Figures
(Frontispiece) An artist's impression of the Earth from space, as it might have appeared some 360 million years ago. The outline of present-day Britain is shown as a dotted line. Reproduced from F.W. Dunning et al. (1978) by permission of the Natural History Museum, London.
(Figure 1) Haytor Rocks, Dartmoor, is not only an important part of Britain's natural heritage for its aesthetic quality, but also for the Earth sciences. Study of the granite rock here has revealed important information about the cooling and crystallisation of molten rock. The rocks form an impressive 'tor', formed by weathering. Photo: S. Campbell.
(Figure 2) Dob's Linn, south-west Scotland. This internationally important site is officially recognised by the International Union of Geological Sciences (IUGS) as the reference section for the boundary between the Ordovician and Silurian Periods (see (Figure 13)). This boundary is used as the global standard for comparative purposes. For example, fossils and other rock attributes that occur at Dob's Linn can be compared with those in rocks elsewhere. Photo: C.C.J. MacFadyen.
(Figure 3) The rocks of the Memorial Crags at Bradgate Park, Charnwood Forest, Leicestershire and reconstruction of Charnia masoni, a primitive life-form. The rocks exposed in the crags are probably 650–700 million years old. Occasionally, the rock surfaces show impressions of some of the first forms of life — imprints of soft bodies of some of the earliest large multi-celled organisms. These include the remains of jellyfish and sea-pen-like animals, including Charnia masoni. The preservation of soft-bodied animals is rare because they usually decay very soon after death or are eaten by scavengers. In this case, the animals were probably engulfed by a catastrophic event, perhaps the mass slumping of sediment, which trapped the fauna. The animals became preserved in the sediment, which eventually became rock. Because of the worldwide rarity of the preservation of these early life-forms, Bradgate Park is of great importance to the study of early life. Photo Leicestershire Museums.
(Figure 4) Moel Tryfan, Gwynedd. This is a historically important site, 400 metres above sea level, that consists of sand and gravel containing fossils of sea-shells. It was cited as evidence for the biblical flood by the Diluvialists. Subsequently it was interpreted as a glacial deposit carried from the sea bed by an Irish Sea ice sheet during the last ice age, about 23,000 years ago. This has a bearing on the dimensions of the last Irish Sea ice sheet, the extent to which it may have depressed the Earth's crust, and the degree of crustal 'rebound' after glaciation (see also (Figure 10)). It is a subject of ongoing research. Photo: S. Campbell.
(Figure 5) Traeth Mawr, Brecon Beacons. This site has a sequence of peat and clay deposits which contain a pollen record reflecting marked fluctuations in climate from 14,000 years ago to the present. It provides information about the nature and rate of climatic and environmental changes. The photograph shows a general view of the site. Photo: S. Campbell.
(Figure 6) Kimmeridge Bay, Dorset. (a) The site is an important location for training courses, universities, schools and geological societies. The photograph shows members of the Dorset Geologists' Association Group visiting the site which displays organic-rich rocks similar to those that have generated oil and gas under the North Sea. Photo: R. Hannock, Dorset Geologists' Association Group. (b) Oil was discovered at Kimmeridge in 1956. Since then, the wellsite has continued to produce 100 barrels of oil a day. Photograph copyright Sillson Photography/BP Exploration Ltd. Reproduced with kind permission.
(Figure 7) Geology is an inseparable part of the natural world. The photograph shows an area of limestone pavement at Scar Close National Nature Reserve in North Yorkshire. Water has percolated through joints in the exposed limestone and produced deep clefts (grykes). In the sheltered grykes, unusual plant life, including many rare ferns and orchids, has developed. The micro-climate in the grykes is more like that of woodland than exposed hillside. Photo: P. Wakely.
(Figure 8) Salisbury Crags and Arthur's Seat, Edinburgh. The diagram shows the relationship between the geology and the ancient volcano. Photograph reproduced by permission of the Director, British Geological Survey. NERC copyright reserved. Diagram after Wilson (1994).
(Figure 9) Cliffs near Barton-on-Sea, Hampshire. The cliffs are made up of sediments deposited in marine, brackish and freshwater environments. Where these sediments occur inland, there are no natural outcrops, the land largely being built over or farmed, and there are few opportunities to see vertical sections through the strata. On the coast, however, fresh sections occur as the sea erodes the cliffs, but they can be obscured by coastal defence works and landslides. Photo: C.D. Prosser.
(Figure 10) The coasts of the islands of Islay and Jura in the Inner Hebrides display raised ice-age shorelines, especially spectacular shingle beach ridges. At one locality, up to 31 unvegetated shingle ridges occur up to 30 metres above present sea level. These were formed at the end of the last ice age, when sea level and the level of the Earth's crust in the Inner Hebrides were below modern sea level. These late-glacial shorelines and shingle ridges were uplifted to their present position when the Earth's crust recovered from the load of the ice sheet. Photo: J.E. Gordon.
(Figure 11) Geological map of Britain and Ireland. Each period, although represented on the map by a single colour, may include a variety of rock types. For example, the Silurian (pale mauve) includes shales and mudstones, and the Jurassic (olive-green) includes limestones and clays. This simplification is necessary to be able to show the geology of Britain on such a small map. See glossary for definition of terms. Reproduced by permission of the Director, British Geological Survey. NERC copyright reserved.
(Figure 12) The principal occurrence of igneous rocks. Extrusive: lava flows; Intrusive: sills, dykes and plutons. Molten rock erupting from volcanoes may also produce ash (referred to as tuff in the key to (Figure 11)). After Wilson (1994).
(Figure 13) The stratigraphic column. At the top, key events in Earth history are compressed into one year to illustrate the immensity of the geological timescale. After Grayson (1993). The stratigraphic column is the array of geological time units that results from stacking them vertically, with the oldest at the base, overlain by successively younger units. In the 1830s, Sir Charles Lyell recognised that in the Cenozoic (sometimes spelt Cainozoic) Era modern species appear as fossils, becoming progressively more abundant in younger sediments. For example, 3% of Eocene species are alive today, and as many as 30–50% of Pliocene species exist today. Lyell chose to use Greek prefixes to subdivide the Era according to this observation. After Wilson (1994).
(Figure 14) The geological structure of south-east England, showing major topographic features associated with the Wealden Anticline, and the London Basin (syncline). Note that the Hastings Beds, Weald Clay, Lower Greensand, Gault Clay and Chalk comprise the Cretaceous shown on (Figure 13). After Edmunds (1983).
(Figure 15) The areas of higher ground in Britain. Nearly all of these are coincident with the relics of past mountain chains (compare with (Figure 16)). After Wilson (1994).
(Figure 16) British mountain belts. (a) Map showing the distribution of the major ancient mountain belts of Britain. Faults are major planar structures across which rocks have been displaced vertically or laterally. For example, the area in Scotland between the Highland Boundary Fault and the Southern Uplands Faults has been displaced downwards between the two faults, whereas lateral displacement occurred along the Great Glen Fault. (b) Chart summarising the ages of mountain building events and igneous activity. After Dunning et al. (1978).
(Figure 17) The distribution of the Caledonian and Variscan mountain belts on a map of the continents reassembled to the positions they occupied before the opening of the present-day Atlantic Ocean. Early protagonists of continental drift used reconstructions such as these as evidence in favour of the former unity of now widely separated continents. After Wilson (1994).
(Figure 18) The structure of the Earth. (a) Diagrammatic section through the Earth showing the core, mantle and crust. The crust is too thin to show to scale on this diagram: variations in its thickness are depicted in (b), a generalised section through the Earth's crust showing variations in the thickness of continental and oceanic crust. Oceanic crust is between 2.8 and 2.9 times denser than water, and is similar in composition to rocks such as basalt and gabbro; continental crust is less dense (2.6 to 2.8 times as dense as water), with a composition similar to granite. Continental crust is less dense and much thicker than oceanic crust, so it floats higher on the mantle. After Wilson (1994).
(Figure 19) The relationships of three crustal plates in the Earth's southern hemisphere. The thickness of the crustal layers is not to scale. New oceanic crust is constantly forming along the Mid-Atlantic Ridge. After Wyllie (1976).
(Figure 20) The present distribution of crustal plates and the earthquake activity at their boundaries. All the constructive plate boundaries are regions of shallow earthquakes, whereas deeper-focus earthquake zones mark the location of destructive plate boundaries. The rates at which ocean crust is forming at constructive plate boundaries are shown schematically by the width between the parallel lines used to depict them. The directions of plate movement are shown by arrows, the lengths of which are proportional to the rate of movement: the shorter the arrow, the slower the plate is moving. After Gass et al. (1972).
(Figure 21) Sequence of events in a cycle of ocean opening and closing, culminating in continental collision. It is possible for both plate margins to be subjected to subduction (as happened during the Caledonian mountain building in Britain), although this is not shown here.
(Figure 22) Precambrian rocks. (a) The oldest-known rocks in Britain: the Lewisian Gneiss, in the north-west Highlands of Scotland. Some of these rocks were formed about 3,300 million years ago, in the Precambrian Era. Photo: R. Threadgould. (b) The Precambrian-age rocks at South Stack, Angelsey were deformed more than once. Photo: S. Campbell.
(Figure 23) Continental drift. Simplified maps illustrating how the continents were distributed during Earth history, indicating the locations of the different parts (dark shading) which have come together to form present-day Britain. After Wyllie (1976).
(Figure 24) The changing latitude of Britain through geological time. After Lovell (1977).
(Figure 25) Typical Lake District scenery in the Borrowdale Volcanic Group. The succession of rocks between the Langdale Pikes and Silver Howe represent a six kilometre thickness of volcanic lava and ash, erupted over a period of ten million years during the Ordovician Period. Photo: F.W. Dunning.
(Figure 26) Carboniferous environments. (a) A coal-bearing sequence exposed in Duckmanton Railway Cutting, Derbyshire; the dark band is a coal seam. Photo: English Nature. (b) Reconstruction of the tropical forest of northern England during the Carboniferous Period. During this time, much of 'Britain' was covered by such forests and swamps. It is from the remnants of these forests that much of Britain's coal reserves are derived. A: a lycopod; B: a cycad; C: the horsetail Calamites; D: Boltonites. Reproduced from Duff et al. (1985).
(Figure 27) East Kirkton, Lothian, Scotland: amphibians and a possible first reptile (shown in the left foreground). The limestone and shale exposures here, which are of Lower Carboniferous age, are very rich in fossils. The site is a disused limestone quarry. The quarry was abandoned in the middle of the last century and its palaeontological significance has been realised only recently. The nature of the limestone and its restricted distribution (600 metres across and less than ten metres thick) indicates that it may have accumulated in an area of hot springs caused by volcanic activity. It has yielded important early invertebrate and vertebrate faunas, including the earliest-known harvest spiders, millipedes, scorpions, the oldest complete amphibians and the earliest known reptile, Westlothiana lizziae, nicknamed 'Lizzie'. Reconstruction © M.I. Coates. First published in Clarkson et al. (1994). Photo: P.A. MacDonald.
(Figure 28) Hartland Point, Devon. These Upper Carboniferous-age rocks were contorted into tight folds, by the Variscan Orogeny. Photo: A.R. Bennett.
(Figure 29) Sully Island, South Wales. Triassic rocks (230–195 million years old) were formed when 'Britain' lay within the arid belt north of the equator. They lie horizontally on the dipping Carboniferous Limestone. This angular discordance is known as an unconformity, and represents a period of several million years when there was no sediment accumulation. The rocks above the unconformity comprise sands and breccias which are interpreted as lake shore deposits. This site is one of the few places in the world where the margin of a former Triassic lake can be studied. Diagram after Wilson (1994). Photo: C.D. Prosser.
(Figure 30) Jurassic environments. (a) Plesiosaurs from the early Jurassic based on specimens collected in Gloucestershire which are now housed in Gloucester City Museum. (b) Scene from mid-Jurassic times, showing a small lake surrounded by seed ferns and conifers based on the fossils from Hornsleasow Quarry, Gloucestershire. Fish (Lepidotus) live in the water, and frogs are present at the lake sides. Dinosaurs include some of the earliest stegosaurs and maniraptorans, plated and small carnivorous dinosaurs respectively. A carcass of a large sauropod dinosaur, Cetiosaurus, is rotting in the water, and Megalosaurus scavenges. Lizard-like animals, crocodiles, pterosaurs, mammals and mammal-like reptiles complete the scene. Paintings by Pam Baldaro. Reproduced by permission of the University of Bristol.
(Figure 31) The Seven Sisters chalk cliffs in East Sussex. The geomorphology of the cliffs is the result of marine erosion into a series of valleys and intervening ridges. Photo: N.F. Glasser.
(Figure 32) The Storr, Skye. The photograph shows the landslipped masses of basalt of the Skye Main Lava Series which occupy the foreground. Beyond the Old Man of Storr pinnacle, further lava flows of the Series form left- to-right-dipping scarps. Photo: David Noton Photography.
(Figure 33) Ice margins of British glaciations. The ages of these ice advances are: Loch Lomond Advance, 11,600 to 12,800 years ago Late Devensian glaciations ('the last glaciation'), 23,000 years ago Early Devensian Glaciation, about 60,000 years ago Ridgacre Glaciation (West Midlands), 160,000 years ago Anglian Glaciation, 450,000 years ago Bristol–Scilly Islands Glaciation, about 640,000 years ago.
(Figure 34) Upland glaciation, Snowdonia, Wales. The photograph shows a series of cirques. A cirque is an armchair-shaped hollow, with a steep rock wall at the rear, and a lip or threshold at the front. The rock head wall is fashioned first by weathering and rockfall processes, whereas the floor of the basin is eroded and moulded by glaciers which occupied the hollow. Where two cirques meet, a precipitous divide called an arête develops (to the right in the photograph). Photo: S. Campbell.
(Figure 35) Schematic diagrams showing the formation of glacial depositional landforms and deposits. (a) Flow tills form on the surface of the retreating glacier from thick sequences of englacial debris. (b) Till cover inhibits melting of underlying ice which is left behind during glacier retreat as an ice-cored moraine ridge. Supraglacial flow till is still active. (c) Outwash from the active glacier is forced to flow between ice-cored ridges and tills flow into the outwash systems. When the outwash dries up, the flow till forms a capping. (d) Dead ice melts, thus reversing the topography and leaving melt-out till in its place. The kame sediments show collapse structures. Such sequences are extremely common in lowland Britain. (e) and (f) Development of the features of a glaciated valley. The principal features are lateral and medial moraines and kame terraces. (g) The formation of the subglacial/proglacial sediment features. The till surface bears drumlins and on it are superimposed fluted moraine ridges; push-moraine ridges are associated with readvance of the glacier front, either in winter during a general retreat phase or in response to longer term cooling; lee-side till forms in a natural cavity where debris falls from the ice roof. Relatively rare eskers form in subglacial or englacial stream channels; proglacial outwash cuts through the till; kettle holes form in old outwash where stagnant ice blocks melt-out (the underlying sediments show collapse structures). A simple stratigraphy of outwash on till is produced by a single glacial episode of advance and retreat. After Boulton and Paul (1976).
(Figure 36) West Runton, Norfolk. Sediments exposed in the cliff and on the foreshore accumulated during two interglacials and three ice ages. Fossil pollen indicating the presence of temperate forests has been obtained from the interglacial deposits, while the ice-age deposits show permafrost structures and subarctic herb floras. The dark band at the bottom of the cliff is the 'Freshwater Bed', deposited by a river. Photo: N.F. Glasser.
(Figure 37) Hutton's Unconformity at Siccar Point, Berwickshire, is one of the most famous and important geological localities in the world. The section at Siccar Point shows upturned Silurian sediments overlain by sediments from the Old Red Sandstone. The unconformity surface which separates these two sets of rocks represents a significant break in the continuity of the geological record. The portrait of James Hutton by Sir Henry Raeburn (detail) is reproduced by permission of the Scottish National Portrait Gallery. Photograph reproduced by permission of the Director, British Geological Survey. NERC copyright reserved.
(Figure 38) Lummaton Hill Quarry Site of Special Scientific Interest, Torquay, Devon. The rocks exposed in the quarry are massive limestones which were deposited in the later part of the Middle Devonian Period (the Givetian Stage). The limestone contains shell-rich pockets seen here in the upper part of the face. This locality is of great historical importance because the rich faunas it has yielded were used, in part, to characterise the original Devonian System of the pioneering geologists Sedgwick and Murchison. Portraits reproduced with permission of the Director, British Geological Survey. NERC copyright reserved. Photo: K.N. Page.
(Figure 39) Graptolites first become significant in the geological record in the early Ordovician Period, and became extinct in late Carboniferous/early Permian times. They were colonial organisms living near the sea-surface, consisting of one or more branches (stipes). The individuals of the colony lived in cups along the stipe. Their evolutionary development, as seen in fossils, led to the definition of the Ordovician Period. The photograph shows the graptolite Didymograptus murchisoni, from Dyfed, from rocks which are Llanvirn in age (between 455 and 470 million years ago). Photo: G. Larwood. Diagram after Rickards (1993).
(Figure 40) The Jurassic rocks of the cliffs near Lyme Regis and portrait of Mary Anning. Portrait reproduced by permission of The Natural History Museum, London. Photo: P. Doyle.
(Figure 41) Pitch Coppice, Mortimer Forest, near Ludlow, Herefordshire, is officially recognised by the International Union of Geological Sciences (IUGS) as the global reference site used to define the base of the Gorstian Stage of the Silurian Period. Typical fossils are used to compare this sequence of rock layers with rocks containing the same fossils in other parts of the world, establishing those too as Gorstian in age. This stratotype site forms part of a geological trail managed by Forest Enterprise. Vegetation is controlled, and the site remains accessible all year round to visiting scientists, educational groups and interested members of the public. The photograph shows visiting delegates of the Malvern International Conference on Geological and Landscape Conservation (1993). Photo: K.N. Page.
(Figure 42) (a) Aerial view of Wenlock Edge, Shropshire, looking north-eastwards towards Hope Dale (to the right of the photograph). The escarpment is formed mainly by the Farley Member beds capped by the Much Wenlock Limestone Formation. Photo: Cambridge University Collection. Reproduced by permission of the Curator of Aerial Photography. (b) Section of Silurian reef limestones of Wenlock Edge. Wenlock Edge is one of the classic areas of British geology and formed part of the Wenlock type area defined by Sir Roderick Murchison in the first half of the nineteenth century. The detailed stratigraphy has since been investigated and revised. Today it is the designated type area for the Much Wenlock Limestone Formation and it forms part of the international type area for the Wenlock Series. Many of the disused limestone quarry faces backing onto Wenlock Edge are now buried beneath extensive earth buttresses constructed to reduce the risk of rock collapse, but sections are still available for study. Photo: M.J. Harley.
(Figure 43) Type specimen of Megalosaurus bucklandi Meyer, 1832. Partial lower jaw. Stonesfield is the most important of the British Bathonian localities in the Cotswolds, and arguably the best Middle Jurassic terrestrial reptile site in the world. Its fauna is diverse and abundant, and consists of more than 15 species of fossil reptile, including turtles, crocodilians, pterosaurs, dinosaurs and rare marine forms (ichthyosaurs, plesiosaurs), as well as mammal-like reptiles and mammals. Stonesfield is the most important site in the world for remains of Megalosaurus. It yielded the 'type' material in the early nineteenth century, and continued to produce hundreds of specimens while the mines were in operation. Diagram after Buckland (1824).
(Figure 44) Glencoe, Lochaber. This dramatic glaciated glen has particular historical significance as the place where'cauldron subsidence' was first recognised in 1909. Volcanologists had long been intrigued by certain collapse features of volcanoes and many workers had been actively seeking to explain their origin. It was an officer of the Scottish Geological Survey, Edward Bailey, who, within days of visiting Glencoe, attributed the beautifully exposed collapse features to a mechanism he termed cauldron subsidence. Bailey was so excited about his findings that he travelled directly to the Geological Society in London and made an impromptu presentation about the Glencoe rocks. Evidence for cauldron subsidence is now preserved in five localities within the SSSI. As Glencoe was the first example of this phenomenon to be described in any detail, it serves as the type example throughout the world. Recent research, mostly concerned with establishing links between the sequence of volcanic eruptions at the surface and the development of igneous intrusions deep in the Earth's crust, has further reinforced interest in the area and its international importance. Photo: P.A. MacDonald.
(Figure 45) Chesil Beach, Dorset, is a site of international importance for the impressive and exceptional size of its storm beach, the systematic sorting by size of the cobbles and pebbles along the shore, and the availability of historical records of beach changes. It is an active coastal geomorphological site. Together with Orfordness and Dungeness, it is one of only three major shingle structures on the coast of England. The 29-kilometre shingle beach is joined to the mainland at the eastern and western ends, but for 13 kilometres it is backed by the Fleet, a shallow brackish lagoon. The pebble beach consists almost entirely (98%) of flint derived from the Chalk. The remainder is composed of chert and quartzite (both resistant rocks) derived from outside the region. The precursor of Chesil Beach probably existed some 125,000 years ago as a shingle bank well offshore from the present beach. The formation of the present Chesil Beach took place between about 15,000 and 5000 years ago, when rapidly rising sea levels caused the erosion of gravel-rich deposits and wave action drove the coarse material onshore as a barrier beach. Photograph reproduced by permission of the Director, British Geological Survey. NERC copyright reserved.
(Figure 46) Rhynie Chert. The site at Rhynie in Scotland is visually unimpressive, and may seem an unlikely geological location, but it is one of the most important palaeontological sites in Great Britain and the world. The Rhynie site contains some of the finest preserved and earliest land plants (Devonian) in the world. It also contains the earliest-known wingless insect (Rhyniella) and one of the finest Devonian micro-arthropod faunas in the world, including mites, springtails and a small aquatic shrimp-like organism, Lepidocaris. The fossils are preserved in chert. The deposit is an excellent example of the freak preservation of life resulting from the flooding of a marsh surface on which these plants were growing, by silica-rich water originating from a hot spring. The hot water killed and preserved the plants and animals before their tissues decayed, and so preserved a complete ecosystem. The arthropods found in the deposit are all primitive forms, and show an early association between plants and their parasites. Preservation is so good that microscopic damage to the plants by these arthropods is seen, as are invading fungal hyphae. The plants are preserved so well that thin sections of rock can be sliced, and examined under a microscope, to reveal the cell structure, including the minute detail of spores as well as cell xylem and stomata. The photographs show a sample and thin section of the chert. The thin section shows the mouthparts of a palaeocharinid (a spider-like arthropod). Photos: C.C.J. MacFadyen (chert sample) and N.H. Trewin (thin section).
(Figure 47) (a) The a palaeogeography of Britain during the late Permian approximately 250 million years ago — an artist's impression of a satellite view. The outline of the present-day coastline of Britain is shown as a dotted line. Much of 'Britain' was desert, with a large inland sea to the east, and a smaller one to the west of the what is now the Pennines, possibly both connected by a sea-way to an open ocean to the north of 'Norway' and 'Greenland'. Reproduced from F.W. Dunning et al. (1978) by permission of the Natural History Museum, London. (b) The extent of the late Permian inland sea (the Zechstein Sea). After Smith (1995).
(Figure 48) Rises and falls of the Zechstein Sea and the resultant rock succession in County Durham. (a) Deposition of limestone shelves, fringed by reefs, occurred during relative sea-level highs. (b) When the relative sea level dropped, the inland sea was probably partially cut off from the open ocean to the north, so that evaporation raised its salinity resulting in the deposition of evaporite minerals. (c) West to east cross-section showing the distribution of the dolomitised limestone and evaporite formations (and their residues resulting from near-surface dissolution). Cycles 1–3 shown on the right side of the diagram relate to the successive periods of high and low sea level depicted in (a) and (b) which resulted in dolomitised limestone formations being overlain by evaporite formations. The Yellow Sands shown at the base of the diagram were deposited from migrating desert dunes (similar sands in the southern North Sea are important gas reservoirs). The Marl Slate is a shale rich in organic material that was deposited immediately after the Zechstein Sea flooded the North Sea area. The numbers indicate the stratigraphical position of sites listed in the table on page 56. (d) Section showing the structure of the reef within the Ford Formation in Cycle 1. Numbers refer to sites listed in the table.
(Figure 49) The distribution of Permian marine rocks in the Durham Province, showing the location of the sites selected for the Geological Conservation Review network for this area. The crest of the Ford Formation reef is shown. After Smith (1995).
(Figure 50) Sequence of diagrams showing igneous processes associated with large-scale crustal movements culminating in the growth of a mountain chain. (a) Igneous intrusions and volcanic rocks prior to mountain building. (b) Generation of magma deep in the crust, and the formation of batholiths. (c) Minor intrusions — dykes, sills — form at the end of the orogeny (see (Figure 12)).
(Figure 51) Simplified geological map of south-west England showing the distribution of igneous rocks and the location of Geological Conservation Review sites. Sites of the Cornubian granite batholith network are numbered as in the site list in the text. After Floyd et al. (1993).
(Figure 52) Schematic diagram of the Cornubian granite batholith. The numbers refer to the sites described in the table on page 60.
(Figure 53) Schematic diagram showing the evolution of structures that are necessary for plants to survive on land. The numbers refer to the sites described in the table on page 62.
(Figure 54) Diagrammatic section of the Lower Thames Valley. Oxygen isotope stages of interglacial deposits (black) are shown circled. After Bridgland (1994).
(Figure 55) The beach-dune-machair network addresses the variations in landforms and processes which occur in the Highlands and Islands area affecting this type of beach complex. The network covers the range and diversity of active and relict geomorphological features. Drawing by C. Ellery.
(Figure 56) List of blocks.
(Figure 57) Kildrummie Kames esker system, Inverness District, viewed towards the east. Two areas of braided ridges (right foreground and centre distance) are linked by a single ridge. These striking features were produced by glacial meltwater rivers at the end of the last ice age. Photo: Cambridge University Collection. Reproduced by permission of the Curator of Aerial Photography.
(Figure 58) Ten sites were selected for the fossil reptiles Cretaceous network in Britain to illustrate the range and diversity of reptiles of this period. Some 150 sites were considered as potential sites for this network. The sites not included as SSSIs may be conserved by other means, such as RIGS or local nature reserves.
(Figure 59) Specimen citation.
(Figure 60) Flow diagram showing a typical site selection process within a GCR block.
(Figure 61) Florence Mine, Cumbria. Mineralogy of the Lake District Block. The importance of this site lies in its excellent exposures within the Beckerment iron ore body, the largest remaining of the iron ore 'flats' (an ore body that has replaced a sediment layer) of the West Cumbria mining province, and its contribution to research into ore mineralistaion in Britain. At the mine, the variety and form of the ore is displayed in situ. This site is one of seven chosen to represent the variety of iron ore deposits across Britain. It is the only one which shows iron ore replacement flats, a type of deposit unrecorded outside Britain. This site was recently added to the Geological Conservation Review. At the time of selection of Lake District mineralogy sites, no good in situ exposures were available at the surface, and a nearby mine dump site was the only available source of material for studying these unique deposits. Florence Mine now supersedes the mine dump site. The photograph shows the mine-roof of kidney ore. This part of the mine is to be conserved with the intention of using it as an educational/visitor resource, consequently no removal of in situ specimens is permitted by the mine management. Photo: T. Moat.
(Figure 62) Coastal defences at Corton Cliff, Suffolk. This site is important as the type section for the Anglian Stage (part of the Quaternary Period), during which the most extensive glaciation of Britain occurred. (a) The coastal section as it appeared in 1964, before modern sea defence works were undertaken. To the right lies the old sea wall, built in the late nineteenth century to protect a private estate. The wall remained intact until the turn of the twentieth century, indicating the extent of cliff erosion over 60 years. (b) The stabilised and vegetated cliffs at Corton. There are two types of structure forming the defence of the cliffs at this locality: a steel and concrete wall and a timber wave screen. Coastal protection works such as these may be in conflict with geological conservation, because for some sites continued erosion is necessary to renew exposures of rock. There is little geological interest in the vegetated slope without resorting to excavation work. Photos: Landform Slides, Lowestoft.
(Figure 63) Fossil Grove, Glasgow. Stumps of a once flourishing forest of lycopods. This tree-like plant grew in a tropical forest which covered this area of southern Scotland during the Carboniferous Period. The trunks, characterised by diamond-shaped leaf scars, grew up to 30 metres before they branched. Photo: A. Gunning.
(Figure 64) Coombs Quarry, Buckinghamshire: a RIGS. A collaborative effort by the Buckinghamshire RIGS group with the County Council Countryside Section and local geologists opened up and improved this site. This involved the clearance of the overgrown face, the creation of a new exposure, the provision of walkways and fencing, and the placing of boards with on-site interpretation. The geological interest of the site was first noted in 1860, during mapping by the Geological Survey. The rocks here, the Blisworth Limestone Formation, date from the Middle Jurassic, and are about 160 million years old. The nature of the different rock types and fossils of the rock beds are now accessible to study. Photo: L. Davies.
(Figure 65) The ripple beds at Wren's Nest National Nature Reserve in Dudley, West Midlands, viewed from the purpose-built observation platform. This visually impressive rock surface provides evidence for the environments of the Silurian Period. Similar ripple marks can be seen today on sandy beaches and river estuaries. Scree, at the base of the slope, continues to yield a wealth of fossils, including trilobites, for which Wren's Nest is particularly renowned. Photo: J. Larwood.
(Figure 66) Hunstanton Cliffs and Morfa Harlech. (a) Cliffs at Hunstanton, Norfolk, exposing normal white Chalk overlying Red Chalk and dark-coloured sandstones. Debris along the foot of the cliff indicates erosion, which ensures that the rocks in the cliff are always well exposed. Because there is no chance of erosion completely removing the rock sequence (as it extends way back beyond the cliffs). It is classed as an exposure site. Photo: C.D. Prosser. (b) Coastal sand dunes at Morfa Harlech, Gwynedd. These landforms would be destroyed by erosion or commercial extraction of sand. Therefore they need conserving, by allowing them to evolve naturally, and so they are an example of an integrity site. Photo: S. Campbell.
(Figure 67) The Shap Granite Quarry, Cumbria, showing regular jointing and the unstable face. This is an example of an exposure site. Photo: J.L. Eyers.
(Figure 68) Close up of a display block in the 'safe' area of Shap Granite Quarry. One of the main features of the granite is the large crystals of pink feldspar. These may have either developed at an early stage during magma cooling and solidification, or grown later in the solidified granite, during metamorphism. The nature of the dark fragments in the granite is also debated. Some believe that these are actually fragments of a darker magma which was present at great depth, and was intermixed with the paler granite by convection processes, engulfing some of the pink crystals en route. Others believe that the dark fragments were part of the surrounding rock which became engulfed and the pink crystals grew within them during metamorphism. Photo: J.L. Eyers.
(Figure 69) The disused Ercall Quarry in Shropshire displays the Vendian (end 'Precambrian')– Cambrian boundary. The steeply dipping beds are of Cambrian age. These beds contrast distinctly with the pale, non-bedded form of the Precambrian quartzite on the far left of the photograph. Photo: C.D. Prosser.
(Figure 70) The rock exposure at the disused Kirtlington Quarry in Oxfordshire is important for Middle Jurassic fish fossils. Photo: J.G. Larwood.
(Figure 71) (a) Diagram of a 'stepped' face in soft sediments which prevents the build up of all of the talus at the cliff foot. Diagrams (b) to (d) show idealised sections of conservation schemes within landfill sites.
(Figure 72) The spectacular, irreplaceable cave formations of the White River Series, Peak Cavern, Derbyshire. Photo: P.R. Deakin.
(Figure 73) Claverley Road Cutting, Shropshire. The site is important for the study of ancient river environments that existed in the Triassic Period. Photo: English Nature.
(Figure 74) Excavation of dinosaur remains at Brighstone Bay, Isle of Wight. The skeleton seems to be that of a sauropod dinosaur which died on a land surface that was subsequently inundated by flooding. The seemingly chaotic disarticulation and distribution of the bones could be explained by scavenging of the carcass prior to flooding. Photo: S. Hutt.
(Figure 75) (a) A river cliff of the outermost part of a meander of the River Dee, between Holt and Worthenbury. The shape of the meander continues to change as the cliff is eroded. Photo: S. Campbell. (b) Meanders of the Dee viewed from the air. Photo: National Remote Sensing Centre Limited (Air Photo Group).
(Figure 76) The rock piles at Writhlington Rock Store SSSI are an important source of plant and insect fossils. Photo: C.D. Prosser.
(Figure 77) The sign board at Hunstanton, Norfolk. Photo: C.D. Prosser.
(Figure unnumbered 1) The photograph shows a fossil ammonite, Asteroceras obtusum, from Charmouth, Dorset. Although superficially like a snail shell, it is actually the remains of a cephalopod. Modern relatives include the squid, octopus and Nautilus. Because of the relative abundance of ammonite fossils, and the relatively rapid evolution of different species, they provide useful 'markers' for comparing ages of rocks at different places. Photo: K.N. Page.
(Figure unnumbered 2) Durlston Bay SSSI, South Dorset, is a good example of a large composite site which incorporates separate and overlapping Geological Conservation Review sites. Photo: J.G. Larwood.
(Map 1) Countryside Council for Wales. Regional and local offices.
(Map 2) English Nature. Regional and local offices.
(Map 3) Scottish Natural Heritage. Countryside Council for Wales. Regional and local offices.
(Front cover) Front cover.
(Rear cover) Rear cover.
(Table 1) Origin of the names of the time periods in the stratigraphic column for the past 570 million years.
(Table 2) Each row represents a period of time, wher stages with odd numbers correspond to interglacials and even numbers to ice ages.