The Geology of Birmingham

A Geological Description of Birmingham from the Triassic to the Present

Many millions of years ago in a climate much hotter than the present, most of the Birmingham area was covered by a vast shallow lake which lay below sea level. As there were no river outlets and water escaped only by evaporation, salts washed down into the lake became concentrated making the lake very salty. Over thousands and thousands of years enormous quantities of fine silt was washed down by floods from surrounding mountains and deposited on the lake bed forming a layer of clay hundreds of metres thick. This clay is known as Mercia mudstone, formerly Keuper marl.

 

The climate changed, the lake vanished and the dry red plain tilted slightly towards the north-east. The clay cracked and when it rained the water flowed along the cracks creating shallow streams and rivers. Gradually the valleys of the Cole, Rea and Tame were formed. However, the clay desert was only lightly grooved as yet.

 

During the most recent Ice Age which ended 10 000 years ago the land was buried beneath 3000 metres of ice. The climate was like that at the North Pole today. Slow-moving sheets of ice ground the tops from the Welsh Mountains and the great glaciers pushed great masses of earth and broken stone across the clay plain. In huge lakes blocked in by ice barriers a mile high, gales blew the water into mighty waves, which pounded the rocks into smooth gravel.

 

When the great thaw came, this rubble was left strewn over the landscape forming an uneven, fairly continuous layer known as glacial drift, composed of water-worn pebbles mixed with sand and clay with a few larger boulders.

 

As the glaciers melted great floods swept in torrents down the river valleys, washing away much of the drift, deepening the river beds into gorges. When conditions stabilised, ours was a sodden landscape: rain and countless tributary rills were starting to smooth and bevel the valley sides. Higher points and the ridges between streams were still covered in drift, but clay was exposed on the valley sides. The swollen rivers oozed through a morass of silt.

 

Vegetation returned, followed by animals and, some 10 000 years ago, by human beings. They found plateaux and ridges dry and firm, patchily wooded, with heath on the stoniest areas. From scores of springs at the edges of the drift, brooks rushed down the clay sides now hidden under dense oak and underbrush forest. The plateaux provided relatively easy travelling, but the slopes were muddy and the woods impenetrable. The valley floors were largely impassable bog: but here and there gravel deposits made the approaches and river bed firmer. These were discovered by animals and used by the hunters who followed their trails.

 

12 000 years of wind and rain and snow have rounded the valley sides, creating today's landscape; only the ridges between the rivers are flat-topped and covered with glacial drift, where it forms the highest ground; being relatively porous it soon dries out on top, but it holds water well and springs flow from its edges across the clay below. The slopes are gentle and valleys are filled with silt with trickles of streams. Overlying both the drift and the clay is 10 000 years' accumulation of topsoil, which is wetter and richer in humus on the clay.

 

Adapted from John Morris Jones 1970-1980 Hall Green & Hereabout and other books, material declared by the author to be free of copyright for non-commercial educational use.

 

 

Surface Geology

sand and pebbles

The main Birmingham plateau can be subdivided into smaller units separated by rivers. North of the River Tame is the low Sutton Plateau which lies west of Sutton Coldfield town centre between Aldridge and Hamstead in the west and Bassetts Pole to Tyburn in the east. On its western edge a ridge runs from Shire Oak to Queslett where it rises up to the prominent landmark of Barr Beacon. The West Bromwich-Harborne plateau is a similar low plateau lying south of the River Tame, west of the River Rea. On the low eastern edge of this plateau was founded the tiny Anglo-Saxon settlement of Birmingham. To the south is the higher ground of the Sedgley-Northfield Ridge which marks part of the main English watershed.


These plateaus overlie a mixture of sand and pebbles, made up of beds of quartzite bunter sandstone and pebbles derived from the sandstone. These are Triassic, probably laid down in desert conditions over 200 million years ago. South of the River Rea is the Clent-Lickey Ridge which includes some of the oldest rocks in our area. Some of these date back to the volcanic times of the Precambrian period over 600 million years ago. These upland areas in the west of our region are the result of the underlying geology. Harder rocks from the Triassic period and earlier have survived the erosion of millennia to a greater extent than the lower lying areas to the east.


Land on the sand and pebble beds was formerly heathland, long tough grasses with low bushes and a few small trees. Stone Age people were able to use the pebbles as tools. The soil is light, it drains very quickly but it is not particularly good for farming. Where there were pebbles early people would find difficulty ploughing, although sandy soils would be easier. from north to south, Great Barr, Perry Barr, Handsworth, Aston, Hockley, Winson Green, Rotton Park, Ladywood, Harborne, Quinton, Bartley Green, and Rubery are on sand and pebble land.

 

sandstone ridge

The Birmingham Ridge runs north to south from Lichfield, through Birmingham city centre and down to Bromsgrove. This is a strip of new red sandstone (Keuper sandstone) about a mile wide which was formed in dry hot desert conditions during the Triassic period. The ridge marks the eastern edge of the areas of harder rock to the west and the softer clays to the east. Outcrops of sandstone are exposed in some places: for instance, on the Tyburn Road at Spaghetti Junction. Sutton Coldfield, Pype Hayes, Witton, Erdington, Birmingham, Edgbaston and Northfield were early Anglo-Saxon settlements on the Birmingham sandstone ridge. Open woods and grassland used to grow on sandstone soil and early hunters would have found deer, hares and birds. Sandstone soil can be good for farming and is easy to plough, but rainwater tends to run through quickly and crops may struggle in dry weather. Travelling on sandstone lands is easy whatever the weather. The stone is easy to cut for building but it wears badly; see some of the stonework of Yardley or Castle Bromwich churches, for instance.


The eastern edge of the sandstone marks a geological faultline which was particularly important to the successful development of Birmingham. Water percolated through the porous sandstone until it met the impervious red clay. Along the faultline was a series of springs which gave ample supplies of water, a factor critical to the town's early industrial development.

red clay

The main part of the Birmingham plateau is separated from the East Warwickshire plateau by the wide valley of the River Blythe. This river runs northwards from Shirley to join the River Tame near Shustoke, and the Tame itself joins the Trent north of Lichfield. The lower-lying Solihull Plateau largely south and west of Solihull town centre is made up of a red clay known as Mercia mudstone, formerly known as Keuper marl. The Rivers Cole and Blythe drain this area on which much of north-east, east and south-east Birmingham is built.


The tiny grains of clay stick together when wet and water cannot pass through. Streams on clay land flood quickly and seriously when it rains, but not for long. On clay land there were thick forests of oak and ash with holly, briar and bramble. Stone Age hunters found hares, deer and wild pigs here as well as nuts and berries. Forest trees were used to build houses and to make carts, ploughs and furniture. Wood was later made into charcoal for melting iron.


Until the Middle Ages the clay lands were part of the Forest of Arden which covered much of Warwickshire north of Stratford-upon-Avon. Early farmers found clay hard to plough, but clay lands make good farmland when broken up. Although clay can be rock-hard when dry, it retains moisture, minerals and nutrients and makes fertile soil. The clay which has a high lime content and was later dug and spread by farmers onto sandy or gravelly land to improve it. Old marl pits were later used to water livestock can be found marked on early Ordnance Survey maps.


In wet weather travel could be very difficult across the sticky clay lands, and in hot weather wheel ruts baked hard and made travel equally difficult. Early settlements on clay lands were usually not on clay but on glacial drift.


This clay is good for making pots and tiles; there were many claypits and brick works in the area. St Andrews Football Ground, for instance, was laid out on the site of extensive clay workings. Thousands of Victorian houses in Birmingham are built of bricks made from Birmingham clay.

 

river valleys

 The gently sloping valleys of the Tame, the Rea and the Cole formed important barrier to travel until modern times. The upper Tame runs south-east from Wolverhampton and cuts the Birmingham Plateau in two from west to east. The courses of the rivers owe much to the melting of the glaciers of the last Ice Age and they wend their way largely over Mercia mudstone, formerly Keuper marl. Both the middle Tame and the Rea were subject to flooding until the early years of the 20th century when they were deeply culverted. Along their courses alluvial deposits have created marshy but fertile land.

 

Alluvium is fertile mud or river silt washed down into the valleys. In some valleys it made large swampy areas which were difficult to cross. Alder and willow grow well near water; the former tree was used for building, the latter for basket making. Alluvium is good black soil for farmers. Long lush grass is good for grazing cattle or for drying as hay for winter. River reeds were used for thatching roofs. The rivers also gave water for drinking, for fishing, for travelling and later power for the water mills.

 

glacial drift

During the Ice Ages huge glaciers pushed millions of tonnes of sand, gravel and pebbles from Wales and from the north of Britain to the Midlands. Glacial drifts with different mixtures of sand and gravel, pebbles and clay are found in many places on top of other rocks. Where sand and gravel drifts are found on top of red clay, trees do not grow closely together.

 

Ploughing is easier and there are drier places to build houses. Springs of fresh water can often be found at the edge of the drift. These were the first places people settled, often on south-facing slopes. Many early settlements including those at Yardley and Moseley were settlements on islands of glacial drift surrounded by clay. Drift makes good routes for travelling even near rivers and in wet weather as long as the muddy valley bottoms are avoided. Drift on river beds makes good crossing places. Many of Birmingham's main roads pick their way from patch to patch of drift to fords with firm gravel crossings. Sand and gravel brought down by the glaciers was quarried commercially.


Gravelly Hill is named after such deposits: there were a number of gravel pits near Salford Bridge. Little Pitts Farm off the Chester Road near Erdington is named after holes left by such excavations; a hollow remains in Pype Hayes Park and there were sandpits on Hodge Hill Common.


 

Geological Table

 

Aeon

Era

Period

Epoch

Began BP

Ice Ages

Evolution of Life

Location of England and Birmingham

BP = years before present

Precambrian Time - extreme geological activity

Hadean Aeon

4600 million years BP

 

No life

Uncertain

Archaean Aeon

3900 million

 

First life: algae /bacteria

Birmingham in the Southern Hemisphere and probably on land.

Barnt Green volcanic rocks laid down as volcanic ash.

Proterozoic Aeon

3500 million

At least four ice ages and interglacials

Soft-bodied invertebrates, including jellyfish

Phanerozoic Aeon

Palaeozoic Era

Cambrian Period

 

540 million BP

 

Age of Trilobites

First fish

Birmingham at the South Pole beneath the sea.

Volcanic activity.

Lickey quartzite laid down on the sea bed.

Ordovician Period

 

505 million

Ordovician Ice Age

  440 - 430 million years before present

First freshwater animals, corals

Birmingham at the Antarctic Circle beneath shallow seas.

Tropical limestone Wenlock reef laid down at Dudley.

Silurian Period

Early/ Late

438 million

 

First land plants, insects

Birmingham on a level with modern South America beneath tropical shallow seas.

Devonian Period

Early/ Middle/ Late

408 million

Permo-Carboniferous

Ice Age 330 - 350 million years before present

First amphibians

Age of Fishes

Birmingham in a hot dry desert on a level with modern South America.

Carboniferous Period

Upper/ Lower

360 million

First reptiles, winged insects, first forests

Birmingham in a tropical swampy river delta on the Equator. South Staffordshire coal deposits laid down.

Permian Period

Early/ Late

286 million

 

More reptiles

Birmingham in hot dry desert conditions now north of Equator.

Clent breccia, compacted gravel laid down by flash floods.

Aeon

Era

Period

Epoch

Began

Ice Ages

Life

Birmingham

Mesozoic Era

Triassic Period

Early/ Middle/ Late

245 million BP

 

First dinosaurs/ flying reptiles

Age of Reptiles

Birmingham on a river delta in hot dry conditions east of the present Caribbean.

Mercia mudstone (clay) and Keuper red sandstone laid down.

Jurassic Period

Early/ Middle/ Late

208 million

 

First birds

Birmingham in the present mid-Atlantic.

Beneath the sea in a climate much warmer than present.

Cretaceous Period

Early/ Late

Lower/Upper

144 million

 

Age of Dinosaurs Early mammals, flowering plants

Globally high sea levels.

Birmingham beneath a shallow sea; moving towards present position.

Central Europe now land.

Cenozoic Era

Tertiary Period

Palaogene Epoch

 

Neogene

Palaeocene Epoch

66.4 million

 

Larger mammals

 

All of Europe now on land,

Britain joined to the continent and situated west of present Spain.

Warm climate.

Eocene

Early/ Late

56 million

 

Grasslands develop

Oligocene

34 million

 

Grazing mammals

Miocene

24 million

 

Apes & whales

Pliocene Early/ Late

5 million

 

Earliest hominids

Quaternary Period

 

Pleistocene Epoch

1.65 million BP

The (Great) Ice Age: at least four glacials and interglacials

Humans

Ice completely covered Midlands on more than one occasion, otherwise frozen tundra. Glaciers moved huge quantities of material southwards – glacial drifts of sand and gravel laid down.

Human stage: Palaeolithic/ Old Stone Age 500 000 – 10 000 years ago.

Holocene

10 000 years ago

Holocene interglacial

The present epoch

Mesolithic/ Middle Stone Age c10 000- 7000 years ago.

Neolithic/ New Stone Age c7000-4000 years ago.

Aeon

Era

Period

Epoch

Began

Ice Ages

Life

Birmingham

 

 

 

Brief Geological History

 

Precambrian Time - Archaean and Proterozoic Aeons


This aeon was named with respect to the Cambrian period which follows it. The terms Archaean and Proterozoic derive from Greek and mean ancient aeon and earliest life aeon, respectively.


The Precambrian lasted some 80% of geological time and was the period when the earth was cooling and its crust thickening. By the end of this time one enormous supercontinent had formed. There was extensive volcanic activity. The oldest known rocks in the world are some 4000 million years old; the oldest in Britain are to be found in north-west Scotland. Sediments world-wide bear witness to numerous glaciations, the most severe and extensive between 1000 million and 600 million years ago. Evidence is to be found on the Isle of Islay off Scotland where sedimentary rock shows 17 glaciations on the site with a further 27 periods of nearby glaciation.


Late precambrian rocks can be found in the Lickeys on Cofton Hill, some of the oldest in the Midlands. This fine-grained brown, green or purple rock, known as Barnt Green volcanic rock, was originally deposited as millions of tonnes of volcanic ash which gradually compacted to form a hard rock.


At this time Britain was located at the South Pole. Due to plate tectonics and continental drift it has moved slowly north and eastwards for some 3000 million years.


The original definition of the Precambrian was that it predated life on earth. However, fossil evidence of early organisms has now been found over 3500 million years old. Consequently the Precambrian is now divided into three aeons: the pre-life aeon is now known as the Hadean, the Archaean Aeon saw the evolution of algae and bacteria, the aeon of soft-bodied invertebrates is the Proterozoic Aeon.

 


Phanerozoic Aeon - Palaeozoic Era
- Cambrian Period


The term Phanerozoic derives from Greek meaning visible life and was coined to indicate the beginning of the fossil record. The present epoch is still part of the Phanerozoic Aeon. Palaeozoic also derives from Greek meaning ancient life. The Cambrian period is named after rocks in south-west England and South Wales and derives from Cambria, the Roman name for Wales.


There were at this time three large and a number of smaller continents. England and Wales and southern Ireland lay near the Antarctic Circle on a smaller sub-continent known as Avalonia which also carried Novia Scotia and New England. (Northern Scotland and Ireland at this time lay just south of the equator.)

 

Avalonia was drifting northwards at some 4cm per year. As it drifted it met with a continental plate below sea level which was moving southwards. The plate moved beneath Avalonia pushing it upwards and causing volcanoes and earthquakes. The Snowdon range and volcanic rocks near Nuneaton date from this time.


The climate during the Cambrian was warmer than today and sea levels rose. Sandstone is commonly found formed from sedimentary water-borne deposits around ancient seashores. The few terrestrial rocks found are water-borne deposits on floodplains and windblown sand. No life, plant or animal, inhabited the desert landscape, and with no plant roots to hold the earth in place, cambrian lands were subject to severe erosion by wind and rain.


Cambrian life was exclusively marine. A wide variety of fossil evidence marks a significant change from the Precambrian. Thousands of species of trilobites have been identified along with other arthropods. The Cambrian is commonly known as The Age of Trilobites. Sponges were common as well as brachiopods; the ancestors of sea urchins and starfish were present as were the molluscs. Graptolites, types of marine plankton are in evidence.
For most of this time Birmingham lay at the bottom of a shallow sea south of the great continent of Gondwana. The Welsh slate used to roof most Birmingham houses during the 19th century was formed as deposits of mud over 5 kilometres deep in still deep marine basins in North Wales.


The Lickey ridge if made up of buff or pink-coloured cambrian Lickey quartzite. This soft sandy sedimentary rock may possibly be the result of wind-blown desert conditions. Darker quartzite on Bilberry Hill shows signs of having been deposited as sand at the bottom of a shallow sea.

 


Phanerozoic Aeon - Palaeozoic Era
- Ordovician Period


The Ordovician System was recognised and described 1879 by Birmingham University professor, Charles Lapworth who so named the exposed rocks of the Arenig Mountains east of Bala, North Wales. He took the name from that of a local Celtic tribe, the Ordovices.


A major glaciation lasting over 10 million years dominated much of the period and substantially lowered sea levels by as much as 170 metres exposing vast new areas of land.


Flora and fauna still existed only in the sea. With no terrestrial life, the land was completely barren and oxygen levels consequently low. At the beginning and end of the period there were mass extinctions caused by the effects of glaciation and the corresponding alteration of sea levels. However, a wide variety of new small marine animals, trilobites, brachiopods, and graptolites appeared across the world. Fossils have been found of the first fish, armoured and jawless. It is thought that the first simple plants developed on land in the tropics in the middle of the Ordovician.


The rocks of the English Lake District were formed at this time. They are made up of a mixture which includes enormous amounts of volcanic ash washed into a shallow sea. Ordovician Birmingham lay beneath a shallow sea and continued to move slowly to the north-eastwards.

 


Phanerozoic Aeon - Palaeozoic Era
- Silurian Period


The period is named after the Celtic tribe of the Silures; the first rocks to be recognized as of this period were identified in south-east Wales.


At the end of the Ordovician ice age, deposits of sedimentary rocks around ancient coasts testify to rising sea levels. There is widespread evidence of land plants and early jawed fish.


Southern Irish and Welsh rocks show evidence of the early land plants. A series of islands lay between warm shallow seas roughly where Brazil is now.


The Wenlock Reef: The Wenlock limestone of Dudley is world famous for the exceptional preservation of fossil marine fauna. Limestone is formed from the remains of coral, shells and calcified algae and was deposited when the West Midlands was covered by a warm shallow tropical sea. Some beds contain many fossil fragments indicating that the animal remains had been subject to the movement of waves; other beds contain complete fossils, perfectly preserved by rapid burial under mud on the seabed perhaps after storms. Most of these fossils were found during quarrying in the 18th and 19th centuries when limestone was used as flux in the Black Country iron industry.

 

The Lapworth Museum at Birmingham University contains the Holcroft Collection, some of the finest collections of fossils of Silurian Wenlock Limestone of the West Midlands and the Welsh Borders, made between 1876 and 1897 by Sir Charles Holcroft, a successful iron and coal master in Dudley. He collected some 4000 specimens including exceptionally preserved examples of more common fossils such as trilobites, corals, crinoids and brachiopods and also some rarer and more unusual fossils. The excellent trilobite specimens are known world-wide as Dudley Bugs.
During the Silurian Birmingham would have been at the bottom of a shallow sea where coral reefs swarmed with millions of tiny creatures in the clear warm water.

 

 

Phanerozoic Aeon - Palaeozoic Era
- Devonian Period


The first rocks to be recognized as of this period were identified in Devon and Cornwall.


The early continent of Baltica of which Britain was a part and Laurentia of which North America was part collided forming a single continent known as Laurussia or Euramerica. Mountains were raised and there was intense volcanic activity along the line of collision; in Britain this was in Scotland. In a climate warmer than the present there was widespread desert. Sediments of sandstone were formed from the eroded mountains. North of a a line from Bristol to Belgium was a great continent; to the south was shallow sea. Birmingham would have been on dry land during the Devonian and situated roughly where Colombia now lies in South America.


A wide variety of invertebrates continued to evolve in fresh and marine waters, but it is the very large number of primitive fish species which has named the Devonian The Age of Fishes. Fish, including the first carnivorous species, inhabited freshwater and marine environments. On land the first amphibians emerged from the sea and fossil evidence of the first tree forests has been found.

 


Phanerozoic Aeon - Palaeozoic Era
- Carboniferous Period


The name Carboniferous is derived from the coal deposits, the fossilised remains of millions of trees growing in warm wet swamp conditions; from Latin carbo = coal.


Laurussia was an early continent north of the Equator consisting of Laurentia (North America) and Baltica (northern Europe) and was largest landmass during the Carboniferous. England and Wales had by now collided with Scotland, uplifting the Scottish Highlands.The coal measures ran in a continous line from Alabama through the Appalachian Mountains, via the Midlands to Germany. The Atlantic Ocean did not exist at this time. The climate was warm and sub-tropical.


Our area was periodically covered with shallow warm sea or by swampy river deltas which ran down from the great land mass to the north into a sea around the Equator. Limestone is found formed from the remains of coral, shells and calcified algae deposited in a warm shallow tropical seas.


The Carboniferous landscape was dominated by plants, from small shrubs to tall trees over 30m in height, the ancestors of our tiny club mosses. Fossil logs have been found measuring as much as one metre at the base. There was now a large variety of insect life on land and in the air. Amphibians date from end of the Devonian, but spread widely during the early Carboniferous as the only land vertebrates and grew to as long as 2m. The earliest reptiles c30cm in length have been found in the Upper Carboniferous in Canada.


South Staffordshire coal measures: Birmingham University's Lapworth Museum contains collections of carboniferous flora and fauna especially from the coal measures of South Staffordshire. Many were collected by Sir Charles Holcroft, a Black Country iron and coal master whose collection came to the museum 1917. The fossils are extremely well preserved and include a wide variety of plants and animal fossils including horseshoe crabs, insects, millipedes, arachnids, crustaceans and fish. 310 million years ago this was a wide flat river delta with a variety of habitats including fresh water, brackish water and dry land.

 

The shape and position of the delta constantly changed over the millions of years of the Carboniferous, so that layers of coal may be interspersed with alluvial deposits. This great river drained from the Mercian Highlands rising south and west of Coventry and fed via a great delta into the sea north of Cannock Chase. Coal deposits are found west of Birmingham from Cannock to Stourbridge in the Black Country and to the east between Tamworth and Warwick.

 

The coal-bearing strata consist mainly of grey shale often with associated sandstones and ironstones, once mud- or sand-banks in a great delta; of seat-earths of ganister, once soils on which forests grew; and of coal, once the peat resulting from the decay of the forests. The rhythm, - shale or sandstone,seat-earth, coal - is often repeated. Sometimes the shale contains marine fossils, but more commonly freshwater and terrestrial forms. It is believed that the rhythm was brought about by the intermittent subsidence of a very flat tract of delta to which rivers were bringing great quantities of sediment. After a subsidence the tract was flooded either by fresh river-water lagoons or by marine or brackish incursions of the sea. The rivers continue to bring in sand and mud, but chiefly the latter, until the surface rose above water level and plants began to colonise it and to convert the latest muds into fireclays. The growth of vegetation in stagnant swamps, and probably a hot moist climate, produced the peats which are now the coals. This picture explains the coalescence of seams when traced from the subsiding region of the Pennines in the north towards the more stable areas in the south where peat formation proceeded without interruption by flooding. It also explains why coals die out in the south, for here the stable land stood too high to become part of the coal swamp, whereas to the north the delta area kept intermittently sinking and this providing space for more sediment.
British Association for the Advancement of Science 1950 Birmingham and Its Regional Setting article Geology by Leonard J Wills p19

 

In 1917 Dr Frank Raw Birmingham University collected series of carboniferous reptile footprints and tail marks on red sandstone near Alveley, Shropshire. The fossil footprints formed trackways made by many different animals. 310 million years ago this was a warm river floodplain rich in plant-life, especially club-mosses. Pools or small lakes on the flood plain were colonised by small arthropods, amphibians and reptiles. Both carnivores and herbivores were present. Some rocks have cracks suggesting that later in the Carboniferous the pools and lakes dried out under intense heat; others have rain prints on them. It is suggested that the footprints and tracks were preserved as a result of being quickly buried by sand brought down by torrential flooding.


Carboniferous deposits of Keele clay are found on Beacon Hill in the Lickeys interspersed with thin beds of sandstone. The clay was deposited by a river into a shallow lake in arid conditions. Periods of increasing rainfall carried sand mixed with the clay into the lake. The present rocks were formed as sediments on the bottom of the lake.

 


Phanerozoic Aeon - Palaeozoic Era
- Permian Period


The Permian is named after the district of Perm in the Ural Mountains in Russia where the sequence of rocks of this period were first identified.


At the end of the Carboniferous and beginning of the Permian the Armorican/ Iberian plate which carried parts of western Europe and Spain collided with Avalonia carrying England and Wales. This collision is known as the Variscan orogeny ie. mountain building, which pushed up the earth's crust creating ranges from Ireland across southern Britain and into Germany. In England this formed the Mercian Highlands which no longer exist.

 

By the middle of the Permian the northern hemisphere continent of Laurasia (present North America and Asia) and southern hemisphere Gondwana (South America, Africa, India, Australia, and Antarctica) formed the supercontinent of Pangaea stretching from pole to pole. While there was extensive glaciation in the south, most of the continent was hot and dry with extensive deserts. Birmingham was roughly in the position of present-day central America and was terrestrial.


Major climate changes affected both marine and terrestrial life. Sea levels fell, the land rose and the climate became much drier bringing to an end the swamps favourable to coal deposits. Climate warming caused widespread extinctions. It is estimated that some 70% of marine species died out at the Permo-Triassic boundary, and 95% of terrestrial animal and plant life. These extinctions later resulted in expansion and diversity in terrestrial plants, insects, and reptiles, particularly pre-mammalian reptiles.


Above the golf-course on Beacon Hill in the Lickeys permian Clent breccia is found. Breccia is compacted gravel, here made up of sharp reddish fragments surrounded by large amounts of muddy rock. It was formed by flash floods rushing down from the Mercian Highlands and laid down in hot desert conditions. Although there is evidence of carboniferous limestone, pebbles are predominantly of precambrian igneous rock suggesting that the Highlands were much reduced by this time.

 


Phanerozoic Aeon - Mesozoic Era
- Triassic Period


Mesozoic derives from Greek and means middle life. Triassic, Greek trias = set of three, derives its name from a central German sequence with three rock formations, the lower being Bunter (German bright or variegated), Muschelkalk (a marine system not found in Britain) and Keuper (a German mining term, pronounced koy-per) uppermost, thought to typify the period.


At the beginning of the Triassic the supercontinent of Pangaea comprised almost all the major landmasses of the world and covered a quarter of the Earth's surface. The climate was largely warm and dry but subject to continental extremes of temperature. Degraded sedimentary rocks of earlier periods accumulated as sediments on land throughout the Triassic. Keuper marl, now known as mercia mudstone, and new red sandstone are examples. Such sediments may be wind-deposited in desert regions or may be the result of river action. Much of Europe lay below the Triassic seas.


In the sea the ancestors of large predatory plesiosaurs evolved, but the largest marine reptiles were carnivorous ichthyosaurs which gave bore live young. At the end of the Permian some 80% of amphibians and reptiles disappeared due to increasing heat and drought. Ancestors of modern animals which appeared in the Triassic include lizards, turtles and crocodiles. Bipedal reptiles made an appearance to evolve into the early predatory dinosaurs which could reach lengths of over 6m. Some early lizards were the first flying vertebrates gliding using skin stretched between extended ribs. This was the Age of Reptiles. The first true mammals appeared at the end of the Triassic Period.


Birmingham lay near the south-west coast of Laurentia in the south of Pangaea on the latitude of the present Sahara Desert, but much to the west of it. As the shallow seas evaporated vast deposits of salt were laid down which are mined to this day across Europe, in Cheshire, for example. Triassic sand and bunter pebble beds are found in Birmingham west of the north-south sandstone ridge and occur in a range of colours, mainly reds, browns and yellows. The beds are a natural source of gravel and sand and made up of a coarse conglomerate of pebbles 2-10cm in diameter, held loosely in sand.

 

The red colour of the sandstone indicates land-borne rather than sea-bed transportation, erosion and deposition. The iron in the wet sand oxidised on contact with the air giving the sand its rusty red colour. The deposits are the result of river action; this was the site of an enormous inland river delta which stretched from south of Worcester to north of Stoke. The pebbles are of Ordovician or Devonian origin having been washed down by this great river from the Mercian Highlands to the south and south-west which no longer exist.


Keuper marl (now known as mercian mudstone, red clay) was laid down in the Upper Triassic in semi-desert conditions. It is likely to be the final remains of the Mercian Highlands to south, degraded sedimentary rock washed down onto a wide plain liable to drying up in a hot arid climate. The plain which covered most of England to the south was probably at or below sea level, and there are signs that the sea covered the area by the end of the period. The mercia mudstone may have been overlaid in subsequent periods by later sediments which have since been completed eroded. However, they compressed the mudstone to its present consistency leaving a layer some 250 metres thick which covers most of the area north-east, east and south-east of Birmingham city centre.


mercia mudstone is thus the most recent rock to be found in our area. Later depositions of rock almost certainly occurred, but all have since been completely eroded away.

 


Phanerozoic Aeon - Mesozoic Era
- Jurassic Period


Pangaea began to break up with North America separating from Eurasia, and Africa from India, Australia, and Antarctica. On warm shallow seabeds carbonates were deposited, the remains of trillions upon trillions of shells, to form the limestone reefs of the French Jura Mountains (after which the period is named) and of southern England. The climate was warmer than present and the polar ice caps had melted. Further coal deposits indicate a moist climate temperate to tropical.


There was abundant marine life, sharks and bony fish being predominant. Marine reptiles, plesiosaurs and ichthyosaurs also shared the warm seas. Frogs, toads and salamanders evolved at this time, but the dominant land animals were reptiles including the dinosaurs. The largest herbivore, apatosaurus reached 30m in length and weighing some 30 tonnes; the fiercest carnivore, tyrannosaurus stood 6.5 m tall with a head 1.3m long and teeth 15cm long and weighed 8 tonnes. Armoured dinosaurs evolved. Crocodiles, marine turtles and lizard appeared. Flying reptiles were common; they were as small as sparrows and probably warm-blooded. The first birds evolved in the Late Jurassic: archaeopteryx had claws at the ends of its wing and feathers. The first small shrew-like mammals appeared.


Although there is no geological evidence in our area of the Jurassic period, it is likely that the Birmingham area was beneath the sea for most of this time and located south and west of its present position. Higher ground in Scotland, Wales and south-west England was above sea level, as at times was the London area.

 


Phanerozoic Aeon - Mesozoic Era
- Cretaceous Period


The name Cretaceous derives from Latin creta = chalk, a fine soft limestone made up chiefly of the armoured plates of planktonic floating algae.


As the break-up of the Pangaean supercontinent continued, continents began to take on their present shapes, although Europe was separated from North America by a very narrow Atlantic Ocean and from Africa by a very wide Mediterranean Sea. Sea levels varied throughout the period but were the highest in the history of the Earth, by the end of the Cretaceous some 250 higher than at present. All continents lost large amounts of land to the sea which lay wide and shallow around the coasts.


A wide variety of ammonites were prey to larger animals including marine reptiles, the mosasaurs. Other reptiles were plesiosaurs and ichthyosaurs. The ancestors of modern fish were prey to sharks and rays. In the air flying reptiles, the pterosaurs held sway, quetzalcoatlus having a 15m wingspan. The Age of the Dinosaurs continued on land. Early cretaceous plants included cycads, ginkgoes, conifers, and ferns; later to evolve were magnolias, poplars, willows, sycamores, and herbaceous plants. New plants brought new insects. At the end of the Cretaceous the dinosaurs became extinct. Although terrestrial plant life was largely unaffected, in the sea little planktonic flora and fauna was to survive. Ammonites became extinct, along with such marine reptiles as ichthyosaurs, mosasaurs and plesiosaurs. It is believed that this mass extinction may have been caused by a massive meteorite impact on the Yucatan Peninsula in Mexico whose shock waves and subsequent dust clouds caused such severe climate change that many species could not adapt quickly enough to survive. It was in the wake of this event that the surviving life-forms adapted to fill the gaps and become the present successful fauna. Placental and marsupial mammals evolved at this time, as did penguins and marine mammals such as the seal and walrus.


At the beginning of the Cretaceous Birmingham was probably at the bottom of a shallow sea, that grew ever deeper, and was at a higher latitude than the present, perhaps on a level with present-day northern Germany.

 


Phanerozoic Aeon - Cenozoic Era
- Tertiary Period

Epochs: Palaeocene, Eocene, Oligocene, Miocene, Pliocene

 


The name Cenozoic signifies recent life; the Tertiary is the third period following the Palaeozoic and Mesozoic. The -cene of the names of the epochs Palaeocene, Eocene, Oligocene, Miocene, Pliocene derives from Greek and means recent with respect to the types of modern flora and fauna to be found. The epochs are thus respectively ancient, dawn, fewest, less, more modern species. American usage is increasingly to dispense with the term Tertiary in favour of Palaeogene (Greek = old type) with reference to the Palaeocene, Eocene and Oligocene epochs, and to use Neogene (Greek = new type) to cover the Miocene and Pliocene. Some also include the Quaternary Period to the present as the Neogene.


The continents are recognisable as the precursors of the present. The Atlantic continued to widen, the Mediterranean to narrow. Europe was approaching its present position in the northern hemisphere. The break-up of the Laurasian supercontinent was completed in the Eocene by the formation of the Norwegian-Greenland Sea which united the Atlantic and Arctic oceans. Climatic conditions remained subtropical at northern latitudes during the Cenozoic Era. The early Eocene witnessed the warmest conditions of the Cenozoic with evidence of subtropical plants in the south-east of England.


During the Oligocene and Miocene periods the earth's mantle swelled up beneath the Irish Sea causing the whole of Britain to tilt. The north-west of England was raised by up to 2km as a result of the same movements that created the Alps. It is likely that the horst of South Staffordshire and the East Warwickshire Plateau were raised up. During this and the succeeding periods of glaciation, erosion has moved millions of tonnes of rock from the surface of Britain, the more so at higher altitudes. The result of this is that older rocks can now be found at the surface in the north-west, with progressively younger rocks at the surface moving towards south-east of England.


This was a time of mammal diversification: mammals had existed for 100 million years but now evolved into many forms and spread dramatically. Hoofed mammals evolved during the Palaeocene Epoch and proliferated into horses, tapirs, and rhinoceroses, and into pigs, peccaries, hippopotamuses, camels, llamas, deer, giraffes, sheep, goats, musk-oxen, antelopes, and cattle. Elephants of many types spread throughout the world. Some mammals grew to giant size in the Pliocene such as the sabre-toothed cat, the giant ground sloths and woolly mammoths. At this time the first hominids appeared. Early humans did not emerge until the Pleistocene Epoch of the Quaternary Period. The first modern humans did not arrive here until after the Great Ice Age at the end of the Pleistocene.

 


Phanerozoic Aeon - Cenozoic Era
- Quaternary Period - Pleistocene Epoch


The Pleistocene Epoch is usually known as The last Ice Age or The Ice Age. Its name derives from Greek = most modern (species) epoch.


The formation of glaciers actually began at the end of the Tertiary Period, but continued and ebbed and flowed throughout the Pleistocene. At times a third of the Earth was covered in ice, as were significant amounts of sea (At present one tenth of the earth is covered with ice.) There were ice sheets in North and South America, in the Alps, Siberia, New Zealand and even on African mountains on the Equator. Across northern Europe the Scandinavian Ice Sheet covered most of Britain (as far south as Bristol and north London) and Ireland, Germany, Poland and Russia. The weight of thousands of metres of ice (Birmingham was over a mile beneath the ic sheet) caused the land beneath to sink and land beyond to rise, the reverse occurring when the glaciers melted. Glaciers pushed huge quantities of rock which were deposited as moraines at the melting ends of the ice sheets. The Scandinavian ice sheet eroded the bedrock leaving patches of glacial drift several metres thick which had been shifted sometimes hundreds of miles.


Glacial ice completely covered the Midlands once only during the Anglian stage c444 thousand years ago. It is possible that ice also covered the Midlands during the Wolstonian stage 128-367 thousand years ago. The north west Midlands were covered during the latter part of the Devensian stage 15-20 thousand years ago This was the most recent ice age in Britain c10-116 thousand years ago.


The solid geology of the West Midlands is overlaid in places by a variable thickness of glacial drift deposits. These may be over 30m thick though 2-10m is more typical. The rock found in Birmingham drifts generally originates from North Wales and are made up of triassic sand and pebbles mixed with carboniferous and trassic clays.
Some large mammals evolved adapted to Arctic conditions, including woolly mammoth, woolly rhinoceros, musk ox, moose and reindeer. They lived in periglacial areas ie. on permafrost or tundra beyond the limit of the glaciers. Large temperate zone mammals present during the warmer inter-glacials included included elephant, mastodon, bison, hippopotamus, wild hog, deer, giant beaver, horse, and ground sloth. However, in general the temperate zone was much further south than the present.


The Pleistocene saw the appearance and evolution of our own genus, homo and is where where geological time merges into human prehistory. The oldest species, homo habilis evolved during the late Pliocene. In Africa fossil evidence has been found 2 million years old. Homo erectus is found in Africa c1.6 million years ago, spreading to other parts of the world during the early Pleistocene; fossils have been found in China and Java c1 million years old. Early forms of our own species, homo sapiens, evolved in the middle Pleistocene c400 000 years ago. More modern forms, homo sapiens neanderthalensis appeared c100 000 years ago during the last interglaciation and are found in Europe and Asia. They became extinct c35 000 years ago replaced by ourselves. At the end of the Pleistocene many large mammals, including mammoths, mastodons, ground sloths, and giant beavers became extinct.


Evidence of homo heidelbergensis and homo neanderthalensis has been found in Essex and in Kent. They may well have walked this way too. In Warwickshire and Worcestershire have been found the fossilised bones of Pleistocene animals: auroch (the ancestor of European bison and domestic cattle), elephant, hippopotamus, hyena, mammoth, stag and wolf. Nearest to Birmingham were auroch, elephant and stag at Shustoke and mammoth bones at Dudley and Minworth. Stone Age handaxes have been discovered at Waverley Wood Farm Pit near Coventry.

 


Phanerozoic Aeon - Cenozoic Era
- Quaternary Period - Holocene Epoch

The present epoch


The Quaternary is the fourth period following the Palaeozoic, Mesozoic and Tertiary. Holocene means most recent epoch ie. the present epoch. The end of the Pleistocene is generally taken to mark the end of the Great Ice Age. However, it cannot be known whether this is true or whether we are at present living in an interglacial period.


At the end of the Pleistocene the ice melted quickly. It is estimated that at its height c8000 before the present some 18 trillion tonnes of meltwater were being released annually raising the sea level by 5cm each year flooding former coastlines. As a result Britain became separated by sea from mainland Europe. Another effect caused by the removal of the tremendous weight of the ice sheets was that the level of the land previously under ice began to rise, in Scotland eventually by some 15 metres. The marginal bulge beyond the glaciers also began to subside: recent studies of the Solent show flooding of areas previously above sea level. The end of the Ice Age also saw an enormous increase in rainfall.


Gradually the ice-age tundra became covered with the arctic trees, aspen and birch, subsequently pine and hazel, then alder and oak, then elm and lime, ash, beech, holly, hornbeam and maple which covered virtually the whole of Britain by 7000 BC. Neolithic people spread across Europe and Asia in a climate pleasantly warmer than the present. There were the beginnings of deforestation and consequent land erosion as Bronze Age people extended pastoral and arable agriculture as well as using charcoal for smelting. During the Holocene the human race has increasingly made a major impact on the Earth. However, despite the effects of global warming it is believed by some that we are at present in an interglacial period and that another ice age may be expected.

 

As for the future: it is estimated that the African continental plate will continue to collide with the Eurasian plate on which the British Isles is situated for many tens of millions of years. Eventually the Atlas mountain ranges of north-west Africa will be pushed up as far as Paris and Berlin. The Eurasian plate is moving north-eastwards at a speed of some 8 mm per year and will, in perhaps 250 million years, lie where Siberia is at present.

 

 

William Dargue 08.04.09