In strictly geological terms, ‘Sussex Marble’ would fall foul of the Trades Descriptions Act.
Sussex Marble isn’t marble:
Let’s get that clear from the start.
It’s an ornamental building stone
To test a mason’s art.
It isn’t metamorphic,
Like proper marble is;
In fact, it’s just a limestone –
(Test with acid, watch it fizz).
It’s riddled through with snail shells,
Borne by waters long ago
Into cosy aggregations
By the swirling currents’ flow.
It looks all rough and lumpy
When you find it in the ground,
But when it’s polished up it makes
The prettiest stone around.
Viviparus sussexiensis,
Those Cretaceous snails are named;
Their sectioned shells well polished,
Now in fonts and pathways framed.
(See also The building stones of Sussex and Paludina)