Human Origins

by S. Laing

Now elevation and depression of large masses of land are, as far as we know anything certain about them, very slow processes, especially in countries unaffected by recent volcanic action, which is the case with nearly all the regions in North America and Europe which were covered by the great ice-sheets. There has been little or no perceptible change anywhere since the commencement of history, and the only accurate measurements of changes now going on are those made in Sweden, where it appears that in some cases elevation, and in others depression, is taking place at the rate of about two and a half feet in a century. In volcanic regions earthquakes have occasionally caused movements of greater amount in limited areas, but there is no trace of anything of the sort in these movements of the glacial period which have apparently gone on by slight secular changes in the earth's crust as they are now doing in Scandinavia.

But in this case a depression of 2000 feet, followed by an elevation of equal amount, at Lyell's rate of two and a half feet per century, would require 160,000 years, without allowing for any pauses during the process. And this only embraces part of the whole glacial period, for the depression did not begin until after the climax of the first great glaciation, when the land probably stood higher than at present. Of course the actual movements may have been more rapid, but unless we resort to the exploded theories of cataclysms and catastrophes, the time for such movements must have been very great.

An equally conclusive proof of the immense antiquity of the glacial period is afforded by the formation known as the loess, which fills up so many of the valley systems of Europe, Asia, and America to great depths, and spreads over the adjacent table-lands. It is a tranquil land deposit of fine glacial mud, from sheets of water which inundated the country when great rivers from glaciated districts ran at higher levels, and began to excavate their present valleys. Lyell estimates the thickness of this deposit in the Rhine valley at 800 feet, and it is found at much higher levels on upland plains. Now this loess is not a marine or lacustrine deposit, as is proved by the shells it contains, which are all of land species; nor is it a deposit of running water, for there are no sands or gravels, but distinctly such a deposit from tranquil sheets of muddy water as is now accumulated in Egypt by the inundations of the Nile. When the Rhine brought down such volumes of muddy water from the glaciers of the Alps as to overflow the upland plains, it must have flowed at a level many hundred feet higher than its present valley, which must have been since scooped out by sub-aërial denudation. The rate of deposition of the Nile mud is about three inches per century, and there seems no reason why that of the fine glacial mud should have been more rapid, charged as the Nile is every year with mud from the torrential rains of the Abyssinian highlands. At this rate it would have required 320,000 years to accumulate the 800 feet of loess of the Rhine valley. Here again the rate may have been faster, but it is sufficient to show that an immense time must have elapsed, and the loess is a distinctly glacial deposit, containing palæolithic human remains and a pleistocene fauna, and embracing only a portion of the quaternary period. Nor is it an isolated phenomenon confined to Europe, but is found over the whole world wherever rivers have flowed from regions which were formerly buried under ice and snow. It is found in great force in the valleys of the Yang-tse-Kang and the Mississippi, and Sir Charles Lyell, referring to the fossil human bone found in it at Natchez, says—"My reluctance in 1846 to regard the fossil human bone as of post-pliocene date arose, in part, from the reflection that the ancient loess of Natchez is anterior in time to the whole modern delta of the Mississippi. The table-land was, I believe, once a part of the original alluvial plain or delta of the great river before it was upraised. It has now risen more than 200 feet above its pristine level. After the upheaval, or during it, the Mississippi cut through the whole fluviatile formation, of which its bluffs are now formed, just as the Rhine has in many parts of its valley excavated a passage through its ancient loess. If I was right in calculating that the present delta of the Mississippi has acquired, as a minimum of time, more than 100,000 years for its growth, it would follow, if the claims of the Natchez man to have coexisted with the mastodon are admitted, that North America was peopled more than a thousand centuries ago by the human race. But, even were that true, we could not presume, reasoning from ascertained geological data, the Natchez bone was anterior in date to the antique flint haches of St. Acheul."

Human remains have since been found in the United States, both in the loess and in drifts, which are presumably older; but even if this were doubtful, the evidence would remain the same for the immense time required for such a deposit, and there is abundant proof in Europe, that human implements, and even skulls and skeletons, have been found at considerable depths in the loess, along with remains of the mammoth and other extinct animals.

It must be remembered also, that the loess is only one part of the work due to glacial erosion. It is, in fact, only the deposit of the fine mud ground from the rocks by glaciers, and carried down further by rivers issuing from them than the coarser débris, which, as we have seen, cover 1,000,000 square miles to an average depth of fifty feet in North America alone. The volumes, therefore, of the loess and of the débris correspond, and tell the same story of enormous erosion requiring immense periods of time.

Even in comparatively recent times striking proofs of immense antiquity are afforded by the amounts of denudation and erosion which have taken place since the ice disappeared and the lands and seas assumed substantially their present contours and levels. I will give one instance which, although comparatively modern, will come home readily to most British readers. Dr. Evans in his Ancient Stone Implements, referring to those found at Bournemouth 100 feet above the present sea-level in the gravels of the old Solent river, which then ran at that height, says—

"Who, standing on the edge of the lofty cliff at Bournemouth, and gazing over the wide expanse of waters between the present shore and a line connecting the Needles on the one hand and the Ballard-Down Foreland on the other, can fully comprehend how immensely remote was the epoch when what is now that vast bay was high and dry land, and a long range of chalk downs, 600 feet above the sea, bounded the horizon on the south? And yet this must have been the sight that met the eyes of those primæval men who frequented that ancient river, which buried their handiworks in gravels that now cap the cliffs, and of the course of which so strange but indubitable a memorial subsists, in what has now become the Solent Sea."

And the same may be said of the still wider strait which separates England from France. No geologist could look either at the Needles and Ballard Foreland, or at Shakespeare's Cliff and Cape Grisnez, without a conviction that the chalk ridge was once continuous, and has been worn away, inch by inch, by the very same process as is now going on. Nor can the action of ice or river floods be evoked to accelerate the process, for evidently it has throughout been a case of marine erosion. The only question is whether this dates back even into the later phases of the glacial period, for the opposite cliffs show no sign of having been either depressed beneath the sea or elevated above it, but rather appear to have stood at their present level since the erosion began. In any case it can only have occupied a comparatively short and recent phase of the glacial period, for there is abundant evidence that the British islands have been connected with the Continent in comparatively recent times.

Great, however, as is the antiquity shown by these comparatively modern instances, they sink into insignificance compared with that shown by a recent discovery, which I quote the more readily because it rests on the high authority of Professor Prestwich, who has been foremost among modern geologists in reducing the time required for the glacial period and for the existence of man. This is afforded by the upland gravels in Kent and Surrey, which are scattered over wide areas of the chalk downs and green-sand, at elevations far above existing valleys and watersheds, and which could only have been deposited before the present rivers began to run, and when the configuration of the country was altogether different. Quite recently Mr. Harrison, a shopkeeper at Ightham in Kent, who is an ardent field-geologist, discovered palæolithic implements, in considerable numbers and in various localities, up to an elevation of 750 feet above the sea level, in these gravels of the great southern drift. These discoveries, which have since been repeated by other observers, led Professor Prestwich to institute an exhaustive inquiry as to these upland drifts; and the startling conclusion he arrives at is, that the oldest of them, or great southern drift, in which the implements are found, could only have come from a mountain range 2000 to 3000 feet high, which formerly ran from east to west in the line of the anticlinal axis which runs down the centre of the present Weald of Kent, between the north and south chalk-downs, and which has been since worn down to the present low forest-ridge by sub-aërial denudation. The reasoning by which this inference is supported seems irresistible. The drift could not have been deposited by the present rivers or with the present configuration of the country, for it is found at levels 300 or 400 feet higher than the highest watersheds between the existing valleys. It consists not only of chalk flints, but to a great extent of cherts and sandstones, such as are found at present in the forest-ridge of the Wealden and nowhere else. It must have been brought by water, for the gravels are to a considerable extent rounded and water-worn. This water must have run down-hill and with considerable velocity during floods, from the size of the rolled stones, and it must have come from the south, because the cherts and grits are only found there, and because the levels at which the gravels are found rise in that direction. By following these levels as far as the present surface extends, which is to the southern edge of the green-sand, it is easy to plot out what must have been the continuation of this rising gradient to the south, and what the elevation of the southern range in which these northward-flowing streams took their origin. Prestwich has gone into the question in full detail, and his conclusion is, that the height of this Wealden ridge must have been at least 2800 feet, or in other words, that about 2000 feet must have disappeared by denudation. This is the more conclusive as Prestwich is the highest authority, and he approached the subject with a bias for shortening rather than lengthening the periods commonly assigned for the glacial epoch and the antiquity of man.

The present average rate of denudation of continents has been approximately measured by calculating the amount of solid matter brought down by rivers. It varies a good deal according to the nature of the area drained, but the average is about one foot in 3000 years. At this rate the time required for the removal of 2000 feet of the Wealden ridge would be no less than 6,000,000 years; but of course this would be no fair test, as denudation would be vastly more rapid than the present average rate, on hilly ranges and under glacial conditions of climate. It is enough to say that the time required must have been extremely great, and quite ample to fit in with the most extended time required by Croll's theory of the varying eccentricity of the earth's orbit.