Chalk, County Antrim

The village of Ballintoy lies at the edge of the Antrim plateau where black basalt gives way to white chalk.

The Chalk was formed by accumulation of the remains of microscopic algae in warm seas about 100 million years ago, whilst the basalt formed by volcanic eruptions around 60 million years ago.

The photo left shows a basalt dyke that has intruded through the chalk, causing it to become altered to a fine, sugary white marble against the contact with the hot magma.