Lizard
The Lizard peninsula is Cornwall's and Britain's most southerly point and its geology, landscape and flora are very special too. Nowhere else in Cornwall has such a density of nationally recognised Sites of Special Scientific Interest (SSSIs) or regionally important County Geology Sites (formerly known as RIGS). The main reason for this is that the rocks on the Lizard are totally different from the rest of Cornwall.
The most extensive rock type is the serpentine which, spanning 20 square miles, is the largest outcrop of such rock in mainland Britain. It is found nowhere else in England. When Queen Victoria and Prince Albert visited the area in 1846, they were so struck by serpentine's unusual characteristics, that their ensuing royal patronage spawned an industry of architectural and decorative stone working that continues, albeit somewhat diminished, to this day.
Originally this altered peridotite was thought to be the root of a volcano, but it is now recognised to be part of the Earth's mantle, today normally tens of kilometres below your feet, which was bulldozed onto the newly evolving Cornish mainland in front of an advancing continent. The actual junction between the Earth's mantle and the crust is today exposed on the foreshore at Coverack. 
This is why you will often see visiting groups of university students on the beach investigating the relations between the serpentinised mantle peridodites and the overlying crustal gabbros. It was a Croatian meteorologist called Mohorovicic who, having constructed his own seismograph to study earthquake shock waves, discovered the distinct boundary that exists between the lighter crustal rocks and the denser mantle rocks, and his name is given to this junction. Today we have shortened it to the Moho.
Between Coverack and Kennack Sands there is a marked narrow promontory known as Carrick Luz. This is the remains of a great fissure in the serpentine that acted as the
feeder for the overlying gabbro. In a few places, such as around The Manacles, Leggan Cove and the West of England Quarry at Porthoustock, instead of gabbro we can see dolerite and basalt dyke swarms that poured lava up through the gabbro onto the ancient sea floor. The actual lavas have since been removed by erosion or metamorphosed almost out of recognition. Some of the oldest known rocks in the whole of Cornwall occur around The Most Southerly Point. These rocks, the Man of War Gneiss and the Old Lizard Head mica schists, are over 500 million years old. The gneiss, with its corrugated texture, can be seen only as boulders on the beaches around The Most Southerly Point. They have been brought in by the waves from the offshore reefs, such as Shag and Labham Rocks. Another rock unique to the Lizard is the Kennack Gneiss. No prizes for guessing where it is best exposed.
There is a huge time gap of 350 million years between the great events that emplaced the rocks of the Lizard on Cornwall, and today. It is becoming clear that many of the faults that control the development of the current shape of the coast and the location of the inland valleys, had formed in the first 75 million years after the Lizard was thrust up. It is within these and associated cracks that you find spectacular minerals, very different in nature from those associated with the granites, which are known as zeolites. Particularly fine collections can be seen in the Helston Folk Museum and the Rashleigh Gallery at The Royal Cornwall Museum in Truro. It is probable that much of Cornwall and the Lizard were covered by the high sea levels that deposited the chalk elsewhere in Britain 65 million years ago. Inland the evidence has been eroded away but flint (weathered out of chalk) is regularly washed up along the south coast, perhaps from the still existing bed of Cretaceous rocks under the sea off Black Head and The Lizard Point. Nearby Loe Bar (SW 643243) is composed of 86% flint.
Just before the turn off for Coverack on the main Helston to St Keverne road there is a small exposure of quartz-rich pebbles and cobbles of Tertiary age, probably deposited 25 or more million years ago and derived from the killas and granites north of the peninsula. There is small picnic area here which should be treated with respect for this really is ancient ground. You can see the quartz Crousa Gravels on the banks of the little pool, known as Dolly's Pool, here. This area is a County Geology Site.
Since these gravels were laid down there has been a tremendous amount of erosion. Much of the peninsula, being composed of hard, dense serpentine gabbro and schists has remained relatively high and treeless, whereas the softer Kennack Gneiss, fault zones, and killas country (The Meneage) that arcs around the peninsula have been eroded into deep wooded valleys.
Each district of the peninsula has been uniquely shaped by its underlying rocks and nowhere is it more evident than near Lizard town itself. Here you can see a vast difference between the fields to the south of the village and those a little further north and west. The very tip of the Lizard is composed mostly of schists and these are quite fertile and grow cauliflowers and potatoes. Whereas, close by (to the north and west) you will see heathland that is quite barren in appearance and this overlies the ultrabasic serpentine with its poor soils. You may even be lucky enough to see the emblem of Cornwall itself, the chough, now breeding in this part of the Lizard again after an absence of many years.
Serpentine and gabbro produce magnesium or calcium rich soils and it is the resulting alkalinity of the soils that has enabled a large number of quite rare plants to thrive on these parts of The Lizard. These include dropwort, salad burnet, bloody cranesbill and the rare Cornish heath which is only found on The Lizard in Britain. On the flattest parts of the peninsula underlain by serpentine, is a fine quartz-rich windblown dust, known as loess, that was derived from the area now occupied by the Celtic Sea during the last cold phase of the Ice Age. The quarry by Goonhilly Earth Station, which is a County Geology Site, is the reference section for loess in Cornwall.
There is a tremendous amount of variety between the farms and villages of individual Lizard parishes. Every village and farm is unique because throughout history, people have always used the local rocks to build with. For example, on the areas underlain by gabbro, the land had to be cleared of large boulders (core stones) to make fields. These ended up in the stone-faced Cornish hedges or in the walls of farmhouses. In places like Main Dale and Crousa Downs you can still see what the landscape would have looked like in the distant past. The churches on The Lizard characteristically have beautifully shaped and polished serpentine fonts, lecterns and bible stands.
