Essays on Darwinism

by Thomas Roscoe Rede Stebbing

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 abundant[60].

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 ash[61].

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 plant[62].

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 concentricus[63]. 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.