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.