Kitabı oku: «Health and Education», sayfa 9

ON BIO-GEOLOGY.
AN ADDRESS GIVEN TO THE SCIENTIFIC SOCIETY OF WINCHESTER

I am not sure that the subject of my address is rightly chosen.  I am not sure that I ought not to have postponed a question of mere natural history, to speak to you, as scientific men, on the questions of life and death, which have been forced upon us by the awful warning of an illustrious personage’s illness; of preventible disease, its frightful prevalency; of the 200,000 persons who are said to have died of fever alone since the Prince Consort’s death, ten years ago; of the remedies; of drainage; of sewage disinfection and utilisation; and of the assistance which you, as a body of scientific men, can give to any effort towards saving the lives and health of our fellow-citizens from those unseen poisons which lurk like wild beasts couched in the jungle, ready to spring at any moment on the unsuspecting, the innocent, the helpless.  Of all this I longed to speak: but I thought it best only to hint at it, and leave the question to your common sense and your humanity; taking for granted that your minds, like the minds of all right-minded Englishmen, have been of late painfully awakened to its importance.  It seemed to me almost an impertinence to say more in a city of whose local circumstances I know little or nothing.  As an old sanitary reformer, practical, as well as theoretical, I am but too well aware of the difficulties which beset any complete scheme of drainage, especially in an ancient city like this; where men are paying the penalty of their predecessors’ ignorance; and dwelling, whether they choose or not, over fifteen centuries of accumulated dirt.

And, therefore, taking for granted that there is energy and intellect enough in Winchester to conquer these difficulties in due time, I go on to ask you to consider, for a time, a subject which is growing more and more important and interesting, a subject the study of which will do much towards raising the field naturalist from a mere collector of specimens—as he was twenty years ago—to a philosopher elucidating some of the grandest problems.  I mean the infant science of Bio-geology—the science which treats of the distribution of plants and animals over the globe, and the causes of that distribution.

I doubt not that there are many here who know far more about the subject than I; who are far better read than I am in the works of Forbes, Darwin, Wallace, Hooker, Moritz Wagner, and the other illustrious men who have written on it.  But I may, perhaps, give a few hints which will be of use to the younger members of this Society, and will point out to them how to get a new relish for the pursuit of field science.

Bio-geology, then, begins with asking every plant or animal you meet, large or small, not merely—What is your name?  That is the collector and classifier’s duty; and a most necessary duty it is, and one to be performed with the most conscientious patience and accuracy, so that a sound foundation may be built for future speculations.  But young naturalists should act not merely as Nature’s registrars and census-takers, but as her policemen and gamekeepers; and ask everything they meet—How did you get here?  By what road did you come?  What was your last place of abode?  And now you are here, how do you get your living?  Are you and your children thriving, like decent people who can take care of themselves, or growing pauperised and degraded, and dying out?  Not that we have a fear of your becoming a dangerous class.  Madam Nature allows no dangerous classes, in the modern sense.  She has, doubtless for some wise reason, no mercy for the weak.  She rewards each organism according to its works; and if anything grows too weak or stupid to take care of itself, she gives it its due deserts by letting it die and disappear.  So, you plant or you animal, are you among the strong, the successful, the multiplying, the colonising?  Or are you among the weak, the failing, the dwindling, the doomed?

These questions may seem somewhat rude: but you may comfort yourself by the thought that plants and animals, though they deserve all kindness, all admiration, deserve no courtesy—at least in this respect.  For they are, one and all, wherever you find them, vagrants and landloupers, intruders and conquerors, who have got where they happen to be simply by the law of the strongest—generally not without a little robbery and murder.  They have no right save that of possession; the same by which the puffin turns out the old rabbits, eats the young ones, and then lays her eggs in the rabbit burrow—simply because she can.

Now, you will see at once that such a course of questioning will call out a great many curious and interesting answers, if you can only get the things to tell you their story; as you always may, if you will cross-examine them long enough; and will lead you into many subjects beside mere botany or entomology.  So various, indeed, are the subjects which you will thus start, that I can only hint at them now in the most cursory fashion.

At the outset you will soon find yourself involved in chemical and meteorological questions: as, for instance, when you ask—How is it that I find one flora on the sea-shore, another on the sandstone, another on the chalk, and another on the peat-making gravelly strata?  The usual answer would be, I presume—if we could work it out by twenty years’ experiment, such as Mr. Lawes, of Rothampsted, has been making on the growth of grasses and leguminous plants in different soils and under different manures—the usual answer, I say, would be—Because we plants want such and such mineral constituents in our woody fibre; again, because we want a certain amount of moisture at a certain period of the year: or, perhaps, simply because the mechanical arrangement of the particles of a certain soil happens to suit the shape of our roots and of their stomata.  Sometimes you will get an answer quickly enough; sometimes not.  If you ask, for instance, Asplenium viride how it contrives to grow plentifully in the Craven of Yorkshire down to 600 or 800 feet above the sea, while in Snowdon it dislikes growing lower than 2000 feet, and is not plentiful even there?—it will reply—Because in the Craven I can get as much carbonic acid as I want from the decomposing limestone: while on the Snowdon Silurian I get very little; and I have to make it up by clinging to the mountain tops, for the sake of the greater rainfall.  But if you ask Polopodium calcareum—How is it you choose only to grow on limestone, while Polypodium Dryopteris, of which, I suspect, you are only a variety, is ready to grow anywhere?—Polypodium calcareum will refuse, as yet, to answer a word.

Again—I can only give you the merest string of hints—you will find in your questionings that many plants and animals have no reason at all to show why they should be in one place and not in another, save the very sound reason for the latter which was suggested to me once by a great naturalist.  I was asking—Why don’t I find such and such a species in my parish, while it is plentiful a few miles off in exactly the same soil?—and he answered—For the same reason that you are not in America.  Because you have not got there.  Which answer threw to me a flood of light on this whole science.  Things are often where they are, simply because they happen to have got there, and not elsewhere.  But they must have got there by some means: and those means I want young naturalists to discover; at least to guess at.

A species, for instance—and I suspect it is a common case with insects—may abound in a single spot, simply because, long years ago, a single brood of eggs happened to hatch at a time when eggs of other species, who would have competed against them for food, did not hatch; and they may remain confined to that spot, though there is plenty of good food for them outside it, simply because they do not increase fast enough to require to spread out in search of more food.  Thus I should explain a case which I heard of lately of Anthocera trifolii, abundant for years in one corner of a certain field, and only there; while there was just as much trefoil all round for its larvæ as there was in the selected spot.  I can, I say, only give hints: but they will suffice, I hope, to show the path of thought into which I want young naturalists to turn their minds.

Or, again, you will have to inquire whether the species has not been prevented from spreading by some natural barrier.  Mr. Wallace, whom you all of course know, has shown in his ‘Malay Archipelago’ that a strait of deep sea can act as such a barrier between species.  Moritz Wagner has shown that, in the case of insects, a moderately broad river may divide two closely allied species of beetles, or a very narrow snow-range two closely allied species of moths.

Again, another cause, and a most common one is: that the plants cannot spread because they find the ground beyond them already occupied by other plants, who will not tolerate a fresh mouth, having only just enough to feed themselves.  Take the case of Saxifraga hypnoides and S. umbrosa, “London pride.”  They are two especially strong species.  They show that, S. hypnoides especially, by their power of sporting, of diverging into varieties; they show it equally by their power of thriving anywhere, if they can only get there.  They will both grow in my sandy garden, under a rainfall of only 23 inches, more luxuriantly than in their native mountains under a rainfall of 50 or 60 inches.  Then how is it that S. hypnoides cannot get down off the mountains; and that S. umbrosa, though in Kerry it has got off the mountains and down to the sea level, exterminating, I suspect, many species in its progress, yet cannot get across county Cork?  The only answer is, I believe: that both species are continually trying to go ahead; but that the other plants already in front of them are too strong for them, and massacre their infants as soon as born.

And this brings us to another curious question: the sudden and abundant appearance of plants, like the foxglove and Epilobium angustifolium, in spots where they have never been seen before.  Are their seeds, as some think, dormant in the ground; or are the seeds which have germinated fresh ones wafted thither by wind or otherwise, and only able to germinate in that one spot, because there the soil is clear?  General Monro, now famous for his unequalled memoir on the bamboos, holds to the latter theory.  He pointed out to me that the Epilobium seeds, being feathered, could travel with the wind; that the plant always made its appearance first on new banks, landslips, clearings, where it had nothing to compete against; and that the foxglove did the same.  True, and most painfully true, in the case of thistles and groundsels: but foxglove seeds, though minute, would hardly be carried by the wind any more than those of the white clover, which comes up so abundantly in drained fens.  Adhuc sub judice lis est, and I wish some young naturalists would work carefully at the solution; by experiment, which is the most sure way to find out anything.

But in researches in this direction they will find puzzles enough.  I will give them one which I shall be most thankful to hear they have solved within the next seven years—How is it that we find certain plants, namely, the thrift and the scurvy grass, abundant on the sea-shore and common on certain mountain-tops, but nowhere between the two?  Answer me that.  For I have looked at the fact for years—before, behind, sideways, upside down, and inside out—and I cannot understand it.

But all these questions, and specially, I suspect, that last one, ought to lead the young student up to the great and complex question—How were these islands re-peopled with plants and animals, after the long and wholesale catastrophe of the glacial epoch?

I presume you all know, and will agree, that the whole of these islands, north of the Thames, save certain ice-clad mountain-tops, were buried for long ages under an icy sea.  From whence did vegetable and animal life crawl back to the land, as it rose again; and cover its mantle of glacial drift with fresh life and verdure?

Now let me give you a few prolegomena on this matter.  You must study the plants of course, species by species.  Take Watson’s ‘Cybele Britannica,’ and Moore’s ‘Cybele Hibernica;’ and let—as Mr. Matthew Arnold would say—“your thought play freely about them.”  Look carefully, too, in the case of each species, at the note on its distribution, which you will find appended in Bentham’s ‘Handbook,’ and in Hooker’s ‘Student’s Flora.’  Get all the help you can, if you wish to work the subject out, from foreign botanists, both European and American; and I think that, on the whole, you will come to some such theory as this for a general starting platform.  We do not owe our flora—I must keep to the flora just now—to so many different regions, or types, as Mr. Watson conceives, but to three, namely: an European or Germanic flora, from the south-east; an Atlantic flora, from the south-west; a Northern flora from the north.  These three invaded us after the glacial epoch; and our general flora is their result.

But this will cause you much trouble.  Before you go a step further you will have to eliminate from all your calculations most of the plants which Watson calls glareal, i.e. found in cultivated ground about habitations.  And what their limit may be I think we never shall know.  But of this we may be sure; that just as invading armies always bring with them, in forage or otherwise, some plants from their own country—just as the Cossacks, in 1815, brought more than one Russian plant through Germany into France—just as you have already a crop of North German plants upon the battle-fields of France—thus do conquering races bring new plants.  The Romans, during their 300 or 400 years of occupation and civilisation, must have brought more species, I believe, than I dare mention.  I suspect them of having brought, not merely the common hedge elm of the south, not merely the three species of nettle, but all our red poppies, and a great number of the weeds which are common in our cornfields; and when we add to them the plants which may have been brought by returning crusaders and pilgrims; by monks from every part of Europe, by Flemings or other dealers in foreign wool; we have to cut a huge cantle out of our indigenous flora: only, having no records, we hardly know where and what to cut out; and can only, we elder ones, recommend the subject to the notice of the younger botanists, that they may work it out after our work is done.

Of course these plants introduced by man, if they are cut out, must be cut out of only one of the floras, namely, the European; for they, probably, came from the south-east, by whatever means they came.

That European flora invaded us, I presume, immediately after the glacial epoch, at a time when France and England were united, and the German Ocean a mere network of rivers, which emptied into the deep sea between Scotland and Scandinavia.  And here I must add, that endless questions of interest will arise to those who will study, not merely the invasion of that truly European flora, but the invasion of reptiles, insects, and birds, especially birds of passage, which must have followed it as soon as the land was sufficiently covered with vegetation to support life.  Whole volumes remain to be written on this subject.  I trust that some of your younger members may live to write one of them.  The way to begin will be: to compare the flora and fauna of this part of England very carefully with that of the southern and eastern counties; and then to compare them again with the fauna and flora of France, Belgium, and Holland.

As for the Atlantic flora, you will have to decide for yourselves whether you accept or not the theory of a sunken Atlantic continent.  I confess that all objections to that theory, however astounding it may seem, are outweighed in my mind by a host of facts which I can explain by no other theory.  But you must judge for yourselves; and to do so you must study carefully the distribution of heaths, both in Europe and at the Cape; and their non-appearance beyond the Ural Mountains, and in America, save in Labrador, where the common ling, an older and less specialised form, exists.  You must consider, too, the plants common to the Azores, Portugal, the West of England, Ireland, and the Western Hebrides.  In so doing young naturalists will at least find proofs of a change in the distribution of land and water, which will utterly astound them when they face it for the first time.

As for the Northern flora, the question whence it came is puzzling enough.  It seems difficult to conceive how any plants could have survived when Scotland was an archipelago in the same ice-covered condition as Greenland is now; and we have no proof that there existed after the glacial epoch any northern continent from which the plants and animals could have come back to us.  The species of plants and animals common to Britain, Scandinavia, and North America, must have spread in pre-glacial times, when a continent joining them did exist.

But some light has been thrown on this question by an article, as charming as it is able, on “The Physics of the Arctic Ice,” by Dr. Brown, of Campster.  You will find it in the ‘Quarterly Journal of the Geological Society’ for February 1870.  He shows there that even in Greenland peaks and crags are left free enough from ice to support a vegetation of between 300 or 400 species of flowering plants; and, therefore, he well says, we must be careful to avoid concluding that the plant and animal life on the dreary shores or mountain-tops of the old glacial Scotland was poor.  The same would hold good of our mountains; and, if so, we may look with respect, even with awe, on the Alpine plants of Wales, Scotland, and the Lake mountains, as organisms stunted, it may be, and even degraded, by their long battle with the elements; but venerable from their age, historic from their endurance.  Relics of an older temperate world, they have lived through thousands of centuries of frost and fog, to sun themselves in a temperate climate once more.  I can never pick one of them without a tinge of shame; and to exterminate one of them is to destroy for the mere pleasure of collecting the last of a family which God has taken the trouble to preserve for thousands of centuries.

I trust that these hints—for I can call them nothing more—will at least awaken any young naturalist who has hitherto only collected natural objects, to study the really important and interesting question—How did these things get here?

Now hence arise questions which may puzzle the mind of a Hampshire naturalist.  You have in this neighbourhood, as you well know, two, or rather three, soils, each carrying its peculiar vegetation.  First, you have the clay lying on the chalk, and carrying vast woodlands, seemingly primeval.  Next, you have the chalk, with its peculiar, delicate, and often fragrant crop of lime-loving plants; and next you have the poor sands and clays of the New Forest basin, saturated with iron, and therefore carrying a moorland or peat-loving vegetation, in many respects quite different from the others.  And this moorland soil, and this vegetation, with a few singular exceptions, repeats itself, as I daresay you know, in the north of the county, in the Bagshot basin, as it is called—the moors of Aldershot, Hartford Bridge, and Windsor Forest.

Now what a variety of interesting questions are opened up by these simple facts.  How did these three floras get each to its present place?  Where did each come from?  How did it get past or through the other, till each set of plants, after long internecine competition, settled itself down in the sheet of land most congenial to it?  And when did each come hither?  Which is the oldest?  Will any one tell me whether the heathy flora of the moors, or the thymy flora of the chalk downs, were the earlier inhabitants of these isles?  To these questions I cannot get any answer; and they cannot be answered without first—a very careful study of the range of each species of plant on the continent of Europe; and next, without careful study of those stupendous changes in the shape of this island which have taken place at a very late geological epoch.  The composition of the flora of our moorlands is as yet to me an utter puzzle.  We have Lycopodiums—three species—enormously ancient forms which have survived the age of ice: but did they crawl downward hither from the northern mountains, or upward hither from the Pyrenees?  We have the beautiful bog asphodel again—an enormously ancient form; for it is, strange to say, common to North America and to Northern Europe, but does not enter Asia—almost an unique instance.  It must, surely, have come from the north; and points—as do many species of plants and animals—to the time when North Europe and North America were joined.  We have, sparingly, in North Hampshire, though, strangely, not on the Bagshot moors, the Common or Northern Butterwort (Pinguicula vulgaris); and also, in the south, the New Forest part of the county, the delicate little Pinguicula lusitanica, the only species now found in Devon and Cornwall, marking the New Forest as the extreme eastern limit of the Atlantic flora.  We have again the heaths, which, as I have just said, are found neither in America nor in Asia, and must, I believe, have come from some south-western land long since submerged beneath the sea.  But more, we have in the New Forest two plants which are members of the South Europe, or properly, the Atlantic flora; which must have come from the south and south-east; and which are found in no other spots in these islands.  I mean the lovely Gladiolus, which grows abundantly under the ferns near Lyndhurst, certainly wild but it does not approach England elsewhere nearer than the Loire and the Rhine; and next, that delicate orchid, the Spiranthes æstivalis, which is known only in a bog near Lyndhurst and in the Channel Islands, while on the Continent it extends from southern Europe all through France.  Now, what do these two plants mark?  They give us a point in botany, though not in time, to determine when the south of England was parted from the opposite shores of France; and whenever that was, it was just after the Gladiolus and Spiranthes got hither.  Two little colonies of these lovely flowers arrived just before their retreat was cut off.  They found the country already occupied with other plants; and, not being reinforced by fresh colonists from the south, have not been able to spread farther north than Lyndhurst.  Thus, in the New Forest, and, I may say, in the Bagshot moors, you find plants which you do not expect, and do not find plants which you do expect; and you are, or ought to be, puzzled, and I hope also interested, and stirred up to find out more.

I spoke just now of the time when England was joined to France, as bearing on Hampshire botany.  It bears no less on Hampshire zoology.  In insects, for instance, the presence of the purple emperor and the white admiral in our Hampshire woods, as well as the abundance of the great stag-beetle, point to a time when the two countries were joined, at least, as far west as Hampshire; while the absence of these insects farther to the westward shows that the countries, if ever joined, were already parted; and that those insects have not yet had time to spread westward.  The presence of these two butterflies, and partly of the stag-beetle, along the south-east coast of England as far as the primeval forests of South Lincolnshire, points—as do a hundred other facts—to a time when the Straits of Dover either did not exist, or were the bed of a river running from the west; and when, as I told you just now, all the rivers which now run into the German Ocean, from the Humber on the west to the Elbe on the east, discharged themselves into the sea between Scotland and Norway, after wandering through a vast lowland, covered with countless herds of mammoth, rhinoceros, gigantic ox, and other mammals now extinct; while the birds, as far as we know; the insects; the fresh-water fish; and even, as my friend Mr. Brady has proved, the Entomostraca of the rivers, were the same in what is now Holland as in what is now our Eastern counties.  I could dwell long on this matter.  I could talk long about how certain species of Lepidoptera—moths and butterflies—like Papilio Machaon and P. Podalirius, swarm through France, reach up to the British Channel, and have not crossed it; with the exception of one colony of Machaon in the Cambridgeshire fens.  I could talk long about a similar phenomenon in the case of our migratory and singing birds: how many exquisite species—notably those two glorious songsters, the Orphean Warbler and Hippolais, which delight our ears everywhere on the other side of the Channel—follow our nightingales, blackcaps, and warblers northward every spring almost to the Straits of Dover: but dare not cross, simply because they have been, as it were, created since the gulf was opened, and have never learnt from their parents how to fly over it.

In the case of fishes, again, I might say much on the curious fact that the Cyprinidæ, or white fish—carp, &c.—and their natural enemy, the pike, are indigenous, I believe, only to the rivers, English or continental, on the eastern side of the Straits of Dover; while the rivers on the western side were originally tenanted, like our Hampshire streams, as now, almost entirely by trout, their only Cyprinoid being the minnow—if it, too, be not an interloper; and I might ask you to consider the bearing of this curious fact on the former junction of England and France.

But I have only time to point out to you a few curious facts with regard to reptiles, which should be specially interesting to a Hampshire bio-geologist.  You know, of course, that in Ireland there are no reptiles, save the little common lizard, Lacerta agilis, and a few frogs on the mountain-tops—how they got there I cannot conceive.  And you will, of course, guess, and rightly, that the reason of the absence of reptiles is: that Ireland was parted off from England before the creatures, which certainly spread from southern and warmer climates, had time to get there.  You know, of course, that we have a few reptiles in England.  But you may not be aware that, as soon as you cross the Channel, you find many more species of reptiles than here, as well as those which you find here.  The magnificent green lizard which rattles about like a rabbit in a French forest, is never found here; simply because it had not worked northward till after the Channel was formed.  But there are three reptiles peculiar to this part of England which should be most interesting to a Hampshire zoologist.  The one is the sand lizard (L. stirpium), found on Bourne-heath, and, I suspect, in the South Hampshire moors likewise—a North European and French species.  Another, the Coronella lævis, a harmless French and Austrian snake, which has been found about me, in North Hants and South Berks, now about fifteen or twenty times.  I have had three specimens from my own parish.  I believe it not to be uncommon; and most probably to be found, by those who will look, both in the New Forest and Woolmer.  The third is the Natterjack, or running toad (Bufo Rubeta), a most beautifully spotted animal, with a yellow stripe down his back, which is common with me at Eversley, and common also in many moorlands of Hants and Surrey; and, according to Fleming, on heaths near London, and as far north-east as Lincolnshire; in which case it will belong to the Germanic fauna.  Now, here again we have cases of animals which have just been able to get hither before the severance of England and France; and which, not being reinforced from the rear, have been forced to stop, in small and probably decreasing colonies, on the spots nearest the coast which were fit for them.

I trust that I have not kept you too long over these details.  What I wish to impress upon you is that Hampshire is a county specially fitted for the study of important bio-geological questions.

To work them out, you must trace the geology of Hampshire, and, indeed, of East Dorset.  You must try to form a conception of how the land was shaped in miocene times, before that tremendous upheaval which reared the chalk cliffs at Freshwater upright, lifting the tertiary beds upon their northern slopes.  You must ask—Was there not land to the south of the Isle of Wight in those ages, and for ages after; and what was its extent and shape?  You must ask—When was the gap between the Isle of Wight and the Isle of Purbeck sawn through, leaving the Needles as remnants on one side, and Old Harry on the opposite?  And was it sawn asunder merely by the age-long gnawing of the waves?  You must ask—Where did the great river which ran from the west, where Poole Harbour is now, and probably through what is now the Solent, depositing brackish water-beds right and left—where, I say, did it run into the sea?  Where the Straits of Dover are now?  Or, if not there, where?  What, too, is become of the land to the Westward, composed of ancient metamorphic rocks, out of which it ran, and deposited on what are now the Haggerstone Moors of Poole, vast beds of grit?  What was the climate on its banks when it washed down the delicate leaves of broad-leaved trees, akin to our modern English ones, which are found in the fine mud-sand strata of Bournemouth?  When, finally, did it dwindle down to the brook which now runs through Wareham town?  Was its bed sea, or dry land, or under an ice sheet, during the long ages of the glacial epoch?  And if you say—Who is sufficient for these things?—Who can answer these questions?  I answer—Who but you, or your pupils after you, if you will but try?