But what has this to do with a gravel-pit?
This first. That all the flints in this pit have come out of the
chalk. They are coloured, most of them, with iron, which has turned
them brown; but they are exactly the same flints as those gray ones
in the chalk-pit on the other side of the town.
How do I know that?
I think our own eyes will prove it: they are the same shapes, and
of the same substance; but as a still surer proof, we find exactly
the same fossils in them; sponges, choanites (which were something
like our modern sea-anemones), corals, and "shepherds' crowns" as
the boys call the fossil sea-urchins. The species of all these, and
of other fossils, in the chalk-pit and in the gravel-pit, are
absolutely identical. The natural conclusion is, then, that the
gravel has been formed from the washings of the chalk. The white
lime of the chalk has been carried away in water by some flood or
floods; the heavier flints have been left behind.
Stop now one moment, and think. You all know how very few flints
there are in the chalk-pit, in proportion to the mass of chalk. You
all know what vast gravel-beds cover the country to the north, and
often to the thickness of many feet. Try and conceive, then, what a
much more vast mass of chalk must have been washed away, to leave
that vast mass of gravel behind it.
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