f the same effect being produced
in widely different plants and animals, and yet by slightly different
means, on which a whole chapter of natural philosophy--say, rather,
natural theology--will have to be written some day.

But now consider what this Lias, and the Oolites and clays upon it
mean. They mean that the New Red sandstone, after it had been dry
land, or all but dry land (as is proved by the footprints of animals
and the deposits of salt), was sunk again beneath the sea. Each
deposit of limestone signifies a long period of time, during which
that sea was pure enough to allow reefs of coral to grow, and shells
to propagate, at the bottom. Each great band of clay signifies a
long period, during which fine mud was brought down from some wasting
land in the neighbourhood. And that land was not far distant is
proved by the bones of the Pterodactyle, of Crocodiles, and of
Marsupials; by the fact that the shells are of shallow-water or shore
species; by the presence, mixed with them, of fragments of wood,
impressions of plants, and even wing-shells of beetles; and lastly,
if further proof was needed, by the fact that in the "dirt-bed" of
the Isle of Portland and the neighbouring shores, stumps of trees
allied to the modern sago-palms are found as they grew in the soil,
which, with them, has been covered up in layers of freshwater shale
and limestone. A tropic forest has plainly sunk beneath a lagoon;
and that lagoon, again, beneath the sea.

And how long did this period of slow sinking go on? Who can tell?
The thickness of the Lias and Oolites together cannot be less than a
thousand feet. Considering, then, the length of time required to lay
down a thousand feet of strata, and considering the vast difference
between the animals found in them, and the few found in the New Red
sandstone, we have a right to call them another world, and that one
which must have lasted for ages.

After we pass Oxford, or the Vale of Aylesbury, we enter yet another
world. We come to a bed of sand, under which the freestones and
their adjoining clays dip to the south-east. This is called commonly
the lower Greensand, though it is not green, but rich iron-red. Then
succeeds a band of stiff blue clay, called the Gault, and then
another bed of sand, the upper Greensand, which is more worthy of the
name, for it does carry, in most places, a band of green or
"glauconite" sand. But it and the upper