Gloucestershire is one of the most geologically and scenically diverse counties in England, with rocks from the Precambrian through to the Jurassic represented. These varying rock-types are responsible for the three major areas of the county, each with its own distinctive scenery and land-use - the Forest of Dean in the west, bordering Wales, the Cotswolds in the east, and in between, the Severn Vale.
The Forest of Dean, situated between the rivers Severn and Wye, is formed of a raised basin of Palaeozoic rocks folded in the Variscan Orogeny, similar to the South Wales Coalfield to the west. Underlain by great thicknesses of the Old Red Sandstone, the basin is filled with Carboniferous limestones, sandstones and coal measures - all of which have contributed to the industrial history of the region. Sometimes called ‘the prettiest coalfield in Britain’, the Forest's main coal output was in the 18th, 19th and early 20th centuries, although for hundreds of years coal has been won in the area via ‘free-mines’, which could only be operated by local people known as freeminers. One or two survive today. Small-scale mining has been enabled by the exposed nature of the coalfield, with seams often outcropping at surface. Iron-ore has been extracted from labyrinthine mines or 'Scowles' in the limestone since at least Roman times. Several large quarries are still at work in the area, providing Carboniferous Limestone for road surfacing and also Pennant sandstone (see picture) - a popular building stone used notably by Thomas Telford for the Over road bridge, spanning the River Severn near Gloucester.
The scenic Wye Valley defines the western edge of Dean as well as the England/Wales border. Impressive cliffs have been cut by the river in lower dolomitic sections of the Carboniferous Limestone, most notably at the popular ‘Symonds Yat’ viewpoint, which affords one of the most famous views in England. Other ‘karst’ features such as caves, rock pillars and sink holes abound in this area.
On the north-east edge of Dean the Silurian period is represented by the distinctive inlier of May Hill, which rises to some 970 feet, crowned with a pine plantation. This isolated hill lies on the north-south Malvern Line and affords superb views from its summit of the Severn Vale, with the Cotswolds forming the horizon beyond. A high degree of faulting complicates the geology of the May Hill area, causing outcrops of Wenlock limestone and Downton Castle Sandstone on its flanks, as well as a possibly Precambrian section of the core of the hill exposed at Huntley quarry. The hilltop is of Llandovery age May Hill Sandstone.
To the east is the wide fertile Severn Vale, floored by Triassic 'New Red' sandstones and marls of the Mercia Mudstone Group (formerly known as the 'Keuper Marls'), and Jurassic lias clays further east. The Triassic deposits were formed in a Sahara -like desert when the British Isles lay about 15 degrees north of the equator, whereas the clays represent deep-water sediments. The landscape here is flattish, with the only feature of note a rather weak low scarp which meanders across the vale from SW to NE marking the Triassic/Jurassic border. This is superbly illustrated at the ‘Garden Cliff’, Westbury-on-Severn (see picture), where the river Severn has sliced a convenient ‘cut-away’ section of this transition from the red Triassic marls, through the thin Penarth Group (formerly 'Rhaetic') strata, to the lias clays and limestones of the lower Jurassic.
Traditional building stone in the Severn Vale is scarce, necessitating brick or half-timbered construction in the main, although along the scarp mentioned above harder limestone bands in the Lower Lias (known as 'Blue Lias') have been used in vernacular building.
Towards the east side of the Severn Vale the Lias clays are overlain by the sands and limestones of the Middle Lias - well displayed on the slopes of Robinswood Hill, a Jurassic outlier overlooking the city of Gloucester. Further east, forming a rather unstable base to the Cotswold escarpment, are the sands and clays of the Upper Lias.
Superficial deposits are widespread. Floodplain alluvium accompanies the course of the Severn itself as well as tributaries such as the Leadon, Chelt, Frome and Cam. Ancient terraces of former, more elevated floodplains mark the position of the major rivers through various glacial and inter-glacial periods in the last ice age. A sheet of mainly Jurassic limestone fan gravel probably covered most of the vale in the past but has since been eroded away leaving isolated deposits, most notably the Cheltenham Sand, which forms a well-draining light soil in the Cheltenham-Gloucester region.
The Middle-Jurassic oolitic limestone series which forms the bulk of the Cotswolds hills contains the best-known of the county's rocks on account of its extensive use throughout the area as a building stone. All from churches to humble cottages have been imbued with a mellow, warm character from the golden yellow colour of the stone - to which many ‘honey-pot’ Cotswold towns owe their modern popularity and prosperity. The series is divided into the Inferior and Great Oolite Groups. The Inferior Oolite, capping the main north-west facing escarpment, comprises up to 100m of mainly oolitic limestones including the Cheltenham freestone - quarried most extensively at Leckhampton and used widely in the distinctive Regency architecture of Cheltenham. The Great Oolite, forming much of the rather barren Cotswold plateau, encompasses a variety of oolitic, shelly, sandy or marly limestone beds, many of which are used for building purposes such as dry-stone walling and roof tiles.
The limestones were predominantly laid down in a shallow warm continental sea, similar to that off the present-day Bahamas, and are rich in fossils of hard-shelled sea creatures such as brachiopods and sea urchins. Clay bands (e.g. the Fuller's Earth Clay at the base of the Great Oolite Series) represent deeper water periods. As the Cotswold dip-slope is followed toward the south-eastern county extremities these clays and mudstones begin to predominate as the Upper Jurassic period Oxford Clay.
Most of the Cotswold rivers flow south-eastwards down the dip-slope, supplying the river Thames, whose headwaters lie at the bottom of the slope on the Upper Jurassic clays. Terrace deposits up to 6m thick of mainly local oolitic limestone gravels have been left by the river Thames in its upper course during glacial and peri-glacial periods. Downcutting and a gradual southerly migration of the river has left a succession of four terraces at varying heights, chiefly north of its present course.
Oolite or oölite is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Ancient Greek word ᾠόν for egg. Strictly, oolites consist of ooids of diameter 0.25–2 millimetres; rocks composed of ooids larger than 2 mm are called pisolites. The term oolith can refer to oolite or individual ooids.
Dorset is a county in South West England on the English Channel coast. Covering an area of 2,653 square kilometres (1,024 sq mi); it borders Devon to the west, Somerset to the north-west, Wiltshire to the north-east, and Hampshire to the east. The great variation in its landscape owes much to the underlying geology, which includes an almost unbroken sequence of rocks from 200 to 40 million years ago (Mya) and superficial deposits from 2 Mya to the present. In general, the oldest rocks appear in the far west of the county, with the most recent (Eocene) in the far east. Jurassic rocks also underlie the Blackmore Vale and comprise much of the coastal cliff in the west and south of the county; although younger Cretaceous rocks crown some of the highpoints in the west, they are mainly to be found in the centre and east of the county.
Somerset is a rural county in the southwest of England, covering 4,171 square kilometres (1,610 sq mi). It is bounded on the north-west by the Bristol Channel, on the north by Bristol and Gloucestershire, on the north-east by Wiltshire, on the south-east by Dorset, and on the south west and west by Devon. It has broad central plains with several ranges of low hills. The landscape divides into four main geological sections from the Silurian through the Devonian and Carboniferous to the Permian which influence the landscape, together with water-related features.
South Wales is an area with many features of outstanding interest to geologists, who have for long used the area for University field trips.
The geology of Cheshire in England consists mainly of Triassic sandstones and mudstones. To the north west of Cheshire, these rocks are heavily faulted and the underlying Carboniferous Coal Measures are thrown up. Around the areas of Poynton and Macclesfield, the coal is close to the surface and was easily mined. Below the Coal Measures is the Millstone Grit, which appears towards the Derbyshire border on the flanks of the Peak District dome.
The geology of England is mainly sedimentary. The youngest rocks are in the south east around London, progressing in age in a north westerly direction. The Tees-Exe line marks the division between younger, softer and low-lying rocks in the south east and the generally older and harder rocks of the north and west which give rise to higher relief in those regions. The geology of England is recognisable in the landscape of its counties, the building materials of its towns and its regional extractive industries.
The geology of Wales is complex and varied; its study has been of considerable historical significance in the development of geology as a science. All geological periods from the Cryogenian to the Jurassic are represented at outcrop, whilst younger sedimentary rocks occur beneath the seas immediately off the Welsh coast. The effects of two mountain-building episodes have left their mark in the faulting and folding of much of the Palaeozoic rock sequence. Superficial deposits and landforms created during the present Quaternary period by water and ice are also plentiful and contribute to a remarkably diverse landscape of mountains, hills and coastal plains.
The Geology of Yorkshire in northern England shows a very close relationship between the major topographical areas and the geological period in which their rocks were formed. The rocks of the Pennine chain of hills in the west are of Carboniferous origin whilst those of the central vale are Permo-Triassic. The North York Moors in the north-east of the county are Jurassic in age while the Yorkshire Wolds to the south east are Cretaceous chalk uplands. The plain of Holderness and the Humberhead levels both owe their present form to the Quaternary ice ages. The strata become gradually younger from west to east.
The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the Low Countries and the north of Germany. It consists of marine limestones, shales, marls and clays.
The Inferior Oolite is a sequence of Jurassic age sedimentary rocks in Europe. It was deposited during the Middle Jurassic. The Inferior Oolite Group as more recently defined is a Jurassic lithostratigraphic group in southern and eastern England. It has been variously known in the past as the Under Oolite, the Inferior Oolite, the Inferior Oolite Series and the Redbourne Group.
The geology of Monmouthshire in southeast Wales largely consists of a thick series of sedimentary rocks of different types originating in the Silurian, Devonian, Carboniferous, Triassic and Jurassic periods.
The geology of Lincolnshire in eastern England largely consists of an easterly dipping succession of Mesozoic age sedimentary rocks, obscured across large parts of the county by unconsolidated deposits dating from the last few hundred thousand years of the present Quaternary Period.
The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.
The geology of Georgia is the study of rocks, minerals, water, landforms and geologic history in Georgia. The country is dominated by the Caucasus Mountains at the junction of the Eurasian Plate and the Afro-Arabian Plate, and rock units from the Mesozoic and Cenozoic are particularly prevalent. For much of its geologic history, until the uplift of the Caucasus, Georgia was submerged by marine transgression events. Geologic research for 150 years by Georgian and Russian geologists has shed significant light on the region and since the 1970s has been augmented with the understanding of plate tectonics.
The geology of Bosnia & Herzegovina is the study of rocks, minerals, water, landforms and geologic history in the country. The oldest rocks exposed at or near the surface date to the Paleozoic and the Precambrian geologic history of the region remains poorly understood. Complex assemblages of flysch, ophiolite, mélange and igneous plutons together with thick sedimentary units are a defining characteristic of the Dinaric Alps, also known as the Dinaride Mountains, which dominate much of the country's landscape.
The geology of Laos includes poorly defined oldest rocks. Marine conditions persisted for much of the Paleozoic and parts of the Mesozoic, followed by periods of uplift and erosion. The country has extensive salt, gypsum and potash, but very little hydrocarbons and limited base metals.
The geology of Afghanistan includes nearly one billion year old rocks from the Precambrian. The region experienced widespread marine transgressions and deposition during the Paleozoic and Mesozoic, that continued into the Cenozoic with the uplift of the Hindu Kush mountains.
The geology of Lithuania consists of ancient Proterozoic basement rock overlain by thick sequences of Paleozoic, Mesozoic and Cenozoic marine sedimentary rocks, with some oil reserves, abundant limestone, dolomite, phosphorite and glauconite. Lithuania is a country in the Baltic region of northern-eastern Europe.
Geology of Latvia includes an ancient Archean and Proterozoic crystalline basement overlain with Neoproterozoic volcanic rocks and numerous sedimentary rock sequences from the Paleozoic, some from the Mesozoic and many from the recent Quaternary past. Latvia is a country in the Baltic region of Northern Europe.
The geology of Syria includes ancient metamorphic rocks from the Precambrian belonging to the Arabian Craton, as well as numerous marine sedimentary rocks and some erupted basalt up to recent times.