The Story of the Earth and Man

by Sir John William Dawson

In closing these sketches it may seem unsatisfactory not to link the geological ages with the modern period in which we live; yet, perhaps, nothing is more complicated or encompassed with greater difficulties or uncertainties. The geologist, emerging from the study of the older monuments of the earth’s history, and working with the methods of physical science, here meets face to face the archæologist and historian, who have been tracing back in the opposite direction, and with very different appliances, the stream of human history and tradition. In such circumstances conflicts may occur, or at least the two paths of inquiry may refuse to connect themselves without concessions unpleasant to the pursuers of one or both. Further, it is just at this meeting-place that the dim candle of traditional lore is almost burnt out in the hand of the antiquary, and that the geologist finds his monumental evidence becoming more scanty and less distinct. We cannot hope as yet to dispel all the shadows that haunt this obscure domain, but can at least point out some of the paths which traverse it. In attempting this, we may first classify the time involved as follows: (1) The earlier Post-pliocene period of geology may be called the Glacial era. It is that of a cold climate, accompanied by glaciation and boulder deposits. (2) The later Post-pliocene may be called the Post-glacial era. It is that of re-elevation of the continents and restoration of a mild temperature. It connects itself with the pre-historic period of the archæologist, inasmuch as remains of man and his works are apparently included in the same deposits which hold the bones of Post-glacial animals. (3) The Modern era is that of secular human history.

It may be stated with certainty that the Pliocene period of geology affords no trace of human remains or implements; and the same may I think be affirmed of the period of glaciation and subsidence which constitutes the earlier Post-pliocene. 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. Unfortunately it happens that our information on these points is still very incomplete and locally limited. In many extensive regions, like America and Australia, while the geological record is somewhat complete, the historic record extends back at most a few centuries, and the pre-historic monuments are of uncertain date. In other countries, as in Western Asia and Egypt, where the historic record extends very far back, the geology is less perfectly known. At the present moment, therefore, the main battle-field of these controversies is in Western Europe, where, though history scarce extends farther back than the time of the Roman Republic, the geologic record is very complete, and has been explored with some thoroughness. It is obvious, however, that we thus have to face the question at a point where the pre-historic gap is necessarily very wide.

Taking England as an example, all before the Roman invasion is pre-historic, and with regard to this pre-historic period the evidence that we can obtain is chiefly of a geological character. The pre-historic men are essentially fossils. We know of them merely what can be learned from their bones and implements embedded in the soil or in the earth of the caverns in which some of them sheltered themselves. For the origin and date of these deposits the antiquary must go to the geologist, and he imitates the geologist in arranging his human fossils under such names as the “Paleolithic,” or period of rude stone implements; the “Neolithic” or period of polished stone implements; the Bronze Period, and the Iron Period; though inasmuch as higher and lower states of the arts seem always to have coexisted, and the time involved is comparatively short, these periods are of far less value than those of geology. In Britain the age of iron is in the main historic. That of bronze goes back to the times of early Phoenician trade with the south of England. That of stone, while locally extending far into the succeeding ages, reaches back into an unknown antiquity, and is, as we shall see in the sequel, probably divided into two by a great physical change, though not in the abrupt and arbitrary way sometimes assumed by those who base their classification solely on the rude or polished character of stone implements. We must not forget, however, that in Western Asia the ages of bronze and iron may have begun two thousand years at least earlier than in Britain, and that in some parts of America the Palaeolithic age of chipped stone implements still continues. We must also bear in mind that when the archæologist appeals to the geologist for aid, he thereby leaves that kind of investigation in which dates are settled by years, for that in which they are marked merely by successive physical and organic changes.

Turning, then, to our familiar geological methods, and confining ourselves mainly to the Northern Hemisphere and to Western Europe, two pictures present themselves to us: (!) The physical changes preceding the advent of man; (2) The decadence of the land animals of the Post-pliocene age, and the appearance of those of the modern.

In the last chapter I had to introduce the reader to a great and terrible revolution, whereby the old Pliocene continents, with all their wealth of animals and plants, became sealed up in a mantle of Greenland ice, or, slowly sinking beneath the level of the sea, were transformed into an ocean-bottom over which icebergs bore their freight of clay and boulders. We also saw that as the Post-pliocene age advanced, the latter condition prevailed, until the waters stood more than a thousand feet deep over the plains of Europe. In this great glacial submergence, which closed the earlier Post-pliocene period, and over vast areas of the Northern Hemisphere, terminated the existence of many of the noblest forms of life, it is believed that man had no share. We have, at least as yet, no record of his presence.

Out of these waters the land again rose slowly and intermittently, so that the receding waves worked even out of hard rocks ranges of coast cliff which the further elevation converted into inland terraces, and that the clay and stones deposited by the Glacial waters were in many places worked over and rearranged by the tides and waves of the shallowing sea before they were permanently raised up to undergo the action of the rains and streams, while long banks of sand and gravel were stretched across plains and the mouths of valleys, constituting “kames,” or “eskers,” only to be distinguished from moraines of glaciers by the stratified arrangement of their materials.

Further, as the land rose, its surface was greatly and rapidly modified by rains and streams. There is the amplest evidence, both in Europe and America, that at this time the erosion by these means was enormous in comparison with anything we now experience. The rainfall must have been excessive, the volume of water in the streams very great; and the facilities for cutting channels in the old Pliocene valleys, filled to the brim with mud and boulder-clay, were unprecedented. While the area of the land was still limited, much of it would be high and broken, and it would have all the dampness of an insular climate. As it rose in height, plains which had, while under the sea, been loaded with the débris swept from the land, would be raised up to experience river erosion. It was the spring-time of the Glacial era, a spring eminent for its melting snows, its rains, and its river floods.[AL] To an observer living at this time it would have seemed as if the slow process of moulding the continents was being pushed forward with unexampled rapidity. The valleys were ploughed out and cleansed, the plains levelled and overspread with beds of alluvium, giving new features of beauty and utility to the land, and preparing the way for the life of the Modern period, as if to make up for the time which had been lost in the dreary Glacial age. It will readily be understood how puzzling these deposits have been to geologists, especially to those who fail to present to their minds the true conditions of the period; and how difficult it is to separate the river alluvia of this age from the deposits in the seas and estuaries, and these again from the older Glacial beds. Further, in not a few instances the animals of a cold climate must have lived in close proximity to those which belonged to ameliorated conditions, and the fossils of the older Post-pliocene must often, in the process of sorting by water, have been mixed with those of the newer.

[AL] Mr. Tylor has well designated this period as the Pluvial age. Journal of the Geological Society, 1870.

Many years ago the brilliant and penetrating intellect of Edward Forbes was directed to the question of the maximum extent of the later Post-pliocene or Post-glacial land; and his investigations into the distribution of the European flora, in connection with the phenomena of submerged terrestrial surfaces, led to the belief that the land had risen until it was both higher and more extensive than at present. At the time of greatest elevation, England was joined to the continent of Europe by a level plain, and a similar plain connected Ireland with its sister islands. Over these plains the plants constituting the “Germanic” flora spread themselves into the area of the British Islands, and herds of mammoth, rhinoceros, and Irish elk wandered and extended their range from east to west. The deductions of Forbes have been confirmed and extended by others; and it can scarcely be doubted that in the Post-glacial era, the land regained fully the extent which it had possessed in the time of the Pliocene. In these circumstances the loftier hills might still reach the limits of perpetual snow, but their glaciers would no longer descend to the sea. What are now the beds of shallow seas would be vast wooded plains, drained by magnificent rivers, whose main courses are now submerged, and only their branches remain as separate and distinct streams, The cold but equable climate of the Post-pliocene would now be exchanged for warm summers, alternating with sharp winters, whose severity would be mitigated by the dense forest covering, which would also contribute to the due supply of moisture, preventing the surface from being burnt into arid plains.