Читать книгу Walks and Talks in the Geological Field - Alexander Winchell - Страница 29

Every one has noticed the curious forms found in the Drift, which so much resemble shells and corals, and buttons or beads. Often they lie loose in the soil; and often we see them imbedded in fragments of limestones and sandstones which are sometimes bowlders transported from a distance, and sometimes fragments derived from a neighboring ledge or outcrop of stratified rocks. In the cliffs at Panama are occasional traces of shells, both bivalve and univalve. The latter is a little shell three-quarters of an inch in diameter, and closely coiled almost in a plane, like a watch spring. I have been amused to hear some of these forms like bivalve shells called “petrified butterflies.” Through western New York, Ontario, Michigan, Ohio, and Indiana we find in the Drift innumerable masses popularly known as “petrified honey-comb,” and “petrified wasp-nest.” There are also quantities of little flat discs like “buttons,” each with radiating striæ or other decorations, and having a hole in the middle, as if intended to be strung like beads. These have sometimes been styled “St. Cuthbert’s beads.”

These curious forms, so much like animal structures, were wondered over, hundreds of years ago. Very few persons would then entertain the suggestion that they are real relics of living things. They indeed bear the similitudes of marine creatures; but such they can not be, it was argued, because they lie hundreds of feet above the sea. Some of the early Italian writers attributed them to “the influence of the stars;” but Leonardo da Vinci demanded “where, in the hills, are the stars now forming shells of distinct ages and species? And how can the stars explain the origin of gravel, occurring at different heights, and composed of pebbles rounded as if by the motion of running water?” Others attributed these forms to the influence of a “plastic force” in nature. Agricola, a German miner, conceived the notion that a “certain fatty matter, set into fermentation by heat, gave birth to fossil organic shapes;” Fallopio thought that petrified shells were generated by fermentation in the spots where they are found; or that they had, in some cases, acquired their form from the “tumultuous movements of terrestrial exhalations.” Olivi thought fossils were mere “sports of nature,” and some indulged in the amusing fancy that they were “prototypes” or “models” after which the Creator subsequently fashioned the living creatures of the sea; and others held that they were “created” just as we find them. The last opinion I have heard dogmatically asserted in America; and probably it still survives.

When it became impossible to resist the evidence that these forms were relics of the sea, the theory obtained a foothold that, as the deluge of Noah had inundated the lands, these forms must be the relics of that recognized universal submergence. It required a century and a half to argue down this error; and, meantime, the geologists who did not subscribe to it, fell under the accusation of “disbelieving the whole of the Sacred writings.”

Thus, in our day, we stand at the outcome of a contest of three hundred years; and, instead of battling against these old errors, we find ourselves in a position to push on to new discoveries.

That the sea has covered the land, and that shore lines have greatly changed, was taught by Pythagoras, and afterward by Strabo and Pliny; but these views were almost forgotten. Many Arabian writers have left on record views and opinions on many subjects, quite in advance of their European, contemporaries. On this subject we find an entertaining revelation of opinion by Mohammed Kazwini, of the seventh century of the Hegira—the close of the thirteenth century of our era. It is given as the narrative of Kidhz, an allegorical personage:

“I passed one day by a very ancient, and wonderfully populous city, and asked one of its inhabitants how long it had been founded. ‘It is indeed a mighty city,’ replied he, ‘we know not how long it has existed, and our ancestors were, on this subject, as ignorant as ourselves.’ Five centuries afterwards, as I passed by the same place, I could not perceive the slightest vestige of the city. I demanded of a peasant who was gathering herbs upon its former site, how long it had been destroyed. ‘In sooth a strange question,’ replied he, ‘the ground here has never been different from what you now behold it.’ ‘Was there not of old,’ said I, ‘a splendid city here?’ ‘Never,’ he answered, ‘so far as we have seen, and never did our fathers speak to us of any such.’ On my return there five hundred years afterwards, I found the sea in the same place, and on its shores were a party of fishermen, of whom I inquired how long the land had been covered by the waters. ‘Is this a question,’ said they, ‘for a man like you? This spot has always been what it is now.’ I again returned five hundred years afterwards, and the sea had disappeared. I inquired of a man who stood alone upon the spot, how long ago this change had taken place; and he gave me the same answer as I had received before. Lastly, on coming back again, after an equal lapse of time, I found there a flourishing city, more populous and more rich in beautiful buildings than the city I had seen the first time; and when I would fain have informed myself concerning its origin, the inhabitants answered me, ‘Its rise is lost in remote antiquity; we are ignorant how long it has existed, and our fathers were on this subject as ignorant as ourselves.’”

This allegory sets forth the nature of the modern scientific conception of changes in relative positions of land and sea. It must not, however, be understood that continents ever occupied the sites of the modern oceans; though these oceans once extended over all the lands.

Thus these strata of sandstone, limestone, and shale are real ancient sea-sediments, as we have already argued; and these forms of life imbedded in the strata are the relics of the animals which dwelt in the sea while the sediments were accumulating. If so long a time as we have concluded was required for the deposition of these materials, then, assuredly, the one hundred and fifty days of the Noachian inundation were egregiously inadequate.

Moreover, if we subject these relics to critical examination, we discover that their resemblance to living forms is in fundamental characters only. As to particular species, we find none, save in peculiar situations, which are identical with living species. We find them less like living species than the leopard is like the tiger, or the hen-hawk like the snowy owl. To maintain, as the old theologians did, that modern species are descended from species whose relics are fossilized in the rocks, is to advocate a theory of transformation which would have been startling, if they could have appreciated the facts. Modern evolution, which maintains such a descent, allows millions of years for the accomplishment of the transmutations; but the diluvialists never claimed over five thousand years, and resented the offer of geology to place more time at their disposal.

If the relics buried in the rocks present undoubted divergences from living forms, it must be because they lived in other ages, and under different physical conditions from modern species. As there is now, so there must always have been, some co-ordination or suitability between the conditions in which species lived, and the structures, instincts, and capabilities of the species. We are witnesses of this great principle—the adaptation of organism to environment. The Hippopotamus and the Elephant, dwellers in warm climates, are almost naked. The White Bear and the Arctic Fox, dwellers in the frigid zone, are densely clad in fur. The Duck is impelled by its instinct to the water; so its feet are webbed to adapt it to movement in the water. These co-ordinations of structure to environment or surroundings, are everywhere seen, and possess extreme interest. Let me ask you, my reader, to study out a great many other examples.

Now, during the long history of rock-accumulation, there must have taken place very great changes in the conditions of the world. This may be inferred from the fact that some changes are taking place before our eyes; and also from the fact, which we must admit, that the ocean was once universal, but is now interrupted by wide continental expanses which deflect the winds and the currents of the sea, and modify the climates of many regions. It might thus be inferred beforehand, that the populations of the world have shown a correspondence with the changing conditions of the world. If the physical world has improved—if it has undergone a progression from some cruder condition to the present, then the populations of the world have progressively improved; and we shall find the records of this improvement in the fossil remains of those populations, as we hunt for them in strata farther and farther from the surface—that is, farther and farther removed in their origin from the present time.

Now, with this preparation of mind, permit me to state what has been ascertained by studying the fossils imbedded in the succession of strata. The deepest rocks of which we have any knowledge are those already named Eozoic. They are mostly hard and crystalline—such as we find in our innumerable bowlders. They were stratified originally, nevertheless; they were marine sediments, and if any marine creatures lived at the time, their relics were inclosed in the sediments. But you see how greatly the sediments have been changed to make of them granites and gneisses. If the change almost or completely obliterated the lines of bedding, it must also have destroyed most traces of the included fossils. As a fact, almost no fossil remains are found. Yet a few have been preserved to us. I do not intend to describe them at present; but you may learn that they belong to the very lowest grade of animal life. The ages during which they existed may be styled the Reign of Protozoans.

The strata next above, in the lower part of the Palæozoic Great System, abound in the remains of marine animals; but no traces of fishes or other vertebrates have been found. This was the Reign of Marine Invertebrates. Their exclusive remains extend through two systems, Cambrian and Silurian. In the next higher formations we detect the bones and teeth and armor-plates of fishes. There were many invertebrates also, but, as the fishes were dominant in rank and prowess, we designate this age the Reign of Fishes. The strata deposited during this Reign form the Devonian System. Next came the relics of the first air-breathers which ever lived. We find their bones resembling those of modern salamanders or amphibians, though often much more powerful. This was the Reign of Amphibians; and the corresponding strata are the Carboniferous System. The Cambrian, Silurian, Devonian, and Carboniferous systems make up the Palæozoic Great System.

Next, as stated in our last Talk, come the strata which form the Mesozoic Great System. Through this, in addition to relics of amphibians, fishes, and invertebrates, we find for the first time the bones and teeth of reptiles. These creatures offer extraordinary interest for us, and we shall take up the study of them in due time. Their empire is known as the Reign of Reptiles. Following this was the Reign of Mammals, since their bones are found distributed through the Cænozoic Great System of strata. Lastly came man. His bones and works are confined to the surface of the earth. They are not found imbedded in solid rocks. This last and highest animal characterizes the Reign of Man. This is a grand progression. These are fundamental conceptions in geological science. They must be made perfectly familiar to the student of Natural history.

As the reader will desire frequently to refer to this classification of formations and of organic history and geological time, I insert the facts in a Table: