Volume III Part 9 (1/2)
But to know even this is much--sufficient, indeed, to establish the chronological order of elevation, if not its exact period, for all parts of any continent that have been geologically explored--understanding always that there must be no scrupling about a lat.i.tude of a few millions or perhaps tens of millions of years here and there.
Regarding our own continent, for example, we learn through the researches of a mult.i.tude of workers that in the early day it was a mere archipelago. Its chief island--the backbone of the future continent--was a great V-shaped area surrounding what is now Hudson Bay, an area built tip, perhaps, through denudation of a yet more ancient polar continent, whose existence is only conjectured. To the southeast an island that is now the Adirondack Mountains, and another that is now the Jersey Highlands rose above the waste of waters, and far to the south stretched probably a line of islands now represented by the Blue Ridge Mountains.
Far off to the westward another line of islands foreshadowed our present Pacific border. A few minor islands in the interior completed the archipelago.
From this bare skeleton the continent grew, partly by the deposit of sediment from the denudation of the original islands (which once towered miles, perhaps, where now they rise thousands of feet), but largely also by the deposit of organic remains, especially in the interior sea, which teemed with life. In the Silurian ages, invertebrates--brachiopods and crinoids and cephalopods--were the dominant types. But very early--no one knows just when--there came fishes of many strange forms, some of the early ones enclosed in turtle-like sh.e.l.ls. Later yet, large s.p.a.ces within the interior sea having risen to the surface, great marshes or forests of strange types of vegetation grew and deposited their remains to form coal-beds. Many times over such forests were formed, only to be destroyed by the oscillations of the land surface. All told, the strata of this Paleozoic period aggregate several miles in thickness, and the time consumed in their formation stands to all later time up to the present, according to Professor Dana's estimate, as three to one.
Towards the close of this Paleozoic era the Appalachian Mountains were slowly upheaved in great convoluted folds, some of them probably reaching three or four miles above the sea-level, though the tooth of time has since gnawed them down to comparatively puny limits. The continental areas thus enlarged were peopled during the ensuing Mesozoic time with mult.i.tudes of strange reptiles, many of them gigantic in size.
The waters, too, still teeming with invertebrates and fishes, had their quota of reptilian monsters; and in the air were flying reptiles, some of which measured twenty-five feet from tip to tip of their batlike wings. During this era the Sierra Nevada Mountains rose. Near the eastern border of the forming continent the strata were perhaps now too thick and stiff to bend into mountain folds, for they were rent into great fissures, letting out floods of molten lava, remnants of which are still in evidence after ages of denudation, as the Palisades along the Hudson, and such elevations as Mount Holyoke in western Ma.s.sachusetts.
Still there remained a vast interior sea, which later on, in the tertiary age, was to be divided by the slow uprising of the land, which only yesterday--that is to say, a million, or three or five or ten million, years ago--became the Rocky Mountains. High and erect these young mountains stand to this day, their sharp angles and rocky contours vouching for their youth, in strange contrast with the shrunken forms of the old Adirondacks, Green Mountains, and Appalachians, whose lowered heads and rounded shoulders attest the weight of ages. In the vast lakes which still remained on either side of the Rocky range, tertiary strata were slowly formed to the ultimate depth of two or three miles, enclosing here and there those vertebrate remains which were to be exposed again to view by denudation when the land rose still higher, and then, in our own time, to tell so wonderful a story to the paleontologist.
Finally, the interior seas were filled, and the sh.o.r.e lines of the continent a.s.sumed nearly their present outline.
Then came the long winter of the glacial epoch--perhaps of a succession of glacial epochs. The ice sheet extended southward to about the fortieth parallel, driving some animals before it, and destroying those that were unable to migrate. At its fulness, the great ice ma.s.s lay almost a mile in depth over New England, as attested by the scratched and polished rock surfaces and deposited erratics in the White Mountains. Such a ma.s.s presses down with a weight of about one hundred and twenty-five tons to the square foot, according to Dr. Croll's estimate. It crushed and ground everything beneath it more or less, and in some regions planed off hilly surfaces into prairies. Creeping slowly forward, it carried all manner of debris with it. When it melted away its terminal moraine built up the nucleus of the land ma.s.ses now known as Long Island and Staten Island; other of its deposits formed the ”drumlins” about Boston famous as Bunker and Breed's hills; and it left a long, irregular line of ridges of ”till” or bowlder clay and scattered erratics clear across the country at about the lat.i.tude of New York city.
As the ice sheet slowly receded it left minor moraines all along its course. Sometimes its deposits dammed up river courses or inequalities in the surface, to form the lakes which everywhere abound over Northern territories. Some glacialists even hold the view first suggested by Ramsey, of the British Geological Survey, that the great glacial sheets scooped out the basins of many lakes, including the system that feeds the St. Lawrence. At all events, it left traces of its presence all along the line of its retreat, and its remnants exist to this day as mountain glaciers and the polar ice cap. Indeed, we live on the border of the last glacial epoch, for with the closing of this period the long geologic past merges into the present.
PAST, PRESENT, AND FUTURE
And the present, no less than the past, is a time of change. This is the thought which James Hutton conceived more than a century ago, but which his contemporaries and successors were so very slow to appreciate. Now, however, it has become axiomatic--one can hardly realize that it was ever doubted. Every new scientific truth, says Aga.s.siz, must pa.s.s through three stages--first, men say it is not true; then they declare it hostile to religion; finally, they a.s.sert that every one has known it always. Hutton's truth that natural law is changeless and eternal has reached this final stage. Nowhere now could you find a scientist who would dispute the truth of that text which Lyell, quoting from Playfair's Ill.u.s.trations of the Huttonian Theory, printed on the t.i.tle-page of his Principles: ”Amid all the revolutions of the globe the economy of Nature has been uniform, and her laws are the only things that have resisted the general movement. The rivers and the rocks, the seas and the continents, have been changed in all their parts; but the laws which direct those changes, and the rules to which they are subject, have remained invariably the same.”
But, on the other hand, Hutton and Playfair, and in particular Lyell, drew inferences from this principle which the modern physicist can by no means admit. To them it implied that the changes on the surface of the earth have always been the same in degree as well as in kind, and must so continue while present forces hold their sway. In other words, they thought of the world as a great perpetual-motion machine. But the modern physicist, given truer mechanical insight by the doctrines of the conservation and the dissipation of energy, will have none of that. Lord Kelvin, in particular, has urged that in the periods of our earth's in fancy and adolescence its developmental changes must have been, like those of any other infant organism, vastly more rapid and p.r.o.nounced than those of a later day; and to every clear thinker this truth also must now seem axiomatic.
Whoever thinks of the earth as a cooling globe can hardly doubt that its crust, when thinner, may have heaved under strain of the moon's tidal pull--whether or not that body was nearer--into great billows, daily rising and falling, like waves of the present seas vastly magnified.
Under stress of that same lateral pressure from contraction which now produces the slow depression of the Jersey coast, the slow rise of Sweden, the occasional belching of an insignificant volcano, the jetting of a geyser, or the trembling of an earthquake, once large areas were rent in twain, and vast floods of lava flowed over thousands of square miles of the earth's surface, perhaps, at a single jet; and, for aught we know to the contrary, gigantic mountains may have heaped up their contorted heads in cataclysms as spasmodic as even the most ardent catastrophist of the elder day of geology could have imagined.
The atmosphere of that early day, filled with vast volumes of carbon, oxygen, and other chemicals that have since been stored in beds of coal, limestone, and granites, may have worn down the rocks on the one hand and built up organic forms on the other, with a rapidity that would now seem hardly conceivable.
And yet while all these anomalous things went on, the same laws held sway that now are operative; and a true doctrine of uniformitarianism would make no unwonted concession in conceding them all--though most of the imbittered geological controversies of the middle of the nineteenth century were due to the failure of both parties to realize that simple fact.
And as of the past and present, so of the future. The same forces will continue to operate; and under operation of these unchanging forces each day will differ from every one that has preceded it. If it be true, as every physicist believes, that the earth is a cooling globe, then, whatever its present stage of refrigeration, the time must come when its surface contour will a.s.sume a rigidity of level not yet attained. Then, just as surely, the slow action of the elements will continue to wear away the land surfaces, particle by particle, and transport them to the ocean, as it does to-day, until, compensation no longer being afforded by the upheaval of the continents, the last foot of dry land will sink for the last time beneath the water, the last mountain-peak melting away, and our globe, lapsing like any other organism into its second childhood, will be on the surface--as presumably it was before the first continent rose--one vast ”waste of waters.” As puny man conceives time and things, an awful cycle will have lapsed; in the sweep of the cosmic life, a pulse-beat will have throbbed.
V. THE NEW SCIENCE OF METEOROLOGY
METEORITES
”An astonis.h.i.+ng miracle has just occurred in our district,” wrote M.
Marais, a worthy if undistinguished citizen of France, from his home at L'Aigle, under date of ”the 13th Floreal, year 11”--a date which outside of France would be interpreted as meaning May 3, 1803. This ”miracle”
was the appearance of a ”fireball” in broad daylight--”perhaps it was wildfire,” says the naive chronicle--which ”hung over the meadow,” being seen by many people, and then exploded with a loud sound, scattering thousands of stony fragments over the surface of a territory some miles in extent.
Such a ”miracle” could not have been announced at a more opportune time.
For some years the scientific world had been agog over the question whether such a form of lightning as that reported--appearing in a clear sky, and hurling literal thunderbolts--had real existence. Such cases had been reported often enough, it is true. The ”thunderbolts”
themselves were exhibited as sacred relics before many an altar, and those who doubted their authenticity had been chided as having ”an evil heart of unbelief.” But scientific scepticism had questioned the evidence, and late in the eighteenth century a consensus of opinion in the French Academy had declined to admit that such stones had been ”conveyed to the earth by lightning,” let alone any more miraculous agency.
In 1802, however, Edward Howard had read a paper before the Royal Society in which, after reviewing the evidence recently put forward, he had reached the conclusion that the fall of stones from the sky, sometimes or always accompanied by lightning, must be admitted as an actual phenomenon, however inexplicable. So now, when the great stone-fall at L'Aigle was announced, the French Academy made haste to send the brilliant young physicist Jean Baptiste Biot to investigate it, that the matter might, if possible, be set finally at rest.
The investigation was in all respects successful, and Biot's report transferred the stony or metallic lightning-bolt--the aerolite or meteorite--from the realm of tradition and conjecture to that of accepted science.