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.
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