Lizard Point: continental collisions
Lizard Point is a great place to discover how continents are created and for investigating the geology of The Lizard of The Lizard.
The southern part of the peninsula is a complex mix of serpentinite, schist, gabbro and granite. These rocks are over 600 million years old. The serpentine rock for which The Lizard is famous is all that remains of an ancient ocean floor, into which other igneous rocks were intruded. As the earth’s tectonic plates moved, what now forms The Lizard was welded onto continental rocks in the mid-Devonian period (roughly 385 million years ago). During the Tertiary period (from about 65 million years ago), the peninsula was submerged beneath the sea, and the subsequent erosion levelled the rocks to produce the plateau we see today. This exposed marine platform is an example of an ophiolite. For more detail take a look at The Lizard’s geological timeline [hyperlink to Lizard timeline], from the very beginning of the Earth’s story until the present day.
The serpentine rock that is widespread across the Lizard peninsula only reaches as far south as Caerthillian Cove on the western coast and Church Cove on the eastern, forming a geological boundary south of which schists dominate. Lizard Point is a great example of what happens when two continents come together.
There are three different kinds of rocks on show at Lizard Point.
Mica schist is a metamorphic rock made from quartz and a layered silicate mineral known as mica. This form of schist makes up the rock below your feet as you stand at the most southerly point and as you walk west and north along the coastal path towards Caerthillian Cove. From the old lifeboat station at Polpeor Cove you can see for yourself the mica schist foliations spanning the caves and cliffs.
Mica schist is often found alongside gneiss formations. The southwestern tip of the peninsula illustrates a gradient between mica schist and granite gneiss, whilst a majority of the rocks made visible at low tide are granite gneiss. The oldest granite gneiss visible from the most southerly point is the Man of War formed 500 million years ago. These islets were on the northern tip of the supercontinent consisting of Africa and South America when it collided with another supercontinent, formed by Europe and North America, 350 million years ago.
The rocky cliffs to the east of Lizard Point are again schist but of a different form. Whilst mica schist was formed by the metamorphosing of sediments, hornblende schist was once as a lava flow which, under extreme temperature and pressure, was altered into the schists we see today. The cliffs beneath the light house all the way to Church Cove are formed from this form of schist.