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Geology & Geography of the North Cornish Coast - a coastal walk alongside the Atlantic Ocean, from Bude to Trevose Head via Crackington Haven & the Ro...

October 31, 2018

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Geology & Geography of the North Cornish Coast - a coastal walk alongside the Atlantic Ocean, from Bude to Trevose Head via Crackington Haven & the Rocky Valley, Cornwall

October 31, 2018

The stunning steep landscape of this part of the North Cornish Coast face head on, both the full force of the Atlantic winds and the powerful Atlantic surf, with the wine dark open sea visible as far as the horizon. 

The steep rugged headlands act like a buttress against endless waves in motion, with the Ocean, at this time of year, particularly wild and brooding, yet other times calm and inviting.

This area of Cornwall, as with the rest of the UK, has experienced both uplift and sinking beneath the sea over the course of time.  It was during the sinking phase, when Cornwall was inundated by the sea, that deposits were laid down, to leave behind sandstones, slates and shales, which dominate the county in the 21st century. 

The oldest rocks in north Cornwall date back to the Devonian & Carboniferous periods, circa 350-400m years before the present.  The exception to the rule is Cornwall’s Lizard Peninsula, where the metamorphic and igneous rocks are much older, of pre Cambrian date, circa 600 plus years ago! Rare examples of Ordovician quartzites (500m years old) and Silurian limestones (440m years old) can be found as Breccias or broken masses – such as Black Rock at Widemouth Bay. 

Cornwall was actually near the equator, before it physically moved much further north, as a direct result of continental drift, which obviously led to a dramatic change in climate, some 200m years ago, including the onset of the Ice age.  Even though the ice sheets covered much of Wales, they only reached as far as the north cost of Cornwall, although the south west peninsula did experience the freeze and thaw processes that we associate with permafrost conditions. 

 

The last and most recent ice age occurred merely 11,500 years ago, but most of Cornwall escaped the glacial ice sheets, , so you do not find the usual features you find in the rest of the UK - as in Scotland, Wales and the Lake District - are associated with glaciation and glacial drift.  Erratics, Scree, Drumlins, Moraines and Boulder Clay, along with Cwms, Pyramidal Peaks (like the Sugar Loaf, Abergavenny) and U shaped valleys are missing in  this region, instead V shaped valleys prevail up and down the the north coast here.

The south west peninsula of Cornwall originally formed part of a vast mountainous landscape, which included south west Ireland and Brittany in France.  This was a direct result of major earth movements in Europe circa 250m years ago, referred to as the “Armorican” period associated with mountain building, whereby the earth crust is made up of plates floating on molten mantle, giving rise to dramatic wave like folds, bends, faults, ridges and valleys, in what was a horizontal rock layer, which can be seen today in this part of Cornwall.

The vast majority of rocks visible on the Cornish coast, were in place before the early Permian period (circa 280m years ago).  It was at this time that Granite existed as liquid magma moving beneath sedimentary rocks above, while at the same time, hot gasses and vapors found gaps through the cracks and then condensed to form rich veins of crystals.  

Inevitably, the molten magma forced its way up through the layered sedimentary rocks, eventually cooling down to form granite.  In land, in Cornwall and Devon today, we can see the exposed clumps of granite or Tors, exposed as a result of millions and millions of years of erosion, as the softer overlying surrounding rock were removed.  Where the granite was decomposed, this gave rise to the formation of Kaolinite - China Clay, for which Cornwall is famous.  Indeed, as a result of this process, Cornwall is covered in a rich supply of minerals, such as Cassiterite, Tin, Copper, Lead & and Iron. 

 

It is no surprise then, that the rocks are being constantly battered and eroded, shaped and modified, in a process which has gone on for over 500m years, leaving behind fascinating and most varied rock formations. 

On the coast itself, the sea level rose all around the British Isles roughly 4,000 years ago.  As a result whole forests were submerged – which themselves were formed some 6,00 years beforehand.  Remnants of tree trunks and stumps are sometimes revealed after heavy seas, when the sand level is lowered and a layer of black peat – which cover the submerged woodland - can still be walked over at low tide at the beach at Harlyn Bay.

The rocky headlands along this particular stretch of Cornwall’s coast - between Sharpnose Point & Trevose Head - have been subjected to denudation and erosion ever since and given rise to a wide variety of different geological features and extraordinary landforms. 

If you walking high up above along the coastal path and/or deep down on the golden beaches at low tide, you will see a wide variety of Synclines - a fold in the rock that dips down in trough like pattern, with the youngest rocks located inside the fold itself - and Anticlines - an arch shaped fold in the rock, that has pushed upwards, with the oldest rocks located inside the fold itself (as opposed to the outside, as with a Syncline). 

In fact north Cornwall contains an amazing variety of geological features, most of which can be seen from the coastal footpath itself, while at sea level you can stumble upon stacks, caves, blow holes and wave cut platforms. 

Geological highlights of the route between the area of Bude Padstow include:

1) Higher Sharpnose Point – steep dipping strata lies at right angles to the coast, with huge slabs on the south side.  On the north the Tidna stream follows the strike of the strata in a hanging valley, before cascading over a waterfall.  Erosion is causing the weaker cliffs to retreat faster than some small streams can cut down, thus forming hanging valleys with waterfalls when they meet the sea.  Sharpnose and Point and Tintagel cove are the best examples. 

 

Ideally a notch is expected to be cut by abrasion at he foot of the eroding cliff.  As a Giants Rock west of Porthleven where the notch has been enlarged into caves.  In contrast debris at the foot of a cliff or back of a beach gives protection against wave attack, so that the cliffs have been weathered back to a gentler angle and stabilized by vegetation. 

2) Lower Sharpnose Point – has three steep narrow sandstone cliffs projecting seawards – made up of hard sedimentary rock that remains after softer rock has worn away

 3) Gull rock - 1 mile north of the village of Morwenstow consists of intensely folded parallel layers of rock strata

4) Bude Haven - the highly contorted bands of sandstone and shale cliffs, to be seen on both sides of the bay, display not only horizontal and vertical bands of rock but all angles as well. 

5) At Compass Point a man made artificial breaker joins the mainland with the rocky headland, but can only be walked on at low tide.   

It is only at low tide that you can also see Whale Rock - by virtue of its appearance - the most impressive example of a pericline, where the layers dip radially form the centre.

6) Lower & Higher Longbeak – more and more folded rocks and fault lines can be traced as you walk westward at sea level from Bude Haven

7) Widemouth Sands consist of clayey material covered by blown sand.  If you study the sedimentary rocks on the beach head more closely here, you can see how the sediment beds were laid down in layers on top of one another in stripes of differing texture.

Some layers are much redder than others, which usually indicates that it originated when the climate here was much warmer and likened to a hot desert landscape. a wave cut platform runs parallel with the beach at Widemouth.  These are formed when the sea cuts a rock plane or bench, as it advances inland.   

The bay itself is dominated by Black Rock, a stack consisting of resistant slump material, referred to as Breccia.   A Breccia (tough igneous rock embedded in fine graded rock) survives way above sea level to dominate the bay here.

Old igneous rocks are also exposed in Wales at St Davids Head, Snowdonia and the Llyn Peninsula, where  they too dominate the landscape.  

8) Millook Haven – access by road is difficult, via steep, narrow and twisting lanes, but well worth the effort as the zig zag folded sandstone and shale rocks at Millook Cliffs are unique and can be seen right up close to the main road.

 

9) Pencannow Point – just north of Crackington, can be seen an impressive waterfall.  The stream falls down into the valley below, which has been cut by the erosion of the sea.  

10) Crackington Haven – this is the meeting point of two valleys, surrounded by towering cliffs of Carboniferous folded shales and sandstones. 

At low tide you can still see the remnants of an engine of a superfast German S Boat - capable of speeds of 40 knots, which sunk soon after WW2, while being towed to Barry in South Wales for scrap.  Relics from on board the E Boat are on display behind the bar at Coombe Barton Pub, in Crackington Haven itself.

11) High Cliff – the coastal path leads up to the highest point in Cornwall at 731ft (223m) above sea level, where you are rewarded with fantastic views of the rocky coastline.

 12) Strangles Beach – below the summit is a remote, isolated and difficult to access beach. 

 But the steep walk is well worth the effort, especially at low tide, in order to see the “Northern Door” an arch,

The dramatic arch was created by exposure to constant wave action - similar in appearance to the “Green Bridge of Wales” in Pembrokeshire.

13) Rusey Beach – adjacent to Strangles.

 Another fine beach, located right smack in the middle of a major fault zone.  

14) Pentargon Cove – further west the path drop down into a steep isolated valley where another waterfall can be seen, surrounded by heavy rock folds. 

15) Penally Point – fine examples of heavilly folded rocks can be seen from this headland, just before the path drops down to Boscastle.

16) Boscastle – the deep valley twists and turns until it meets the coast, offering natural protection to the harbor here.  Just north of the harbor itself, as is a massive blow hole, which throws sea water high in to the air as the tide moves in, attracting many tourists as it does so.  The Carboniferous “Culm” measures, which are unique to the SW peninsula, can be seen here at Boscastle, and stretch as far eastwards as the Devon border.

17) Rocky Valley – is a picturesque gorge valley which dates as far back as the Devonian period.  The valley is dominated by a fast flowing stream, all year round, which tumbles directly into the sea basin far below. 

This was a result of significant fall in ground base level, combined with the downcutting of a rejuvenated stream, culminating in THE most dramatic of waterfalls, that I have seen on the coast. 

 

18) Tintagel Haven – the situation is further complicated by land movements, resulting in faults best seen from the beach, below the Castle.   Here, the cove has been cut right back by the sea and the valley stream itself cascades to the beach as another waterfall.  The sea has also exploited weaknesses in the fault zone and eroded through a cave at both Barras Nose and Merlin’s Cave beneath the Island of Tintagel. 

19) Tintagel – the headland here display a complex mix of Devonian, Carboniferous and even older Volcanic rocks. The Devonian Rocks seen here, consist of fine grained grey slates, and can be traced as far as Launceston, further inland.  Metamorphic rocks are made up of a combination of igneous and sedimentary rocks.  Most prevalent here are the Cornwall slates. Slates have been mined extensively from Delabole & Tintagel itself.  Slate splits easily, making them ideal for buildings, roof tiles, walls and gravestones.

 

Marble Another metamorphic  rock seen on the coast here is Marble, which his metamorphosed limestone.  Polished marble is also used in buildings, gravestones and statues. 

 

20) Trebarwith Sands – landslips are common here and the Pub Car Park recently disappeared, having fell into the sea after a storm.  On the shore, you can see volcanic rocks, which have are full of pot holes caused by the stream running down the valley here.  Further along the superb beach can be seen a major fault, which has completely turned upside down the natural sequential sequence of rock formation, which has resulted in the older Devonian Slates overlaying the more recent Carboniferous Slates.  As if proof were needed, fossils dating back to Devonian times, are often found in the nearby slate quarry.

21) Pentire Head – sections of Pillow Lava, up to 200ft (60m) thick, can be seen on this beautiful dramatic peninsula, which are a result of large scale volcanic activity around.  Pillow Lava seen here are smooth in appearance grouped together in pillow like rounded blobs. They originate from molten rock which rapidly becomes solid rising up from volcanoes under the sea.  

The “Rumps” are a matching pair of extremely steep and resistant greenstone cliffs, which can be accessed via a narrow neck, consisting of softer slates.  

 It was once an Iron Age settlement, and you can see why, with views in all directions and direct access to the sea for fishing.

 22) At the nearby Merope Island, dark grey slates can be seen alongside bands of purple and green slates.  The whole are is rich in minerals and lead, silver were mined at nearby Pentireglaze. 

23) Trebetherick -  another fine example of green and purple bands of slates can be seen on the beach head between Polzeath and the Rock.

24) Harlyn Bay – the glorious yellow golden sand is glorious under foot here and you can see a fine example of rock hard cemented shell sandstone, right on the high tide mark.  As mentioned in the introduction, the remains of a fossil forest can be seen underfoot at low tide.

 

25) Cataclews Point – gives its name to Cataclews limestone, which is blue grey in colour and can be easily carved.  It has been quarried since medieval times and was used to make the font, situated in the interior of nearby  Church at St Merryn.  

 26) Trevose Head – the peninsula is a low lying neck of land dominated by a large lighthouse.  The headland is characterized by distinctive thick bands of green coloured intrusions, visible alongside the thinner limestone bands.  

Just a few miles out to sea from here, on 8 August 1944, a German U Boat U667, torpedoed & sunk the Corvette, HMS Regina, with a largely Canadian crew of 90. 30 drowned and bodies were washed up as far north as Wanson Mouth Bay near Bude. 

27) Dinas Head - the Bull and the Quies are a pair of stack rocks can be seen just beyond Dinas Head and a large blow hole can be viewed with caution when standing on the cliff top, just to the south of the NT car park.  Blow holes are formed when the roof of the sea cave below, eventually collapsed.  

Credit & acknowledgement goes to “South West Coast Photos” for a selection of images used in the production of this blog.  Excellent images of the whole of the South West Peninsula can be purchased from David Evans.  Access "The South West Coast Path Photo Tour" website via www.southwestcoastphotos.com

   

   

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