How, then, you may well inquire, does the pre-historian get to work? What is his method of linking facts together? And what are the sources of his information?
First, as to his method. Suppose a number of boys are in a field playing football, whose superfluous garments are lying about everywhere in heaps; and suppose you want, for some reason, to find out in what order the boys arrived on the ground. How would you set about the business? Surely you would go to one of the heaps of discarded clothes, and take note of the fact that this boy's jacket lay under that boy's waistcoat. Moving on to other heaps you might discover that in some cases a boy had thrown down his hat on one heap, his tie on another, and so on. This would help you all the more to make out the general series of arrivals. Yes, but what if some of the heaps showed signs of having been upset? Well, you must make allowances for these disturbances in your calculations. Of course, if some one had deliberately made hay with the lot, you would be nonplussed. The chances are, however, that, given enough heaps of clothes, and bar intentional and systematic wrecking of them, you would be able to make out pretty well which boy preceded which; though you could hardly go on to say with any precision whether Tom preceded Dick by half a minute or half an hour.
Such is the method of pre-history. It is called the stratigraphical method, because it is based on the description of strata, or layers.
Let me give a simple example of how strata tell their own tale. It is no very remarkable instance, but happens to be one that I have examined for myself. They were digging out a place for a gas-holder in a meadow in the town of St. Helier, Jersey, and carried their borings down to bed rock at about thirty feet, which roughly coincides with the present mean sea-level. The modern meadow-soil went down about five feet. Then came a bed of moss-peat, one to three feet thick. There had been a bog here at a time which, to judge by similar finds in other places, was just before the beginning of the bronze-age. Underneath the moss-peat came two or three feet of silt with sea-shells in it. Clearly the island of Jersey underwent in those days some sort of submergence. Below this stratum came a great peat-bed, five to seven feet thick, with large tree-trunks in it, the remains of a fine forest that must have needed more or less elevated land on which to grow. In the peat was a weapon of polished stone, and at the bottom were two pieces of pottery, one of them decorated with little pitted marks. These fragments of evidence are enough to show that the foresters belonged to the early neolithic period, as it is called. Next occurred about four feet of silt with sea-shells, marking another advance of the sea. Below that, again, was a mass, six to eight feet deep, of the characteristic yellow clay with far-carried fragments of rock in it that is associated with the great floods of the ice-age. The land must have been above the reach of the tide for the glacial drift to settle on it. Finally, three or four feet of blue clay resting immediately on bed-rock were such as might be produced by the sea, and thus probably betokened its presence at this level in the still remoter past.
Here the strata are mostly geological. Man only comes in at one point. I might have taken a far more striking case—the best I know—from St. Acheul, a suburb of Amiens in the north of France. Here M. Commont found human implements of distinct types in about eight out of eleven or twelve successive geological layers. But the story would take too long to tell. However, it is well to start with an example that is primarily geological. For it is the geologist who provides the pre-historic chronometer. Pre-historians have to reckon in geological time—that is to say, not in years, but in ages of indefinite extent corresponding to marked changes in the condition of the earth's surface. It takes the plain man a long time to find out that it is no use asking the pre-historian, who is proudly displaying a skull or a stone implement, "Please, how many years ago exactly did its owner live?" I remember hearing such a question put to the great savant, M. Cartailhac, when he was lecturing upon the pre-historic drawings found in the French and Spanish caves; and he replied, "Perhaps not less than 6,000 years ago and not more than 250,000." 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; what was the number, extent, and relative duration of its ups and downs; and at what time, roughly, it ceased in favour of the temperate conditions that we now enjoy. The pre-historians, for their part, must be content to make what traces they discover of early man fit in with this pre-established scheme, uncertain as it is. Every day, however, more agreement is being reached both amongst themselves and between them and the geologists; so that one day, I am confident, if not exactly to-morrow, we shall know with fair accuracy how the boys, who left their clothes lying about, followed one another into the field.
Sometimes, however, geology does not, on the face of it, come into the reckoning. Thus I might have asked the reader to assist at the digging out of a cave, say, one of the famous caves at Mentone, on the Italian Riviera, just beyond the south-eastern corner of France. These caves were inhabited by man during an immense stretch of time, and, as you dig down, you light upon one layer after another of his leavings. But note in such a case as this how easily you may be baffled by some one having upset the heap of clothes, or, in a word, by rearrangement. Thus the man whose leavings ought to form the layer half-way up may have seen fit to dig a deep hole in the cave-floor in order to bury a deceased friend, and with him, let us suppose, to bury also an assortment of articles likely to be useful in the life beyond the grave. Consequently an implement of one age will be found lying cheek by jowl with the implement of a much earlier age, or even, it may be, some feet below it. Thereupon the pre-historian must fall back on the general run, or type, in assigning the different implements each to its own stratum. Luckily, in the old days fashions tended to be rigid; so that for the pre-historian two flints with slightly different chipping may stand for separate ages of culture as clearly as do a Greek vase and a German beer-mug for the student of more recent times.
Enough concerning the stratigraphical method. A word, in the next place, about the pre-historian's main sources of information. Apart from geological facts, there are three main classes of evidence that serve to distinguish one pre-historic epoch from another. These are animal bones, human bones, and human handiwork.
Again I illustrate by means of a case of which I happen to have first-hand knowledge. In Jersey, near the bay of St. Brelade, is a cave, in which we dug down through some twenty feet of accumulated clay and rock-rubbish, presumably the effects of the last throes of the ice-age, and came upon a pre-historic hearth. There were the big stones that had propped up the fire, and there were the ashes. By the side were the remains of a heap of food-refuse. The pieces of decayed bone were not much to look at; yet, submitted to an expert, they did a tale unfold. He showed them to be the remains of the woolly rhinoceros, the mammoth's even more unwieldy comrade, of the reindeer, of two kinds of horse, one of them the pony-like wild horse still to be found in the Mongolian deserts, of the wild ox, and of the deer. Truly there was better hunting to be got in Jersey in the days when it formed part of a frozen continent.
Next, the food-heap yields thirteen of somebody's teeth. Had they eaten him? It boots not to inquire; though, as the owner was aged between twenty and thirty, the teeth could hardly have fallen out of their own accord. Such grinders as they are too! A second expert declares that the roots beat all records. They are of the kind that goes with an immensely powerful jaw, needing a massive brow-ridge to counteract the strain of the bite, and in general involving the type of skull known as the Neanderthal, big-brained enough in its way, but uncommonly ape-like all the same.
Finally, the banqueters have left plenty of their knives lying about. These good folk had their special and regular way of striking off a broad flat flake from the flint core; the cores are lying about, too, and with luck you can restore some of the flakes to their original position. Then, leaving one side of the flake untouched, they trimmed the surface of the remaining face, and, as the edges grew blunt with use, kept touching them up with the hammer-stone—there it is also lying by the hearth—until, perhaps, the flake loses its oval shape and becomes a pointed triangle. A third expert is called in, and has no difficulty in recognizing these knives as the characteristic handiwork of the epoch known as the Mousterian. If one of these worked flints from Jersey was placed side by side with another from the cave of Le Moustier, near the right bank of the Vezère in south-central France, whence the term Mousterian, you could hardly tell which was which; whilst you would still see the same family likeness if you compared the Jersey specimens with some from Amiens, or from Northfleet on the Thames, or from Icklingham in Suffolk.