The cliffs at Saunton and the rock-pools at their base provide interest to many people who visit the beach. What many people do not realise however, is how the cliffs can tell a fascinating story that spans some 300 million years. Here is local geologist Paul Madgett to explain more:
“Braunton is a very large parish, encompassing a range of landscape features, from the wide open spaces of the Taw Estuary and Braunton Marsh and the sand-dunes of the Burrows, to the rounded hills and deep-cut valleys around Fullabrook at the other extreme corner of our parish. Where the two types of landscape meet are the southern slopes of West Hill and East Hill, and the steep slopes behind Lobb.
Reading the Landscape
Essentially this landscape can thus be divided into three (present day rocks and landscape, rocks and landscape of the “recent” past, rocks of the “ancient” past) and the reasons for the differences can be found in the underlying rocks, which tell the geological history of the area – so long as you know how to “read” this.
Once you do, Braunton becomes a very exciting place! You “see” a very different landscape “hiding” behind the present veil.
Firstly, remember that “rocks” includes those soft muds and sands around the estuary and Burrows, not just the solid rocks seen along the Saunton foreshore and in old quarries and deep-cut lanes.
Muds and Sands
The muds and sands are obviously “young” as we see them being formed and re-formed today – travel down to Broad Sands and Crow Point, then along the foreshore sands towards Airy Point, before crossing the dunes along the board-walk back to Broad Sands. You will see how these estuary, marsh and sand-dune areas are the product of processes of erosion and deposition happening today and in the recent geological past – essentially the last few thousand years.
Waves, currents and tides, along with the wind and rivers, have moved these sediments into place and are constantly keeping them on the move. Exactly which processes are involved determines whether we have sandy beaches, muddy salt-marshes, or high sand-dunes.
Moving now to the cliffs at Saunton we see cemented sands overlain by a rather chaotic layer of coarse fragments of sandstone and slate, mixed with sand and silt.
The cemented sands contain at their base some modern-looking sea-shells, with fossil barnacles stuck to the underlying ancient rocks below the sands. Occasionally huge boulders of non-local rock, including the famous “Saunton Red Granite”, can be seen at the base of these sands, or loose on the foreshore rocks.
These cemented sands of the lower part of Saunton cliffs are essentially remnants of a former version of our present-day Saunton Sands and Braunton Burrows – formed at a time of slightly higher sea-level, several metres above the present one – so comprise a “Raised Beach”, perhaps 100,000 years old.
Above these sands, the fragmented materials of the upper part of the cliffs (described by locals to early geologists as “Head” because of their position, a name which has stuck) tell us of a time of intense cold, these fragments being frost-shattered rocks from further up the slope of Saunton Down – obviously later than the Raised Beach as they are on top of these sands. This “Head” is not forming at the present day, but relates to a former cold period of around 20,000 years ago, when huge ice-sheets reached as far south as the present coast of South Wales.
The lower slopes of Saunton Down, below the road to Croyde, are part of the “apron” of such frost-shattered debris from a former cliff-line at roughly the position of the road. This cliff would have been actively cut by the seas which formed the Raised Beach sands. At the time of the latter the estuary mouth would have been much wider, and most of Braunton south roughly of the line of Fairlynch Lane to Higher Park Road would have been under tidal waters. The flat land of Braunton Great Field is interpreted as a river terrace – in other words the alluvium deposited alongside the Taw estuary, probably at roughly the same time as the Saunton Raised Beach was forming.
West and East Hills
The southern slopes of West Hill and East Hill represent the old, now degraded, cliff-line. During that last “Glacial” episode the “Head” material would have sludged over these cliffs, partly burying them, and producing the more gentle slopes below them.
The “non-local boulders” referred to above seem to have come a long way, some from NW Scotland, possibly from as far as East Greenland in one or two cases. These “erratic boulders” must have been brought by ice, either in the form of icebergs grounding against an earlier coast-line, or possibly as an ice-sheet even more extensive than the last one, extending way south of the Welsh coast to impinge upon our North Devon & Cornish coast-line all the way to the Scillies. Possible age of this early glacial episode is about 500,000 years.
Thus there must have been at least two cold (Glacial) periods with an intervening warm (Interglacial) period affecting the development of our present-day Braunton landscape, with the last cold period producing much of the detail of the landscape we see today, away from the present-day estuary, salt-marshes and dunes. These latter features are forming in what is in reality the latest Interglacial period.
The Most Ancient Rocks
To see the most ancient rocks, which are the foundation stones of all of our North Devon landscape, we need to scramble along the Saunton foreshore a short way. Although originally soft muds and sands, laid down horizontally on a sea-bed, they are now hard and splintery sandstones and slates, their layers contorted and often near-vertical, fissures within them exploited by the sea into deep gullies.
These rocks have been fashioned by the power of the waves using loose sand and pebbles as a kind of “sand-paper” into a “shore platform” of fairly uniform height, but cut across by numerous gullies running mainly either east-west or NW-SE or NE-SW. The E-W gullies can be seen to be more or less parallel to the steeply-sloping layers of sandstone and slate, though in places tight folding of these layers is apparent.
The gullies cutting across these layers represent breakages of the ancient rock, often with opposite sides of the break failing to line up properly – these are geological faults, caused by earth movements – which we would have felt as earthquakes had we been around at the time. Such earth movements were responsible for the folds as well, the original sub-marine sands and rocks (they contain fossils of animals which today only occur in the seas) of Devonian age (roughly 350 – 400 million years old) having been uplifted to form a giant E-W trending mountain chain the size of our present Alps – the Variscan Mountains of about 300 million years ago.
From Chapel Hill
Inland, by climbing to the top of one of Braunton’s several hills – Chapel Hill is a good vantage point – we see a fairly “flat” landscape if we consider the wide expanses of fairly high ground to our west, east and north, but dissected by deep-cut valleys. These valleys are not related to the folds in the ancient rocks, though may follow the lines of weakness imposed by the faults within them; neither do the hills relate to the ancient mountain chain inferred above – that has long disappeared, probably gone by 250 million years ago.
Therefore our present inland landscape, extending across much of Devon, was formed by long-continued erosion, the flattish and fairly even-height summit areas perhaps representing a time when Britain tilted gently from west to east, the land being eroded in the west, the loose materials transported by rivers to shallow seas in the east – quite probably the sands near to, and the clay underlying the capital (in which the Tube system has been dug) are partly the “rubbish” from Devon, dumped on the site of London!
If we then look west from Saunton Down we see Lundy – this is mainly granite, formed from upwelling molten material, but much younger than the granite of Dartmoor (which is related to the rise of the Variscan Mountains). Lundy’s granite is “only” about 50 million years old, the same age as the lava flows of the Giant’s Causeway in Antrim – a period when geologists think that the present-day North Atlantic was just a rift valley like the East African Rift of today. Thus molten rock was up-welling to the west of our present Britain, initially causing this west to east slope mentioned in the previous paragraph.
Eventually the crust ruptured completely, with volcanoes lining northwest Britain; progressively this rupture widened, so that the present up-welling occurs under places like Iceland and the Azores, and we are now thousands of kilometres from our former neighbouring regions of East Greenland and eastern North America.
If you have visited all these parts of our parish, and have looked at the landscape and rocks with an observant eye, then you are now on the way to becoming an expert rock and landscape detective, and can go on to investigate other parts of the country – and perhaps write your own “Rocky History”.”