Lundy, although a small island, has attracted and intrigued geologists since the nineteenth century, as it is formed from rocks that are of a very different type and age to the nearby rocks of Devon and South Wales. It is formed mainly of granite (a coarse-grained igneous rock, composed of the minerals feldspar and quartz, often with biotite and amphibole) intruded into metamorphosed sedimentary rocks. Both of these rocks are intruded by dykes, sheet-like intrusions of igneous rock that have a vertical or near-vertical orientation.
The Lundy granite is similar to the granites of Devon and Cornwall, which were emplaced in Carboniferous times (362-290 million years ago) and was originally thought to be the same age. However, radiometric dating of the Lundy granite showed that it was much younger, having a Tertiary age (65-62 million years ago). This makes it part of the British Tertiary Volcanic Province, mainly located in Scotland and Northern Ireland. Lundy is therefore of special interest in that it is the southern-most part of the Province.
It is likely that Lundy was formed as part of a volcano, which would have been one of the most spectacular geological events in this area.