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.

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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.