THE RELATIONS OF PALEONTOLOGY TO STRATIGRAPHY.
By G. W. LAMPLUC.H, F.R.S., F.G.S.
Address delivered at a meeting of the Hull Geological Society, in Hull, on Friday, April 2nd, 1925.
I dare say that many members of this Society, like myself, had their interest in Geology first aroused by the fossils that are so abundant on our coasts and in our quarries, and began by collecting these fossils. Then, no doubt, like me, they wanted names for their specimens; and probably believed, as I did, that every, or nearly every fossil had its name, if one could only get hold of the person who knew it. This desire for the name of a thing is deeply implanted in our nature, as witness the old story in Genesis of how Adam's first business on earth was to give names to the newly-created animals. The fact is, we do most of our thinking by using names as symbols; so, of course, we are anxious to get hold of a distinguishing symbol we have to deal with or think about, and it seems contrary to the proper order to find things without names. In my own case, my youthful impression that an unnamable fossil was a great rarity was fortified by a well-remembered conversation with a gentleman who watched me chipping out fossils from the chalk scars at Sewerby one summer evening about fifty years ago, and told me that if I kept it up long enough I might someday find a new species and have it named after me, which he implied was about as big a piece of luck as could happen to anyone.
How times have changed! Now-a-days one counts it luck to find .any fossil that can have a good, sure ready-made name attached to it, and most of the specimens in our cabinets are, at the best, cfs. or affr. or ? s, even when they happen to have been subjected to the examination of qualified specialists. This change de- notes an alteration in the relation between stratigraphy and paleontology which has been in slow progress for many years, but has proceeded more rapidly of late. I propose now to consider some aspects of the relation- ship, and to note some of the advantages, as well as some of the difficulties, which have arisen from it.
Ever since the pioneer work of William Smith, stratigraphers have recognized the importance of fossils as determinants of the sequence and correlation of the strata, and it soon became habitual for them to pin their faith on the fossil evidence. The broad distinctions between the commoner forms were readily learnt, and for general purposes the stratigrapher found no difficulty in acquainting himself with the main types characterizing the different formations. So far as his aim was simply to trace the course of the formations, and to interpret their structural arrangement, he had no need to consider the value and meaning of the fossils as indicators of former life: their usefulness to him would have been the same if they had been, as was once believed, mere simulacra or markings stamped at creation in the rock by inorganic tendencies. The markings, whatever they meant, were found to be of the same kind in strata of the same order in the sequence: and that was the really significant factor. "Medals of Creation," they were figuratively called by Gideon Mantell--and the term is quite appropriate from the stratigrapher's point of view.
With the rapid accumulation of specimens, however, the geologist soon found such immense variety among his "medals," that he was glad to make over the business of sorting and naming them to other hands, and their study grew quickly into the separate science of paleontology. But when the paleontologist got to work, he found many interests in them other than the stratigraphical, and generally swung over, almost of necessity, to regard their zoological aspect as the more important. So it has come about that instead of being content to remain as auxiliary to the stratigrapher, the advanced paleontologist of the present day is inclined to turn the table and to consider stratigraphy mainly .as an adjunct to assist him in following up the evolution of life on the earth.
And there is much to be said for this attitude, as it is only from the fossils that the zoologist, the botanist and the biologist can hope to gain any sure information about the ancestry of the existing forms of life, and so about the course of evolution. Moreover, the fossils have revealed to him a multitude of highly interesting organisms, of which he would otherwise have remained in total ignorance, and the knowledge thus acquired profoundly affected the interpretation of the anatomy and derivation of every living thing.
But the development of palaeontology on the biological side has required such a prolonged and intensive study of the fossils, that it is only by individual specialization of effort in a narrow field that further progress can be achieved. The early type of paleontologist, who ranged to the best of his ability over the whole of the animal and vegetable kingdom of all the geological periods, and fitted approximate names to almost every fossil submitted to him, is no longer to be found; and in his place we have a group of specialists, each concentrating his study on some particular Class or Order of organism, and unwilling to devote attention to any fossil outside his province. And since these special studies are voluntary and un-coordinated, it happens often enough that the fossils about which we may be most anxious to obtain expert advice do not fall within the scope of any specialist at the time of our enquiry.
As an inevitable result of close specialization in paleontology, it has followed that the broad distinctions for genera and species introduced by the older workers are found quite inadequate for the needs of the specialist who has learnt by continuous intensive examination to recognize differences as of prime consequence, which had been previously overlooked or regarded as of no particular significance. A copious crop of new names has been required to denote these newly-discovered features and relationships, and the old names have been scrapped or restricted or re-combined to suit the special requirements of the investigator, often to the confusion of the stratigrapher who could make good use of the old term, while quite unable to follow the refinements of the new work. Moreover, with the constant intensification of paleontological research, every successive specialist on a particular class of organisms has found reason to amend, amplify or discard much of the nomenclature of his predecessor; so that now the study of the mere synonymy or literature relating to a fossil may be a more arduous task than the study of the fossil itself.
The modern paleontologist says in effect, "You must not use a name unless you use it correctly (i.e., as I myself should use it), or else you will deceive me." We are told, too, that most of the old-fashioned familiar names of the commoner fossils are really only "omnibus" names, or" collective" names, covering several different species, sometimes even assignable to different genera,
and that we may mislead if we use the name except in its newly restricted sense. But often enough the stratigrapher will find that if he gives up the old usage of a name, he is left with no name at all, perhaps because his material is not well enough preserved to allow the finer shades of determination, or because he cannot obtain the advice of the expert qualified to apply the new nomenclature. This raises a real and growing difficulty in attempting the description of field work .on fossiliferous rocks, and, I think, renders it necessary that we should seek some way to obviate it. To this purpose I have adopted, in my recent papers, the plan of indicating that the name of a fossil is used in the broad old sense by printing it in ordinary Roman type instead .of in italics, reserving italics for such names, if any, as have been conferred on the fossil after its scrutiny by a specialist. By this method the paleontologist is warned against accepting inexpert determinations, while at the same time an idea of the general characters of the fossil is conveyed to him as well as to the stratigrapher. I commend the method to your attention, with the anticipation" that it--or something equivalent to it-- will go some way toward relieving the difficulty in question.
It is a commonplace to say that the application of paleontology to stratigraphy has cleared up many obscurities and corrected many misconceptions which could not otherwise have been removed. Perhaps the most striking example in our own country, and the one which has had the greatest influence on the relationship of the two branches of our science is Charles Lapworth's elucidation of the close-folded structure of the Lower Palaeozoics of the Southern Upland by means of the graptolites, after the failure of ordinary stratigraphical methods of survey.
The demonstration, so immediately convincing, seemed at the time to have a touch of wizardry in it, and the application of the method successfully to similar regions all over the world put the paleontologists on a pedestal on which they have ever since maintained themselves.
But it must always be remembered that Charles Lapworth's results, both here and in the north-west Highlands, were attained by a combination of thorough stratigraphy with palaeontology, and that it is the same combination which has proved so powerful in in- numerable later instances, of which I may mention as typical and local, the unravelling of the Carboniferous Limestone by Vaughan, followed by Garwood and other workers, and the correlation and zoning of the Chalk by A. W. Rowe. For work of this kind, broadly conceived, and carried out mainly in the field, we can have nothing but admiration.
There is, however, another type of paleontological work, carried out mainly in the cabinet and museum, which, while of immense importance to the biological sciences, and often also yielding valuable aid to stratigraphy, has yet to be regarded critically when it seeks, as sometimes happens, to impress its conclusions as to the proper order of the rocks as final. From the intensive study of large quantities of material, the palaeontol0gist is led to believe that he can follow the course of evolution in some particular group through successive strata, or sometimes even through successive formations, and can produce an accurate family tree enabling him to assign any particular form to its proper place in the sequence. In many cases he has indeed justified his claim, and the stratigrapher finds that the succession of forms in the strata is the same as that deduced by the palaeontologist in the study. But this is not always so, and I want to dwell upon some of the uncertainties that beset the study of phylogeny, as this tracing of ancestors is called.
To begin with, it is always to be remembered that the fossil in most cases represents only the extraneous parts or mere skeleton of the living animal--the shell, test, carapace, bone, or what not--and even these, with imperfection of varying degree. In the absence of other evidence, it has to be assumed that the living structure can be deduced from these remains; and the assumption can no doubt be made safely where the fossil has closely allied living analogues in which the relation- ship of the hard and soft parts of the animal can be investigated. But as we descend in the geological scale we encounter an ever-widening divergence between the living forms and those of the past, so that the assumption carries an increasing charge of speculation and dubious analogy.
In some cases, no doubt, the fossil remains do actually reveal the lines of descent by the changing details of their shape, ornamentation, or other structural characters, as, for example, Dr. Rowe has proved in respect to some of the echinoderms of the Chalk ; but in other cases the palaeontologist has found that the criteria at first depended upon are misleading, as, for example, in respect to the shape and external characters of the Carboniferous brachiopods, and the ornamentation of the shell of the Mesozoic ammonites. A good illustration of false analogy came within my own experience in my younger days. When I had accumulated a large collection of the Chalk Sponges from Sewerby Sponge-beds, I noticed, as everyone who has collected there must do, that they presented an infinite variety of shapes. Being deeply imbued with the Darwinian theory -- then in the flush of its vigour -- I began to arrange the collection in an evolutionary sequence according to external shape, regardless of any other character, and found, bye and bye, that I had a practically unbroken chain, starting from the long cucumber form--Spongia radiciformis we called it then--through shapes with a gradually expanding top, to the mushroom shape, Spongia plana, and thence through a series of more and more deeply notched and cup-like forms to the involute Spongia convoluta, leading on to the complex twisted forms for which we had no name, the whole sequence embracing all the shapes to be found in the beds, so that there was an appropriate place in it for every fresh specimen that I obtained.
I remember that I was quite proud of this " evolutionary sequence" (in fact some of you may have seen the display) ; but I know now that the external shapes I depended upon have no biological significance, and are well-nigh useless as determinants of the genetic affinities and relationship of the sponges.
It is recognized now that the older pulmonologists have followed many false trails of this kind; and if we may judge by the constant rejection by the latest specialist of the methods and conclusions of his predecessors, it is pretty certain that there are really but few cases where, as yet, the true trail has been struck. After the surface ornament had been proved untrustworthy, it was held that the sutures of the chambers were the only true guides to the phylogeny" but I understand that the latest work has shown that the sutures have also proved unworthy of the trust placed in them, and that some of the conclusions based upon them will have to be revised.
Now, as long as this kind of uncertainty exists, it is obviously unsafe to trust wholly to a time-scale based on the supposed family tree of the fossils. Long family trees, even among us humans, have generally to be taken with a grain of salt--and when we come to, say, ammonite family trees that are longer by many a hundred thousand times, and are inferred only from the shapes of the coffins, it must not be imputed as an insult if we .adopt a critical attitude toward the paleontologist.
Certainly we must listen to him, even if he says we have got our beds upside down, and we must go into the field again to see whether by any chance this is so. But when we are quite sure that it is not so, and that the sequence of the beds is beyond question, it is time to tell the paleontologist that there is something amiss with his phylogeny, and that he must shape the idea into accordance with the facts. To do otherwise will only lead to ultimate confusion and error on both sides. Stratigraphy must be the final court of appeal in disputes as to time and sequence, and we must take care to maintain its rights.
It is true that there are ways in which the stratigrapher may be misled by the present position of fossils.
There is, for instance, the possibility that the fossil may be a derivative from some older bed. Yorkshire geologists need no reminder of this possibility, with the conspicuous case of the "omnium gatherum," the boulder-clay, always before them. But usually the character of the deposit will be a sufficient warning to the geologist. If it is a pebble-bed, and any of the pebbles are from fossiliferous rocks, derivative fossils are of course to be expected. But in fine-grained sediments we may safely regard the fossils as indigenous, unless there is very strong evidence to the contrary. Now, I find that the zonal paleontologists are far too ready to write down a fossil as derivative whenever it happens to occur in a position not in accordance with their phylogenetic scheme, and I often feel that this way of dealing with the evidence is not justifiable. To discard all the awkward pieces as "derivative" and to retain just those which will fit nicely into a pre- conceived scheme, is surely not a satisfactory way of playing the game. Yet it is a way that is not uncommon, and has lately also invaded the field of palaeolithic culture-classification rather badly.
Fossils preserved in phosphatic nodules are particularly liable to be dealt with in this manner, with perhaps a certain measure of justification, since the nodules are hard enough to bear some degree of transportation, and are generally surrounded by material that is soft and readily disintegrated. But most phosphatic nodules weather quickly and wear down rapidly under attrition, and I am satisfied for several reasons that many of the so-called derivative fossils of our Mesozoic phosphatic nodule-beds are really in their proper stratigraphical position. What I find usually to be the case is that the fossils of the nodule-band are all newer than the stratum next underlying it, and all older than the stratum next overlying it, but that the band itself is a " condensed " bed, marking a comparatively long interval of time, and containing within itself all that remains of the life of perhaps more than one zone as known elsewhere. I am sure that misconceptions have constantly arisen from the habit of the palaeontologists to write down any inconvenient fossil of such a band as an alien.
Another difficulty besetting the stratigrapher in the use of fossils is the relatively great proportional thickness of strata from which fossils are absent even in formations regarded as rich in fossils. For the inches of fossiliferous rock one usually finds at least as many feet containing no remains or mere traces too badly preserved for identification.
By concentrating on the rich inches one gets together a good collection, and is apt to forget the barren feet. But it is clear that in most cases the record of life which we obtain is widely discontinuous. Even in the most fossiliferous bands we are aware that the relics we find must represent only one in a thousand, or in ten thousand, or in a million, of the once living animals, while the barren beds represent in themselves the greater part of the time. " The imperfection of the geological record" so strongly and rightly insisted upon by Darwin and other great naturalists of the last century is a ruling factor which the field-geologist is not likely to lose sight of, though the paleontologists of late seem too ready to ignore it in building up their ancestral trees.
And when one considers the conditions, there is really some excuse for the palaeontologist in this. Whatever the branch or twig of the tree of life that he chooses to specialize upon --foraminifera, corals, brachiopods, gastropods, cephalopods, crustacea, fish, reptiles, plants, or what not-- he finds already in our public and private collections an accumulation of more material than will suffice for his life's work, and becomes naturally to regard it as sufficient also to build up the story which he has set himself to tell, and will cover all the ground. But in reality the story can only be a clever linking up of detached pieces of evidence by processes of deduction varying in soundness with the ability of the investigator. The results attained may be and have often proved to be very useful in stratigraphy; but if they should clash with good stratigraphical evidence, they should be "referred back" to the palaeontologists for further consideration, and not allowed to distort the simpler evidence of the strata.
Another difficulty besetting the specialist in palaeontology is that as his studies progress he becomes aware of more and more minute shades of difference between Specimens with a general resemblance, and finds it necessary to distinguish these shades by name or symbol, as they have sometimes proved to be more important as guides to the phylogeny than other more conspicuous differences. But a close enough study of any animals, living or dead, always tends to show that no two individuals of a kind are exactly alike, any more than are the individuals of the human kind ; and it is much more difficult with fossils than with living animals to tell which differences are of specific rank, and which merely individual. So it comes about that one specialist sometimes unmakes as many so-called " species " of his predecessor as he makes new ones of his own.
One might run over many more such points of imperfection in paleontological method if time had permitted, but it is not really necessary to do so. It will be acknowledged on all hands that paleontology is now a separate and rapidly advancing science with great achievements to its credit on many sides, but still in the turmoil of discovery where fact and conjecture, both helpful, tend at time to become confused. Some of the conjectures are likely to be so wide-reaching in their influence upon human thought in biology and philosophy that one can understand an occasional attitude of superiority of the palaeontologist toward the mere stratigrapher. I may briefly refer, as an example of the great things that may spring from the specialist's work on fossils to a conception which is tinging the whole of modern palaeontological research, and is profoundly affecting our ideas as to the course and method of evolution. The conception is that evolution is not primarily brought about by the play of external conditions as supposed by Darwin, but that the changes are in some mysterious way inherent 'in the organism, and follow a definite course, while only the rate of change has been retarded or accelerated by external conditions. This is the doctrine or theory of orthogenesis, and if it should be firmly established, it will mean a radical revision of the Darwinian teaching. Dr. Lang for the polyzoa, Dr. Gertrude Elles for the graptolites, Mr. Buckman for the cephalopods and brachiopods, other workers for the oysters, others for the corals, others for the reptiles all declare that they have come across strong evidence for this orthogenesis, and are compelled to adopt it as an explanation of the facts of observation. It is really the old puzzle of predestination, which has worried man ever since he became capable of abstract thought, cropping up in a new place. If these modern palaeontologists are right, it means that just as there are predestined and inevitable stages in an individual life --stages of inception, youth, maturity, old age, and extinction -- so there are equivalent stages in the composite life of the species, the genus, the family, the order that must continue in a proper and discoverable sequence unless the strand of life is prematurely snapped by untoward circumstances, but cannot be prolonged indefinitely by any circumstance.
So far as I have been able to grasp the idea, it seems to be expressed by the quatrain of Fitzgerald's "Omar," ending:
And the first morning of Creation wrote
What the last dawn of Reckoning shall read.
With matters of this portentiousness to deal with. it is not to be wondered at that the modern paleontologist is inclined to shake himself free from the trammels of strict geology and to build on his own account, in- dependently of the stratigrapher. Instead of allowing paleontology to continue to serve as "the hand-maid of Geology," he tends, as I have already said, to view the relationship in reverse order, and regards stratigraphy only as a useful helper in his efforts to grasp the scheme of life, and to be looked at askance when the desired help is not forthcoming. But in point of fact it must be recognized that the two sciences are united by inseparable bonds, and that paleontology without stratigraphy would be no science at all, but merely a field for speculative dogma.
While, therefore, it behoves the geologist to listen with respectful attention to every sincere attempt of the paleontologist to explain the order and succession of life by the relics obtained from the rocks, it behoves him also to listen critically; and whenever there may seem to be a clash between the two lines of evidence, to revise his own observations carefully in order to make sure that there is no error on his side; and when he is sure, to give his verdict firmly as from the final court of appeal. To do otherwise would be, as I have said before, hurtful in the long run to both sciences.
And on this note of warning I will conclude
Copyright Hull Geological Society 2016