the advent of man.
itherto we have met with no trace of man or of his works. Yet there have been in our upward progress from the dawn of life mute prophecies of his advent. Man is in his bodily frame a vertebrate animal and a mammal; and when first the Amphibians were introduced in the Palæozoic, the framework of man’s body was already sketched out and its principles settled. Those great reptilian lords, the biped Saurians of the Mesozoic, already foreshadowed his erect posture, though their limbs may have been more ornithic than mammalian. The gradual advance in the brain-development of the Tertiary mammals presaged a coming time when mind would obtain the mastery over claw and tooth and horn; and in the Miocene ages there was already some hint of the precise style of structure in which this new creative idea would be realised. Yet it might have been impossible to imagine beforehand the vast changes which this new idea would inaugurate. In the lower animals such intelligence as they possess is so tied to the physical organisation that it manifests itself as a mechanical unvarying instinct. Man bursts this bond, and in doing so revolutionises the whole scheme of nature. Old things are now put to new uses, the face of nature is changed, varied arts are introduced, and thought enters into the domain of general and abstract truth. Objects are arranged, classified, understood, and while in some respects the whole creation is made to groan under the tyrannous inventions of man, yet these are the inventions of imagination and design. They are the triumph, not of brute force, but of will and intelligence.
That man was not in all the earlier ages of the world, except in these prophecies of his coming, geology assures us. That he is, we know. How he came to be, is, independently of Divine revelation, an impenetrable mystery—one which it is doubtful if in all its bearings science will ever be competent to solve. Yet there are legitimate scientific questions of great interest relating to the time and manner of his appearance, and to the condition of his earlier existence and subsequent history, which belong to geology, and in which so great stores of material have been accumulated that a treatise rather than a chapter would be required for their discussion. We may endeavour to select a few of the more important points.
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. In the later Eocene and Miocene the extent of land became greater, but it was so disposed as to allow the influx into the Arctic Sea of vast volumes of heated water from the equatorial regions; and there may have been also astronomical causes at work to increase this influx of warm water, and so to raise the temperature of the Arctic regions still higher.[83] The middle period of the Tertiary was undoubtedly a time very favourable to the wide distribution of the higher forms of life both animal and vegetable. But we cannot trace man or any of the contemporary mammals back to the Miocene. In the Pliocene the continents had attained to their present elevations, and climates were not dissimilar from those prevailing at present; but still we have no certain indication of the presence of man; and if other modern mammals extend back to this period their number is very small. In this age also the greater part of the continents must have been covered with a great thickness of soil and disintegrated rock favourable to vegetation, and there seemed nothing to preclude the introduction of man. But a new and at first sight most unfavourable change was to intervene. Whether through internal changes affecting the distribution of land and water, or through astronomical vicissitudes, the northern hemisphere, and possibly the whole world, entered on an era of refrigeration, the so-called “Glacial Age” of the Post-Pliocene or Pleistocene period. That in this period our continents as far south as the latitude of 40° were overwhelmed with ice or ice-laden seas is rendered evident by the fact that the whole surface up to several thousands of feet above the sea-level has been bared of its accumulated débris and polished and grooved by ice, and laden with boulders and other glacial deposits, while in many places at heights of even 1,000 or 1,200 feet these deposits contain sea-shells of species now living in the colder parts of the ocean. These phenomena do not exist in the tropical regions, except in the vicinity of high mountains, but they recur in the southern hemisphere. It is still uncertain whether the period of greatest cold in the two hemispheres was at the same time or in successive ages. Geologically, however, they are approximately contemporaneous, both occurring between the end of the Pliocene and the modern period; but nevertheless they may not have coincided in absolute date.
Very different views have been held as to the precise condition of the continents in the Glacial Age, though all agree in the prevalence of cold and the action of ice, and in the fact of a great submergence at one or more stages of the period. My own conclusions, which I have advocated elsewhere,[84] and which are based on extensive study of the northern parts of America, where the deposits of this age are more widely developed than elsewhere, are that there was one great subsidence, leading to a condition in which the lower levels of the continents were covered with ice-laden water and the higher regions were occupied with permanent snow and glaciers. This submergence went on till even high mountains 4,000 feet or more in elevation were under water. Then there was a gradual though intermittent elevation, during which the climate became ameliorated, and lastly there was a condition in which the land of the northern hemisphere stood higher than at present, and which immediately preceded the modern period. As these conditions have great significance in relation to the appearance of man, I have tabulated them for reference as they occur in Scandinavia, Great Britain, and North America. The so-called “Interglacial Periods” of some geologists are in reality local results of the stages of intermittent elevation in which were deposited beds which in some cases, as in Scotland, Sweden, and Eastern Canada, hold sea-shells, and in others, as in the central areas of North America, contain remains of plants of northern species.
We shall name, for convenience, the parts of this Pleistocene revolution which include the great subsidence and glaciation, the Glacial Age, that extending from the re-elevation to the modern the Post-glacial.
The Glacial Age proved fatal to a large proportion of the land life of the previous periods. According to Professor Boyd Dawkins, out of fifty-three species known in Britain in the Post-glacial, only twelve are survivors of the Pliocene; and probably the proportions would not be greater in any part of the northern hemisphere. Some, however, did survive, either by migrating southward or by being inhabitants of places less severely affected than most by the general cold and submergence. There was thus no absolute break in the chain of life effected by the Glacial Age.
Table of Pleistocene Deposits in Scandinavia, England, and America. (Order descending.)
| SCANDINAVIA. (Torell.) | GREAT BRITAIN. (Lyell, &c.) | NORTH AMERICA. |
| Valley-clays and Heath-sands of Sweden. (No fossils.) | Hoxne Deposits and Upper Terrace Gravels. Palæolithic Implements. | Terrace Gravels and Loess Deposits. |
| Terrace-gravels of Norway and Sweden. (No fossils.) | Upper Glacial Beds. Bridlington Beds. Upper Boulder Beds. | Placer Gravels of West. |
| Do. Sand and Gravel, Newer Boulder Drift. | ||
| Dryas-clay with Fossil plants of northern species. | So-called “Interglacial” Deposits. | So-called Interglacial Beds, with Plants, &c. Loess Deposits of Mississippi. |
| Uddevalla beds with Boreal Marine shells. | Clyde Beds and Marine Clays. |
Upper Leda Clay and Champlain Clay, with
Boreal Shells. White Silts of British Columbia. |
| Mid-Glacial Sands. | Erie Clays and similar Beds of West. | |
| Yoldia Clay and Sand. Arctic Marine Shells. | Lower Leda Clay, with Arctic Shells. | |
| Yellow Stony Clay and Sand, and Gravel of Scania. | Port Hudson Deposit of Mississippi. | |
| “Syrtensian” Beds of New Brunswick. | ||
| Orange Sand of Mississippi. | ||
| “Moraines de Fond,” or Boulder Clay proper. | Till, or Older Boulder Clay. | Boulder Clays, with Local and some Travelled Boulders. |
| Ancient Diluvial Sand. | Pebbly Beds and Weyburne Sands, Lignitic Forest Beds. | Old Land Surfaces--Peat under Boulder Clay, Local Gravels and Sands. |
| Pre-glacial Gravels of British Columbia. |