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.