Quantocks and North Somerset Coast (eBook)

CHAPTER 1

Geology and Scenery in West Somerset

For the purposes of this book, I am taking West Somerset to mean (very approximately) the area covered by a rectangle between the towns of Minehead, Bridgwater, Taunton and Dulverton. It covers the Bridgwater lowlands, the Vale of Taunton Deane including the Blackdown Hills escarpment and Wellington, the Quantock Hills (designated the very first Area of Outstanding Natural Beauty, in 1957), the Vale of Stogumber, the Brendon Hills and the Exe valley, the Vale of Porlock, the Cleeve lowlands around Minehead and the hills around that town.

It is an area of great contrasts in both geology and the scenery related to it. Inland, there are the uplands of the Quantocks and Brendon Hills, founded on tough, ancient, twisted and partly metamorphosed Devonian rocks, the two hill ranges being separated by the lush and fertile Taunton to Williton valley, eroded into bright red New Red Sandstone laid down in the hot deserts of the Permian and Triassic Periods. It is so strange that this distinctive sheltered vale, with its beautiful, warm stonebuilt villages and sunken lanes, has no formal name, beyond being a northern extension of the Vale of Taunton Deane. Many commercial organizations are starting to use the term ‘Quantock Vale’, but there is an older term, used by A.N. Thomas in his 1940 geological paper on the Triassic rocks: the ‘Vale of Stogumber’. The southern boundary is framed by the imposing escarpment of the Blackdown Hills, composed of silica-rich sediments deposited much later, in the Cretaceous Period.

On the coast, late Triassic and early Jurassic sedimentary rocks laid down in a shallow tropical sea around 200 million years ago form the majority of this spectacular cliffed shoreline. Inland, the same rocks form the Cleeve Lowlands, east of Minehead, and the rolling country between East Quantoxhead and Combwich. The exceptions to this are lowlying areas, especially around Bridgwater, that were drowned by the rise of the sea level as the last Ice Age waned and have been reclaimed by drainage schemes over the centuries. These areas have a veneer of recently deposited sediment dating from the last 10,000 years – the Holocene Period – and are extremely flat.

Not all of the scenery of the area is related to underlying rock types; for many millions of years, the Bristol Channel has been an active tectonic zone. As we shall see, some geologists believe it was a crustal scale fracture akin to the famous San Andreas Fault in California, but we know that there are thick Triassic and Jurassic sediments under the channel, laid down in a sinking graben (or rift valley) between faults aligned east to west along the channel. At various times in the last 300 milliom years, the faults have woken into reactivation, causing earthquakes and shattering rocks along the line of the faults. On land, the fault zones have brought rocks of different resistance next to one another (such as the Cothelstone Fault), providing the locus for intense erosion along the narrow zone of broken and weakened rock to form straight deep valleys (the prime example being along the Monksilver Fault), and have allowed some areas to rise and start to be eroded, and some areas to sink, in some cases below sea level. All of the rocks of the area have had sets of cracks (joints) imposed upon them, due to the stresses exerted during these episodes. These have had a profound impact, best visible where the rocks are completely exposed, along the coast.

West Somerset Geology and People

The economy and settlement of the region is also closely related to the underlying geology. The older and more resistant rocks of the uplands have long been exploited for building materials. These include the metamorphic slate of the Oakhampton (Morte Slates) and Treborough (Ilfracombe Slates) quarries, once used for flooring and fireplaces, as well as roofing and walling, but now mainly infilled; and the hard quartzitic sandstones such as the Pickwell Down Sandstone in Wiveliscombe, or the Hangman Grit exploited at West Quantoxhead, used for building stone and latterly as aggregate for tracks, roads and concrete. The weaker New Red Sandstone of the Vale is more easily worked and has been extensively used as building stone, though it is sometimes more susceptible to weathering than the stronger Devonian rocks.

Bricks and tiles have been made from Triassic Mercia Mudstone in Minehead, Wellington and Taunton, as well as some smaller yards such as Blue Anchor and Wiveliscombe (where Aylesbeare Mudstone was used), and in Bridgwater, where modern alluvial clays were dug. On the coast, harder Triassic and Jurassic limestones have been used for building, producing distinctive pale-grey to cream-coloured buildings.

In the absence of extensive glaciers and their far-travelled load, the soils of the region, and thereby the use to which the land is put, are derived from the local underlying rocks. The harder quartz-rich sandstones of the uplands break down very slowly and do not contain a good supply of elements such as calcium to counteract the acidifying effect of high rainfall and downward leaching of soil nutrients. Consequently, soils are thin, stony, acid and poor in nutrients, producing moorland vegetation of heather, gorse, bracken and coarse grasses used mainly for extensive grazing and often nowadays almost abandoned by agriculture in favour of recreation and forestry.

The mudstones of the upland areas, now metamorphosed to slates, such as the Ilfracombe and Morte Slates, produce less high ground, form thicker soils and retain water, impeding leaching. Consequently, they are mostly farmed, the majority being under permanent pasture and the better drained districts used for arable crops. The tendency towards acid soils in these wet upland areas can be rectified using lime (calcium carbonate), an alkaline substance produced today by crushing limestone, but in the past, without crushing machinery, the easiest way was by ‘burning’ or calcining limestone by heating it to over 850°C in a limekiln with wood and/or coal to drive off carbon dioxide and produce quicklime (calcium oxide) powder. When spread on to the soil, the quicklime was ‘slaked’ back to calcium carbonate by taking up water from the soil and carbon dioxide from the atmosphere. Something of a fad in the eighteenth and nineteenth centuries, the repeated application of these caustic alkaline substances eventually destroyed the soil fauna, therefore also humus production and leading to loss of fertility. A German adage from the late nineteenth century says ‘Lime lime and nothing more, makes fathers rich and sons poor’.

Another major use for quicklime was in the production of lime mortar and for whitewashing buildings. The main source for lime in this area was thin, often impersistent limestones (four or five bands) interbedded with slates in the Ilfracombe...