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.