Geological period

“ This period, long as it appears, is very short as compared with the myriads of ages of geological development that preceded it, and represents only the last and the shortest of the geological periods. The question arises, How has the human race been able to spread itself over the whole surface of the globe? Is it the product of different and independent origins in the several continents, or have all men sprung from a common cradle, a "mother-region"? ”

“ AT the end of that long course of geological ages, from the Archæan to the Tertiary, which built up the solid portions of the earth in their present configuration, geologists now universally recognize, in the evidence before them, the presence of a remarkable and stupendous period—a period so startling that it might justly be accepted with hesitation ”

“ It is quite significant that each geological era, occasionally a geological period, has its characteristic grouping of life developed from the life of preceding periods. As we climb higher in the geological column, life becomes more and more complex and specialized. ”

“ When we inquire what information geology affords respecting the period under consideration, the answer may be full and explicit. Geological discovery has carried us back to an epoch corresponding with the beginning of this day, and has disclosed a long and varied series of living beings, extending from this early period up to the introduction of the higher races of animals. ”

“ Such effects, though attributable mainly to man, are produced in some degree by all other animals.
Besides these general effects, it is the existence of organic forms that has conferred on all the sedimentary rocks their fossiliferous character. The records of the climate of each geological period, of the physical geography, of the vegetable productions, and of the animal forms by which the earth was peopled, consist in the remains of the living beings of these several periods, imbedded in the contemporaneous rock formations. ”

“ To see how, following a definite plan, the vast continents have grown to their present size and form; to see how animal and vegetable life have evolved successively higher and higher forms; to see where in this wondrous drama of creation, this strange unfolding of life, the first faint, indecisive traces of man’s presence are to be found; to learn what great changes in climate, in Geogony, and in life, had occurred before man’s appearance, let us pass in brief review the history of early geological periods. ”

“ To this day the fundamental principle guiding our identification of geological formations in different ages rests upon the assumption that each period has had one character throughout; whereas the progress of geology is daily pressing upon us the evidence that at each period different latitudes and different continents have always had their characteristic animals and plants, if not as diversified as now, at least varied enough to exclude the idea of uniformity. ”

“ Thus, for example, if a certain mineral occurs as a primary constituent of a rock of remote geological period, it can safely be assumed that its age is greater than that of a similar or different mineral occurring in a later formation. ”

“ On the three principal tests of relative age — superposition, mineral character, and fossils — Change of mineral character and fossils in the same continuous formation — Proofs that distinct species of animals and plants have lived at successive periods — Distinct provinces of indigenous species — Great extent of single provinces — Similar laws prevailed at successive geological periods — Relative importance of mineral and palæontological characters — Test of age by included fragments — Frequent absence of strata of intervening periods — Principal groups of strata in western Europe. ”

“ These rocks contain the fossiliferous and organic remains of the early and primitive inhabitants of the earth, and indicate the order of man's moral and intellectual development; for as each successive layer or stratum of fossiliferous rocks, in which the organic remains of man are found, marks a distinct period in his history, and the growth of his moral and intellectual brain is found in all cases to correspond to the age and growth of these strata, the question is thus settled and demonstrate! by the facts of geological science. ”

“ With the rise of the land out of the Glacial sea indications of man are believed to appear, along with remains of several mammalian species now his contemporaries. Archæology and geology thus meet somewhere in the pre-historic period of the former, and in the Post-glacial of the latter. Wherever, therefore, human history extends farthest back, and geological formations of the most modern periods exist and have been explored, we may expect best to define their junctions. ”

“ 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. ”

“ I did not, at the time, fully appreciate the deep conviction which it displays of the slow manner in which geological changes have taken place, and the insignificance of thirty or forty centuries in the history of a species, and that, too, at a period when very narrow views were entertained of the extent of past time by most of the ablest geologists, and when great revolutions of the earth's crust, and its inhabitants, were generally attributed to sudden and violent catastrophes. ”

“ Each of these facts carries us back to a period immeasurably anterior to the creation of man, as the epoch when the sedimentary deposits commenced. There are no facts in geology which point to a different conclusion. It is of the utmost importance to the geological student to familiarize himself with this principle. It will assist him in comprehending the greatness of geological changes, and in applying other principles in explanation of geological phenomena. ”

“ Computation of the Average Annual Amount of Subaërial Denudation.—The geology of the district above alluded to may assist our imagination in conceiving the extent to which groups of ancient rocks, each of which may in their turn have formed continents and oceanic basins, have been disturbed, folded, and denuded even in the course of a few out of many of those geological periods to which our imperfect records relate. It is not easy for us to overestimate the effects which causes in every day action must produce when the multiplying power of time is taken into account. ”

“ But while thus culling freely from the dominions of other sciences, geology claims as its peculiar territory the rocky framework of the globe. In the materials composing that framework, their composition and arrangement, the processes of their formation, the changes which they have undergone, and the terrestrial revolutions to which they bear witness, lie the main data of geological history. It is the task of the geologist to group these elements in such a way that they may be made to yield up their evidence as to the march of events in the evolution of the planet. ”

“ For what geology properly investigates is the antiquities of this terrestrial planet, and the primal condition of the mountain ranges, observing and seeking to read the long-hidden memorials that are daily brought to light of pristine convulsions, and to number the successive epochs of gradual change and decay. But it was not at once that geological science made any progress beyond the mere acquaintance with the surface of our globe. ”

“ 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. ”

“ The geologist is now prepared to read the physical history—the geographical development—of any country or of any continent by means of its formations, when he has given each formation its true place in the geological record as a time scale. ”

“ But both ends of the geological scale, comprising those ancient systems older than the Coal, and representative of periods in which, so far as is yet known, life, animal and vegetable, first began upon our planet, and those systems of comparatively modern date, representative of the periods which immediately preceded the human epoch, were equally unknown. ”

“ T THE problem of the origin of the earth is essentially astronomical rather than geological, because geological history is considered to have begun when common earth processes, such as erosion, deposition, and transportation of sediments, etc., were brought into play. ”

“ Our theoretical journey backward into the ages begins with the Recent or last-formed deposits—those which lie nearest the outer surface of our earth. The Recent or Quaternary period forms a division of the Tertiary period, that is, the latest of the three great epochs into which, for purposes of classifying fossil forms by their relative ages, the geologist divides the rock-formations. ”

“ In studying the periods of Palæolithic and Neolithic man we have stood on the borderland where Geology and Archæology meet. We have seen that vast geological changes have taken place since man appeared on earth. ”

“ This vast period of time, which includes the beginning, is known among geologists as Archean time.
From the close of this age, the history of life properly commences. It might be well to explain the means which the geologist uses to interpret the history of the globe. It is now understood that the forces of nature have always produced the same results as they do now. From the very earliest time to the present, rocks have been forming. ”

“ I should like to make a stay here for a day or so. Your work opens right into my hands. I cannot remember seeing a geological formation which interested me so much. Look at the face of that cutting, for instance. Why! you can almost read the history of the geological world from yesterday—this morning as it were—beginning with the super-surface on top and going right down through the different layers and stratas—through the vanished ages—right down and back to the pre-historical—to the very primeval or fundamental geological formations! ”

“ But I have been renewedly impressed with the opinion, so very opposite to the present geological theory, that less than seven thousand years is sufficient, on scientific principles, to account for all the phenomena of fossil plants, shells, bones and organic remains, as well as the displacements, disruptions, subsidences and rising of strata, and other evidences of extensive physical changes and disturbances on the earth’s surface. And I hope to live to see some American geologist build up a theory on just philosophical and scientific principles, which shall bear the test of truth. ”

“ When it was acknowledged on all hands that on geological grounds the age of the earth was certainly very great, many times the few thousand years hitherto relied on, it is not strange that popular thought swung to the other extreme, and hundreds of millions of years were thought necessary to explain the series of changes which the geologists unfolded. ”

“ It will be preferable to turn to the positive facts of paleontology, and to inquire what they tell us.
We are all accustomed to speak of the number and the extent of the changes in the living population of the globe during geological time as something enormous: and indeed they are so, if we regard only the negative differences which separate the older rocks from the more modern, and if we look upon specific and generic changes as great changes, which from one point of view, they truly are. ”

“ All the palæontological, no less than the geological and physical evidence, at present available, points to the great land masses of the Northern Hemisphere as being of immense antiquity, and as the area in which the higher forms of life were developed. ”

“ The younger science treats, it is true, of recent periods, when compared with the eras of geological computation, and of a race newer than any of those whose organic remains are classified in the systems into which the strata of the earth's crust have been grouped. ”

“ Although belonging to a posterior geological epoch, these hillocks of gravel and sand are thus the collected records of primeval times, attesting that mighty agencies have been at work in rending the globe, re-adjusting its materials, and preparing them for future combinations.
How speedily, in these first days of creation, does geology make us acquainted with the liability to change and mutation stamped upon all earthly things! The mountains are raised up, and their earliest struggles are to get down again. ”

“ Animal life has undergone continuous change since its introduction upon the earth, so that each group of strata, representing a particular geological age, contains a characteristic assemblage of fossil animals.
4. Many of the changes in the history of animals have been progressive or evolutionary, so that strata of early geological time contain distinctly more primitive or lower order forms than the strata of late geological time. But, while the line of evolution has been maintained without a break, culminating in man, there have been many offshoots of a retrogressive nature. ”

“ Now, as all historic records end, for each country, with the surface,—terminate at some point of man's history posterior to the preparation of that tract for his residence, we see how far more ancient than the historic date of the human race is the series of productions which lie below the surface. The limit of least antiquity of the scale of geological time is in every country beyond the date of the present surface. The series of strata is so ancient, that even its uppermost and newest term in every country is older than the race of man now existing there ”