CHAPTER V.THE CRETACEOUS SYSTEM.
The history of our globe during the deposition of theChalk Formation, and the changes therewith connected, have now to be considered. By whatever causes effected—from whatever sources derived the materials—the line of demarkation is here complete. The sands of Africa, suddenly converted into or drifted over by the snows of the Alps, would not present a greater diversity of outline than is the transition to the geologist, when for the first time he steps into a chalk district, and marks the obvious contrast with all the surrounding scenery. From Gloucester into Wiltshire we pass, as it were, into a new zone of latitude.
The details contained in the two last chapters are in strict conformity with the laws of nature: the animals connected with the epoch possessed functions of life and an external adaptation of things suited to each other. Similar arrangements exist at present under nearly similar circumstances: the tropical animals bear a close affinity to the extinct races; and show that, however nature may contrive to display her exhaustless powers of invention in her forms of living creatures, she still conforms to a type, and has her limits of divergence. The past and the present so agree in all essential points as clearly to demonstrate a wise and controlling agency, a measure of enjoyment combined with an adjustment of figure, which, though approaching the marvelous, has resulted from design and the profoundest intelligence. Accordingly, the symptoms of the change we now witness are cotemporaneous. With the cretaceous system are introduced new mineral conditions, and along with these there are new forms of existence.
The animals of the chalk and oolite periods are essentially different—still generically shading, indeed, into each other—but sodiffering in species, and the appearance for the first time of new creations, as again to announce to us that we tread on sacred ground, and witness in its arrangement and contents the direct agency of Omnipotence. We can form no opinion, no notion whatever, in these changes, of themodus operandi. We remark simply the effects; and science, amidst all its otherwise barren and useless details, then achieves its loftiest purposes when it thus traces the footsteps and actings of the Great First Cause.
1.Range and Structure of the Chalk Formation.Considered mineralogically, this rock can never fail to arrest attention or inquiries, even among the least observant, as to its nature and origin. There is no trace of it in the northern portion of the island; and when one for the first time sees whole mountains of it, his sensations are not a little exciting. For our own part, we felt as if we entered a new world when we gazed upon hills, and their long-furrowed escarpments, of this calcareous snow-drift. Our acquaintance with the mineral had hitherto been limited to the fragments with which we were wont to trace the lines of our schoolboy pastimes. We got no deeper into its mysteries when, on a higher scale of action, we saw it delineate the diagram, or run over the fluxional problem on the black-board in academy and college-hall. But here! and half an island is covered with these stores of knowledge and of industry. Nine or ten counties on a stretch, from Dorset to Flamborough Head, and from Bridport to Deal, are covered over, and for hundreds of feet in depth, with the milk-white earth; and, whichever way you turn and bend toward the Capital, there are ample opportunities for the study of this curious page of geological history.
The chalk beds are not composed of one uniform compact mass of the useful mineral itself, which consists of nearly pure carbonate of lime, of soft earthy texture. Geologically considered, the cretaceous system comprises a series of green and ferruginous sands, clays, marls, gray and white limestones; and these again are arranged under three leading groups—chalk, gault, and green sand. Thechalk—properly so called—is subdivided into the upper and lower,—containing in the upper numerous veins and nodules of flint, and varies in color through several intermediatehues, until, in its contact with trap, it assumes a deep red. Thegaultis an argillaceous deposit of stiff, dark blue clays, highly calcareous, and effervesces freely with acids. Thegreen sandis a triple alternation of sands, cherty limestone, and friable sandstone, with beds, in some places of ocher and Fuller’s earth. The whole series may be estimated at nearly two thousand feet in thickness, formed in a deep sea basin, the materials floating in very still waters, and aggregated successively through the combined influence of mechanical, chemical, and organic agencies.
Themechanicalinfluence is very apparent in the sands and marls, which are evidently the spoils of islands and continents, washed down by currents and floods of fresh water, and deposited over an ancient ocean bed. Thechemicalcomposition of the flints or concretionary nodules, which give such a remarkable character and appearance often to the chalk, is equally demonstrable; from fifty to a hundred beds of chalk, pure and beautifully white, will sometimes be seen alternating with as many bands of dark-colored flints, all regularly arranged as cannon-shot of all sizes on a floor, and presenting, for miles along the cliffs of the sea-shore, lines of beautifully defined fortifications. Theorganicagent is visible in the nucleus of these round masses, which consists of an animal or vegetable substance, as a coral, a shell, a piece of flustra, or sponge. The nodules assume various shapes, that seem to be molded according to the cavities of the matrix in which they are imbedded, but are actually the forms of the bodies or organic substances to which they are attached. The explanation given is, that a chemical attraction has taken place between the vegetable or animal remains, strewed abundantly through the waters, and the silicious matter held in solution. The silex in solution gradually incrusts, or incorporates with, the organized substance,—and thus were produced at once the flinty concretions and the wonderful petrifactions contained in them. Break any one of these nodular masses, and minute drops of moisture will, if immediately inspected, be seen to ooze out from its pores: thus clearly furnishing a proof of the state of solution in which it originally existed, and the watery menstruum in which it was produced.
The mineralogical history and arrangement of the chalk group of rocks are therefore in many respects very interesting. Thechalk overlies the wealden, which was a mere delta at the river’s mouth. The bed of the river suddenly disappears, and now there rests upon it a deep sea formation. How stupendous and overwhelming the forces of nature through all her operations! How vast her affluence and prodigality, which could so thoroughly alter all her exterior and interior arrangements, and fill the seas with this new matter.
II.The Organic Remainsdisplay the boundless profusion of animal life which prevailed during the cretaceous period. The wealden furnishes no grounds of comparison, as that is simply a local fresh water deposit, and consequently can furnish no test of the general condition of life upon the surface of the globe. But when we go back to the oolitic period we obtain a standard by which to measure the doings of nature in the interval, what new creations started into being, and what provisions were made for their subsistence. The state of the temperature cannot be determined, as the products, with the rarest possible exceptions, are wholly marine, and therefore affected by atmospheric influences in a very small degree. Neither can much be conjectured concerning the state of the land, as scarcely a fragment of true terrestrial life has been detected in the deposit; and yet, from the stillness and comparatively small dimensions of sea-basins into which the earthy ingredients were floated, the probability is that the land was both lofty and widely extended. One mammalian, and the remains of a solitary bird, and a meager sprinkling of vegetables, constitute the whole, and even dubious, amount of contributions from this department of nature. To Neptune, therefore, the palæontologist turns his undivided attention; and, comparing one period with another, he finds the following results:
The cretaceous deposits all liewithin the areaof the oolites. They areconformablegenerally in position, and display, in proportion to their extent, a like superabundance of calcareous earth. Hence a return to polyp and shelly types of life, which we find so characteristic and diversified in both epochs.
Thus of the first order, Amorphozoa, the oolitic age produced only one genus; in the cretaceous we find thirteen genera, in thelist Spongia, which is common to both. Of Zoophytes, there are twenty-three genera in the former, and seventeen in the latter—of which nine are common to both periods. The Echinodermata number eighteen in the oolite, and twenty-five in the chalk—five only common. The genus Foraminifera is entirely new in the latter formation, and consists of twelve ascertained genera, and nearly double the number of species. Of Annelida there are four genera in the oolite, and six in the chalk, in which the new order of Cirrhipeda occurs likewise. The Astacus is the only crustacean in the oolitic group: this and three new genera are found in the chalk. The Conchifera are very numerous in both deposits; forty-six in the older, and thirty-eight genera in the newer, of which eight are peculiar to the chalk. Monymaria are nearly in the same relative proportions.Rudistesoccurs, as a new order, for the first time in the chalk, while again the Brachiopods, Gasteropods, and Cephalopods, are about equally abundant in both formations, with additions in the chalk to the generic models. And here too the new order Pteropoda, of a single genus and species, is introduced to our contemplation. Ammonites and Belemnites do not pass this age.
1. Pecten quinque-costatus.2. Plagiostoma Spinosum.3. Hamites intermedius.4. Spatangus cor-anguinum.5. Galerites albogalerus.6. Scaphites Striatus.7. Belemnites mucronatus.
1. Pecten quinque-costatus.2. Plagiostoma Spinosum.3. Hamites intermedius.4. Spatangus cor-anguinum.5. Galerites albogalerus.6. Scaphites Striatus.7. Belemnites mucronatus.
The fishes of the two periods are equally striking in their contrasts; the two orders of Ganoids and Placoids are common toboth, while the Ctenoids and Cycloids appear for the first time in the history of our planet, and which were afterward to contribute so largely to the sustenance and comforts of man. The Reptilians show a declension in the latter period in numbers, with the introduction, however, of four new genera—one of which (the Iguanodon Mantelli), is also found in the wealden.
The Cimoliornis Diomedeus, described by Professor Owen, is the only specimen of the order Aves or bird-tribe that as yet appears over this waste of waters. The termcimoliornismeans simply the chalk-bird, and is allied, in some of its osseous processes, to the albatross, but also differs in too many points to be regarded as the ancestor of that courageous storm-braving animal. The claims of this fossil, indeed, to its true place in the system, have not yet been fully established. “Of the few actually fossilized remains of birds,” says Professor Owen, “that have been discovered in England, the most complete and characteristic are those from the London clay. Some fragmentary Ornitholites have been discovered in the older pliocene crag, and in the newer pliocene fresh water deposits and bone caves. Extremely scanty have hitherto been the recognizable remains of birds from the chalk formations. The fossil from the wealden, which I formerly believed, with Cuvier and Dr. Mantell, to belong to a wading bird, I have since adduced reasons for referring to the extinct genus of flying reptiles called Pterodactyle.” The fossil bones of the Cimoliornis were obtained by the Earl of Enniskillen from the chalk beds near Maidstone, and resemble the humerus of the albatross in form, proportions and size; there are no distinct traces of the attachments of the quill-feathers in any of the fragments; but in other points there are analogies to the osseous structure of birds; and there are bones so gigantic as will assign them a place, if the proofs are completed, among the enormous foot-print class of the permian age, and go almost to realize the fabulous “roc” of the Arabian romance.
Our attention in this group of deposits, however, is riveted more by the little than the great—by the microscopic than the gigantic forms of life. It is astounding, indeed, to contemplate the myriads of creatures which swarmed in the seas during this period. A fragment of chalk, the size of a garden pea, containsthousands of perfect shells; these shells inclose still, in many instances, the pulpy animal matter; and consist of a series of distinct well-defined chambers. In a cubic inch of the rock it is calculated that there are upward of a million of infusorial animalcules. Yet their orders are determined, their genera fixed, their very species are described, so perfect is the structure, and so thoroughly preserved all the parts of their minute shelly coverlets. The microscope has restored, under the action of certain dilute acids, the contour and shape of entire hosts of these creatures. Some specimens, so positively can it speak of them, appear to consist of tubes placed edgewise,—one projecting sometimes beyond another. Others are seen to possess a series of tubular organs placed parallel, and disposed in long lines of fragile reticulated riband. Some are oblong figures. Others are complicated, exhibiting numerous projecting processes, and of every variety of shape. Some resemble the shell of the nautilus; others are still detected with the skin adhering to the skeleton; while in the stomachs and digestive sacs of others the more minute infusoria, which the diminutive monster had swallowed, are made palpable to the sight.
All this may be called trifling, a misapplication of talent, a waste of ingenuity. What terms too grand to describe the lofty speculations of the astronomer, who points his telescope to some dark point in the blue sky, and descries in its infinite depths a cluster of closely aggregated shining particles, minute as the motes in the sunbeam, and hails it as the discovery of a new system of worlds. He cannot count them, for they are innumerable. He cannot measure them, for they have no dimensions. He cannot tell their relations, nor describe their orbits of motion, for a sparkling heap of star-dust is all that flits before the reflector. But the boundaries of knowledge are enlarged, and though man nor any of the arts may ever be benefited thereby, the fortunate discoverer will have his name inscribed in that distant region of the universe, and transmitted from generation to generation with increasing luster.
The discoveries of the geologist may be inferior in grandeur, but are they practically less illustrative in their bearings on existing arrangements? He sees the past in the present, the near andthe distant in time brought together. A charm is thereby thrown over studies and speculations which would otherwise be useless. Thus, in the mineral structures resulting from the agencies of these invisible organic bodies, the mind is struck with the resemblance to similar processes that may be now going forward in the ocean: it sees in the discoloration of the waves, as the voyager steers his vessel over the main, a light by which to decipher the story of an age; and, while no voice issues from the countless myriads of animals which thicken the waters, rocks are elaborating and depositions made that will yet be raised into islands or continents. “On the coast of Chili, a few leagues north of Conception, the Beagle,” says Dr. Darwin, “one day passed through great bands of muddy water, which, when taken up in a glass, was found to be slightly stained as if by red dust, and after leaving it for some time quiet, a cloud collected at the bottom. With a lens of one-fourth of an inch focal distance, small hyaline points could be seen, darting about with great rapidity, and frequently exploding. Examined with a much higher power, their shape was found to be oval, and contracted by a ring round the middle, from which line curved little setæ proceeded on all sides; and these were the organs of motion. The animals move with the narrow apex forward, by the aid of their vibratory cilia, and generally by rapid starts. Their numbers were infinite, and in one day we passed through two spaces of water thus stained, one of which alone must have extended over several square miles. The color of the water, as seen at some distance, was like that of a river which has flowed through a red clay district; but under the shade of the vessel’s side, it was quite as dark as chocolate.”
These are the foundation-builders of future islands, of the very color and size, it may be, as those which piled up these masses of the brick-red chalk. In an ounce of sea-sand, from three to four millions of these minute bodies have been enumerated. Twenty-two thousand can be placed side by side on a linear inch of surface. One single individual, in the course of a month in summer, will produce as many as 800,000,000. In a globule of water, a cubic inch contains more inhabitants than are now existing of the human family on the face of the globe. The skeletons of the animalcula are transported through the air in the form of a fineimpalpable dust, covering the decks of vessels, and darkening the atmosphere many hundred miles distant at sea. The eye can trace nothing of structure—not even of granular form—and while clothes, rigging, and every crevice is filled and discolored with the organic nebulæ, it is not until the highest microscopic powers are applied, that it becomes resolvable and demonstrated to be a system of living creatures, moving through space, and fulfilling their destiny!
The views of nature thus opened up are boundless and infinite, in either terms of the scale, ascending or descending. The immensity of things on the one side, and their minuteness on the other, carry them equally beyond the reach of direct observation, and the intervention of means must in both cases be provided, ere they can become the subjects of human perception and examination. But what is it to me, some will reason, if there lie within the depths of space myriads of rolling worlds, when I see them not, and whose revolutions can in no way affect my condition on earth? These rocks around are but obstacles in my way, or stones for which I have no regard, as I can apply them to no useful purpose. I know that every blade of grass, every leaf in the forest, every drop of water, every grain of sand, teem with living creatures. And, in the air I breathe, systems more, beyond the ken of human view “both when we wake and when we sleep,” revel in the irresponsible enjoyment of sentient existence. Science, viewed in this light, and calculated upon the rule of mere statistical enumeration, may be reckoned as utterly valueless, and knowledge as but a term forMaterialism.
But neither astronomy nor geology will permit our speculations thus to terminate. A principle of causation is involved in both, and to trace this through a chain of sequences and effects, whether in the great or little, in the remote or near, is the one grand aim of philosophy. If I can perceive no bounds to the vast expanse in which natural causes operate, and can fix no border or termination of the universe; and if I am equally at a loss to discern things in their elements, and to discover the limits which terminate the subdivisions of organic matter, my inquiries will not here cease. The mind will not be satisfied so to close and to shutup the thesis propounded. I am compelled to advance onward, even as the objects recede from the view, or expand in magnitude beyond the grasp of comprehension. The soul is filled with the idea of immensity, as it familiarizes itself to the thought of the highest mountains of the earth being but specks on its surface—the terraqueous globe as an atom compared with the sun—the sun itself dwindling to a star from some point in the distant fields of space—and even all the systems that sparkle in the clearest sky only as faint streaks of light, or not discernible even for millions of years after their creation, in the systems that replenish and shine in the still remoter void. Speculations, lofty as these, do leave something behind—something nobler than arithmetical calculation—and knowledge becomesspiritualizedby them.
The same result follows, when we descend in the scale of nature toward the other limit, when we perceive a like gradation from minute bodies to others incomprehensibly more minute, and are led as far below sensible measures of perception, as we were before carried beyond them, until vision is lost in utter vacuity and obliteration of all organic form. But the more attenuated and fragile the structure, the more the manifestation of Omnipotence and superintending care. If from microscopical observation we discover animals, thousands of which scarce form an atom perceptible to unassisted sense—each of which are endowed with a system of vessels, and fluids circulating in those vessels—if we can trace the propagation, nourishment, and growth of these animals—observe their motions, capacities of action, limits and conditions of existence—all this through countless millions and multiplications of tribes and generations—and, finally, after their term of being ended, now find them entombed in rocks, and elaborated into useful minerals;—knowledge thus pursued becomes again the handmaid ofreligion, and terminates in the conviction, that we live in a universe over which the eye of Omniscience and love has been ever wakeful and predominant. The telescope leads to one verge of infinity, the microscope brings us to another; and in the discoveries of both there is the firmest assurance, that as nothing is too distant and vast for the Creator’s control, so nothing is too minute for His wise and fatherly care.