE GREENLAND FLORA.

A very valuable report of Prof. Steenstrup, published in Copenhagen in

1883, the year in which Heer died, contains the results of his last

work on the Greenland plants, and is so important that a summary of its

contents will be interesting to all students of fossil botany or of the

vicissitudes of climate which the earth has undergone.[FQ]

[FQ] Meddelelser om Gronland, Hefte V., Copenhagen, 1883.

The plant-bearing beds of Greenland are as follows, in ascending order:

1. Cretaceous.

1. The _Komé_ series, of black shales resting on the Laurentian gneiss.

These beds are found at various other localities, but the name above

given is that by which they are generally known. Their flora is limited

to ferns, cycads, conifers, and a few endogens, with only _Populus

primæva_ to represent the dicotyledons. These beds are regarded as Lower

Cretaceous (Urgonian), but the animal fossils would seem to give them

a rather higher position. They may be regarded as equivalent to the

Kootanie and Queen Charlotte beds in Canada, and the Potomac series in

Virginia.

2. The _Atané_ series. These also are black shales with dark-coloured

sandstones. They are best exposed at Upernavik and Waigat. Here

dicotyledonous leaves abound, amounting to ninety species, or more than

half the whole number of species found. The fossil plants resemble those

of the Dakota series of the United States and the Dunvegan series of

Canada, and the animal fossils indicate the horizon of the Fort Pierre or

its lower part. They may be regarded as representing the lower part of

the Upper Cretaceous. The genera _Populus_, _Myrica_, _Quercus_, _Ficus_,

_Platanus_, _Sassafras_, _Laurus_, _Magnolia_, and _Liriodendron_

are among those represented in these beds, and the peculiar genera

_Macclintockia_ and _Credneria_ are characteristic. The genus _Pinus_ is

represented by five species, _Sequoia_ by five, and _Salisburia_ by two,

with three of the allied genus _Baiera_. There are many ferns and cycads.

3. The _Patoot_ series. These are yellow and red shales, which seem to

owe their colour to the spontaneous combustion of pyritous lignite, in

the manner observed on the South Saskatchewan and the Mackenzie rivers.

Their age is probably about that of the Fox-Hill group or Senonian,

and the Upper Cretaceous of Vancouver Island, and they afford a large

proportion of dicotyledonous leaves. The genera of dicotyledons are

not dissimilar from those of Atané, but we now recognise _Betula_ and

_Alnus_, _Comptonia_, _Planera_, _Sapotacites_, _Fraxinus_, _Viburnum_,

_Cornus_, _Acer_, _Celastrus_, _Paliurus_, _Ceanothus_, _Zizyphus_, and

_Cratægus_ as new genera of modern aspect.

On the whole there have been found in all these beds 335 species,

belonging to 60 families, of which 36 are dicotyledonous, and represent

all the leading types of arborescent dicotyledons of the temperate

latitudes. The flora is a warm temperate one, with some remarkable

mixtures of sub-tropical forms, among which perhaps the most remarkable

are _Kaidocarpum_ referred to the _Pandaneæ_, and such exogens as _Ficus_

and _Cinnamomum_.

2. Tertiary.

4. The _Unartok_ series. This is believed to be Eocene. It consists of

sandstone, which appears on the shores of Disco Island, and possibly at

some other places on the coast. The beds rest directly and apparently

conformably on the Upper Cretaceous, and have afforded only eleven

species of plants. _Magnolia_ is represented by two species, _Laurus_

by two, _Platanus_ by two, and one of these said to be identical with a

species found by Lesquereux in the Laramie,[FR] _Viburnum_, _Juglans_,

_Quercus_, each by one species; the ubiquitous _Sequoias_ by _S.

Langsdorfii_. This is pretty clearly a Lower Laramie flora.

[FR] _Viburnum marginatum_ of Lesquereux.

5. The _Atanekerdluk_ series, consisting of shaly beds, with limestone

intercalated between great sheets of basalt, much like the Eocene of

Antrim and the Hebrides. These beds have yielded 187 species, principally

in bands and concretions of siderite, and often in a good state of

preservation. They are referred to the Lower Miocene, but, as explained

in the text, the flora is more nearly akin to that of the Eocene of

Europe and the Laramie of America. The animal fossils are chiefly

fresh-water shells. _Onoclea sensibilis_, several conifers, as _Taxites_

_Olriki_, _Taxodium distichum_, _Glyptostrobus Europæus_, and _Sequoia

Langsdorfii_, and 42 of the dicotyledons are recognised as found also

in American localities. Of these, a large proportion of the more common

species occur in the Laramie of the Mackenzie River and elsewhere in

northwest Canada, and in the western United States. It is quite likely

also that several species regarded as distinct may prove to be identical.

It would seem that throughout the whole thickness of these Tertiary beds

the flora is similar, so that it is probable it belongs altogether to the

Eocene rather than to the Miocene.

No indication has been observed of any period of cold intervening between

the Lower Cretaceous and the top of the Tertiary deposits, so that, in

all the vast period which these formations represent, the climate of

Greenland would seem to have been temperate. There is, however, as is

the case farther south, evidence of a gradual diminution of temperature.

In the Lower Cretaceous the probable mean annual temperature in latitude

71° north is stated as 21° to 22° centigrade, while in the early Tertiary

it is estimated at 12° centigrade. Such temperatures, ranging from 71°

to 53° of Fahrenheit, represent a marvellously warm climate for so high

a latitude. In point of fact, however, the evidence of warm climates in

the arctic regions, in the Palæozoic as well as in the Mesozoic and early

Tertiary, should perhaps lead us to conclude that, relatively to the

whole of geological time, the present arctic climate is unusually severe,

and that a temperate climate in the arctic regions has throughout

geological time been the rule rather than the exception.

III.--MINERALISATION OF FOSSIL PLANTS.

The state of preservation of fossil plants has been referred to

incidentally in several places in the text; but the following more

definite statements may be of service to the reader.

I. Organic remains imbedded in aqueous deposits may occur in an unchanged

condition, or only more or less altered by decay. This is often the case

with such enduring substances as bark and wood, and even with leaves,

which appear as thin carbonaceous films when the layers containing

them are split open. In the more recent deposits such remains occur

little modified, or perhaps only slightly changed by partial decay of

their more perishable parts. In the older formations, however, they

are usually found in a more or less altered condition, in which their

original substance has been wholly or in part changed into coaly, or

bituminous, or anthracitic or graphitic matter, so that leaves are

sometimes represented by stains of graphite, as if drawn on stone with a

lead-pencil. Yet even in this case some portion of the original substance

remains, and without any introduction of foreign material.

II. On the other hand, such remains are often mineralised by the filling

of their pores or the replacement of their tissues with mineral matter,

so that they become hard and stony, and sometimes retain little or

nothing of their original substance. The more important of these changes,

in so far as they affect fossil plants, may be arranged under the

following heads:

(_a_) _Infiltration_ of mineral matter which has penetrated the pores

of the fossil in a state of solution. Thus the pores of fossil wood are

often filled with calcite, quartz, oxide of iron, or sulphide of iron,

while the woody walls of the cells and vessels remain in a carbonised

state, or converted into coaly matter. When wood is preserved in this

way it has a hard and stony aspect; but we can sometimes dissolve away

the mineral matter, and restore the vegetable tissue to a condition

resembling that before mineralisation. This is especially the case when

calcite is the mineralising substance. We sometimes find, on microscopic

examination, that even cavities so small as those of vegetable cells and

vessels have been filled with successive coats of different kinds of

mineral matter.

(_b_) Organic matters may be entirely _replaced_ by mineral

substances. In this case the cavities and pores have been first

filled, and then--the walls or solid parts being removed by decay or

solution--mineral matter, either similar to that filling the cavities,

or differing in colour or composition, has been introduced. Silicified

wood often occurs in this condition. In the case of silicified wood, it

sometimes happens that the cavities of the fibers have been filled with

silica, and the wood has been afterward removed by decay, leaving the

casts of the tubular fibers as a loose filamentous substance. Some of

the Tertiary coniferous woods of California are in this state, and look

like asbestus, though they show the minute markings of the tissue under

the microscope. In the case of silicified or agatized woods, it would

seem that the production of carbon dioxide from the decaying wood has

caused the deposition of silica in its place, from alkaline solutions

of that substance, and thus the carbon has been replaced, atom by atom,

by silicon, until the whole mass has been silicified, yet retaining

perfectly its structure.

(_c_) The cavities left by fossils which have decayed may be filled with

clay, sand, or other foreign matter, and this, becoming subsequently

hardened into stone, may constitute a _cast_ of the fossils. Trunks of

trees, roots, &c., are often preserved in this way, appearing as stony

casts, often with the outer bark of the plant forming a carbonaceous

coating on their surfaces. In connection with this state may be

mentioned that in which, the wood having decayed, an entire trunk has

been flattened so as to appear merely as a compressed film of bark, yet

retaining its markings; and that in which the whole of the vegetable

matter having been removed, a mere impression of the form remains.

Fossils preserved in either of the modes, (_a_) or (_b_), usually show

more or less of their minute structures under the microscope. These may

be observed:--(1) By breaking off small splinters or flakes and examining

them, either as opaque or as transparent objects. (2) By treating the

material with acids, so as to dissolve out the mineral matters, or

portions of them. This method is especially applicable to fossil woods

mineralised with calcite or pyrite. (3) By grinding thin sections. These

are first polished on one face on a coarse stone or emery hone, and then

on a fine hone, then attached by the polished face to glass slips with

a transparent cement or Canada balsam, and ground on the opposite face

until they become so thin as to be translucent. In most cities there are

lapidaries who prepare slices of this kind; but the amateur can readily

acquire the art by a little practice, and the necessary appliances can

be obtained through dealers in minerals or in microscopic materials.

Very convenient cutting and polishing machines, some of them quite small

and portable, are now made for the use of amateurs. In the case of

exogenous woods, three sections are necessary to exhibit the whole of the

structures. One of these should be transverse and two longitudinal, the

latter in radial and tangential planes.

IV.--GENERAL WORKS ON PALÆOBOTANY.

In the text frequent reference has been made to special memoirs and

reports on the fossil plants of particular regions or formations. There

are, however, some general books, useful to students, which may be

mentioned here. Perhaps the most important is Schimper's "Traité de

Paléontologie Végétale." Very useful information is also contained in

Renault's "Cours de Botanique Fossile," and in Balfour's "Introduction to

Palæontological Botany," and Nicholson's "Palæontology." Unger's "Genera

et Species," Brongniart's "Histoire des Végétaux Fossiles," and Lindley

and Button's "Fossil Flora," are older though very valuable works.

Williamson's "Memoirs," in the "Philosophical Transactions," have greatly

advanced our knowledge of the structures of Palæozoic plants. Lastly,

the "Palæophytology" of Schenk, now in course of publication in German

and French, in connection with Zittel's "Palæontology," is an important

addition to manuals of the subject.

INDEX.

Acer, 228.

Acrogens, 6.

Agassiz, Prof., 16.

Alaska, Flora of, 245.

Algæ, real and spurious, 26, 230.

Amboy clays, Flora of, 203.

America, Cretaceous of, 190.

Angiosperms, 6.

Annularia, 122.

Anogens, 6.

Antholithes, 132.

Aporoxylon, 25.

Araucarioxylon, 148.

Araucarites, 134.

Archæocalamites, 170.

Archæopteris, 77, 85.

Arctic origin of plants, 221, 238.

Arthrophycus, 30.

Arthrostigma, 67.

Asterophyllites, 78, 122, 170.

Asteropteris, 77, 85.

Astropolithon, 30.

Atané, Plants of, 242, 281.

Atanekerdluk, Plants of, 283.

Australia, Palæozoic flora of, 147.

Tertiary flora of, 217.

Bauhinia, 204.

Bear Island, 241.

Betula, 198.

Bilobites, 28.

Bovey Tracey, Plants of, 226.

Brasenia, 207.

Buckland, Dr., 179.

Buthotrephis, 37.

Calamites, 77, 123, 166.

Calamodendron, 125.

Cambrian flora, 20.

Canada, Erian of, 103.

Carboniferous of, 110.

Laramie of, 209.

Pleistocene of, 227.

Carbon in Laurentian, 9.

Carboniferous flora, 110.

Carboniferous, Climate of, 138.

of Southern Hemisphere, 147.

Cardiocarpum, 82, 153.

Carruthers, Mr., 24, 98, 180.

On modifications of modern plants, 225, 269.

Carya, 196.

Cauda-galli fucoid, 105.

Caulerpites, 29.

Caulopteris, 75, 94.

Clarke, Prof., 51.

Climate, Causes of, 247.

Climate and plants, 216, 220, 232.

of Carboniferous, 138.

of Cretaceous and Eocene, 216.

of Devonian, 47.

of Early Mesozoic, 178.

Climate and plants of Laurentian, 17.

of Pleistocene, 227, 230.

of Pliocene, 223.

Coal, origin of, 117, 139.

Comparison of floras, 272.

Composite, 266.

Cone-in-cone, 36.

Coniferæ, Erian, 78, 96.

Carboniferous, 134, 148.

Mesozoic, etc., 181.

Cope, Mr., 215.

Cordaites, 78, 130, 151.

Corylus, 213.

Crepin, M., 99.

Cretaceous, Flora of, 190.

Climate of, 216.

Croll on climate, 252.

Cromer, Plants of, 224.

Cycads, Mesozoic, 178.

Cyclostigma, 157.

Dadoxylon, 96, 134, 148.

Dawson, Dr. G. M., 52, 210.

Delgado, Prof., 26.

Dendrophycus, 33.

Derby, Orville, 53.

Devonian flora, 45.

Devonian or Erian, 107, 279.

Climate of, 47.

Dicotyledons, Cretaceous, 192.

Table of, 192.

Dictyolites, 33.

Dictyospongia, 39.

Disco, Exotic plants at, 256.

Flora of, 245, 282.

Drepanophycus, 39.

Drosera, 228.

Dunvegan beds, 244.

Eocene, Flora of, 208, 214.

Climate of, 216.

Eophyton, 31.

Eopteris, 72.

Eozoon of Laurentian, 9.

Equisetum, 176, 230.

Erian flora, 45, 279.

Climate of, 47.

Erian or Devonian, 107.

Ettingshausen, Dr., 187, 215.

Exogens, Cretaceous, 192.

Tertiary, 213, 224.

Fagus, 196, 197.

Ferns, Erian, 72.

Carboniferous, 126, 171.

Fructification of, 128.

Stems of, 90, 129.

Tertiary, 212.

Filices, 72, 126, 171.

Flora of Cambrian, 26.

of Carboniferous, 110, 274.

of Cretaceous, 190.

of Early Mesozoic, 175.

of Erian, 45, 279.

of Jurassic, 177, 186.

of Laramie, 209.

of Laurentian, 8.

of Miocene, 220, 223.

of Modern, 219.

of Permian, 274.

of Pleistocene, 223, 227.

of Tertiary, 191, 208, 214, 219.

Fontaine, Prof., 130, 176.

Fontinalis, 230.

Fort Union beds, 210.

Fucoids, 27.

Gardner, Mr. Starkie, 212.

Geinitz, Dr., 174.

Geological formations, Table of, 4.

Glossopteris, 147.

Glyptodendron, 25.

Glyptostrobus, 194.

Goeppert, Dr., 99.

Grant, Col., 36.

Graphite from plants, 8.

Gray, Dr., Origin of floras, 223, 237.

Greenland, Climate of, 216.

Fossil flora of, 247.

Gulielmites, 35.

Gymnosperms, 6.

Haliserites, 39.

Hartt, Prof., 53.

Heer, Dr., 108, 181.

Helderberg period, Sea of, 250.

Heterangium, 77.

Hicks, Dr., 21.

Hunt, Dr. Sterry, 13, 143.

Huxley, Prof., 53.

Hymenæa, 204.

Insects, Erian, 83.

Juglans, 196.

Jurassic flora, 177.

Kainozoic flora, 191, 208, 214, 219.

Kidston, Mr. R., 128, 273.

King, Mr. Clarence, 211.

Komé, Plants of, 242, 281.

Laramie flora, 209, 215.

Laurentian plants, 8.

Laurentian, Climate of, 17.

Laurophyllum, 193.

Laws of introduction of plants, 237, 266.

Leda clay, Flora of, 232.

Lepidodendron, 120, 156, 162.

Lepidophloios, 121, 157, 165.

Leptophleum, 157.

Lesquereux, Mr. L., 169, 214.

Licrophycus, 30.

Lignitic series of America, 208.

Liquidambar, 197.

Liriodendron, 199.

Lower Carboniferous flora, 277.

Logan, Sir W., 48.

Lyell on climate, 249.

Magnolia, 200.

McConnell, Mr., 209.

McNab, Prof., 169.

Megalopteris, 76.

Megaphyton, 129.

Mesozoic flora, 175.

Climate of, 178.

Migrations of plants, 240, 245.

Miller, Hugh, 98.

Miocene flora, 220.

Miocene, Supposed, 242.

Modern flora, 219.

Modern plants, how modified, 269.

Modifications of plants, 266.

Nathorst, Dr., 26, 196.

Nematodendreæ, 25.

Nematophycus, 23.

Nematophyton, 21, 22, 42.

Newberry, Dr., 200, 203, 214.

Newfoundland, Fossil plants of, 242.

Newton, Mr., 52.

Nicholson, Dr. A., 20.

Niobrara series, 243, 246.

Noeggerathia, 130.

Northern origin of plants, 238.

Origin of plants, 237.

Orton, Prof., 51.

Pachytheca, 21.

Palæanthus, 205.

Palæochorda, 30.

Palæophycus, 30, 38.

Palæozoic floras compared, 273.

Palms, 188, 194.

Pandanus, 188.

Patoot beds, 282.

Peach, Mr., 98.

Petroleum, Origin of, 56.

Phymatoderma, 29.

Plants, Classification of, 6.

Platanus, 198.

Platyphyllum, 74.

Pleistocene climate, 227, 230.

Pleistocene flora, 223, 227.

Pliocene climate, 223.

Podozamites, 178.

Poles, Supposed change of, 248.

Populus, 191, 228.

Potamogeton, 229.

Potentilla, 228.

Protannularia, 21.

Protichnites, 27.

Protophyllum, 199.

Protosalvinia, 52.

Protostigma, 20.

Prototaxites, 21.

Psaronius, 93.

Psilophyton, 64.

Ptilophyton, 62, 86.

Quercus, 197.

Rhizocarps, 48.

Rill-marks, 33.

Rusichnites, 28.

Saccamina, 57.

Salisburia, 180.

Salter, Mr., 98.

Salvinia, 54.

Saporta, Count de, 26, 193.

Saportea, 57.

Sassafras, 199.

Scalariform tissue, 70.

Schimper, Dr., 116, 169, 208.

Scolithus, 30.

Scottish Devonian, 98.

Sequoia, 181.

Shrinkage cracks, 33.

Sigillaria, 71, 112, 154.

Southern Hemisphere, 217, 273.

Carboniferous in, 147.

Tertiary in, 217.

Sphenophyllum, 61, 122, 171.

Spirophyton, 38.

Spitzbergen, 241.

Sterculites, 193.

Sternbergia, 137, 152.

Stigmaria, 115.

Stur, Dr., on Sigillaria, 116.

Symphorocarpus, 214.

Syringodendron, 156.

Syringoxylon, 82.

Table of formations, 4.

Tasmania, Fossil plants of, 217, 246.

Tasmanite, 57.

Tertiary period, Flora of, 191, 208, 214, 219.

Tertiary of Australia, 217.

Thallogens, 6.

Thomas, Mr., 51.

Thuja, 213, 229.

Time, Geological, 5.

Trapa, 196.

Tree-ferns, 90, 129.

Triassic flora, 176.

Trigonocarpum, 136, 153.

Tyndall, Prof., 138.

Ulrich, Prof., 57.

Unartok beds, 281.

Ursa stage of Heer, 108, 241.

Walchia, 134, 138.

Ward, Mr. L. T., 192, 212, 215.

Wethered, Mr. E., 52.

White, Dr., 215.

Williams, Prof., 51.

Williamson, Dr., 26, 31, 71, 167.

Williamsonia, 188.

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upon ants, because they show more power and flexibility of mind; and

the value of his studies is that they belong to the department of

original research.""

"We have no hesitation in saying that the author has presented us

with the most valuable series of observations on a special subject

that has ever been produced, charmingly written, full of logical

deductions, and, when we consider his multitudinous engagements,

a remarkable illustration of economy of time. As a contribution

to insect psychology, it will be long before this book finds a

parallel."--_London Athenæum._

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New York: D. APPLETON & CO., 1, 3, & 5 Bond Street.

_D. APPLETON & CO.'S PUBLICATIONS._

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Dr. H. ALLEYNE NICHOLSON'S WORKS.

=TEXT-BOOK OF ZOÖLOGY,= for Schools and Colleges. 12mo. Half roan,

$1.60.

=MANUAL OF ZOÖLOGY,= for the Use of Students, with a General

Introduction to the Principles of Zoölogy. Second edition.

Revised and enlarged, with 243 Woodcuts. 12mo. Cloth, $2 50.

=TEXT-BOOK OF GEOLOGY,= for Schools and Colleges. 12mo. Half roan,

$1.25.

=INTRODUCTION TO THE STUDY OF BIOLOGY,= Illustrated. 12mo. Cloth, 60

cents.

=THE ANCIENT LIFE-HISTORY OF THE EARTH.= A Comprehensive Outline of

the Principles and Leading Facts of Palæontological Science.

12mo. Cloth, $2.00.

"A work by a master in the science who understands the significance

of every phenomenon which he records, and knows how to make it reveal

its lessons. As regards its value there can scarcely exist two

opinions. As a text-book of the historical phase of palæontology is

will be indispensable to students, whether specially pursuing geology

or biology; and without it no man who aspires even to an outline

knowledge of natural science can deem his library complete."--_The

Quarterly Journal of Science_.

"The Professor of Natural History in the University of St. Andrews

has, by his previous works on zoology and paleontology, so fully

established his claim to be an exact thinker and a close reasoner,

that scarcely any recommendation of ours can add to the interest

with which all students in natural history will receive the present

volume. It is, as its second title expresses it; a comprehensive

outline of the principles and leading facts of palæontoiogical

science. Numerous woodcut illustrations very delicately executed, a

copious glossary, and an admirable index, add much to the value of

this volume."--_Athenæum_.

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New York: D. APPLETON & CO., 1, 3, & 5 Bond Street.

* * * * *

Transcriber Notes

All images were moved so as to not split paragraphs.