An Overview of the Geology of Britain

An Overview of the Geology of Britain

The very creation of Britain as an island is a represented, with Proterozoic rocks of fascinating story in itself resulting from hun- between 1,500 and 3,000 million years of age dreds of millions of years of tectonic activity sharing the island with much younger sedi- wherein land masses collided and split apart ments from the Palaeogene less than 60 mil- again as they moved across the surface of the lion years of age. This diversity is readily globe in their tectonic ballet. Even since apparent as one journeys around Britain, as Precambrian times, which ended 542 million has been discovered during the preparation of years ago, the various land masses have been this book. This section provides a brief over- pirouetting across the globe with areas which view, with the following sections providing a are now oceans variously covered by land and greater level of detail for specific areas of vice versa. The history of the Earth of course interest. reaches much further back to 4,600 million If we start in East Anglia and work our way years ago, but if we documented the various clockwise around Britain we shall discover tectonic events just since the Precambrian much of this interesting geological variation. period, we should have an interesting list. If On the eastern coasts of Norfolk, Suffolk and just one of these events had been different, if a Essex, the geology is quite young with the moving land mass had altered its course by just sedimentary layers being deposited primarily a few degrees, if a continental split had occurred within the Palaeogene period, less than 65 at a slightly different position, if the timings million years ago. This strata sweeps along had been slightly desynchronised, then Britain the northern shores of the Thames Estuary as we know it may not have been created at all. and extends westwards well past London. It Even much later on, if ice ages, glaciations and exists of shales, mudstones, sandstones, clays subsequent melts had not contrived to form the and of course chalk. Combinations and varia- North Sea and the English Channel, then there tions of these may be found throughout the would be no Britain as a separate entity. The area, with the chalk exposed at certain sites very existence of Britain is as a result of and clays and gravels at others. The coastlines ­random tectonic and climatic activity. Conse­ tend to be relatively soft and vulnerable, espe- quently, Britain owes its existence as an island cially the eastern Norfolk coast whose cliffs as much to chance as anything else. And yet, of soft sandstones and mudstones are easily this island embodies a pocket history of much eroded giving cause for concern, especially of the aforementioned activity, nicely wrapped with the spectre of future rises in sea level to and presented in a beautiful little package. It is consider. indeed an island gem. On the northernmost Norfolk coast, as one Due to the aforementioned tectonic ballet, our looks towards Hunstanton, we find strata island gem contains remnants from land from the Cretaceous period laid down between masses we now know as North America and 65 and 142 million years ago. These include Europe as well as oceanic and arid desert sandstones and mudstones and the distinctive environments which were once situated in the red chalk to be found within the Hunstanton tropics. These have all been jumbled together cliffs. This Cretaceous swathe extends in a and fashioned by successive glaciations to south westerly direction down to the south produce our current distinctive land form. As coast where it skirts above the coastline adja- a consequence, we are blessed with a rich cent to the Isle of Wight and briefly touches variety of geology within a very small land the Dorset coast. From here it also extends mass. Similarly, a broad time period is eastward to cover Sussex and most of Kent,

J. Ashbourn, Geological Landscapes of Britain, 19 DOI 10.1007/978-90-481-8861-1_2, © Springer Science+Business Media B.V. 2011 20 An Overview of the Geology of Britain

excluding the north Kent coastline which ago. At Lyme Regis the beautiful limestone displays later strata. The southern part of this pavements and associated features have long coastline includes the distinctive white cliffs attracted fossil hunters as this area has pro- of Dover and those of the Seven Sisters fur- duced some of the most significant fossils ther to the west. These beautiful cliffs actually from the period. Ammonites and fossil consist of many layers, often separated visu- remains of small marine creatures are to be ally by thin seams of flint nodules, spaced found in abundance. Unfortunately, the adja- fairly regularly upon the exposed faces. cent cliffs are somewhat unstable and the area These cliffs are also subject to erosion and has been prone to mudslides and partial cliff one can often find sizeable chunks of the collapse. Most recently, this activity has chalk which have been detached from the obscured certain parts of the beach where fos- main cliff and are being slowly eroded by sils were readily found. It is almost as though wave action. This south eastern section of the nature, having once presented us with such south coast nonetheless provides some inter- rich finds, is now burying them once again. esting variation, including pebble and shingle On the Dorset coast, we find several well beaches and a range of habitats atop the cliffs formed bays and some interesting features as one looks inland. such as Durdle Door, where the waves have Moving westwards along the south coast we etched a beautiful archway into the limestone enter the what has become known as the finger protruding out to sea. Within the adja- Jurassic Coast, with mudstones, sandstones cent bays to the east of Durdle Door, one can and limestones laid down during the Jurassic find similar fingers of rock stretching out to period between 142 and 205 million years sea at low tide. The bays themselves have

Fig. 1 The chalk cliffs meet the sea at Seven Sisters Fig. Exmouth at found those as sand- such cliffs, stone red and with orange burnt appearance beautiful some visual striking occasionally a which exhibit mudstones and sand- mostly stones are These east. further found rocks Cretaceous the age, than older considerably of years million 417 and 354 between strata from coast the weDevonian find period lower As the we move across further westward to right the Devonshire Midlands. cuts it doing, so before appearing again briefly in . In the Cretaceous strata at the coast around Hull, easterly direction to The Wash, skirting around north a in coast south the from extends strata the form coastline we see today. The swathe of Jurassic to activity geological underlying some dramatic been has there Clearly cation. distinct folding and - extreme angles of stratifi some exhibiting occasionally sandstone, and some very interesting formations of limestone 2 2 The soft sandstone cliffs at Happisburgh on the Norfolk coast Norfolk the on Happisburgh at cliffs sandstone soft The coast, reach out to sea towards Portland in a in Portland towards sea to out reach coast, Dorset the on eastward further at beach, Chesil those pebbles, of Speaking age. the of years of that million 440 around are to which rocks Brittany similar material, hard quartzite a of composed are coast, south the on that at beach found others anyunlike pebbles, point. These the characterise which bles peb- dense large distinctive particularly the Salterton, Budleigh at including, found be to sand and pebble of variations many are there beaches adjacent the On sun. morning the in whitegleam and chalk of composed are rocks coastal the where Beer, at found be may tion coastline. this of beauty excepinteresting An - the to adds simply which places in layering distinctive some exhibit also They east. the to coast the along further those than durable more rather be to seem cliffs these position, sea. adjacent the relativelyWhile com- in soft of hues the against contrasting Sidmouth, and

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long spit well over 20 kilometres in length clay. The area contrasts notably with that which serves to protect the largest tidal lagoon further along to the west. in Britain. The Fleet lagoon forms a natural Inland from the south Devonshire coastline nature reserve within which many species we find the distinctive granite intrusion thrive and are effectively protected by the which is Dartmoor. Dartmoor rises up from pebble spit of Chesil beach. the surrounding area in a beautiful gently There are so many interesting features undulating plateau which is broken through along this stretch of coastline. Kimmeridge in many places by the granite tors. These tors gives its name to a distinctive Jurassic clay range in both size and texture, some like which may be found within the bay. The Haytor, becoming a favourite with rock clay is interspersed with limestone and climbers anxious to practice their skills upon there are some interesting limestone pave- these small scale ‘mountains’. A little further ments and spits reaching out to sea which north, Houndtor presents a subtly different render Kimmeridge Bay a most interesting picture with the granite appearing more rug- spot for those wishing to observe marine ged and twisted as though having taken a life in the shallows. The rocks are particu- tortuous path before finally breaking free at larly distinctive with yellows, browns, greys the surface. Each of the Dartmoor tors has its and some very dark mudstones providing a own special character however and indeed, colourful spectacle, interspersed by some the granite can assume a quite different equally interesting pebbles and overseen by appearance at various places across the the Kimmeridge cliffs with their distinctive moors. Often, in the riverbeds for example, layering of large swathes of Kimmeridge the granite may be interspersed with calcite

Fig. 3 Extreme stratification and folding of the sedimentary rocks at Durdle Door Fig. on wti tee ok. n diin there addition, In rocks. these within be found to folding and compression much of is evidence there Europe, across and Brittany Variscan geological strata which south runs to the of Part slate. of deal great a and siltstones sandstones, include These age. of years lion mil- 417 and 354 between period Devonian cliffs the and from rocks baysupon predominantly founded picturesque its with coast Cornish the to come wewest further at Moving coast the along Cornwall. in End Lands further evident also is which sub-system granite larger a of part is granite on Dartmoor The precarious. a little travel foot make can which found be to also are bogs peat moors, the of east north the to a and particularly places, In thrive. flora mosses of variety sphagnum which ideal upon ture the for provides moorland environment, the mois- supporting underpinning ite ticularly colourful and distinctive. - This gran par becoming rocks individual with seams 4 The beautiful red sandstone at Sidmouth on the south Devoncoast south the on Sidmouth at sandstone red beautiful The - around the coastline we come to Lands End,Lands to come we coastline the around way our work and Lizard The round we As crust. continental as exposed and uplifted been has crust good oceanic a also but wherebyof ophiolite, section an examplea of Britain in point rock ernmost serpentine south- the only not hard is it sea to out of stretching fingers its have With would which Lizard. areas The is them to appealed undoubtedly the of One est. inter this to response in 1814 in established with the Royal Geological geologists Society attracted of Cornwall also has area the of ogy and early twentieth centuries. The varied geol- nineteenth the in intensifying years, of sands literallythou- for area the in undertaken been has ores of variety a for mining and rich eral min- relatively been landscape. has course this of Cornwall of creation the in involved processes dynamic the of us remind to serve which intrusions of all places, several in granite surface which aforementioned the are -

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where the hard Cornish granite is surfaced in up the Bristol Channel and continue our a spectacular and rugged manner. From here journey into South Wales. we can explore the north Cornwall coastline The Brecon Beacons and surrounding area with its bays and sandy beaches as it reaches offer some interesting contrasts and show us up to the north Devon coast with its high that, as we head north, the geology is chang- cliffs which often exhibit some intense fold- ing somewhat. Much of the area consists of ing, as may be clearly seen at Hartland Quay Devonian sandstones, siltstones and mud- where the rocks adopt a concertina like form stones including the distinctive ‘old red sand- in several places. Moving north along this stone’ to be found across much of the area. coastline we shall also encounter younger However there are older rocks from the rocks from the Carboniferous period laid Silurian period, around 417–443 million years down between 290 and 354 million years of age, and some strata from the Ordovician ago. However, moving back inland we period from around 443–495 million years encounter Exmoor with its gently rolling ago. The area also shows evidence of some hills which are formed upon an anticline of severe faulting and folding among the rocks, Devonian strata with the associated syncline with the faults extending in a northeastward dipping down northwards into the Bristol direction right across the area. As we head Channel. Exmoor supports both woodlands westward we have the Gower peninsula to the and moorlands, providing a range of natural south with its sandy beaches and interesting habitats within its boundaries. Across sedimentary strata and Pembrokeshire before Somerset we encounter younger rocks from us with its equally interesting coastline and the Triassic and Jurassic periods as we move cliffs of Carboniferous limestone. The

Fig. 5 The exposed granite of Haytor on Dartmoor Fig. nearly 90 miles across southern Wales and it Walesand southern across for miles 90 nearly extended coalfield southern The silent. developed, although the mines steadily are now mostly been has coal extracting of process area goes back to 1324 and since this time the Pembrokeshirethe in coalmining to reference earliest the fact, In Revolution. Industrial the in particular which played part a in significant coalfields southern the is it but Wales,south and north both in havecoal of exposedseams associated folding and compression processes the and rocks Carboniferous of combination in seen way.under whereactiveis places erosion readily The be may effects its and with wave action constitutes a force to be reckoned and winds high rain, of combination the line, coast- this on turns weather the Indeed,when erosion. marine and weathering of sequence cast into these 300 million year old rocks as a con- features other and arches caves, holes, blow- including textures, and patterns sional Pembrokeshireero- cliffstheir notable for are 6 Waters flowing through the limestone at Aira Force in the LakeDistrict Forcethe Aira in at limestone the through flowing Waters elgcl etrs o e on wti the within found be to features other geological many are There own. its of character a providingwith Snowdoniapeaks, other and some Idris Cadair shape , on features distinctive to served have rocks volcanic is Cambria name derivedfor name Roman Wales.the from The very the Indeed, strata. well as younger Ordovician and Carboniferous as age of years million 545 and 495 between period Cambrian the from here rocks ancient the in some are There area. the part of history industrial significant a played has which slate, course of and seams coal rocks, canic vol- sediments, uplifted of collection esting inter Walesan North constitutes area. entire the across diversity interesting an with but of mountains the by somewhat dominated landscape dramatic increasingly an find we and Wales, north into up Moving com- overyears.munities the affected the in part significant a such played has mining coal that surprising not is -

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area, including the Harlech Dome of Cambrian quently containing a good deal of coarse strata between Snowdon and Cadair Idris and grained mixed debris. There are also quartz- much evidence of glacial activity which has ites and metamorphic rocks, including some helped to shape the north Wales we are famil- which suggest an origin of undersea lava iar with today. A journey along the Miners flows. The island also has limestones and a Path and up to the top of Snowdon unveils central outcrop of intrusive granite making many of these features, including lakes and a the area particularly interesting from a geo- variety of exposed sedimentary strata as well logical perspective and, indeed, the island has as volcanic rock on the mountain itself. To the attracted geologists since the early nineteenth north west of Snowdonia lies the isle of century due to this interesting diversity of Anglesey where some of the oldest rocks in structures. Britain may be found, dating from the late Across from north Wales moving inland and Precambrian, early Cambrian periods between slightly northward we find the Peak District in 500 and 700 million years of age. In fact, Derbyshire which sits at the southern end of Anglesey is something of a geological mixed the Pennine hills which run like a backbone bag as there are a variety of interesting rocks up through northern . The southern and associated strata to be found here with part of the Peak District, often described as evidence of fairly intense folding and com- the White Peak, is limestone country with pression in places. The compositions of many Carboniferous deposits originally laid down of the sandstones and siltstones suggest that around 325–350 million years ago to be they are turbidites, originally laid down within found, together with a good deal of quarrying turbulent underwater currents and conse- activity. The northern part of the Peak District,

Fig. 7 Erratics left at High Tove in the Fig. of history.associated and area fascinating a features geological interesting of full Britain, is It District. Peak the from country the throughout wereshipped also millstones centuries, seventeenth and here sixteenth the times. mined Throughout Roman since been have lead, especially als, miner and area Peak White the within found stone. There are many caves and caverns to be - grit and limestone of outcrops with inter spersed hills rolling gently and plateaus with moor-like is landscape the time of Much broad period. a from layers composite of ple exam interesting - an Peakis the District Thus rocks of volcanic origin have also been found. and ago years million 495 and to 350 between back dating origin Ordovician even and has activity Devonianlowerof are strata there shownthat boring However, surface. the at exposed rocks the are limestone. These the features upon overlain shales and Peak, sandstones younger Dark the as described often 8 Seams of calcite high up in the rocks at Arrochar in in Arrochar at rocks the in up high calcite of Seams - - being the group of sedimentary sedimentary of Eycott and Borrowdale overlainthe byrocks, group Skiddaw the earliest being the with sandwich thick incredibly an of something form three rocks of The groups main area. picturesque this of valleys and fells the throughout found be to are rocks sedimentary and volcanic ancient of nation 443 and 495 million years ago and the combi- have rocks between Ordovicianperiod the in origin their these of Some peaks. the volcanic between rocks softer the scouring area, this through forged which glaciations the of a course, of courtesy selection of beautiful lakes and tarns with, garnished and together mudstones and even mixed intrusions, granite sandstones, limestones, slate, rock, volcanic of combination curious a embodies District beneath Lake geology.The action, interesting an lays which glacial by sculpted scape wonderfulland- a a District, exampleLakeof the enter we west, the towards back moving now and northward journey our Continuing

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volcanic groups which, in turn are overlain by small outcrops of volcanic rock. A little fur- the Windermere group of sedimentary rocks. ther north we find further diagonal swathes These layers are thousands of metres in depth, of volcanic and Devonian rocks reaching creating a substantial mass of material. Around right across the country. There are also of the eastern and northern periphery of this course the lochs, many of them displaying a mass there are younger rocks to be found variety of rock formations and habitats from the Devonian, Carboniferous, Permian around their shores, including the impressive and Triassic periods. The lakes themselves are Loch Ness which also stretches out in a fascinating, each with an interesting character north-easterly direction across much of the and a story to tell as to its formation. It is an country. The Cairngorms provide a moun- area which has inspired poets, writers and tainous landscape shaped by the various painters as well as attracting geologists from glaciations of the last and feature far and wide. mostly Precambrian metamorphic rocks Moving further north through and a more than 500 million years of age. Now we patch of Jurassic rock and into the Scottish are discovering some of the oldest rocks, not Lowlands, we come across a good deal of only in Britain, but which are to be seen gen- older strata from the Silurian and Ordovician erally. Much of this area, right into the periods between 417 and 495 million years Scottish Highlands, feature strata from the of age. These reach across in a north-easterly Lower Palaeozoic and Upper Proterozoic direction from the west coast right up to periods formed between 500 and 1,000 mil- Edinburgh, where there are also some lion years ago. In the northern highlands and Devonian rocks to be found as well as some outer Hebrides we find rocks from the Lower

Fig. 9 The jagged slate pushed up adjacent to Loch Long Fig. a retains yet respects, many in of contrasts land a thus is It country. the runs across right which Fault Glen Great the including faults, notable some exhibits also Scotland a often as movesone to area. diversity area equally rich from is there although found be to often is expression rugged more rather a mountains, the In rocks. exposed the carpet around rich a provides seaweed low the as at tides appearance colourful sometimes a The exhibit lichen. similarly sea the to of open which lochs variety a of attachment the often and weathering to due appearance tinct dis- visible a adopt of often rocks range coastal The strata. age the across including many providing contrasts, perspective logical close in proximity. often It is a fascinating area from a geo- formations, rock morphic meta- and sedimentary igneous, of a mixture provides Scotland indeed. rocks old very are These age. of years around million 1,500–3,000 periods Archaen and Proterozoic 10 The smoothly rounded landscape at Glen LyonGlen at landscape rounded smoothly The ned a b fud hogot h Dales, the throughout found be can indeed and as layering, the distinct exhibit dominate They Pen-y-ghent landscape. to tend which Whernside, of three the peaks of form the in interest have additional Dales Craven The waterfalls. notable aboveinteresting severalwith streams ground streams and caverns in several areas as well as underground also are there and forms many takes limestone the of Weathering Ingleton. around exampleswonderful some with found be to pavements limestone many are There period. Carboniferous the in ago years lion mil- 354 and 290 between down laid mostly course, of country limestone is This teristics. and rivers all with their own particular charac- plateaus peaks, hills, rolling of series a of sist features. interesting The Yorkshirecon- Dales of wealth a provides particular in Yorkshire Heading back south into the north of England, overworld.all the from people attracts which character overall ­discernable

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often in repeating series of limestone, sand- east Yorkshire coastline. This area consists stone and shales. This often gives the land- mostly of Jurassic sediments laid down scape a stepped appearance as the different between 142 and 205 million years ago. There layers have various resistance to weathering. is an early limestone layer, interspersed with Indeed, layering and steps are a familiar theme sandstones and shales, as outcropped along throughout the , especially much of the coast, and a later limestone layer where rivers have cut their way through the as exposed within the Tabular Hills. There are landscape. Another familiar sight are lime- also gorges and, perhaps unexpectedly, a dyke stone scars, often accompanied with acute of injected into the central weathering. Napa Scar for example exhibits a moorlands known as the Cleveland Dyke. The veritable avalanche of broken limestone, fairly moors can be quite beautiful and colourful uniform in individual rock size, many of with their swathes of purple heather and which are relatively fossil rich. The distinctive golden grasses rolling across the contours of shape of many of the crags and hills owes the land. While the upper moors tend to be much to glacial activity as is the case with so raised and tilted up towards the north, it is a much of northern Britain, and it is perhaps not different story in the south and particularly surprising that humans have occupied this along the south eastern coast where erosion landscape for thousands of years, with its can be significant. The coastline of the north- clear waters and diverse but easily navi- ern Yorkshire Moors is itself quite spectacular gated habitats. with its beautiful cliffs of Jurassic sandstone To the east, we have the Yorkshire Moors with adopting a variety of interesting forms. Many their gently rolling hills leading down to the particularly interesting fossils have been

Fig. 11 Weathered limestone at Napa Scar in Yorkshire Fig. fens moors, gentle from landscapes, of ety age. Wevarihavea - additionallyencountered of years billion three around to age of years of millions of tens few a from ranging rocks of Britain we have encountered a wide variety tour of circuitous short a within Thus, ago. years million 142 and 55 betweenaround ods peri- Palaeogene and Cretaceous the in down East laid of Anglia, rocks earlier the to return eventually we geology, of underlying areas Jurassic through south further head we As Coast. Dinosaur the of nativename alter its to leading coastline this along found 12 The mudstone and sandstone cliffs at Whitby in Yorkshirein Whitby at cliffs sandstone and mudstone The - photographs. accompanying the via yourself for diversity this of much witness to you allow and detail greater in areas these explore lowingsections small relatively island. Such is the geology a of Britain. The fol- upon this of All periods. Mesolithic and Neolithic our the from of ancestors shadows the in walked and natural habitats of variety a enjoyed of have We type rock. every almost and chalk gritstones, lavas, granites, sandstones, mudstones, shales, leys and lakes. We have walked upon volcanic val - mountains, magnificent to plateaus and

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Fig. 13 Rocks tumbling down towards Thirlmere in the Lake District