you what steady and sharp head-work this same geology requires, even
in the nearest gravel-pit.

Well, then. I do not think our gravel-pit will tell us what we
want: but I know one which will.

You have all heard of Lady Grenville's lovely place, Dropmore,
beyond Maidenhead; where the taste of that good and great man, the
late Lord Grenville, converted into a paradise of landscape-
gardening art a barren common, full of clay and gravel-pits. Lord
Grenville wanted stones for rockwork; in those pits he found some
blocks, of the same substance as those of Stonehenge or Pirbright.
And they contain the answer. The upper surface of most of them is
the usual clear sugar-sandstone: but the under surface of many has
round pebbles imbedded in it, looking just like plums in a pudding;
the smaller above and the larger below, as if they had sunk slowly
through the fluid sand, before the whole mass froze, as it were,
suddenly together. And these pebbles are nothing else than rolled
chalk flints.

That settles the matter. The pebbles could not come from Wales;
there are no flints there. They could not have been made before the
chalk; for out of the chalk they came; and the only explanation
which is left to us, I believe, is, that over the tops of the chalk
downs; over our heads where we stand now, there once stretched
layers of sand and gravel, "Tertiary strata" as I have been calling
them to you; and among them layers of this same hard sandstone.

When the floods came they must have swept away all these soft sands
and gravels (possibly to make the Bagshot sands, of which I shall