Tag Archives: Geological Site

Seljalandsfoss

I know it’s been over a month since I came home from the the land of fire and ice, but here are a few more pictures from the wonderful land of Iceland.  In this case it of the waterfalls around the area of Seljalandsfoss.  This particularly wonderful foss is on the main round south-east before you get to Vik.  It drops about 60m from the volcanic cliffs above and has calved out a plunge pool and has a fantastic undercut rock shelter that allows visitors to walk behind the falls (though I would say to watch your step as the patch can be wet and slippery – and when the weather is as windy as it was on our trip the spray will soak you).

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DSCN2634DSCN2623DSCN2639About 500m along the cliffs to the northwest of Seljalandsfoss is the hidden waterfall Gljúfrafoss.  This is worth having a look at, though your feet will get wet as you have to walk along the stream to get into the cave.  With Gljúfrafoss you have a waterfall that has cut back into the cliffs and you have to do a bit of exploring to see this beautiful foss.

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Fenn’s, Whixall & Bettisfield Mosses

On a cold but sunny winters day I made what is my second visit this area.  The picture above is from a previous trip when the weather was a lot warmer.  It was still freezing on my visit the other day, despite it being in the middle of the day.
DSCN0641Location & Access: The Fenn’s, Whixall & Bettisfield Mosses straddles the English-Welsh border about 5 miles south-west of Whitchurch.  There is no major road to the site, so you’ll have to take one of the narrower country lanes off the A495, B5476 or B5063.  If you fancy taking a boat though the Llangollen Canal runs through the middle of the site.  The site is relatively flat and shouldn’t provide any problems, though the walk from one of the carparks can be a bit of a trek if you have mobility problems.

Geology: The geology of the area is perhaps less obvious than the hills & valleys I normally write about.  The Mosses are a rare environment, being a lowland raised bog and small areas of wetland it is a unique habitat for wildlife too.  Their formation began about 12,000 years ago as the ice sheets retreated north.  In amongst the till were depressions filled with water and melting ice.  These formed the kettle holes that dominated the north Shropshire, south Cheshire and Wrexham area.  Some of the these holes remained full of water and form the numerous kettle ponds that can be found in the area.  Good examples can be found in Ellesmere and Delamere.  In the case of the Mosses the hole filled up with layer upon layer of peat.  This has created an acidic peat bog that has made a fantastic, albeit soggy under foot, environment and a link to our country’s icy past.

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Wildlife: Besides the peat bog and its like to an ancient glacial past the Mosses is a great place for wildlife…well when its not frozen over ;).

Alongside the myriad of insects and spiders there are also adders and a wide range of birds, and according to one local I spoke to, the rarely sited water shrew.  Unfortunately due to it being winter I didn’t see most of these.  I did manage to get some pictures of the water fowl in the area.

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These are my first attempts at photographing flocks of birds in flight.  I had mixed results with many of pictures focusing on the background rather than the birds, but I don’t think they’re too bad for a first timer.  The ducks that I’ve managed to get shots of include Shovelers (Anas clypeata), Wigeons (Anas penelope), Teals (Anas crecca) and Mallards (Anas platyrhynchos).  I also saw some Pintails (Anas acuta) and Lapwings (Vanellus vanellus) but happened to be changing the battery at the time.

References: Fundamentals of the Physical Environment (3rd Edition) by P. Smithson, K. Addison & K. Atkinson (2002).  Geology (2nd Edition)by S. Chernicoff (1999).  Geology of Shropshire (2nd Edition) by P. Toghill (2006).  The Geology of Britain – An Introduction by P. Toghill (2006).   iGeology map from the BGS (2015).  Information leaflet from the site and produced by Natural England and Cyngor Cefn Gwlad Cymru (Countryside Council for Wales).

 

Lilleshall Mount

About halfway between Telford and Newport, along the A518 is the lovely little village of Lilleshall.  Watching over it is the Lilleshall Hill.  At 132m high above the flat farmland it’s pretty hard to notice,  especially with a 21m high monument sitting on top of it.

Location & Access: The Hill is just to the east of the A518 and can be accessed via a small tract just off a road called Hillside East which comes off just opposite the church.  There isn’t a lot f space to park in the village so you may have to pull in to the side of the road just outside.  At just over 100m above the plain it’s hardy a struggle to climb up, though the path can be a little muddy after it has rained.  The path slopes gently and so should prove too much of a problem.

Geology: Lilleshall Hill represents the northern most exposure of the Uriconian Volcanic group and is itself made up of a mixture of rhyolite, andesite, basalt and tuff.  This would make the formation about 542-635 million years old.

DSCN0432There are a few decent exposures for anyone who wants a sample, and being the short then its relatives the Wrekin and Caradoc it takes a little less effort for those who don’t want to climb for too long.

For a modest sized hill you can get a decent view of the Wrekin to the south-west as well as the sandstone ridges that rise out of the North Shropshire and South Cheshire plains.

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Other Stuff: The Monument is dedicated to the first Duke of Sutherland and is pretty impressive.

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Dedicated to George Granville Leveson-Gower, the 1st Duke of Sutherland, it looks to be made of local sandstone.  I rather enjoy the inscription and how he is described as “the most just and generous of landlords”.  I’d like to hear what his tenants really thought of him, though I shall be very unscientific and read between the lines of the “he went down to his grave with the blessing of his tenants” as perhaps giving a hint of that.  For those who maybe unaware, this Duke of Sutherland was one of the richest men of his era and he was in part responsible for the Highland Clearances that were taking place in Scotland at the time…a fantastic example of the needs of the rich capitalist overriding those of the poor labourer…sorry went on a ‘high horse’ moment there.  But seriously if you’re unaware of the main cause for the Scottish Highlands being one of the least populated parts of Europe then I suggest you read up on it.

Anyway back to happier things.  The light scrub land around the hill, coupled with the farmers’ fields in the area makes it a good place to see wildlife (in particular birds).  Sparrowhawks, buzzards, wrens, finches and woodpeckers are common sights.

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Reference: The Geology of Britain; An Introduction by Peter Toghill (2006),  iGeology map from the BGS (2014) and the notice board from the site, Wikipedia for the Duke of Sutherland.

 

Hulme Quarry

For today’s geological site, I’ve gone beyond the boundaries of my native Shropshire to neighbouring Staffordshire.

Location & Access: Hulme Quarry is located to the east of Stoke-on-Trent, about 1km north-east of Longton at 52*59’49” N, 2*06’28” W.  The whole area is a country park (Parkhall Country Park), nature reserve and a designated SSSI.  The site can be reached from either the A520 (Weston Road) or the A5272 (Park Hall Road).  There are plenty of carparks at the site and most of the paths are wide and well maintained.  There are a few inclines, but nothing too steep (depending upon the path).  There are multiple paths so that someone with mobility issues should still be able to enjoy the place.

Geology: The whole quarry is dominated by the Hawksmoor Formation 246-251Ma which puts it at the very early Triassic Period.  The whole quarry is a collection of red sandstone and conglomerate, and is an excellent place to see this formation.  The quarry sides are easily observable and accessible (though be careful of falling rocks).

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The conglomerate and sandstone can be seen on top of each other in bedding layers.  In the sandstone you can see the cross bedding from the movement of the ancient sand dunes.  There are small layers of pebbles in the sandstone suggesting periodic water movement over the sand dunes.  The conglomerates are the result of a river that moves over the area, and was probably ephemeral.  This is evidenced by the presence of regular graded bedding amongst the pebbles, suggesting regular changes in the flow of the water.  The pebbles themselves are made up mostly of well rounded quartz.

iphone pics 09_14 720The red colour of the rock comes from the presence of iron oxides, left behind by evaporating water.  The combination of red colour, cross bedding sand dunes and ephemeral streams shows that this place was once a desert.  This is typical of rocks from the Permian and Triassic that can be found around Britain.  Occasionally you might find a small patch of mudstone.  I remember being shown some when I visited this site at university several years ago, though I couldn’t find it again this time.

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Other Stuff: The whole area is a beautiful place to walk around.  There are numerous paths, plenty of places to walk, pine tree forests and areas of lowland heath & brush.  There’s bird watching for those that are into that sort of thing, plus plenty of places to ride a bike.  On a hot summers day, with the brush and the red sand, it’s easy to imagine the areas desert past.

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Reference: The Geology of Britain; An Introduction by Peter Toghill (2006), Geology (2nd Edition) by Stanley Chernicoff (1999), Sedimentary Petrology (3rd Edition) by Maurice E. Tucker (2001), iGeology map from the BGS (2014) and the notice board from the site.

 

Rock Box – The Rock Cycle

Welcome to my new series of posts called Rock Box.  I will work on these as and when the mood takes me, but my aims are thus; 1) when work commitments prevent me from adventuring out and about, it gives me a chance to do some ‘arm-chair geology’; 2) over the years like many a geogeek I have gathered up a small collection of rock samples…and they could do with organising, so this gives me an excuse; 3) it allows me to explain some basic geological principles to the masses.  So let’s dive in to my rock box. My first post will be a basic introduction to the rock cycle and the major rock groups.  This is to provide a foundation for the rest of the Rock Box series.

The Rock Cycle

Rock Cycle 1a The above diagram is a simplified look at the rock cycle.  The rock cycle starts with magma – molten rock.  As it cools it solidifies into one of the many types of igneous rocks.  From this it can either be eroded away into sediment, or re-heated to form a metamorphic rock.  The sediment will eventually be deposited to form a sedimentary rock and this in turn can either be eroded again into sediment or put under intense heat & pressure to form a metamorphic rock.  And as you’ll have probably guessed by now, the metamorphic rock will either be eroded into sediment or melted into magma.

Igneous Rocks

Igneous rocks are usually put in to two categories; plutonic and volcanic.  In the case of the first, the molten rock moves towards the surface, through pre-existing rock layers, but cools & solidifies before it actually reaches the surface.  Under these circumstances the magma usually cools slowly allowing large crystals to form from minerals with a higher melting temperature.  As the temperature reduces, minerals with a lower melting point start to solidify around the larger crystals.  Examples include granite, gabbro and diorite.

Volcanic rocks occur where the magma has reached the surface (now referred to as lava) and then cooled.  Contact with the air or water usually means that these rocks solidify very rapidly, this causes the crystals to be smaller as they don’t have time to grow.  In the case of more explosive volcanic eruptions the rock can contain air bubbles (both from the dissolved gases in the magma, and from the air it enters whilst cooling). Basalt, rhyolite, pumice and andesite are examples of volcanic rocks. Igneous rocks where the crystals are large & easily visible are referred to as having a phaneritic texture.  Rocks where the crystal are small have a aphanitic texture.

To complicate things even further igneous rocks are also divided by their mineral composition into felsic, intermediate, mafic and ultramafic. Igneous types chart 1aSome examples of good places in the UK to look at igneous rocks;

  • The Uriconian Hills of Shropshire (yeah I’m a Shropshire lad so you can guess why this is top of the list)
  • The Snowdon (Yr Wyddfa) range in Wales
  • Cairngorm & Nevis Ranges in Scotland
  • Central Lake District
  • The Granite domes of Cornwall – Dartmoor, Bodmin Moor & Lands End
  • The Isle of Skye (highly recommend)
  • The Giants Causeway, N. Ireland

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Hay Tor – Granite (Dartmoor, Devon, UK)

Common characteristics of Igneous Rocks are;

  • Solid & hard rock
  • Dense crystal structure
  • Non-porous
  • Often associated with hills & mountains as they tend to be more resistant to erosion
  • Often contain heavy metals & precious stones

Sedimentary Rocks

Sedimentary rocks are formed by the layered deposition of material, often sourced from other rocks.  Sedimentary rocks can be put into several broad categories;

  • Detrital/Siliciclastic
  • Organic Sedimentary
  • Inorganic Chemical
  • Volcaniclastic sediments

Detrital or Clastic rocks are made up of the eroded remains of other rocks cemented together.  Those rocks made up of larger grains (in this case pebbles) cemented together are called conglomerates and breccias.  As the gains get smaller you come to the sandstones, which sometimes contain small pebbles, but are dominated by sand-sized grains.  Finally you reach the mudstones. siltstones and shales which are made up of very small grains (<0.063mm).  These rocks are typically the result of a watery depositional environment such as a river, lake or shallow sea.  This is however not always the case, and other environments such as hot deserts also leave clastic remains.  An example would be the red sandstones from the Permian & Triassic Periods that are common across Europe.  The orange/red colour coming from a layer of hematite that coats the grains.

Organic sedimentary rocks are a mixed group, but all have an organic origin.  One type is limestone which is made up of calcite.  There are a few varieties of limestone from the oolitic with its calcium covered spherical grains to the fossiliferous with its mass of broken fossils.  There are also lime-rich muds and chalk which is made up of the calcium rich remains of microbes called coccolithophores.  As well as the limestones there are the organic ‘rocks’ we commonly refer to as fossil fuels; coal, oil and mineral gas.  OK oil and gas aren’t technically a solid rock, but they have the organic origin and are made from the remains of marine organisms.  These are characterised by the high content of hydrocarbons…something we have found very useful in the 20th century.

Inorganic chemical sedimentary rocks are those that are the result of an inorganic process that deposits the rock layer.  One of the most common of these are the evaporites, rocks that form when water containing dissolved salts evaporates, leaving the salts behind.  Common evaporites are halite, gypsum and anhydrite. Last of all is a cross over of igneous and sedimentary rock.

The volcaniclastic sediments are mainly the result of layers of ash (called tuff), along with pyroclastic flows and occasionally volcanic mud flows called lahars.

Some examples of good places in the UK to look at sedimentary rocks…well most places really, they are really common on the surface;

  • For limestone the Wenlock Edge in Shropshire and the cliffs of Lyme Regis have a lot of fossil rich material, the Yorkshire Dales with their limestone pavements and the North & South Downs plus the White Cliffs of Dover with their chalk.
  • Coal can be found in several layers in amongst the Carboniferous rocks of the Midlands, Pennines and up towards Leeds, along with the Glasgow area.
  • Permo-Triassic rock, including evaporites forms the foundation of much of Cheshire.
  • The Padarn Tuff Formation near Bangor in Wales will be the place to go for volcaniclastic rocks.

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Bedding planes – Comley Sandstone (Ercall Quarry, Shropshire, UK)

Common characteristics of Sedimentary Rocks are;

  • Wide variety of grain sizes depending upon the depositional environment.
  • Often porous and form the source of aquifers and hydrocarbon stores.
  • Contain fossils, and in some cases are almost entirely made up of fossils.

Metamorphic Rocks

The last type of rock is metamorphic rock.  Metamorphic rocks are formed when heat and/or pressure is applied to a rock.  In the earth’s crust & upper mantle the temperature increases at an average rate of 20-30*C per kilometre of depth.  A temperature of about 200*C is needed to start metamorphose of rock and is usually reached about 10km depth.  Pressure is applied to rocks in two different formats.  Lithostatic or confining pressure pushes on the rock from all sides, compressing it fairly evenly.  This usually takes place as a result of deep burial.  In this case the becomes compressed into a smaller, denser form, but maintains the same basic shape.  Directed pressure results when force is applied from a principle plane of direction.  This commonly occurs at tectonic plate boundaries, fold mountains and faults.  This typically deforms on the plane on which the highest pressure is applied.

Rocks that have been metamorphisied are denser than their parent rock.  This is because the pressure pushes the grains together, closing the pores between them.  In directed pressure the grains usually line up perpendicular to the principle direction of pressure.  This prefered alignment is known as foliation.  This often results in metamorphic rocks having a coloured banded pattern.  The increased pressure also has another side effect.  The pressure releases fluids (such as water) from the rock.  This helps facilitate chemical reactions, often resulting in the metamorphic rock having a different chemical composition to its parent rock.

There are several different types of metamorphism, with contact & regional being the most common types.

Contact Metamorphism: This is when a the metamorphism takes place as a result of contact with a heat source.  This is common when you have a magma intrusion.  The metamorphism decreases with increased distance form the heat source.  This type is usually very local.  A good place to see this is around the granite outcrops in Devon.

Regional Metamorphism: This is when the metamorphism is over a large region.  This has two sub-types; burial and dynamothermal.  Burial metamorphism takes place when rocks are overlain by 10km or more of rock.  Dynamothermal metamorphism occurs during mountain building when the rocks are deformed and heated, with some of them being pushed upwards to form the mountains and some of it being pushed downwards to form the mountain base, where heat & pressure work on the rock.  One of the best places in the world to see regional metamorphism this is in Canada where the Canadian Shield covers about half of the country and used to be at the base of a mountain range.

Hydrothermal Metamorphism: This is when a chemical alteration of the parent rock occurs when it comes into contact with hot water.  This is common in volcanic areas with hydrothermal vents.

Fault-zone Metamorphism: Rocks on either side of the fault generate direct pressure on each other, along with frictional heat.

Shock Metamorphism: This occurs where a meteorite hits the ground and the intense heat & pressure causes the metamorphosis.

Pyrometamorphism: Probably the coolest sounding type (yeah I know, not a very scientific thing to say) and is the result of high temperatures but without the pressure.  This can happen in such occurrences as lightning strikes and natural underground coal fires.

Good places to see metamorphic rocks in the UK are;

  • Contact metamorphic zones around the granite outcrops in Devon & Cornwall
  • The slate mine & hills of northern Wales
  • By far the best place, and one that I would recommend if you ever get the chance is the north-west Highlands of Scotland.

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Lewisian Gneiss Formation – gneiss with granite and dolerite (Laxford Bridge, North-west Highlands, Scotland, UK).

Common characteristics of metamorphic rocks;

  • Dense, hard and heavy.
  • Non-porous.
  • Multiple coloured banding.
  • Traces of parent rock.

Final Thoughts

I hope this has been of use/interest to people and not just me whittering on.  I plan on using it as a foundation of other geologically related items, especially as I go through the laborious task of organising my rock collection.  This is a very brief introduction to the rock cycle and the various rock groups.  If you want to know more I suggest finding a good geology textbook.

 References: Fundamentals of the Physical Environment (3rd Edition) by P. Smithson, K. Addison & K. Atkinson (2002).  Geology (2nd Edition)by S. Chernicoff (1999).  Geology of Shropshire (2nd Edition) by P. Toghill (2006).  The Geology of Britain – An Introduction by P. Toghill (2006).  Fossil Revolution – the finds that changed our view of the past by D. Palmer (2003).  Sedimentary Petrology (3rd Edition) by Maurice E. Tucker (2001).

Ingleborough Cave

Time for my second post of my Yorkshire Dales trip.  As I alluded to in my last post about Malham Cove, one of our goals for the trip was to visit Gaping Gill.  Sadly this wasn’t open due to a technical fault, so instead we visited the nearby Ingleborough Cave.  One thing to note is that this isn’t a potholer’s cave, it’s a show cave.  My own potholing experience amounts to a trip down an abandoned slate mine in Wales…anything more adventurous and I’m likely to become a troglodyte.  Oh and apologizes for the quality of some of the images, it’s a little hard to take photos in the dark cave light.

Location & Access: To get to the cave, park in the village of Clapham, just off the A65.  The cave is about 2km north of the village located around 54*08’05” North, 2*22’38” West.  To get to the cave you follow the path north out of the village.  The path is wide and in very good condition (rather bizarrely a toll path too so bring some pennies), so you shouldn’t have to much trouble walking to the cave.  Sadly there is no closer public vehicular access, so you’ll have to walk.  Being a show cave, Ingleborough Cave is geared towards families, the access is good and the cave floor has been given a layer of concrete to allow disabled usage.  This doesn’t spoil the aesthetic to much.  The tour of the cave does involve a guide and will cost money some bring some cash.

Geology:  The cave is in the bedding planes of the Garsdale Limestone Formation (331-339Ma) and like Malham Cove it was once a shallow, carbonate sea.  In some places you can actually see the fossils of the coral and other organisms.

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The cave was carved out by river water and was partially filled in by glacial till, some of which has been removed to open up the cave.  Not all of it has been and the full extent of the cave is not yet know.

IMG_2206Excavations are still on going and have brought up the remains of a woolly rhinoceros tooth, from the Devensian Glaciation (about 10,000 years ago).

There are several underwater pools still in the cave, and the cave itself is regularly flooded when there are heavy thunderstorms.  When the cave was first explored in 1837 it was flooded, the water held back by a calcite dam.  This was blasted to drain the lake at the time, but parts of another calcite dam can be seen.

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The historic level of the cave water is marked out at a level where you find the cave coral deposits below the waterline and the flowstone above.

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There are plenty of stalactites and stalagmites in the cave of various sizes, the biggest of which is The Sword of Damocles and is a few metres long.

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Along with these you will see plenty of helictites and speleogens as well as other cave formations.  A look at the feature image to this post shows how the natural cleavage & faults in the rock are exploited by the water and form the basis of the stalactites.

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Overall this a good cave to visit, especially if you are not an experienced caver, and a good alternative to Gaping Gill if the winch is broken.  It’s a show-cave, but a good one.  There are plenty of formations to see, and if you are in the area I would recommend visiting the cave if you have a spare couple of hours.  They also have a good website explaining the cave and showing more pictures at www.ingleboroughcave.co.uk.

Reference: The Geology of Britain; An Introduction by Peter Toghill (2006), Geology (2nd Edition) by Stanley Chernicoff (1999), http://www.ingleboroughcave.co.uk and the tour guide on the day.

Malham Cove

This week I have had the opportunity to visit the fantastic Yorkshire Dales in the north of England.  I got a chance to visit a few sites.  Much to our disappointment we weren’t able to get down Gaping Gill due to a technical fault with the winch, so we instead saw a few other places and I’d thought I’d share them with you.  The first is epic Malham Cove.

Location & Access:  Malham Cove is located in the south half of the Yorkshire Dales National Park at approximately 54*21’41” North, 2*09’28” West, about 1km from Malham village.  You can park a car in the village (itself a wonderful place to see) and walk up the road to the cove.  The road is good and there is a slight incline.  just above the village is a clearly marked, good quality path to the cove…and to be honest you really can’t miss it from there.  People with mobility issues shouldn’t have much trouble walking along the path, though the road can be a bit of a trek.  Warning!  The main path goes through a field of cows so beware of bovines.

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Geology:  The underlying rock is Carboniferous Limestone from the Garsdale and Danny Bridge Formations (331-339Ma), and represents a depositional environment of a shallow carbonate sea, full of corals and shell creatures.  That was then, what about now?  Like much of northern England the current landscape is largely the result of the various glaciations of the past, in particular the Devensian glaciation which ended about 10,000 years ago.  Malham Cove is thought to have been formed slightly earlier (about 12,000 years ago) as the ice retreated north.  The melting glaciers produced a large amount of run-off, and with the ground still being semi-frozen permafrost the water eroded the limestone instead of infiltrating into and dissolving it as happens now.

This led to the wonderful dry water seen today.  The semi-circular Malham Cove is about 80m high and about 300m across.  This makes it higher, but only about half as wide as the horse-shoe at Niagara Falls.  This gives you an idea of what the falls would have looked like in full flow 12,000 years ago.

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IMG_2331You can see the bedding planes in the limestone and if you look at the right of the image above you should be able to see two climbers ascending the cliff face (right of the centre tree, about half way up the picture in yellow).  This gives you an idea of the scale of the place.  At the base of the cliff is a small stream, exiting from one of the many underground river systems in the Dales.

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Although you should always be careful approaching a cliff face I would recommend getting as near to the base as possible and looking up…it’s fantastic.  I tried to take a few pictures, but none of them do it justice, so you’ll just have to go there yourself.  Stand in the centre of the horse-shoe, close to the base and look up, it’s this wonderful bowl shape.

Above the falls is another wonder of the Dales; the limestone pavement.

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These are a special feature, common to the Dales, but rare in the rest of the UK.  The flat surface is a bedding plane in the limestone, exposed by glacial & periglacial erosion.  This produces the flat ‘paving slabs’ called clints.  The gaps in between are the result of rain water getting into cracks in the limestone and dissolving some of it.  These gaps are called grykes.  Walking along a limestone pavement is quite an experience, but be warned some of the clints are wobbly and the grykes can be wide and deep.  Some of them may even be filled in with a thin layer of soil & grass so watch your step.

Other Stuff: You’ve got glacial valleys & erosion, caves, underwater rivers & springs, a dry waterfall higher than Niagara and limestone pavements…what more could you want? OK well aside from the geology it is also a great pace to catch a glimpse of one of my favourite birds; the Peregrine Falcon.  These nest up on the cliff face your chances of seeing one is good.

To sum up, if you are ever in the north of England Malham Cove is worth the visit.  The pictures I’ve posted really don’t do it justice, you’ll have to go see it for yourself.  Stay geogeeky as I’ve got more from the Dales that I’ll post soon.  Enjoy.

Reference: The Geology of Britain; An Introduction by Peter Toghill (2006), Geology (2nd Edition) by Stanley Chernicoff (1999).

 

 

Geological Time Part 2 – The Periods in Shropshire

As part of my geological time series I thought I’d have a look at where rocks/features of the periods can be found in Shropshire.  Shropshire is a very geologically diverse county and if you look hard enough you can find examples from all of the time periods except for the Cretaceous (though the Tertiary is a little dodgy) .  I will say that the examples I am giving are not the only ones to be found in the county.  There are many other formations, rock types and sites that can be used to represent the time periods, I’ve just pick a selected few.  So prepare for a few explanations and quite a lot of pictures.  Just as a remind ma stands for millions of years ago.

Shropshire’s Geological Timeline

Shropshire Geology Time 2

Shropshire Base Map 1

 

I’ve included a brief timeline and a small map giving the rough location of the sites I visited (blue circles) with the major towns in the county for reference.

Quaternary Period (2ma to present)

As we are still living in the Quaternary then many landforms can be seen to represent what has and is still going on in the county.  For a more pre-historical landform a good example would be the glacial relics, of which the kettle holes and peat bogs around Ellesmere would be a good place to start.

DSCF2941DSCF3579These features were formed after the ice of the Devensian Glaciation retreated around 11,000 years, leaving layers of sand and gravel (commonly called glacial till).  The kettle hole forms when a block of ice falls of the retreating glacier and melts, leaving a water-filled depression.

Neogene, Paleogene and Cretaceous Periods

Sadly these formations are missing from Shropshire.  There is rumour of a Tertiary (possibly Neogene) outcrop near Whitchurch, but I haven’t been able to confirm it and I can’t find it on a map, so for now it’ll have to remain a mystery.

Jurassic (200 to 145ma)

You’ll be lucky to find this one.  There is only one real outcrop of Jurassic age rock in the county and that is around the village of Prees, about 5 miles south of Whitchurch.  There is some Jurassic bedrock under the layers of glacial till, but Prees is the only place it comes to the surface.  You can see one exposure, just east of the A49.  To get to it you can follow a public footpath.  The rock is mudstone from 183-190ma and the environment was once a shallow, tropical sea.

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Triassic (252 to 200ma)

The Triassic and Permian are both present in Shropshire, but the exact boundary has caused a little confusion in the past.  This is largely down to the similarities in the formations and the fact that they rest one on top of the other in the same locations.  Personally I think the best place in the county to see both Triassic and Permian is around Bridgnorth, though there are some other impressive red-rock formations that form several ridges in the north of the county.  The Triassic rocks are to the east of Bridgnorth, further up the hill and form part of the Kidderminster Formation.  It is mostly made up of red sandstone and conglomerate.  The image below is that of an exposure on the A442 near Allscott, just north of Bridgnorth and shows a layer of conglomerate sandwiched between two layers of sandstone.  It is a good example of cross-bedding between the strata and is representative of a river running through a desert environment.

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Permian (299 to 252ma)

As I said in the Triassic section, Bridgnorth is the place to see Permian rocks, in fact most of the town is built on it and some of the older buildings are made from it.  The Permian sandstone is also red, shows cross-bedding as the result of wind-blown desert sand, but seems to be a little tougher.  My Triassic samples half crumbled as I was extracting and transporting them.  Again the ancient environment was a desert.

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Carboniferous (359 to 299ma)

For the Carboniferous Period I’ve chosen something a little special; the Tar Tunnel.  Unlike my other choices this is something of a minor tourist attraction and as such will require the parting of a couple of coins.  It’s found in the east end of the Ironbridge Gorge.  The rock in the surrounding area is a mixture of limestones, coals, sandstones, mudstones, and conglomerates from the late Carboniferous Period.  When the Industrial Revolution was in full swing in Ironbridge a tunnel was built to act as short cut between the mines and the River Severn.  Upon digging the tunnel the walls started to ooze natural bitumen.  This was then extracted for a number of years before the industry moved on.  Is there likely to be an oil rush in Shropshire?  Not likely but it is an interesting phenomenon and one that I don’t think can be seen anywhere else in the UK.  If like me you are a ‘geo-geek’ it’s worth seeing.

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If it was red you’d think you were in a cheap horror movie.  The image below shows an pool of tar in a side chamber.

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For a more mundane sample from further up the gorge (Jigger’s Bank) you can see an exposure of the Lydebrook Sandstone.  This layer is made up of a pebbly sandstone and includes layers of conglomerate, and was what I used in the geological timeline above.

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Devonian (416 to 359ma)

Devonian rock actually forms the bulk of Shropshire’s tallest hill; Brown Clee Hill (not to be confused with the neighbouring Clee Hill or Titterstone Clee Hill).

Below is an image of Brown Clee Hill taken from the Wenlock Edge.

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Silurian (443 to 416ma)

The Silurian is very well represented in Shropshire.  One of the best formations in the county (and possibly the country) to see rocks of Silurian age is the beautiful Wenlock Edge.

The Edge is an escarpment that runs for almost 20 miles in a north-east to south-west direction and is made up of of a knoll-reef limestone with lime-rich mudstones & shales surrounding it.

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There are numerous walks along the Edge and due to the old (and current) quarrying activities there are plenty of places to see the local geology.  The above picture showing some wonderfully defined bedding planes.  It is also a good place to go fossil hunting.  There are several places both on and under the Edge were you can collect some nice samples like the one shown below.

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Ordovician (488ma to 443ma)

Like the Silurian the Ordovician Period is well represented in Shropshire, but I’m going to go for a well known formation; the Stiperstones Hills.  The Stiperstones are made up of quartzite and like the Wrekin Quartzite is a misnomer as it is a hard, white sandstone and not a metamorphic rock (like true quartzite is).  The Stiperstones have the added advantage that besides the Ordovician rock, you also have the tors formed from millennia of ice/frost shattering.

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Cambrian (542ma to 488ma)

The Cambrian witnessed a massive diversification of animal lifeforms (often called the Cambrian Explosion) and there some good locations and rocks to be seen in Shropshire.  The Ercall quarry has some wonderful quartzite to sandstone formations, showing beach ripples, conglomerates and inclined strata (see my Ercall post for more)

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The Wrekin Quartzite gives way to the Comley Sandstone.  The type site is the sadly neglected Comley Quarry (located on the north-east slope of Caer Caradoc) where Shropshire’s first Cambrian trilobites were found.  Unfortunately the rock faces are now overgrown and difficult to see.  It can be seen in better condition a the Ercall.

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Precambrian (4600ma to 542ma)

Being such a long eon the Precambrian goes from the formation of the earth to around 542ma.  The Precambrian rocks in Shropshire are mostly from towards the younger end; around 570ma with the gneiss and schist of Primrose Hill possibly being older.  My choice for the Precambrian is the Uriconian Volcanic formation which makes up a number of hills, including the Wrekin, Caer Caradoc and the Lawley.

This photo was taken from the Long Mynd (itself a sedimentary formation from the Precambrian) showing Caer Caradoc (centre right), the Lawley (centre left, and a bit in the distance) and on the left horizon is the Wrekin.  These hills are made up mostly of rhyolite, andesite and basalt.

Below is a sample of basalt from the Wrekin.

IMG_1862Well there you have, a brief geological tour of Shropshire.  The county has seen volcanoes and beaches, deserts and tropical seas and now the efforts of an enthusiastic geo-geek.  Hope you enjoy.

 

The Ercall

Due to some technical issues with my computer I haven’t posted anything in a few weeks.  Now I’m back up and running I plan on posting on a more regular basis.

Today’s monologue is about a fantastic geological site next to the Wrekin; the Ercall.

Location: The Ercall (pronounced ar-cal) is just north of the Wrekin in Shropshire, at around 52*40′ North, 2*31′ West, less than 1 km south-east of Junction 7 of the M54.

Access: The Ercall is open to the public at all times and access is easy.  There is a well maintained path and for the main quarry the gradient is low.  Other areas of the hill can be a little steep so if you have any mobility issues then they may be a little difficult to reach.  You can walk or scrabble over pretty much the whole hill as there are multiple small paths coming off the main track.  There are several small quarry holes as well as the main quarry and the whole place is worth exploring.

Geology: The various quarries in the Ercall are a fantastic place to see several geological features.  WARNING: wear a hard hat if you going to get close to the cliffs as there is the risk of falling rocks.

The featured image above is in the main quarry and shows a feature called an unconformity; specifically a nonconformity.  This is were there is a break in the rock sequence.  A nonconformity is the boundary between an underlying layer of igneous or metamorphic rock and an above layer of sedimentary rock.  In this case the igneous rock to the left of the image is an orange-pink coloured granophyre.  This is related to the Uriconian volcanics and is about 560 million years old.  The rock to the right of the picture is a pale grey Wrekin Quartzite and is about 533 million years old.  It is one of only a few places in Shropshire that you can see Cambrian aged rocks.  The Wrekin Quartzite is a bit missed named as a true quartzite is a metamorphic rock not a sedimentary one as found into the Ercall.

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The above image is a close up of the nonconformity.  Mixed in amongst the quartzite are several layers of conglomerate (see below).

DSCF4925To the east of the the nonconformity the quartzite mixes with the Lower Comley Sandstone and you get some impressive examples of a sedimentary bedding planes.  These are well jointed and are an excellent example.  These bedding planes have been lifted and incline downwards to the south-south east.

DSCF4916There is one more geological gem (figuratively speaking) to be found at the Ercall; ripples.  Mixed in in the layers of conglomerate are some wonderful examples of ripples.  These can be found higher up at both the west and east sides of the main quarry.  The ones to the west are in slightly better condition.  They can best be seen on a slightly cloudy day, just after it’s rained as the light & shadows more clearly define the ripples.

DSCF3340DSCF3354Combining this with the conglomerate, sandstone and quartzite gives us the origin of these rocks; an ancient beach.

For such a small site the Ercall really does have a wide range of geological features that can be seen really easily.  They’re great examples of nonconformities, bedding planes and ancient beaches.

Other Stuff: The Ercall is a nature reserve operated by the Shropshire Wildlife Trust, and a wide range of wildlife can be seen. There is a mixed deciduous forest with a small  stream running through it.

DSCF4881In spring the forest floor is covered in bluebells.

The local animal life is typical of a British woodland.  You can see finches, woodpeckers, Nuthatches, Treecreepers, Common Buzzards and if you’re really lucky a Peregrine Falcon.  It is a great place for a casual walk and has some wonderful geological sites to see.

Reference: Geology of Shropshire (2nd Edition) by Peter Toghill (2006), Geology (2nd Edition) by Stanley Chernicoff (1999).

The Wrekin

I’ve chosen for my first post a hill that is close to home.  The Wrekin is one of Shropshire’s most prominent landmarks that’s held in high esteem by many of the locals, including myself.

Location: The Wrekin is found in the centre of Shropshire, less than 1 km south of Junction 7 on the M54.  If you want a geographical coordinate then the top of the hill is about 52*40′ north, 2*33′ west.  To visit it simply turn south off Junction 7 and unless it’s foggy you can’t miss it.

Access: The hill is open to visitors all the time and there is ample parking space.  The path is well marked, but due to some steep inclines people with mobility issues may have problems walking up the hill.  You have two choices when going up the hill.  You can follow the main path that turns left at a hairpin bend up towards a building know as Halfway House or you can take the side path around the hill with the choice of going up the steeper SW slope.  Either are good walks.  At an average walking pace it should take 45mins-1 hour to climb the hill.

Geology: The Wrekin forms a spectacular feature in Shropshire’s landscape and has captured the imagination of the locals for centuries.  Battling giants are included in the myths about its origins, but the real story of its formation is just as epic.  The hill forms part of a geological formation know as the Uriconian Volcanics.  This formation is also responsible for other hills in Shropshire; including Lilleshall hill, the Lawley and Caer Caradoc near Church Stretton.  Sadly despite its name this does not mean that these hills are extinct volcanoes, but rather they are the remains of lava and ash flows from a series of volcanoes long since gone.  The remains of these volcanoes have either been eroded away or deeply buried by younger rocks.  The formation of the lavas that make up these hills is thought to have occurred during a thinning of the crust along with a subduction of a nearby tectonic plate.  A situation similar to the Mount St Helens region of the NW United States.

So how old is it?  The lava flows that make up the Wrekin are between 560-570 million years old, making them some of the oldest rocks in Shropshire.  The hill is made up mostly of Rhyolite, a dark reddish coloured volcanic rock.

DSCF4570Outcrops of the Rhyolite can bee seen on top of the hill, and in some locations (in particular going through the inner gate of the iron-age hill fort) you can see the fine lines in the rock know as flow banding.  This is caused when the slow moving lava stretches out the minerals in it.

DSCF4549Towards the end of the eruption phase a number of intrusive lavas made a series of dykes in the hill.  These are made of dolerite and are a dark black-blue colour.  You can see them at several locations as you walk up the hill where the path turns from a reddish colour to a grey.  One of the best places to see one of the dykes is in the main carkpark at the bottom of the hill.  Between the two halves of the carpark is this formation.DSCF4524

Around the rest of the hill is a mixture of much younger sedimentary rocks; Wrekin Quartzite, Lower Comley Sandstone and the Bridgenorth Sandstones (I’ll go into these another time)

Other Stuff: A side from a look into Shropshire’s volcanic past what else is on the Wrekin?  As mentioned earlier there is the remains of a Hill Fort, first occupied around 3,500 years ago with extensions around 450BC.  The main path takes you up through the both the outer and inner gates.DSCF4544Wildlife is abundant on the Wrekin.  The SE slope is dominated by a mixed deciduous woodland, whilst the NW slope has a pine forest plantation.  There are deer on the Wrekin, and if your’re lucky enough you might catch a rare glimpse of them, along with a wide variety of birds.  Some of the more notable species include nuthatches, treecreepers, ravens, green woodpeckers, buzzards, kestrels and occasionally peregrine falcons.

Overall the Wrekin is a great place for a short walk.  The geology is easily accessible and gives us a fascinating insight into Shropshire’s early history.

Reference: Geology of Shropshire (2nd Edition) by Peter Toghill (2006), The Wrekin Hill by Allan Frost (2007).