FIG 59. Sketch map showing the orientation of some of the main faults in West Cornwall.
Another similarity to Land’s End is the widespread topographic platform at about 140 m above sea level. This platform is particularly clear north of the Carnmenellis granite but is also obvious in the Godolphin granite (Fig. 57). In the Porthmeor and Camborne areas the platform is particularly distinctive, and the continuity of its landward slope is clear on the slope map. It has generally been assumed that these platforms were cut by storm waves when the sea stood at this level about 3 million years ago. At this time, West Cornwall would have consisted of granite islands, like the present Isles of Scilly, while the surrounding Devonian bedrock (killas) was submerged.
The western part of the St Austell granite (A5) lies within Area 1, and again its resistance to landscape erosion is shown by the high ground that it occupies. The remarkable feature of this granite is the way it has been altered by the circulation of hot fluids. Much of the feldspar in this granite has been altered to the mineral kaolinite, which is a member of the clay mineral group that is the key component of china clay. The result of this is that the St Austell granite has been quarried, particularly in its western part within Area 1. The kaolinite has been extracted from the rotted granite by high-pressure water jets, which leave large volumes of quartz and feldspar grains that are heaped up in enormous and obvious spoil heaps.
Most of the original heathland and moorland on the St Austell granite has been destroyed by the mining industry. More recently, the Eden project redevelopment of one quarry complex (in Area 2) has brought many visitors to the area.
Landscape B: The Lizard
Lizard Point is the most southerly headland in Britain, part of a wider Lizard landscape comprising a flat heathland plateau bounded by dramatic cliffs and small coves (Fig. 60). Notice how steep many of the sea cliffs are, and that they show little in the way of well-developed, regular layering or fracturing. Unlike the other upland areas of Cornwall, the Lizard is not underlain by granite. As mentioned in the general section of this chapter, some of the area is underlain by serpentinite, a distinctive, decorative rock that was originally part of the Earth’s mantle, below the crust and many kilometres below the surface (see Chapter 3). Other parts of the Lizard bedrock were originally basalt lavas and minor sheet-like intrusions along with small amounts of sediments, all similar to successions elsewhere that appear to have formed in or below the Earth’s oceanic crust. During the Variscan mountain building, this mixture of distinctive bedrock types appears to have been squeezed up amongst the strongly compressed Devonian killas. Today, the exceptional bedrock chemistry of the unusual Lizard rocks is the reason why the peninsula has such a variety of rare plant habitats. Much of the peninsula is a National Nature Reserve (NNR) or owned by the National Trust.
As in Carnmenellis and Land’s End, a wave-cut platform has been identified on the Lizard, although its level is rather lower. In fact, the platform actually forms the Lizard Plateau and is remarkably flat, the ground surface varying between 60 and 100 m above sea level over large areas. This relative flatness probably reflects the rather uniform composition of the rock materials involved, and their uniform resistance to weathering and erosion.
The coast of the Lizard Peninsula is formed almost entirely of steep cliffs, particularly around its southwestern perimeter. A few small beaches do occur in sheltered locations, such as at Coverack (b1), and picturesque fishing villages are scattered along the east side of the peninsula around small coves and gullies.
FIG 60. The Lizard coastline. Note the contrast between the jagged coastal cliffs and the flat inland landscape. (Copyright Dae Sasitorn & Adrian Warren/ www.lastrefuge.co.uk)
Landscape C: Cornish killas
Most of the bedrock of West Cornwall is Devonian sediment, folded, faulted and – locally – altered during the Variscan mountain-building episode (see the general section of this chapter). The Devonian sediments, known to miners and quarrymen as killas, have been less resistant to landscape weathering and erosion than the granites (A) and the Lizard Complex (B), and so have been preferentially eroded to form lower landscapes. All the major bays and estuaries of this Area, such as St Ives Bay (c4) and the Carrick Roads at Falmouth (c7), are situated in killas areas for this reason. The Variscan folding and faulting that deformed the killas has also locally influenced the directions of valleys and their slopes, which have picked out variations in the killas layering, giving an east-west grain to the landscape (Fig. 61).
FIG 61. Slope map of the eastern part of West Cornwall. The main granite bedrock areas are outlined and important boundaries in the Devonian bedrock indicate the direction of the Variscan folding. Note the circular china-clay workings that are visible in the St Austell granite (A5).
FIG 62. Complex landscape of the North Cornwall coast, looking eastwards from Crantock Beach, over the Pentire Ridge towards Newquay (Fig. 52, c2) and Watergate Bay. (Copyright Dae Sasitorn & Adrian Warren/ www.lastrefuge.co.uk)
FIG 63. Headlands, bays and beaches of the Newquay area (Fig. 52, c2), looking eastwards from a point 2 km west of Figure 62. Crantock Beach is visible in the middle distance. (Copyright Dae Sasitorn & Adrian Warren/www.lastrefuge.co.uk)
The Flandrian sea-level rise, which ended only 5,000 years ago, has also left its mark on West Cornwall. The most obvious legacy is the extensive array of tidal estuaries at the mouths of the main rivers, which are flooded river valleys or rias. The most striking example is the series of branched rias around Falmouth known as the Carrick Roads (c7). These extend northwards across half of the width of West Cornwall and have had an obvious major influence on the road and rail transport pattern of the area. Major branch rias to the west, north and east around the Carrick Roads divide this part of the Cornish landscape into numerous isolated peninsulas. The inland valleys of the killas areas tend to be deeply incised with little widening, and the branching patterns of these valleys are very clear on the slope map. The rias are obviously the direct result of the drowning of valleys of this form by the Flandrian sea-level rise.
The coastline of the killas landscape of West Cornwall is extremely varied: small, sandy coves alternating with rocky promontories and high cliffs are typical of this part of the north coast (Figs 62 and 63). This irregular coastline is due to local variation in the type and strength of the killas bedrock, with weaker units (often slates) eroding to small bays while the more resistant rocks (often limestones or quartzites) form the headlands.
The sandy bays of north Cornwall (c1, Padstow and the River Camel Estuary; c2, Newquay Bay; c3, Perranporth and Perran beach; c4, St Ives Bay) are famous for surfing, due to the splendid waves that roll in from the Atlantic Ocean. Apart from Padstow Bay (c1), at the mouth of the River Camel, most of the north Cornwall beaches are not obviously linked to river sources of sand and so must have been filled by sand transported from offshore sources by storm waves. At many famous surfing beaches, such as Perranporth (c3), sand banks built up by winter storms can be eroded in the summer, resulting in dangerous currents sweeping out to sea. The wind-blown dunes of the Penhale Sands, north of Perranporth,