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Cheshire Geology


This page contains some information about the geology of Cheshire, the Wirral, Merseyside and the surrounding areas (North Wales, Shropshire, the Pennines and the Irish Sea). Hopefully, you will find this more entertaining and readable than most of the books on the geology of the British Isles, which are written by real geologists for other real geologists.

I am not a geologist and geology was not taught when I was at school 50 years ago. It may be different nowadays and I may well be preaching to the initiated. Some of my facts may be inaccurate so please do not use this as a basis for anything serious. If you have any constructive comments (good or bad), please let me know; email comments@CheshireTrove.com.

Edition 1, 25th August 2013. Brendon Cox.

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The 'Suture Line' map below is based on an outline map of the UK reproduced from Ordnance Survey map data by permission of the Ordnance Survey © Crown copyright 2010.



600 million years ago

Britain in Two Halves, 600 Million Years Ago


The earth was formed about 4,000 million years ago. It seems that life existed on earth very shortly afterwards, maybe only a hundred million years or so later. The most remarkable fact that we will ever learn is that life only began once on this planet. I read that in a Bill Bryson book and I think we both read it previously in Richard Dawkins' Climbing Mount Improbable. Our DNA shows that we are related closely to every blade of grass and very closely indeed to our dog or cat. Everything on this planet started from the same cell, which had the ability to split and become two identical 'living' cells.

When a dry-rot expert came to sort out a problem in our house, he told us, "These dry-rot spoors are everywhere. They've even been found in outer space". So I have wondered ever since if these primitive life-forms originated on the earth and rose up, or did they start up there and come down to land on my house? And maybe the very first living cells didn't start on earth at all.

Until recently, it was thought that nothing much happened until about 600 million years ago, after which time identifiable fossils started to appear. Because these fossils had obviously been life forms, this point in time marked the beginning of what became known as the 'Phanerozoic' age (Phanero meaning 'obvious' and Zoic meaning 'life'). The time between then and about 500 million years ago was named the 'Cambrian' period (because the rocks in which these early fossils were first found were in the Cambrian mountains, near Harlech in North Wales). The period before the Cambrian period is known, unsurprisingly, as the 'Pre-Cambrian', and includes the 'Proterozoic' (early life) age.


500 Million Years Ago

500 Million Years Ago


400 Million Years Ago

400 Million Years Ago


Suture Line

The 'Suture' Line: The two continents joined here


At that time, England and Wales were on a continental plate somewhere around the South Pole and drifting north, floating on the molten 'mantle' beneath the crust, towards another continental plate that contained North America, Greenland, Scotland and Northern Ireland. From the late Cambrian period through the next ('Ordovician' and 'Silurian') periods, about 500 to 400 million years ago, we (in Cheshire) travelled from about 70o South (in the Antarctic Circle) to about 20o South (in the southern Tropics), where the North American plate had remained fairly stationary.

Shortly afterwards, the two continents collided and crumpled up. The Cairngorms, the Southern Uplands, the Lake District, Snowdonia, the Appalachians and the Irish mountains were formed, together with mountains in Norway and Greenland. The mountains at the time would have been huge, comparable with the Himalayas of today; they have since been eroded by the weather to their present size. Major faults, notably the Great Glen fault (running from Inverness to Fort William and beyond), were formed in a SW-NE direction. These occurred at the time of, or shortly before, the collision as the two continental plates slid past each other, in the manner of the San Andreas fault today in California.


300 Million Years Ago

Two halves joined together: 300 Million Years ago


Scotland and the north of Ireland were welded to England and Wales. The 'suture' line between England and Scotland is uncannily close to the modern political border line. The Irish dividing line is not so close to the political line. The suture line through Ireland and Britain runs in a remarkably straight line from the Shannon estuary through Clougherhead (on the coast 10 miles north-east of Drogheda) then south of the Mourne mountains, north of the Isle of Man (close to a village called Andreas, strangely enough) and continues via Solway Firth and on to Lindisfarne on the north-east coast of England.

Scotland and northern Ireland stuck to England and Wales. North America split away and bounced off into the sunset, to which it is still moving. America and Europe are drifting apart at the rate of 4cm per year. As we move apart, there is a weak spot running North-South in the middle of the Atlantic Ocean through which molten lava pours. Because of the extreme pressure of water at the bottom of the ocean, the lava cannot move very far and quickly forms 'pillows' of solid rock. On occasion, through continental collision and upheavals, this pillow lava is raised above the surface. You can see an example of this on the beach at Newborough Warren at the South-West corner of Anglesey. This place must have been at the bottom of a deep ocean at one time. Even if you can't find it, it's a nice day out.


South Stack

Pre-Cambrian rocks at South Stack


Rhoscolyn Head

Pre-Cambrian cattle at Rhoscolyn Head


Moel Famau 1

Old Silurian rock of Moel Famau behind
coal and grit above Flint


The oldest exposed rocks in Scotland are very old. The oldest exposed rocks in England and Wales are the much younger Pre-Cambrian rocks at places such as South Stack lighthouse and Rhoscolyn Head on Holy Island on the west coast of Anglesey, at the end of the Lleyn Peninsula, on Bardsay Island, at the Long Mynd in Shropshire and at Charnwood Forest in Leicestershire by Sherwood Forest. It was in a quarry at Charnwood that a schoolboy named Roger Mason became famous in 1957 by finding a clearly identifiable fossil in the Pre-Cambrian rock there. A year earlier, a schoolgirl (Tina Negus) had noticed the same fossil and informed her teachers. They refused to believe her because life was not supposed to exist before Cambrian times. About the same time (or rather later) the teachers at my school in Chester were insisting that it was mere coincidence when we suggested that the shapes of continents seemed to 'fit together' jigsaw-fashion (such as the east coast of South America and the West Coast of Africa). A lot has been learned since then. It has only been since the invention of the electron microscope, a few decades ago, that we have found out what chalk is.


Moel Famau 2

Front to back: Limestone quarries, Moel Famau,
sharp drop at fault line, Vale of Clwyd beyond


In general, the exposed rocks in Great Britain range from the oldest and hardest in the West and North to the youngest and softest in the East and South. The island is tilted about a NE-SW axis and the newer, softer covering of rocks in the West has eroded away, leaving the older rocks exposed. In fact, we are continuing to tilt. Ben Nevis is getting higher and London is sinking. The North-West of this island is bouncing back after the melting of the ice that formed a few thousand years ago in the Ice Ages.


Llangollen Limestone

Limestone Cliffs behind Llangollen


After the collision with America, the united halves of Britain (the united kingdom?) continued to move northwards and 100 million years later we were crossing the equator submerged in a tropical sea during what is known as the 'Carboniferous' period (about 350 to 300 million years ago). The fossil record shows that life up to now consisted of fairly rudimentary sea creatures and plants such as corals. As they died, the calcium carbonate of their bodies built up to gradually be pressed into a horizontal layer of limestone on the sea bed. This could be kilometers in depth. When eventually raised above sea level, for whatever reason, some spectacular limestone cliffs emerged, as at World's End near Llangollen. This rock is called Carboniferous limestone.

In north-west England, the land rose or the sea-level dropped and we found ourselves in a river delta system, still close to the equator. The surrounding rocks were weathered by river or sea water into sand. This is sand that didn't travel very far with each new tide, so the grains remained sharp and not worn smooth. Layer on layer of this sharp sand built up and was compressed to form 'Millstone Grit'. As its name suggests, it has been used for centuries to grind wheat into flour. In the Pennines, you will find it is also the standard building material: drab-looking, but very strong and 'safe as houses'. The millstone grit sat on top of the Carboniferous limestone. We were still in equatorial latitudes.

The next thing that happened in the Carboniferous period was that life started moving ashore. Trees and other plants started to thrive above the delta sands along with insects. If you believe artists' impressions of this period, there are dragonflies with 2 metre wingspans. Swamps formed and over those tens of millions of years, huge amounts of carbon-based vegetation lived and died. This carbon was compacted under its own weight and the weight of 300 million years of other rock on top of it. It became peat and coal, oil and natural gas. We are sitting on top of a lot of this stuff. I always wondered if the people at the Stanlow oil refinery near Ellesmere Port had ever thought of drilling down under their feet. They must have, surely.


Carboniferous Rock Sequence

Carboniferous Rock Sequence


So, 300 million years ago, this region (Cheshire, Wirral, Merseyside, North Wales and the Irish Sea) was a swamp on the equator, on top of 50 million years' worth of carbon-based fuel, under which are deep layers of gritty sandstone and limestone.

At the end of the Carboniferous period, it looks as though we collided again with something else - something like Siberia. The rocks again folded up, this time in a north-south direction, which created the Pennines and the Clwydian range and a few north-south fault lines.

If you stand near the new lifeboat station on the front at Hoylake and look west towards Wales, you will see the end of the Clwydian range of hills south of the Point of Ayr lighthouse near Prestatyn. With some poetic license, you will see the brown top of Moel Famau and other peaks in the range; there is a better view from West Kirby or Red Rocks at the end of Stanley Road, Hoylake. What you are actually looking at is the dark green grass covering a layer of coal seams which sits on top of a layer of millstone grit and under that a deep layer of limestone. Under all of this are the old Silurian rocks. The layers are eroded in turn as you look higher so that at the top you are looking at the exposed Silurian rocks of the peaks. In the distance, along the coast, is the Carboniferous limestone of the Great Orme at Llandudno. Anglesey, beyond and to the right, is very different geologically to anything else around here.

The coal, grit and limestone layers of the Clwydian hills drop steeply down to the River Dee and then deep down under where you are standing (i.e. under the Wirral and Cheshire). If you look to the east, on a reasonably clear day you will see it all rising again the other side of Liverpool and Bootle, through the coalfields of St Helens and Wigan and, beyond that, the millstone grit and limestone of the Pennines. There are some good walks in the limestone country out there around Clitheroe. A good place to look for fossils is in the local stone in the walls around the fields. Around there, you will see pieces of fossilised coral from the equatorial regions of 300 million years ago.


200 Million Years Ago

200 Million Years Ago


After the Carboniferous period came the Permian and Triassic periods (very roughly 300-250 and 250-200 million years ago respectively). Sea water and rivers flowed into the troughs left by the folding of the rocks and the region filled with sediment, in the form of sand and salty mud. This compacted into sandstone and mudstone, the mudstone sitting above the sandstone.


Peckforton Fault

Looking East from the Edge of the Peckforton Fault


Running north-south through the middle of Cheshire is a sandstone ridge of hills called, unsurprisingly, the Mid-Cheshire Ridge. This is lovely walking country (the Sandstone Trail runs along it from Frodsham to Bickerton and on towards Whitchurch) with fine views in all directions. There are a couple of castles and good pubs, not to mention a candle workshop and an ice-cream farm. There is a north-south geological fault immediately to the east of the ridge (the Peckforton Fault). To the west, the exposed rock is sandstone. The land to the east has dropped and the salty rock has been protected from erosion, so that the area around Northwich and Middlewich has been an important salt supplier since Roman times. You can visit a salt mine at Winsford.

By now we had moved above water into northern tropical regions (at the latitude of the Sahara desert today), and were, in fact, in a desert. Sand dunes developed which were held in place and compacted into stone by the weight of sand piling up on top. You can see the swirling shapes of the dunes sometimes: in the very yellow rock to the right of the train in the tunnel as you drop into Lime Street station Liverpool, for example. I don't know why it is yellow.

The sandstone we see in this region is red, or rather a reddish-brown rust colour. In fact, that is what you are looking at: rust, iron oxide. There is iron in the sandstone, but not in quantities that can be retrieved economically.


Permo-Triassic Rock Sequence

Rock Structure across the Area


The words Permian and Triassic come from two places (Perm and Trias) where the definitive rock structure for these two ages comes from. Outside our region, the fossils found in these two periods are clearly defined and show something startling. They show that 95% of the species existing in the Permian period were missing in the Triassic. There was a mass extinction between the two periods which eclipses later 'mass' extinctions such as that of the dinosaurs. In fact, dinosaurs didn't become extinct. They still exist and are called 'crocodiles'.

In this part of the world, there is no record of this mass extinction. The Sahara-like desert we are in is barren through these two periods; there are no fossils, and geologists have to refer to the sandstone here as 'Permo-Triassic' because they cannot be differentiated.


Thor's Stone 1

Thor's Stone, Thurstaston Hill...


Thor's Stone 2

...with some permanently triassic people on the top


Little Barrow Pebbles

Chester Pebble Bedding at Little Barrow


Just as the Nile today flows through the Sahara, a long river flowed in those days northwards through our tropical desert, via Cheshire and out into a sea somewhere beyond the current Irish Sea. The river carried pebbles with it, which, because of the long distance involved, became very smooth and rounded. When the pebbles stopped moving they became lodged in the sand surrounding them and cemented into place as the sand turned to stone. In the Chester area, some of the rock is marked on geological maps as Chester Pebble Beds. The sandstone is 250 million years old. The pebbles inside it must be much older. Some of the pebbles are known to come from what is now France. At Little Barrow, north of Tarvin in Cheshire, there is a track leading down from what used to be the Foxcote pub (now, February 2013, a tea room at weekends) towards Plemstall and the River Gowy. A hundred yards or so along this track (a public footpath), there are good examples of this pebble bed rock where the path has worn or been cut through the sandstone. The pebbles are sticking out proud of the rock. The Foxcote, by the way, was a steam engine that ran on the line between Chester and Manchester through the station at the bottom of the hill.


Parkgate Wall

Old, hard,rounded pebbles in the sea wall
at Parkgate on the Dee estuary


At Parkgate on the Dee side of the Wirral, the sea wall is built of, presumably, locally quarried stone. Children and adults of all ages have ambled along the wall for centuries and it has worn accordingly. If you walk north towards the Boathouse pub/restaurant and look at the blocks of stone making up the wall, you will notice the same pebble-bedded structure, the pebbles standing proud of the worn sandstone. The pebbles are older and harder than the sandstone. Next time you are there, tell the person next to you that those pebbles are French. Or maybe that's not a very good idea.

The geological periods following the Triassic period are called the Jurassic (after the Jura mountains of Switzerland and France) and the Cretaceous ('chalk'). The Jurassic period was roughly 200 to 150 million years ago; the Cretaceous about 150 to 66 million years ago. This was the age of the dinosaurs. It has been suggested that the film Jurassic Park should really have been called Cretaceous Park since the the dinosaurs shown in the film belong to the latter period.

There is no sign of rocks of these periods in Cheshire. There is, however, an area of Jurassic cover at Prees Heath, just south of Whitchurch, over the border in Shropshire. This land was used for airfields in the last war, and Tern Hill is still used by the RAF, as an outpost of Shawbury (further south), for helicopter training. It is possible that layers of chalk and Jurassic rock may have covered the whole area and simply eroded away.

The area was affected by glaciation in the last Ice Age of a few thousand years ago as the ice moved south from the Lake District, through what is now the Irish Sea and Liverpool Bay and into Cheshire, carving out features such as Helsby Hill as it went. There is an interesting suggestion in a book called The Streets of Liverpool, written 150 years ago, that there is no mention in Roman times of the river Mersey meeting the sea between present-day Liverpool and Birkenhead and Wallasey, but that instead it flowed through what is now Birkenhead docks, between Wallasey and Bidston Hills to reach the sea at Leasowe and Meols. In other words, the ice had not broken through completely. This would help to account for the fact that Meols was a major port in the North-West of England at the time, as evidenced by the large number of coins and other artefacts of the age that have been discovered there.


Urchins Kitchen

The Urchin's Kitchen, a Glacial Meltwater Channel

Much of Cheshire is now covered by a layer of glacial deposits left behind by the retreating ice from the last Ice Age. Much of this is in the form of important gravel and sand deposits ground down by the ice from the sandstone from here and the Irish Sea area. This is mined around the Oakmere area, close to what remains of the ancient Delamere Forest, for its high quality and its particular suitability for use in concrete, mortar and asphalt.

Oakmere is one of a large number small lakes (or flashes) in the area to the east of the mid-Cheshire ridge fault line. They are all called 'meres' and are formed by the collapse of old mine workings or the dissolving of the halite (rock salt) underground, causing the glacial covering to drop and fill with water. Much structural damage to buildings has been caused by this in the past. Northwich is known for its higgledy-piggledy buildings. It should be stressed that this is a thing of the past. Present-day Northwich is solid as a rock.

Just north of Oakmere is a different kind of lake, Hatch Mere, which is called a kettle hole. Kettle holes are caused by a lump of ice breaking off the end of a retreating glacier and staying put. The retreating glacier is melting and the meltwater flows out from beneath it, carrying the sediment it has created in its travels. The streams flow around the stationary lump of ice and deposit the glacial sediment to form a cup surrounding the ice, which eventually melts and a lake is formed. The area contains a number of glacial meltwater channels such as at Urchin's Kitchen on the Sandstone Trail in Primrosehill Wood, to the east of Kelsall.


Sunset at Red Rocks

Bye-Bye America.
from Red Rocks, Hoylake.

A geological description of a drive from East to West through Cheshire, and on the A55 along the North Wales Coast to Holy Island on the West coast of Anglesey, will appear here, hopefully soon. This is currently 'In Progress' and not available at the moment.

A short list of sources should appear here at some point in time. In the meantime, I should say that I have leaned heavily on The Geology of Britain - An Introduction by Dr Peter Toghill (Airlife Publishing,2005).

Brendon Cox, 25th August 2013 (email comments@CheshireTrove.com).

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