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