Geological epoch

“ Many persons, even among scientific men, who have not given much attention to the question, look upon the whole subject of the glacial epoch as a geological theory made to explain certain phenomena which are otherwise a puzzle ”

“ Though this epoch is incredibly more remote than any historical record, it is perhaps not incomparable with the duration of the human race; while compared with the vast lapse of geological time, such periods seem trivial and insignificant. Geologists have long ago repudiated mere thousands of years; they now claim millions, and many millions of years, for the performance of geological phenomena. ”

“ It cannot be too frequently stated, nor too prominently kept in view, that, although gaps occur in the succession of organic remains as recorded in the rocks, they do not warrant the conclusion that any such blank intervals ever interrupted the progress of plant and animal life upon the globe. There is every reason to believe that the march of life has been unbroken, onward and upward. Geological history, therefore, if its records in the stratified formations were perfect, ought to show a blending and gradation of epoch with epoch. ”

“ Even on this assumption we have at least 90,000,000 years as a minimum duration of geological time.
Age of the earth as determined by the date of the glacial epoch.—Professor A. Winchell, by a most careful examination of the probable relative lengths of geological periods, arrived at the conclusion that the time which elapsed since the beginning of the glacial epoch is to the time which has elapsed since the solidification of the earth’s surface as 1 to 250. [55] According to the eccentricity theory of the cause of the glacial epoch, that epoch began 240,000 years ago ”

“ In this discovery of organic remains in the primary rocks, we hail with joy the dawn of a new epoch in the critical history of these earlier formations. Already in its light, the primeval geological time is seen to be everywhere animated, and peopled with new animal forms of whose very existence we had previously no suspicion. Life, which had hitherto been supposed to have first appeared in the Primordial division of the Silurian period, is now seen to be immeasurably lengthened beyond its former limit, and to embrace in its domain the most ancient known portions of the earth's crust. ”

“ The terms used for the more important divisions of geological time are, in descending order of magnitude, era, period, epoch, age or stage, and the general scheme of the eras and periods, which is in almost uniform use throughout the world, is given in the table, which is arranged so as to give the succession graphically, with the most ancient rocks at the bottom and the latest at the top. ”

“ The publication of 'The Principles of Geology,' in 1830, constituted an epoch in geological science. But it also constituted an epoch in the modern history of the doctrines of evolution, by raising in the mind of every intelligent reader this question: If natural causation is competent to account for the not-living part of our globe, why should it not account for the living part? ”

“ Date of Last Glacial Epoch and its Bearing on the Measurement of Geological Time.—Directly we go back from this stable period we come upon changes both in the forms and in the distribution of species; and when we pass beyond the last glacial epoch into the Pliocene period we find ourselves in a comparatively new world, surrounded by a considerable number of species altogether different from any which now exist, together with many others which, though still living, now inhabit distant regions. ”

“ If changes of any sort which interrupt the continuity of geological processes intervened between successive maxima of advance of the ice, the separation of the later advance from the earlier, as a distinct ice epoch, would be favored. How great the intervening changes should be in order to constitute the re-advance a distinct ice epoch, is a point concerning which there might be difference of opinion. ”

“ If the existing Classes, Orders, and Families of Marine and terrestrial Articulated animals have thus pervaded various geological epochs, since life began upon our planet, we may infer that the state of the Land and Waters, and also of the Atmosphere, during all these Epochs, was not so widely different from their actual condition as many geologists have supposed. ”

“ The circumstances which help to define our notions of the time elapsed in the formation of the crust of the globe,—to translate, as it were, the symbolical notation of the geological scale of time into intelligible periods, having relation to the duration of the human race,—are various, and all concur in impressing the mind of a candid reasoner with ever growing convictions of the immense antiquity of the globe ”

“ As to the cosmical nature of the periods, while some geologists appear to regard the whole of geological time as a continuous evolution without any breaks, it is evidently more in accordance with facts to hold that there have been cycles of repose and activity succeeding each other, and that these have been of different grades. ”

“ Over against this marvel of a mild climate, luxuriant vegetation, and nearly equal days and nights within the Polar Circle, we may set that other wonder of the glacial or ice age—the time when the polar cold wandered beyond its bounds and came down into the temperate zone to stay, for how long we cannot tell; for very long indeed, no doubt, though not for as long as a world-building epoch. The Glacial age was only a portion of the age that came just before the human period. ”

“ The conditions of life must have been greatly modified by these geographical changes. The life-forms bear testimony to this changed condition. Old forms die away, and are succeeded by those approaching more nearly our own times. The name of this period is the Mesozoic time, or the period of middle life forms.14 It is instructive to notice the steady advance in the type of life, both animal and vegetable. The abundant flowerless vegetation of the coal formation of the preceding epoch dwindles away. ”

“ The fossil remains of the Tertiary rocks, both animal and vegetable, present us with many instances of this kind.
The discussion of the distribution of animals and plants, when carried on in the light of geology, raises many interesting questions as to time, which we have already glanced at, but which deserve a little more attention. As to the vast duration of geological time all geologists are agreed. It is, however, now well understood that science sets certain limits to the time at our disposal. ”

“ Every rock beneath our feet has its story of change to tell us. Mountains, valleys, and plains, continents and islands, have passed through vicissitudes innumerable, and bear within them the evidence of a gradual development or evolution. Looking back through the vista of the past one sees the dry lands gradually separating from the ocean, and gathering together into continental masses according to a definite plan. It is this slow growth, this august evolution, carried on through countless æons, which most impresses the student of physical geology. ”

“ Hence, trifling as the results during a human life may appear, if we realize the multiplying influence of time we are led to perceive that the apparently feeble superficial agents can, in the course of ages, achieve stupendous transformations in the aspect of the land. If this efficacy may be deduced from what can be seen to be in progress now, it may not less convincingly be shown, from the nature of the sedimentary rocks of the earth’s crust, to have been in progress from the early beginnings of geological history. ”

“ Can you measure either of those intervals in the years of common chronology? Yet all over the world the succession of geological strata proclaims the recurrence over and over again of such intervals; silent, indeed, as to positive evidence, but widening the possible limits of time’s duration to the furthest stretch of fancy.
All our great continents have been ever so many times, either in the mass or piecemeal, under the waves of the ocean. Nothing hinders that the bed of every great ocean should have been ever so many times turned into dry land. ”

“ If glacial epochs in temperate lands and mild climates near the poles have, as now believed by men of eminence, occurred several times over in the past history of the earth, the effects of such great and repeated changes, both on the migration, modification, and extinction, of species, must have been of overwhelming importance—of more importance perhaps than even the geological changes of sea and land. ”

“ INTRODUCTION The following study is an attempt to reconstruct in some detail the sequence of climatic changes through which the world passed during that important stage of its geological history which is variously known as the Ice Age or Glacial Period, the Pleistocene, the Quaternary, or the Human Period. That time saw the growth of humanity from a primitive stage but little removed from the higher animals to the beginnings of a complicated civilization, and it saw that human life spread from its cradle or cradles to the ends of the earth ”

“ Careful investigation has convinced geologists that all the existing great chains owe their origin to a series of earth movements which occurred in the period called Tertiary, that is, in the third of the great geological periods, the one immediately preceding that in which we live. ”

“ The records of the Glacial epoch are so plain and full that we are compelled to believe what otherwise would seem almost incredible, —that following the mild climate of the Tertiary came a succession of ages when ice fields, like that of Greenland, shrouded the northern parts of North America and Europe and extended far into temperate latitudes. ”

“ One of the first questions meeting us is that which relates to the point in geological time signalised by the advent of our species. In the Eocene period our continents were being gradually raised out of the ocean, and were still in great part under the waters, which several times returned upon the land, and seemed ready again to engulf it. In this period not only have we no traces of man, but all the higher animals of that age are now extinct. ”

“ It is enough, from our present point of view, to be assured that the main features of the country were chalked out, as it were, at a very distant geological period, and that all the infinite variety in the relief of our land has been brought about directly, not by titanic convulsions and earth-movements, but by the long-continued working of rain and rivers—of frost and snow and ice, supplemented from time to time by the action of the sea. ”

“ For certainly on my theory such strata must somewhere have been deposited at these ancient and utterly unknown epochs in the world's history.
I can answer these questions and grave objections only on the supposition that the geological record is far more imperfect than most geologists believe. It cannot be objected that there has not been time sufficient for any amount of organic change; for the lapse of time has been so great as to be utterly inappreciable by the human intellect. ”

“ Dane’s “Manual of Geology,” p. 538. Wright’s “Studies in Science and Religion,” p. 308. “Men of the Drift,” p. 71. Geikie’s “Great Ice Age,” p. 93. “Men of the River Drift.” Abbott’s “Primitive Industry,” p. 545; Quoted from “Geology of Minnesota.” Report, 1877, p. 37. Geikie’s “Great Ice Age,” p. 97. The astronomical theory, which we will first examine, was first enunciated by Mr. Croll, following a suggestion of the astronomer Adhemer. Mr. Croll’s views were set forth in many able papers, and finally gathered into a volume entitled “Climate and Time in their Geological Relation.” ”

“ If we reflect on the long series of events of the post-pliocene and recent periods contemplated in this chapter, it will be remarked that the time assigned to the first appearance of man, so far as our geological inquiries have yet gone, is extremely modern in relation to the age of the existing fauna and flora, or even to the time when most of the living species of animals and plants attained their actual geographical distribution. ”

“ In the first place, we fully admit that the extreme 283 Antiquity of the Earth is a necessary consequence of our theory. Setting out from the present stage of the world’s existence, Geology carries us back from epoch to epoch, through a long succession of ages, each extending over many thousand years, until the mind is lost in the seeming infinity of the past. It may be asked, perhaps, in what way Geology can testify to the great length of each successive period in the history of the Globe. ”

“ Yet that time must have been a fact not less possible of verification than that geological period when “the earth was absorbed in producing the carboniferous vegetation which still supplies us with the means of warmth, light, and life, accumulating during enormous periods of time small deposits of organic matter forming the strata of the globe on which we live. ”

“ The backbone of our present system of determining the series of pre-historic epochs is the geological theory of an ice-age comprising a succession of periods of extreme glaciation punctuated by milder intervals. It is for the geologists to settle in their own way, unless, indeed, the astronomers can help them, why there should have been an ice-age at all ”

“ In our own day the geographical conditions are such that, were eccentricity to attain a high value, the climate of the Pleistocene would be reproduced, and our hemisphere would experience a succession of alternating cold and genial epochs. ”

“ As the outer layers of the globe cooled, and the disturbances due to internal heat and chemical action became less marked, the conditions would arise in which the materials for geological history were accumulated. The influence of the sun, which must always have operated, would then stand out more clearly, giving rise to that wide circle of superficial changes wherein variations of temperature and the circulation of air and water over the surface of the earth come into play. ”