The general who is for ever counter-marching and skilfully executing retrograde movements cannot always sustain the enthusiasm of his own troops, much less excite in his favour that of the civilian multitude. To many minds, the reliance placed on the imperfection of the geological record appears to be a rather damaging retreat in the strategy of science. They were just beginning to believe in geology as a wonderful revelation of the past history of the globe, when suddenly they are told that the fragments of that history which have been saved are merely tattered pages out of different chapters, giving no adequate notion of the enormous bulk and varied contents of the whole volume. Since, without the geological evidence of time’s duration and of the countless changes in organic structures which that duration embraces, the theory of development could never have been imagined, it seems half ungrateful and inconsistent in the author of the theory to turn round upon geological evidence and tax it with its extreme poverty and even delusive misleading appearances. But, in fact, Mr. Darwin in no way detracts from the value of geological evidence. The researches necessary to extend it are invested, to those who accept his theory, with tenfold interest. The deficiencies and interruptions in it which he has pointed out as necessarily occurring must sooner or later have become apparent. They were dangerous to science only as long as they were unobserved, or not sufficiently taken into account.
That the record is really imperfect is not a matter which admits of controversy. No one supposes that every species and variety that ever existed in past ages on the globe is represented at this very day by fossil specimens in prime enough condition to exhibit all the characteristics of the creature as it once lived. No one supposes that, if such specimens existed, all of them ever could or would be found by human beings. It is not in the nature of a fossil to present all the characteristics of the creature as it once lived. It cannot possibly do it; for the fossil is without life and motion. There is no respiration, no circulation of the blood going on. As a rule, only the hard parts of the creature, such as shell, scales, or bony skeleton, can be preserved. In most cases all these relics have been chemically altered. Nevertheless, in fossils from the very lowest strata, from the very earliest formations that yield any, we find certain analogies to creatures now living. We reason from these analogies without any hesitation to the characteristics which the fossil creature will probably have presented in its living state. Our reasonings may often be erroneous, but the mere fact of our accepting the apparent analogies as a ground for reasoning at all, implies a belief in the uniformity of the conditions of animal existence between our own times and the most distant ages of the past. We argue as if generation had succeeded generation without interruption, not as if there had been new independent creations from time to time, since these would imply new conditions replacing the old, and make the argument from analogy between the items of the different creations of no value. For these independent creations, whether capricious or not in themselves, could only exhibit to our minds the symptoms of caprice. The mere fact of their being independent one of another would be so wanting in congruity with all the rest of our experience, that we should reasonably expect their minor details as well as the general plan to be wholly fantastic. In other words, the fossil memorials of life in past ages, imperfect as we confess and maintain them to be, still present so many general resemblances to one another and to living structures of the present day, that if they do not prove the continuity of life upon the globe, they cannot be held to prove anything at all; they should be regarded as a very elaborate practical joke played upon the human reason.
PalÆontology is defined as ‘the science which treats of fossil remains both animal and vegetable.’ This principle of the continuity of life from age to age may be considered as one of its definite acquisitions. There is no single point of geological time at which it can be said, ‘at this epoch clearly all old species had passed away, all kinds of life had become new.’ Not only is there no indication of such a break, but there is the strongest evidence against any such having ever occurred. In spite, however, of the completeness of the evidence required for proving this single conclusion, the general incompleteness and enormous deficiencies in some parts of the palÆontological record can be established beyond dispute. We are in the position of a man who has kept the title-deeds to a large estate, while almost all the estate itself has been buried under the encroachments of the sea. Here and there some old landmarks may be discernible far out in the waters, showing the extent of what had once been meadow and woodland, farm and garden, but unable to show how these were distributed, or to exhibit any of their details.
Mr. Parfitt, in his paper on ‘Fossil Sponge Spicules,’ told the Devonshire Association last year (1870) that we have evidence more or less exact of sponges in a fossil state as far back in time as the Silurian system, mentioning specimens of Acanthospongia Siluriensis, Cliona antiqua, and Cliona prisca, and stating in regard to the two latter that the genus is still in our own seas. He then referred to large masses of a fossil in the Devonian rocks of Cornwall, believed by some to be sponges, and by others to be the remains of fish. That these are in reality fish-remains has, in fact, been shown pretty conclusively59. From this point, however, up to the Great Oolite, Mr. Parfitt tells us that scarcely a vestige of the sponges is to be found, although since that time they have been very abundant. Between the Silurian and the Great Oolite the interval of time must have been enormous. It is occupied by a vast series of sedimentary rocks, embracing very varied mineral characteristics. From this series our museums have been, and are still being, supplied with vast heaps of fossil organic structures, including among numerous others, plants and corals and fish and reptiles. Through all that protracted period there is no reason to suppose, in regard to the outer rind of the globe, that the general conditions of earth, air, and water were other than they are now. All England may have been under water; delicate creatures may have wintered at the North Pole for the sake of its genial climate; and an infinity of other local and temporary differences may have prevailed, without making the habitable globe of those days essentially different from our own. The laws of chemistry and mechanics, the laws of heat and motion, must have been just the same as they are now. Then, as now, there must have been oceans and continents, winds and currents, forests growing, decaying, and being buried, sand and chalk being deposited in layers, molten minerals thrown up by volcanoes, ice forming at a definite temperature, glaciers scoring the rocks, icebergs transporting boulders, rains and rivers slowly washing down the hills, and waves corroding the cliffs on the sea-shore. We have evidence also that life in many forms abounded. Those forms, though seldom transmitted to creatures of the present day with anything approaching an exact likeness, can yet be classified under the same general names with the most modern forms of life. Now sponges are forms of an extremely simple organization. The silicious spicules are well adapted for the wear and tear of a fossil existence. In the greensand and the chalk they are actually found in extraordinary abundance. It would be inconvenient upon any theory to have to suppose these very simple structures introduced into the world for the first time quite late in the series of living organisms, and after beings much more complicated and higher in the scale of existence, unless, indeed, we suppose that about the time of the Great Oolite the evolution of man was first thought of, and the sponge accordingly prepared for him to wash his face with. But even if the bath and the basin be admitted as the final causes of sponge-existence, the conception of it must be carried back, as we have seen, to the Silurian period; while, according to Mr. Parfitt, the immense interval of Lias and Trias, Permian, Carboniferous, and Devonian remains black and spongeless, as though it were the appropriate era of the great unwashed. But if the Darwinian theory be a true one, sponge-life having begun in the Silurian period, and being in existence now, must have been continuous through the whole interval; every single deposit in the entire series since the Silurian must have been contemporary with some of the sponges; and, as a matter of fact, Mr. Parfitt’s statement, however true of the condition of our knowledge a few years back, must now be qualified by the addition of several species spread over the interval in Britain alone, even if we exclude some indefinite structures, of which no opinion can be at present pronounced with safety. Mr. Parfitt himself, in a paper read at Honiton in 1868, remarks that ‘the Devonian formation has furnished a great number of specimens of what appear to be species of sponges.’ From Permian and Triassic beds on the continent of Europe, a very large number of forms are said to be more or less distinctly made out. Mr. Salter, in 1864, reported the discovery of Protospongia Fenestrata in the Lingula flags of St. David’s, thus carrying back this form of life beyond the Silurian to the Cambrian era. It is an interesting illustration of the great ambiguity of these ancient fossils, that two such authorities as Mr. Salter and Dr. Bowerbank differed about the Protospongia, the one supposing it to exhibit the spicules, the other the fibre of the sponge. The simple facts that species have to be moved backwards and forwards between the amorphozoic and zoophytic groups, that relics may pass for fish in one year and sponges in another, and by-and-by be recognised again as fish, show the often imperfect condition of the record, even where it is not a complete blank.
Where direct evidence of any kind is still unavailable, it may possibly be said that no sponges are found for such and such a period, because none existed in it. The plausibility of such an opinion can only be tested in fresh illustrations of the general argument. The coalfield of Nova Scotia has been described by Professor Dawson of Montreal. As it afforded a fine field for the exertions of the geologist, so it repaid him by its great richness in the fossil remains of plants. But in the coal formations of England and of Westphalia insects also had been found of different genera in addition to plants, while Nova Scotia, with all its vegetable wealth, yielded the anxious explorer but a single specimen of the still more interesting relics. That specimen consisted of the head and some other fragments of a large insect, probably neuropterous. That single specimen Professor Dawson tells us he found in a coprolite, in the fossil excrement of a reptile enclosed in the trunk of an erect sigillaria. Could any one invent a more curious cabinet to preserve so fragile a specimen for millions of years? Can it in this case be argued, that of insect remains nothing was found in the carboniferous of Nova Scotia but the head and some other appurtenances of a single neuropterous insect, because that head and those appurtenances were all that had ever flourished there? It cannot so be argued, not only because the analogies of the carboniferous formation in other parts of the world are conclusive against such argument, but also because within the last three or four years, after long and diligent search, two more species have been added to the collection of carboniferous insects from Nova Scotia itself. Two delicate wings, one very large and one small, have been found, each sealed, as it were, with a fern-leaf; each a frail but enduring record of life that must once have been brilliant and abundant60.
When the zeal of a collector adds a new species to those already known, by finding the fragment of a butterfly’s wing that had been for millions of years in a seam of coal, how many considerations are forced upon the mind! Our sensitive nerves are comparatively seldom troubled by the perceived presence of dead creatures. With the exception of our own food, such sights are pretty well confined to the carcase of a dog floating on a pool, the feathers of a torn bird, a parched mole, and a sprinkling of blue-bottles in an unused room. Yet countless millions of creatures are annually dying, ready and willing to become fossils. Fossils, however, they do not become, simply because other creatures eat them up. For this reason alone, not one in ten thousand of any particular terrestrial species is likely to become fossil, because to some creature or another it is almost sure to be good eating, and therefore in the living state or the dead, sure to be ravenously seized upon and devoured.
Some forms of marine life are indeed represented by a wonderful number of specimens or fragments of specimens. Silicious and calcareous exuviÆ of minute creatures deposited in the still depths of the ocean may be preserved by myriads, but neither these ‘in number numberless’ nor the giant-bones of ancient Saurians convey any adequate notion of the whole population of the globe at any one era. The palÆontologist, guiding himself only by prominent details of this description, would be like a child over a child’s history of England, to whom the fabric of the Constitution and the Reformation of the Church seem matters obscure, and scarcely worthy of notice, while Alfred burning the cakes, and Henry VIII in his well-known character of Bluebeard, stand out in bold relief.
No one will doubt, that within the last ten years tens of thousands of the common white butterfly have disported themselves in England, yet a man might easily starve if he were allowed no food till he had found some of their fossil remains. The dodo has not long been extinct, but nevertheless fossil dodos are extremely rare. It may be thought that the date of extinction has little to do with the matter, and that each relic when enshrined in the rock, may claim to be by a sort of indelible character ‘once a fossil and always a fossil.’ This, however, is in reality far from its true condition. Let a creature’s remains escape being devoured, or burnt, or trampled to pieces, or being dissolved by the rain, or crumbled into dust by rolling waves and mud and stones gathered upon them, their perils are not yet over. Even in the grasp of the hard rock, the fossil may be horribly distorted by pressure, split asunder by cleavage, boiled and baked and crystallized, till none of its features remain what they were, or till the very fact of its presence becomes only the question of a dim surmise. The rude jolt of an earthquake, that splits asunder a mountain, may sometimes be tender over a butterfly’s wing; but there are chemical agencies which work without any compassion for what is fine and delicate, and by these we find great thicknesses of rock apparently stripped of their fossils. Where the whole stratum consists of remains of once living organisms, as in seams of coal, it has been shown that we have no reason to suppose that any complete or adequate memorials are left us of the whole vegetation of any particular period or any particular area; since Dr. Lindley has found, by actual experiment, that different vegetables have very different powers of resisting decay, and that pines and ferns and lycopodia will be well preserved after long immersion in water, while the same treatment causes the disappearance of grasses and sedges, of the oak-tree and the ash61.
Even those rocks which preserve fossils most carefully may themselves be crumbled to pieces, fossils and all, by the process of denudation.
Denudation is the laying bare of one stratum, or portion of a stratum, by the removal of another. It is carried on principally by rains and rivers and the action of the sea-waves upon the sea-border. To the last-mentioned agency the geologist is highly indebted; to the others also he owes a debt: but consider how they all do their work. Much of the material dealt with they pound into mud or sand, and in these any fragments that escape the trituration are, sooner or later, again buried. They may tear open the rocks, and expose for a brief period the most interesting and unique fossils; but, unfortunately, they carry on their work by night as well as day, on desolate coasts, in places where the PalÆontographical Society has no missionaries, or when the missionary, if there be one, is in-doors writing a book; so that a very small percentage of all that might be discovered is ever actually found.
In the artificial denudation of mining and quarrying, though the rude forces of Nature are dispensed with, the enlightened hammer of the geologist can do very little by itself. In most cases it can but follow where commercial enterprise leads the way, and be grateful for permission to rummage among the dÉbris, when pickaxe and blasting have done their work.
The chances against a fossil’s being found to any useful purpose in quarrying are very numerous. The rock must chance to split so as to disclose it; the workman must chance to notice it; he must chance to have knowledge enough to think it worth notice; have time enough to stop from his work and take it; have sense enough to keep it safe; have memory enough to recollect where he hides it; and, lastly, have the luck to meet with a customer who knows its scientific value.
Numbers of rare specimens must continually be consigned to the furnace and the limekiln, or buried under mounds and hills of refuse. Sometimes the character of the matrix, by its hardness or its softness, makes it impossible to disengage the fossil without complete disfigurement; sometimes the fossil itself is so fragmentary as rather to confuse than to teach. Dr. Hooker gives an instance, in which a geologist assigned three pieces of fossil-leaf to plants of three different genera, which a subsequent observer maintained to be merely the separated portions of a single leaf of one and the same plant62.
In the slates and limestones of Torquay, full as they are of marine fossils, no fish-remains have been identified, with one exception. Yet these rocks have been searched by numerous sharp eyes and clever hands, professional as well as amateur, with regular investigation, and in the sometimes more successful trifling of idle moments. It is worthy of note that the one exception is no scarcely decipherable relic, the nature of which might remain an open question, but a beautiful and finely-preserved scale of phyllolepis concentricus63. Had there been only one fish in the ‘Devonian’ waters of the neighbourhood, the one fish must have had more than one scale; yet none of the others are forthcoming. The science of to-morrow may find them; to the science of to-day they are lost irrecoverably.
The still-living varieties of the oyster are a miserable remnant of the 255 fossil species from the chalk described in Coquand’s recent work. Professor Flower, in reviewing this monograph, remarks, that ‘with these mollusks, numerous as they are, there are no forms that can fairly be recognized as transitional.’ But inasmuch as the succession in time of these species is well-established by the different zones of the chalk in which they are found, we must either accept some nine or ten successive creations concerned in the production of oysters, or we must allow the various fossil species to be connected with one another by descent. Upon the latter alternative, a whole chain of transitional links must once have existed between the earliest form of oyster and the latest; and though many of these links have been preserved, still more must have been lost, or deprived of their distinctive features; so that here, where the geological record is, to all appearance, unusually perfect, its actual imperfection is more clearly than ever established.
To conclude, then, in few words:—The majority of dead creatures never become fossils at all.
The majority of fossils perish miserably in their hiding-places.
Of those that are saved, the majority cannot be got at by man.
Of those that can be, the majority never are.
Of those that are, a large number prove illegible; a large number are fragments; a large number duplicates; and, lastly, a large number fall into hands which again lose or destroy them.
We cannot therefore argue, because fossils of such-and-such forms of life have never been found, that such-and-such forms never existed. They may have existed, and left no fossils. The fossils may have been left, and subsequently destroyed. The fossils may be undestroyed, but never have been found. The sum-total of acquisitions is small, but precious; it never can make a complete record, but it may make one sufficiently ample to establish the Darwinian Theory, or to replace it by some still wider and still simpler generalization.