The Lizard Peninsula
There are few places in Cornwall, or for that matter in Britain, that are made up of such a singular mix of elements as the Lizard Peninsula. In its buildings and place names it is recognisably Cornish, but in its scenery, rocks and plants it is strikingly different. You intuitively recognise this as you walk the coast or cross the downs, although it's often hard to pin down exactly where this feeling of dislocation comes from. The coast is as spectacular as any in Cornwall and yet there is an extra edge to the cliffs at Black Head, The Rill and Vellan Head. Here the dark cliffs seem to suck in and trap the sunlight and one immediately senses that below the thin layer of vegetation there is an alien quality to the rocks. Similarly, in the centre of the Lizard on Goonhilly Downs you'll find an area of barren heath that has resisted all attempts at cultivation and instead is peopled with the burial mounds of the prehistoric dead.
Yet, in this troubling, looking-glass landscape there is also a visual and sensory richness that can take your breath away – the aquamarine sea; the astonishing variety of plants; the pebbles of every colour on the beaches. If you drop to your knees on the coast path or on the downs, another scale of richness is revealed – a world of miniature plants found nowhere else in Britain, like fringed rupture-wort and land quillwort. In the winter the downs at Predannack and Goonhilly are as bleak as any in Cornwall, but in the summer they vibrate to the hum of iridescent dragonflies and with the colour of a hundred flowering plants. The most conspicuous is Cornish or Goonhilly heath, a plant found almost nowhere else in Britain and whose home is really on the Atlantic coasts of France and Portugal. It's in these eye-catching contrasts that the character of the Lizard is to be found: a kaleidoscopic world of colourful plants and pebbles set against an acutely austere landscape; the primal heath of Goonhilly set against the modernity of the Earth Station. At Downas, Carleon and Kynance the Lizard possesses some of the most beautiful coves in Cornwall, but they are set against and surrounded by some of the most bleak and unforgiving coastline in Cornwall.
The explanation for these contrasts lies squarely beneath your feet, because on the Lizard peninsula Mother Nature has reluctantly given up a medley of igneous and metamorphic rocks that properly belong in the Earth's oceanic lithosphere and are only rarely found on dry land. The impact of the geology is so pronounced that you can often guess the type of rock under your feet by the landscape and vegetation in front of your eyes. Compare, for instance, the landscape of Goonhilly Downs and Kynance with that around Lizard Point or Gunwalloe. It is these unusual rocks that underpin the distinctiveness of the Lizard, their boundaries that provoke abrupt changes in vegetation and soil fertility, their colourful pebbles that catch the eye.
The most unusual is serpentinite. It makes up the great volume of the Earth's upper mantle and is only very occasionally found at the surface. This is the rock that makes up the dark cliffs of Vellan Head and The Rill and underlies the heathland at Goonhilly. It's such an alien rock in its composition that it has an ecology all of its own, drawing together a disparate collection of plants whose main characteristic is simply their ability to tolerate the peculiarities of the poor soils. Rather surprisingly, this has created a mosaic of specialised habitats each with their own delights. In the first part of this guidebook we'll look at the origin of the Lizard's remarkable rocks and at the unusual habitats associated with them and how they combine and interact with climate and humans. This unusual combination of factors attracts botanists and geologists from all over the world. This is certainly Cornwall, but not as we know it.
The Lizard Peninsula - A landscape of serpentine
Even today the Lizard Peninsula remains a slightly uncharted part of Cornwall, a sidestep away from the more well-worn path that leads to the Land's End Peninsula just across Mount's Bay. Both places are strongly framed by the character of their dominant rocks: Land's End by granite, a rock of continental lithosphere; the Lizard by serpentinite and the dark rocks of oceanic lithosphere. Both are impressive landscapes, and as you wander the coast and downs you are inevitably drawn into making comparisons between the two.
One of the qualities of granite is the way it seems to engage so freely with the imagination. The great rounded blocks on the carns readily take on the forms of animals or human faces, and folk tales seem to naturally attach to particular places and even to individual rocks. Often prehistoric tombs are sited to specifically take in views of the most impressive carns, creating a conversational to and fro between human and landscape. The Lizard is very different; the serpentinite creates a 'take it or leave it' landscape, rather featureless and often devoid of farms and settlements. It is one that manages to be both remarkably austere but also, at a smaller scale, riotously exuberant in its rocks and plants. This odd, unsettling combination of bleak and beautiful, of austere and vibrant, is at the root of the strong reaction many people feel to the Lizard's unusual and compelling landscape.
We start at Nare Point on the banks of the Helford estuary and as you walk towards Porthallow you are walking on Roseland Breccia – the jumble of rock debris that was propelled before the advancing Lizard rocks as the Rheic Ocean closed. At Porthallow we cross onto oceanic lithosphere for the first time, and between Porthallow and Porthoustock almost every part of the schist and gabbro cliffs has been quarried away. The first real taste of serpentinite scenery comes south of Coverack on the cliffs at Black Head and Downas Cove where beautiful polished serpentinite rocks are revealed on the beach as the tide recedes. Between Kennack Sands and Landewednack the cliffs are interspersed with small coves and shallow wooded valleys like Gwendreath and Poltesco that reach up to Goonhilly Downs, the great central area of heathland, the focal point of a prehistoric ritual landscape and today's Earth Station.
Poltesco (Carleon) Cove
South of Cadgwith things change again; the tip of the Lizard is formed by rocks of the Man O'War Sheet, partly blue schists that form the beautiful cliffs above Housel Bay and Bass Point, and partly sandy schists of Old Lizard Head. At Lizard Point crowds flock to the most southerly place in mainland Britain. As we round Old Lizard Head these west-facing cliffs become wind-blasted, weatherbeaten and almost treeless.
At Caerthillian Cove we cross onto the serpentinite of the Goonhilly Sheet again and there is hardly a farm now until Predannack. Instead shallow isolated valleys work inland from Caerthillian, Kynance Cove and Gew-graze to Predannack and Lizard Downs. In the summer the grassy cliffs are a seaside riot of flowers. At Ogo-dour Cove the serpentinite gives way to Traboe Schist and almost at once, around Predannack Head, the dark cliffs and barren downs are replaced by farmland and softly bevelled grassy cliffs. Just to make the point, the serpentinite makes a final dramatic reappearance above Porth Pyg and Mullion Cove, forming some of the highest cliffs on the whole peninsula and the backdrop to the last of the Lizard's sublime beauty spots.
Past Polurrian the rocks revert to the more familiar slates of Cornwall and a very different coastline emerges, softer and more indented, full of caves, coves, sandy inlets and shingle bars. A trio of great family beaches follow in quick succession – Polurrian, Poldhu and Church Cove (Gunwalloe Beach). Past the cliffs at Halzephron the four kilometres of flint and quartz pebbles that make up Bar Sands are an ideal place for a blowy walk followed by a pint at the Halzephron Inn. Around Loe Bar the sand and shingle has blocked the estuary of the River Cober, trapping behind it Loe Pool and Carminowe Creek. In wind-blasted West Cornwall, the woodland walks around the pool are a rare treat. The busy harbour at Porthleven is surrounded by craft shops, restaurants and artists' studios. It's also a haven for foodies, with its locally caught smoked fish and spring food festival. A pint in the Ship Inn at the entrance to the harbour on a winter's day is rarely bettered.
Adventures for smaller children...
Helston Boating Pool, Lizard Lighthouse – climb the tower, sound the foghorn, Helston Folk Museum, Barbecue at Cadgwith Cove, Roskilly’s to see the animals and eat ice-cream, Seal Sanctuary at Gweek
Adventures for teenagers...
Coverack Windsurf Centre, Surf School at Poldhu and Kennack Sands, Lizard Adventure – coasteering and kayaking
Trips can be organised from Porthleven, Cadgwith and Mullion Cove in the summer.
Parking can be tricky in the summer as the most popular car parks fill up quickly. We’ve marked the larger car parks as well as the smaller ones on the maps. There are lots of smaller lay-bys and pull-ins, often only big enough for a couple of cars and we marked them too but be warned, many will be occupied in the busy summer months. Don’t be tempted to park in front of farm gates even if they look like they haven’t been used for a while.
In Helston the Museum of Cornish Life in the Old Butter Market is full of all sorts of fascinating objects from prehistory to tin mining and agriculture. Some of the best are domestic objects from the 1960s and 70s. You could follow that with Flambards Theme Park. It has rides for all ages plus static displays of helicopters and aircraft from next door Culdrose air base. It can be very busy in school holidays, especially on overcast days. Reduced entry in the afternoon. It's fun just wandering around Porthleven, Coverack and Cadgwith. They are full of boats, craft shops, cafes and restaurants. Roskilly's near St Keverne is ice-cream heaven and there are pigs and goats to see as well as wildlife ponds. For a taste of the serpentinite downs try Windmill Farm Reserve. It has boardwalks through wetland areas, dragonfly ponds, adders and a viewing gallery in the old windmill.
Many Lizard beaches all but disappear at high tide so it's wise to check tide times before you set off. For the remote and difficult to access beaches some pre-planning is needed, so as well as checking tide times, take lots of water and sun cream. A backpack is very helpful to keep your arms free if you have to scramble over rocks.
Church Cove, Gunwalloe
The following are the most popular beaches and have parking nearby, lifeguards, cafe and loos. On the west coast, Harbour Beach at Porthleven, Gunwalloe (Church Cove), Poldhu, Polurrian and Kynance. On the more sheltered east coast Coverack Cove and Kennack Sands are the key family beaches. There are also a couple of small coves that just happen to be conveniently sited next to facilities but are not really on the main family beach list. First, the tiny swimming beach at Cadgwith (west of The Todden). Secondly, just outside Mullion Cove is Porth Pyg. If you’re lucky there will be sand exposed for a few hours around low tide. Accessed via tunnel from the floor of Mullion Harbour under the concrete bridge.
More remote beaches
These beaches are less used, although often it's simply because they're stony or involve a walk. Starting at the northeast corner of the Lizard and running clockwise along the coast, Porthallow has a large pebbly beach and like Porthoustock you can park right on the beach itself. These two beaches are actually best at high tide. Godrevy Cove is a 20min walk from Roskilly's. In Coverack, if you want something a little more out of the way, Mears Beach (Porthbeer Cove) is revealed by the falling tide. It's a 20min walk from Coverack. More remote still is Downas Cove where sand is exposed for an hour or two each side of low water. Next is Lankidden Cove an unofficial naturist beach. The access from the coast path here is a little tricky. Housel Bay is a beautiful beach and a great place to swim – lots of rocks and small islands to explore and jump off. Park above Lizard Point then its a 1km walk along the cliff path. On the east coast, Pentreath is a glorious sandy beach at low water. Kids love the old ship's boiler stuck in the sand. Good surfing. Best accessed from the low cliffs north of Caerthillian Cove. Soapy Cove is about as remote and out-of-the-way as it gets, although this involves a tricky scramble down the valley from the coast path over boulders and through the stream bed.
Rocks of the Lizard - a slice of oceanic lithosphere
Basalt pebble, Lizard Point
Sit on a Lizard beach and you can't help but notice the great variety of colourful pebbles at your feet. Of course, there are lots of places in Cornwall where you can happily while away the hours combing the beach for shells and stones, but nowhere comes close to having the marvellous variety, colour and texture of pebbles seen here. For beachcombers, the Lizard is a sweetshop treat full of gobstopper colours and dolly mixture shapes. The origin of the Lizard rocks puzzled geologists for many decades. In fact, it remained a mystery long after the rocks were first described in detail in the second half of the 19th century. It just wasn't clear why these unusual, colourful and contrasting rocks were attached to the far end of Cornwall – a county otherwise made up of straightforwardly familiar rocks like slate and granite.
We now recognise that the Earth has two distinct types of outer layer or lithosphere – oceanic and continental. Oceanic lithosphere is fed from sources deep inside the Earth, and because heavier elements like metals were concentrated in the core when it was forming, so it too is dense, heavy and metal-rich. It forms a thin solid crust about seven kilometres thick at low points on the Earth's surface and therefore is usually covered by deep seas. Continental crust is made up of a mix of sedimentary rocks plus smaller amounts of igneous and metamorphic rocks. It is less dense, much thicker and more 'buoyant' than oceanic crust and so sits at higher elevations on the planet. This explains why it makes up most of the dry land and underlies most shallow seas like the English Channel.
In the normal course of events, oceanic lithosphere is formed out-of-sight under the sea at mid-ocean ridges and doesn't make it onto dry land at all as it tends to be overridden by the 'lighter' continents and drawn back into the deep mantle to be recycled. It's this 'invisibility' that explains why the origin of the Lizard rocks remained a puzzle for so long. It was simply assumed that the ocean floor was formed of similar rocks to those found on dry land. It was only in the Cold War when accurate nautical charts were needed to allow nuclear submarines to safely navigate the deep ocean, that the planet-wide scale of mid-ocean fracture zones and deep trenches was fully revealed. The new discoveries fitted with a theory put forward by Alfred Wegener in 1912 but dismissed at the time as fanciful. He observed that if you ignored the oceans, many of the Earth's continents fitted neatly together like a jigsaw puzzle as if they had once been a single landmass. The question of what process could have rifted the continents apart and created the oceans that now separated them, remained unanswered. It was only with the formulation of plate tectonic theory in the late 1960s that a mechanism to fit Wegener's idea was accepted. It proposed that the very high temperatures and pressures in the interior of the planet allowed rocks to flow in a very viscous way. If they could flow then powerful convection currents driven by upwellings of hot material from deep inside the planet could pull on the solid crust at the surface, rifting it apart and allowing new material to rise and replace it at mid-ocean ridges. The fracture zones discovered by survey are where the Earth's crust is rifting apart and where new oceanic lithosphere is being formed, and the deep sea trenches are where it is being consumed. Because the continents are more 'buoyant' they tend to sit above this process and are less likely to be recycled. Subsequent research has confirmed that parts of some continents are as much as four billion years old and show signs of having broken apart, moved off and reattached to other continental landmasses a number of times in their life. In contrast, oceanic crust is rarely more than a few hundred million years old, being constantly overridden and then recycled in the mantle. Before plate tectonics, few people could accept that the Earth was in such restless motion, creating and destroying oceans by rifting continents apart and then forcing them together again.
Plate tectonic theory was the key to unlocking the origin of the Lizard rocks. It turns out that about 450 million years ago the Lizard was part of an ocean floor between two continents, Gondwana to the south (present-day Africa, South America and southern Europe) and Laurasia to the north (present-day North America, Greenland, northern Europe and most of Britain and Ireland). As they moved apart, new oceanic lithosphere was created and above that the Rheic Ocean formed. Around 370 million years ago the mantle convection currents altered and the Rheic Ocean was caught in a collision between two converging continents. The Lizard sits right on the suture line where the continents met and where the Rheic Ocean finally closed, a line that continues east–west for thousands of kilometres. All along this line there are traces of the crash where fragments of oceanic lithosphere have been exhumed. The Lizard is one of the best examples, illustrating an almost complete sequence including the source rock from the mantle and the rocks that make up the crust.
At a mid-ocean ridge where mantle convection currents are rifting the solid crust apart, mantle rock is able to rise and melt to form a magma chamber close to the sea floor. Oceanic lithosphere created this way displays a very characteristic sequence of interrelated rocks called an ophiolite that are like a signature written in stone. If you keep this simple sequence in mind as you walk across the Lizard you can identify how far 'inside' the Earth you are. Starting on the ocean floor and moving down into the Earth they are:
OCEAN SEDIMENTS – a thin layer on the ocean floor
PILLOW LAVA AND BLACK BASALT DYKES – down to about 3km
GABBRO – from about 3km to 7km down
TROCTOLITE (CUMULATE) – about 7km to 10km down
MANTLE PERIDOTITE (SERPENTINITE) – 7km to 400km below the ocean floor
Some of these rocks, like gabbro and basalt, aren't exclusively found in oceanic lithosphere; they also crop up in continental crust as the result of volcanic activity that draws on the same source rocks deep inside the planet. It is the physical sequence that defines oceanic lithosphere.
Most oceanic lithosphere at the bottom of the Rheic Ocean was overridden and returned to the mantle, but two small slithers, represented by the Goonhilly and Crousa Sheets, were instead caught up in the collision and thrust upwards. They are no more than a kilometre thick and are twisted and tilted against each other. The classic sequence is most complete and clearest on the Crousa Sheet, which has been tilted towards the horizontal so that as you walk south from Manacle Point to Coverack and Kennack Sands it's as if you were walking into the Earth's interior. The top of the sequence – pillow lava and ocean sediments – are missing or hidden under the sea, but at Dean Quarry and Leggan Cove, swarms of basalt dykes injected into fractures in the solidifying gabbro mean this was a section close to the floor of the Rheic Ocean. At Godrevy Cove and Lowland Point you're walking on gabbro that cooled slowly in the main magma chamber a few kilometres below the ocean floor. At Coverack Cove you cross onto mantle peridotite, so here you are seven to ten kilometres down. South of Coverack at Black Head and Downas Cove you are on mantle peridotite ten kilometres 'inside' the Earth.
The rocks on the Goonhilly Sheet show a greater degree of deformation than the Crousa Sheet. A central ridge or dome of mantle peridotite (Goonhilly, Predannack and Lizard Downs) showing different levels of deformation is partly surrounded by rocks that were once cumulates (the Traboe Cumulates). Areas of gabbro and basalt have been heavily altered to the layered Traboe Schists found at Mullion Cove and between Porthkerris and Porthoustock (page 18). Since the acceptance of plate tectonic theory in the 1960s, it's been assumed that the slices of oceanic lithosphere on the Lizard represented a mid-ocean ridge ophiolite. However, more recent analysis has suggested it could be interpreted as an upwelling of mantle rock to form a magma chamber beneath thinning continental crust (for those into plate tectonics, this happens in a back-arc basin behind a subduction zone). If this is correct, the origin of the Lizard as mid-ocean ridge ophiolite is in doubt. For our purposes, we'll stick with the ophiolite explanation as the rock types in both instances are very similar, even if the processes are slightly different. What is important is that the Lizard is undoubtedly oceanic lithosphere, part mantle rock from deep inside the planet and part oceanic crustal rocks that melt out of it, and it is very unusual to find this sequence on dry land. In particular, the source rock, mantle peridotite (altered to serpentinite on the Lizard), has a very powerful effect on the landscape and ecology of the Lizard, and we'll now look at this rock in a little more detail.
Oceanic lithosphere - The source rock – mantle peridotite and serpentinite
The rocks of the oceanic crust come from the same source – mantle peridotite (peri-dot-ite). This rock makes up the great volume of the Earth down to about 400 kilometres. It's made up of green minerals like olivine and pyroxene that are stable at the extremely high temperatures and pressures found there – imagine the weight of a hundred kilometres of rock at a temperature of 1,200°C. One of the properties of mantle peridotite at this temperature and pressure is that it is able to flow in a very viscous way, allowing heat from the hot interior of the planet to be carried to the cooler surface. It is these convection currents that generate the movement of the continental plates at the surface, pulling them along at 10cm to 20cm per year (Figures 1 and 2). Mantle peridotite is only rarely found at the surface because it's not stable at the lower pressures near the surface and fractionates or melts to form the crustal rocks above or is drawn back into the Earth's mantle as more 'buoyant' continents override it. Occasionally, though, when ocean basins are closing and two continents collide, a section of ophiolite can be physically caught up in the collision and thrust upwards or obducted. This explains why ophiolite sequences are usually found entombed in the mountain ranges that form where continents collide like the Coastal Range Ophiolite of California and the Dun Mountains of New Zealand. On the Lizard the mountains of the period have been long since eroded away and the whole peninsula has been planed flat by the sea. Relatively unaltered 'fresh' examples of peridotite can be seen at Kennack Sands, Carleon Cove and Dollar Point at Coverack. It has a luscious deep green-black groundmass with lighter crystals (photo figure 3). Where peridotite is thrust upwards it rarely makes it to the surface unscathed and almost always it is altered or metamorphosed, although rather surprisingly it's not the rough passage from the mantle that does the most to alter the nature of the rock – it's simply contact with water.
Serpentinite – altered peridotite
Peridotite serpentine at Downas Cove
When peridotite encounters seawater or groundwater a strong chemical reaction follows, raising the temperature of the rock and increasing its volume by as much as half. The green pyroxene and olivine minerals are altered to rich shades of red, green and yellow to make the mineral serpentine named after its resemblance to the skin of a serpent (that it is found on the Lizard is just a coincidence). This altered rock is serpentinite and it comes in so many different colours and textures that it's sometimes hard to believe it is the same rock. The change started as soon as the peridotite encountered seawater 380 million years ago and is still happening today. It explains why serpentinite, despite being a tough rock, is a poor building stone – rather than repelling rainwater it wants to bond with it. Out on the downs and cliffs the natural serpentinite outcrops are covered with a deeply fissured rind where the exposed surface has weathered, expanded and cracked. If you were to split open these rocks you would find a much 'fresher' rock inside. Weathered serpentinite often has a reddish appearance because it is basically magnesium iron silicate and the iron part oxidises like rust. It also takes a polish, and where it is worn smooth by the sea (Downas Cove and Kynance) or by feet on a stile, the beautiful colours are brought out. To the modern eye, the deep rich colours of polished serpentinite can be a bit garish, but the Victorians loved it and an industry grew up to supply columns and mantelpieces for London mansions and banks supplied from a factory at Poltesco. A few craftsmen continue to make ornaments today in Lizard Town and Lizard Point.
Oceanic lithosphere - Crustal rocks – troctolite, gabbro and basalt
New oceanic lithosphere is formed when the mantle convection currents rift the overlying crust apart. This allows mantle peridotite to rise and at a specific point, when the weight of the overlying rock is no longer great enough to keep the component parts of peridotite stable, it starts to melt or fractionate out forming a magma chamber. This point is known as the Moho (Mohorovičić discontinuity) and it is typically located seven to ten kilometres below the surface. It defines the boundary between the mantle and the crustal rocks above. We know its location because seismic waves from earthquakes suddenly increase velocity as they pass from the lower density crustal rocks into the higher density mantle peridotite.
The stuff that melts out of the mantle peridotite at the Moho is, broadly speaking, basalt magma. At a mid-ocean ridge it is able to reach within a few kilometres of the ocean floor where, in a magma chamber, the first crystals form (this takes tens, if not hundreds of years) and fall like snowflakes to the base of the chamber near the Moho. They eventually solidify into a 'cumulate' rock called troctolite or trout stone made up of olivine and plagioclase. A red variety can be seen at Mill Beach in Coverack and a greener one at nearby Perprean Cove. Similar cumulate rocks crop out in a broad arc around the serpentinite of Goonhilly Downs but they're not well exposed and have been deformed. The one place on the Goonhilly Sheet where you can see these Traboe Cumulates is in the quarry north of Porthkerris. The magma that cools slowly in the main part of the magma chamber forms a coarse-grained igneous rock called gabbro. This has a lovely greyish-green hue from the olivine and pyroxene crystallised from the melt. Great boulders sit on the foreshore between Coverack and Lowland Point, and on the surface of Crousa Downs and Main Dale, places really worth visiting for both geology and flora. The boundaries between peridotite, troctolite and gabbro are often blurred and infolded with one another. On the beach at Coverack the Moho itself is exposed, and here you'll find beautiful transitional varieties of gabbro and depleted peridotite including a handsome variety with a bronze lustre (below).
As the crust is continually rifted apart, minor earthquakes fracture the solidified gabbro and liquid magma from the chamber is injected into the fissures where it rapidly chills. These are the fine-grained black basalt dykes seen at Dean Quarry, Leggan Cove and Godrevy Cove, and they form the upper part of the crust close to the ocean floor. At the top of the ophiolite sequence they make up most of the crust. Some lava is squirted directly out onto the sea floor like toothpaste, building up layers several kilometres thick. A steady rain of ash and other deep sea sediments settle on these pillow lavas completing the ophiolite sequence. Mullion Island is a raft of pillow lava (probably part of the Roseland Breccia) and boat trips get close enough for the pillow shapes to be visible. These rocks form most of the oceanic crust which, as it moves away from the ridge, cools and solidifies.
At Coverack Cove, rather amazingly, you can actually stand on a solidified section of Moho and see some of these transitions with your own eyes. Here, within 300 metres you can walk from the dark green peridotite of the mantle at the south end of the beach, to a depleted peridotite (where minerals have started to melt out) to all sorts of transitional varieties and colours of gabbro on the north end of the beach. And this is the key point about the geology of the Lizard: there are few places on Earth where you can stand on the rocks of the Moho that come from so far inside the planet and where the physical structure of the crust and mantle is so conveniently laid out before you in the rocks and pebbles of the seashore. It's not often Mother Earth lifts her skirt so you can glimpse her petticoats, but on the Lizard that's exactly what she does and why geologists travel great distances to see it.
Metamorphism - Rocks deformed and altered
Traboe schist, Million Cove
All the Lizard rocks have been altered or metamorphosed to some degree, and we've already seen how mantle peridotite is fundamentally changed to serpentinite simply by coming into contact with water. The intense forces that thrust up the Lizard rocks have also had an effect, altering most to schists. This is a rock of any origin that has been so heavily squeezed and stretched that it partially recrystallises – often into bands of different composition and colour to become 'foliated' or layered. Schists often have a granular texture like sugar. At Bass Point the Landewednack Schist built into the hedges sparkles in the sunshine.
Of the two sheets of oceanic lithosphere on the Lizard, the Crousa Sheet is the least deformed, although even here you can see that the large crystals in the gabbro have started to shatter. This is the best place to start exploring the rocks of the Lizard ophiolite as the rocks retain much of their original structure and almost the whole ophiolite sequence is displayed on the coast. Coverack Cove stands on the Moho: walk south towards Downas Cove and you're moving 'deeper' into the planet on mantle peridotite (altered to serpentinite); walk north towards Lowland Point and Manacle Point and you are walking 'up' towards the floor of the Rheic Ocean, at first just on gabbro but then as you get nearer to the top of the sequence around Godrevy Cove and Dean Quarry, increasing numbers of black basalt dykes fill fractures in the gabbro.
On the Goonhilly Sheet the rocks are more heavily deformed and it's sometimes difficult to recognise them as the equivalent rock on the Crousa Sheet, although modern geochemical analysis enables us to more accurately identify their origin. You see the characteristic schist layering in the serpentinite west of Kynance Cove and in the blue Traboe Schists (once gabbro and black dykes) south of Porthkerris and at Mullion Cove, but they look very different to the much less deformed gabbro boulders on Main Dale and Coverack Cove. Lovely examples of cumulates altered to schist can be seen in the quarry north of Porthkerris and at Carrecwynn near Goonhilly Earth Station.
The Man O'War Sheet - The Gondwanian continent
Man O'War Gneiss, near Lizard Point
The Gondwanian continent makes it ashore south of Lizard Town and on a thin coastal exposure as far as Cadgwith. This sheet is made up of a mix of oceanic and continental rocks that are about 500 million years old and so pre-date the creation of the Rheic Ocean and the rocks of the Goonhilly and Crousa Sheets. The rocks on the Man O'War Sheet have been altered to schists and some have been subjected to still higher pressures and temperatures to form a gneiss (pronounced nice).
The eastern corner of the sheet is made up of pillow lavas that have been altered to the lovely glossy blue Landewednack Schists that form the handsome cliffs around Housel Bay, Landewednack and Bass Point (page 65). The rock is sometimes shot through with layers of green volcanic ash that settled on the sea floor above and between the pillow lavas (above). There is an obvious similarity in appearance with the Traboe Schists of Predannack and Porthoustock.
Old Lizard Head Schist, Lizard Head
The western corner from Polpeor Cove near Lizard Point to Caerthillian Cove is made up of Old Lizard Head Schist, originally mud and sandy sediment on the bottom of a sea. Small blocks of this pretty rock also turn up on the south side of Porthallow Beach and in blocks along the main fault lines between the Lizard rocks and the Roseland Breccia. The rafts of quartzite in the Roseland Breccia and at Nare Head were also once Gondwanian sandstones.
The third type of rock is the Man O'War Gneiss, which just makes it onto the southern tip of the Lizard at Old Lizard Head and offshore on the Man O'War Reef. These rocks were probably once granites but have been subjected to severe pressures. It has a rather dreamy, corrugated appearance. Pebbles lie on the beaches at Polpeor Cove and Pystyll Ogo. Similar rocks make up much of Brittany and the Channel Islands, which are part of the same Gondwanian continent.
Kennack Gneiss and Roseland Breccia - Evidence of obduction and collision
The distinctive pink rock you find on the beaches on the east coast between Kennack Sands, Carleon Cove and Landewednack is Kennack Gneiss. This rock formed when the still hot block of Lizard ophiolite was being thrust upwards. The surrounding continental rocks melted to Kennack Gneiss and mingled with a darker basalt magma from the ophiolite to form the banded rock you can see on the foreshore south of the road at Kennack Sands. Kennack Gneiss forms the valleys at Poltesco, Cadgwith and Gwendreath and extends inland to Goonhilly Downs. It is noticeably more fertile than the surrounding serpentinite and, in contrast to the treeless valleys found on serpentinite like Downas Cove and Gew-graze, will support woodland. The elm woods at Gwendreath behind Kennack Sands have avoided Dutch Elm Disease precisely because the serpentinite acts as a protective treeless quarantine zone.
One of the consequences of the closing of the Rheic Ocean was that as the Gondwanian continent (the Man O'War Sheet) drove north it acted like a giant bulldozer, scraping and uplifting everything in its path, including sections of its own continental rocks that fell off its front edge as it advanced. Great rafts of pillow lava and quartzites, some hundreds of metres wide, were scooped up and mixed together with limestones and slates to form a three kilometre wide rock jumble spanning the width of the peninsula – this is the Roseland Breccia. It makes up much of the good farming land of the Meneage south of the Helford estuary. It is best seen on the walk north from Porthallow where crags of milky quartzite stand out at Nare Head and huge blocks have tumbled down to the shore. Exactly the same rock crops out on the other side of Falmouth Bay at Tregeagle's Quoits near Veryan on the Roseland. Perhaps the best place to appreciate the mixed-up nature of the breccia is at Men-aver near Nare Head. Here a mix of small rocks and pebbles that once filled an underwater canyon near the advancing front edge of Gondwana, form a conglomerate on the sea shore – a plum pudding mix of pebbles of every kind.
Plants of the Lizard - an inadvertent Eden
I recently saw the barely clad bottom of a naturalist sticking out of a small stream near Kynance. The only things he had on, besides his skimpy trunks, were a snorkel and mask. His head was underwater – no doubt searching for some rare plant or animal. You should expect to encounter this sort of behaviour on the Lizard – the sudden gleeful yelps as botanists and lichen hunters stumble across rarities. The Reverend Charles Johns, who in 1848 wrote one of the first guidebooks about the Lizard, laid his hat on the ground at Caerthillian Valley and covered three different species of clover – two found nowhere else in Britain. Famously in the world of lichens, five species new to the UK were discovered on a single morning in 1986. No wonder so many botanists are held spellbound on the Lizard.
There are more than 600 species of flowering plants on the Lizard, nearly a quarter of all UK species. It's all the more extraordinary when you consider that half of the Lizard is underlain by serpentinite, a spectacularly barren, almost toxic bedrock that usually produces a markedly sparse and specialist flora. The explanation for this paradoxical richness is found in part in the many different and unusual Lizard rocks. But above all, it seems to be a serendipitous coming together of multiple factors: a very mild maritime climate, but one prone to gales and salt winds; waterlogged and boggy soils, but ones that often parch and dry out in the summer; soils of greatly contrasting fertility and pH; and lastly man's influence, because the Lizard is far from the wild place it first seems.
Any single factor taken on its own would have an interesting effect on the flora; taken together, they combine, overlap and interact in fascinating and surprising ways. Contrasting plant communities grow side-by-side in a mosaic that changes within metres but also changes markedly over time with the cycle of heath fires. It's not so much that conditions are ideal for growth, but that there is such a variety of different, difficult conditions. Each habitat, with its own combination of factors, attracts its own specialist plants.
The influence of soil and bedrock - An odd mix of assorted opportunists
Water hemlock near Coverack
The Lizard has a great variety of soils because it has a great variety of different rocks, and each one has its own peculiarities that affect the flora. The most distinctive are the serpentinite soils. As we've seen, serpentinite is really a creature of the Earth's deep interior and, as if to make a point of its reluctant appearance at the surface, left to itself it forms a particularly sullen, unwilling and barren soil with few of the nutrients, like nitrogen, phosphorus and calcium that are needed for plant growth. If that wasn't enough, it's also laced with metals like magnesium, chromium and nickel, which many plants find toxic. So it's no surprise that serpentinite is closely associated with the areas of uncultivated heathland. Where it is cultivated, usually for grassland, it requires high levels of fertiliser to make it productive.
In places in the world where serpentinite occurs it usually hosts a sparse and specially evolved or endemic flora. Plants that can tolerate the conditions tend to diverge into new sub-species as successive generations become better adapted. In this respect the Lizard is unusual as recent ice ages have swept away any endemic flora and instead, an odd mix of assorted opportunists which would not normally grow together, fill niches in the ecosystem. Most plant life is a bit nonplussed when faced with the odd ingredients in this soil, and those plants that do prosper have strategies that allow them to deal with its peculiarities. For instance, many plants cope with the low nutrient levels by simply being small and slow growing; serpentinite soils rarely support lush vegetation or woodland. Some plants like dodder, lousewort and broomrape have parasitic lifestyles that reduce their reliance on the soil – they get their nutrients directly from their hosts. Others, like the insectivorous pale butter-wort and round-leaved sundew, supplement the meagre nutrition available by catching insects on their sticky leaves to make a nutritious fly soup.
In this way the Lizard is atypical of most serpentinite areas because, far from having a limited flora, it's something of a botanical wonderland. One example of this is that you'd expect to see a base-loving flora because it's an ultra-basic rock. Instead, on many parts of the downs you come across a familiar cast of characters from the acid soils of Cornish cliff and moor: the demur pink-flowered ling or heather; the deep purple flowers of bell heather; in damper corners the glamorous cross-leaved heath and the sweet coconut scented gorse. Between them you'll find lousewort, tormentil and devil's-bit. This is odd because base-loving and acid-loving floras have contrasting and mutually exclusive biochemical needs. Acid-loving plants cannot thrive on base soils and vice versa, but on the Lizard they are frequently found growing side-by-side. The explanation lies in the soil's origin because in many places on the Lizard the soil has been imposed from above rather than deriving from the bedrock below. Where this happens, the influence of the base-rich serpentinite and gabbro is masked by layers of acidic peat and loess – a wind-blown silt that covered Europe during glacial periods. Where serpentinite emerges at the surface; where peat and loess have been eroded away on valley slopes; where man has dug a quarry, a ditch or a prehistoric barrow or where the peat and soil have been removed for fuel, then the base-loving flora proclaims itself. This is most clearly signalled by the appearance of the free-flowering Cornish or Goonhilly heath. Unusually for the heather family, this is one member that loves, and is confined to, base-rich soils.
Cornish or Goonhilly heath
The very high levels of magnesium in serpentinite seem to be a particular problem for many plants, although some coastal species like thrift and scurvy grass seem at home here. After a fire on the downs, they often turn up along with drifts of ox-eye daisy much further inland than you would normally expect. It's possible they've evolved strategies for dealing with magnesium in the salt-drenched soils of the coast and that adaptation, along with the infertility of the serpentinite soil, protects them from being crowded out, as they usually are, on more 'normal' soils by more vigorous inland species. Plants that love basic soils like dropwort, meadowsweet and bloody cranesbill typically favour chalk and limestone – soils rich in calcium – but they also thrive here despite the poverty of calcium in the serpentinite soils. Their ability to thrive on the Lizard neatly illustrates they are not true calcium-loving plants or calcicoles, but rather they seem able to tolerate the high levels of magnesium common to limestone, chalk and serpentinite. Spring sandwort is so adapted to metal-rich soils it is almost completely confined to spoil heaps of old lead mines in the Mendips and the Dales. It's so specific to metal-rich soils that it is considered an indicator species for metal contamination and yet, on the Lizard, it grows widely on the serpentinite soils.
In one of those eye-catching contrasts so typical of the Lizard, the gabbro soils where the bedrock is deeply rotted can be remarkably fertile. The fields south of St Keverne have the texture and colour of velvety cocoa. The contrast between serpentinite soils and those of the weathered gabbro is best seen at Gwenter behind Kennack Sands. A small stream follows the line of a fault between the Crousa and Goonhilly Sheets so there isn't the usual gradual transition between the two here. To the west is the uncultivated serpentinite of Barrow Croft and Goonhilly Downs; to the east on the weathered gabbro are the farms of Trelan and Gwenter. Sit on one of the barrows overlooking this little valley and you can see at a glance, just from the vegetation, where the serpentinite ends and the gabbro begins. It's a very striking moment – one that also gives you an insight into the large-scale tectonic processes that thrust the Lizard rocks to the surface. On Crousa Downs and Main Dale the gabbro is only lightly rotted and large blocks of gabbro, called crusairs, weather out and sit above the surface (page 46). Here you find a variation in the heath flora of the serpentinite, and between the Cornish heath you find slender St John's wort with heath spotted, lesser butterfly and fragrant orchids. These are two of the best places to visit for serpentinite/gabbro flora (and both are close to ice-cream heaven at Roskilly's).
Fringed rupture-wort, Lizard Point
The schist soils formed from recrystallised gabbro and basalt are mostly free of the difficulties associated with serpentinite and are generally fertile and farmed. At Predannack Head the Traboe Schists form an island of fertility surrounded by serpentinite heath, and like at Gwenter, the type of bedrock and its location can be inferred from changes in the vegetation. On the Man O'War Sheet around Lizard Town, the Old Lizard Head Schists are particularly freely draining, and in the summer this often induces drought conditions that mimic a Mediterranean climate. This is the only outpost for Lusitanian plants like fringed rupture-wort on the British mainland. Dried and taken with wine, it was thought to cure rupture or hernia – hence its Latin name Herniaria ciliolata. It is also said to be efficacious on gonorrhoea and festulous ulcers, especially the sort that are foul and spreading – a big claim for a little plant. Look out for it on the path below Lizard lighthouse. The south-facing slopes of Caerthillian Valley are famous for their clovers, including long-headed, upright, bird's foot, suffocated, twin headed and zigzag among others.
The influence of climate and exposure - A northern outpost of Lusitania
The chemistry of the soils and bedrock are primary influences on the flora but there are other important influences that straddle the geological boundaries – in particular, the impact of climate and exposure. The climate here is deeply influenced by the surrounding sea and it's warm, moist and almost frost-free. It's so mild that the Lizard is a far northern outpost for Lusitanian plants like Cornish heath, pale butter-wort and fringed rupture-wort – species that really belong on the Atlantic coasts of Portugal, Spain and France.
Wet and boggy soils that parch in the summer
Windmill Farm Nature Reserve
Serpentinite weathers to a claggy, thin and impervious yellow clay that impedes drainage. After rain the downs can be like a lake with water standing, often for days and sometimes for weeks, in pools, track ruts and in the runnels between tussocks of purple moor grass. This is aggravated by the absence of a clear pattern of drainage, as even millions of years of rain and wind have made little impact on the serpentinite landscape and it retains a striking tabletop flatness from when it was planed flat by the sea. In addition to the more-or-less permanent pools at Bray's Cot, Hayle Kimbo, Croft Pascoe and Ruan's Pool (which may well have been dug by prehistoric man for their livestock), the downs are covered by numerous ephemeral pools and patchworks of micro-habitats in cart tracks, bomb craters and old quarry pits. Here in the spring and early summer before the pools dry out, pillwort, water-crowfoot, chives and yellow centaury bloom.
The wettest areas are revealed by the presence of black bog rush and large tussocks of soft rustling purple moor grass – areas which you soon learn to avoid as you walk the downs. The damp runnels between the tussocks (which turn white in the winter) have an ecosystem all of their own with bog pimpernel, creeping willow and land quillwort. Great burnet, usually a plant of flooded meadows, survives prolonged periods of flooding by retreating to its thick underground stems (rhizomes) and grows happily in the waterlogged conditions on the highest point of the downs at Dry Tree along with spiky yellow bog asphodel. The high rainfall and lack of drainage promote the acidic conditions needed for the formation of peat, and it takes only a few centimetres to form a pocket large enough for acid-loving heathers to get established. This explains the curious phenomenon of base and acid-loving plants growing side-by-side. Wherever relief can be found from the boggy conditions – on hedges, walls, prehistoric barrows, even the little mounds that used to hold anti-glider poles – bell heather and gorse are noticeably heathier. In boggy areas heather keeps its feet dry by growing into the tussocks of purple moor grass.
The thin soils over the serpentinite, gabbro and the free-draining schist struggle to retain water in the summer and are soon parched, mimicking a Mediterranean climate, and southern African plants like Hottentot fig and mesembryanthemum thrive on the cliffs. Many animals and plants alter their life cycles to avoid the summer drought. The tiny land quillwort grows during the winter, becoming dormant in the summer and you can find tadpoles in the deep track ruts at Croft Pascoe Forest at Christmas while the rest of the UK is covered in ice.
On the cliffs
In general, the difficulties of living on the exposed coast, with its drying winds, burning salt spray and meagre soils, trump the influence of any particular bedrock, and it's a place were coastal specialists dominate. Anything that pokes its head up risks getting it blown off, so this is no place for delicate leaves and flowers. Specially adapted low-growing forms of species are common, like prostrate asparagus on Asparagus Island and the juniper bushes in Gew-graze Valley. In places the heather and gorse are pruned by the wind so they are only ten centimetres high. They hug the ground where the wind is slower and where cover reduces drying out of the soil. The flora alters subtly as it approaches the coast, and Cornish heath and gorse become less frequent and heather dominates. Gathering and retaining water is one of the great challenges in this environment. Many plants have small, waxy fleshy leaves to store water and reduce water loss. On the lowest parts of exposed cliffs, well within reach of the spray from waves, is rock samphire. Its long woody roots penetrate deep into bare rock crevices. A little higher up the cliff thrift and rock sea-spurrey perform a similar feat. On the rocky outcrops English stonecrop seems to exist on bare rock alone.
In the summer, the grassy cliffs like Pen Olver, Kynance Heights and Lizard Head and the sheltered slopes of headlands like Chynhalls and Lankidden put on one of the most colourful shows on the coast. One of the first flowers to appear in early spring is the adorable spring squill, dusting the cliffs in blue sparkles. Sea campion forms great drifts on the sunny side of field walls along with kidney vetch, rest harrow, sea carrot and bird's-foot trefoil. Later in the summer, the small pink flowers of common centaury are accompanied by wild thyme and sheep's-bit scabious, particularly on the schists of Housel Bay and Lizard Point. On Kynance Heights thyme broomrape takes all the nutrients it needs from the roots of wild thyme, sending up a stubby red flower stalk in early to mid-summer. It's not the only parasitic plant on the coast. Gorse and heath are often covered in the tangled pink and red threads of dodder.
The influence of humans - A history of beneficial exploitation
The downs that feel so wild are, to a large degree, a product of human activity, and from the first moment they set foot in this landscape humans have cut, burnt and cleared to create favourable habitats for prey and livestock. More recently, in the Medieval period, it was humans that stripped away the peat and soil for fuel, and in doing so unmasked the full influence of the serpentinite bedrock on the flora. Quarrying has created numerous pools and ponds that teem with amphibians and insects. Even the Luftwaffe joined in, adding dozens of bomb craters on Goonhilly in 1941. And, a little surprisingly, at a time where human influence on the environment is often portrayed as wholly malign, the effect has been to increase the richness of habitat and biodiversity, creating a sort of inadvertent Eden.
The most recent glacial period reached its peak about 20,000 years ago. Enormous ice sheets reached as far south as the Bristol Channel and the Lizard was a sub-arctic landscape of grassland, birch, Scots pine and juniper (a few bushes still cling on at Gew-graze Valley). Humans, who had reached Britain in previous warm periods, had long retreated to warmer refuges in southern Europe. When the thaw came, about 13,000 years ago, they started to move up from Iberia to Brittany and across to Cornwall. So much water was still locked up in the northern ice sheets that it's possible they walked across what is now the bed of the English Channel to get here. They carried with them, on their clothes and belongings, spores and seeds of plants from their Lusitanian home, species like Cornish heath and fringed rupture-wort. A sudden and rapid rise in sea levels 6,000 years ago stranded these Lusitanian plants far from their homeland.
When the first prehistoric people arrived here it seems unlikely that the downs or the more exposed parts of the west coast were ever thickly wooded because the soils are just too poor and the exposure just too great. The camps of the first (Mesolithic) people seem to be mostly on these naturally open areas, although many coastal camps from this period must now be lost under the sea. Hazel nut fragments radiocarbon dated to around 7,500 years ago have been found northwest of Croft Pascoe Forest on Goonhilly and at a coastal settlement at Poldowrian. After farming was introduced about 5,700 years ago, the downs seem to have been intensively grazed, encouraging the growth of grasses and holding in check natural regeneration of scrub and woodland. This is inferred from excavations which showed that Bronze Age (2000–800BC) barrows were being built on top of grassland at Goonhilly. A combination of nutrient loss and heavier rainfall seems to have led to an increase in the formation of peat about 3,000 years ago, favouring the acid-loving flora. As the cliffs and lower slopes of the high ground were progressively cleared for cultivation, so grazing on the downs seems to have reduced in intensity, allowing the development of the sort of heathland we see today.
Heathland appears to have evolved as a coastal habitat, and both heather and gorse are well adapted to regenerate if their buds and foliage are burnt off by gales or salt winds. So when humans deliberately set fire to the heath to promote soft growth for cattle to graze, the plants are well adapted to regenerate and survive, indeed they seem to thrive. Controlled burning also has the effect of resetting the biological clock so the habitat is kept in a state of perpetual adolescence. After the canopy of heather and gorse is burnt away, at least for a few years, foxglove, ox-eye daisy and thistles carpet the blackened downs as Cornish heath and gorse regenerate from their charred stumps.
Pollen evidence seems to suggest that in prehistory Cornish heath was not the dominant plant of the downs that it is today. Widespread cutting of peat to fuel the smelting of tin in the 14th and 15th centuries pared away the masking effect of the loess and peat to reveal the full effect of the base-rich bedrock. It's at this time that the base-loving flora and, in particular, Cornish heath seems to have become dominant. This dynamic ecosystem is reliant on human activity, and left to itself it would probably revert to the sort of scrubby willow carr you see around Windmill Farm. In the last fifty years grazing on the heath has greatly reduced and that has reduced the variety of habitats and the diversity of species. The National Trust and Natural England have introduced hardy highland cattle and Shetland ponies to reverse the loss, and you might see trucks touring the downs to keep micro-habitats in track ruts open. Continued human exploitation and management of the downs is essential to support its biodiversity.
Conclusion - A story told in pebbles and plants
I hope that gallop through the geology and flora of the Lizard goes some way to explaining why this corner of West Cornwall excites so much interest and ardour. It's been fifty years since plate tectonics finally unlocked the puzzle of how these unusual rocks came to be here and unravelled the story of their birth. Even so, it's difficult to comprehend the forces that could pick up a block of oceanic floor twenty kilometres wide and thrust it onto a Cornish shore. One of the things that is so interesting about the Lizard is the way the landscape can be read like a geological or botanical textbook with the pages laid out beneath your feet. You are walking across a story as well as a landscape. On the Lizard a colourful pebble or a rare flower unlocks a much bigger story. Just from looking at the colourful pebbles on Lizard beaches a story has unfolded of how the Lizard was the sea floor of a lost ocean and of how that slice of ocean floor was trapped in a vice between two colliding continents and thrust upwards to the light rather than being recycled in the Earth's mantle.
Folded slates near Loe Pool
Where else do you get the chance to actually walk across the structure of the Earth's interior so that as you walk from Godrevy Cove to Coverack and Kennack Sands you are taking a journey into the centre of the Earth? From the pillow lavas of the Rheic Ocean seabed to the grey-green crystals of gabbro in the magma chamber to the mantle rocks south of Coverack, it is a window that allows us to peer deep inside the Earth. After a swim at Jangye-ryn, take a moment to examine the contorted strata in the low cliffs behind the beach – they tell a story of a restless planet where oceans, mountains and continents are perpetually created and destroyed. A serpentinite pebble at Kynance is a postcard from the Earth's deep interior, a memento of the doomed Rheic Ocean.
For botanists too, the Lizard is full of surprising moments. The very particular and unusual circumstances on the Lizard – its variety of rocks and soils; its exposure and climate; its various and diverse habitats – show how plants improvise and adapt. It's striking how many plants appear in slightly odd situations and in odd combinations as if they've been thrown together on some sort of seaside vacation. Where else can you step from a Mediterranean flora to that of the moors of northern Europe or in the space of a few metres move from the serpentinite flora of La Coruña and the Massif Central to a flora more reminiscent of the chalk downs of Dorset?
These extracts are from the Lizard Guidebook