Monday 31 December 2012

Mam Tor landslide - BGS

It's new year's eve and in a idle moment (acually all day at work today is an idle moment!) I was surfing the BGS website and found an interesting link to the landslide:

The landslide


The landslide itself is over 4000 years old and is a rotational landslide which has developed into a large debris flow at its toe (Waltham and Dixon, 2000). It is over 1000 m from backscarp to toe, has a maximum thickness of 30-40 m and the backscarp is over 70 m high. 
Waltham and Dixon (2000) have divided the landslide into three distinct zones (backscarp area, transition zone and debris flow) according to their structure as follows:
  1. The upper part of the slide material is a series of rock slices or blocks that were produced by the non-circular rotational failure of the original slope; most of these slices above the upper road show little sign of current movement
  2. The central part of the slide is a transition zone, forming most of the ground between the two segments of road; it lies between the upper landslide blocks and the lower debris flow. It is composed of an unstable complex of blocks and slices, some of which can be identified by ground breaks along their margins; they overlie the steepest part of the landslide's basal shear, which was the hillside immediately downslope of the initial failure. The upper road lies along the highest section of the transition zone, which is currently the most active part of the whole slide.
  3. Disintegration of the lower part of the slipped material has created a debris flow that now forms half the total length of the slide. This is described as a flow because it moves as a plastic deformable mass, but it may also be regarded as a debris flow slide because it has a well-defined basal shear surface.
The literature listed below give good accounts of this landslide in more detail.

The geology

Underlying the landslide are Dinantian limestones which are not included with the landslide (Waltham and Dixon, 2000). Overlying the limestone is the Bowland Shale Formation which consist of dark grey mudstone. The top of the landslide exposes the Mam Tor Beds. These are a sequence of turbidites of mudstones siltstones and sandstones.

Further reading

Aitkenhead, N., Barclay, W.J., Brandon, A., Chadwick, R.A., Chisolm, J.I., Cooper, A.H. & Johnson, E.W. (2002). British regional geology: the Pennines and adjacent areas. 4th ed British Geological Survey, Keyworth, Nottingham.
Arkwright, J.C., Rutter, E.H. & Holloway, R.F. (2003). The Mam Tor landslip: still moving after all these years. Geology Today, v.19, pp.59-64.
Cripps, J. C. and Hird, C. C. (1992) A guide to the landslide at Mam Tor, Geoscientist v.2 (3), pp. 22-27.
Dixon, N. and Brook, E. (2007) Impact of predicted climate change on landslide reactivation : case study of Mam Tor, UK in Landslides : Journal of the International Consortium on Landslides, v. 4 (2) pp. 137-147.
Donnelly, L.J., (2006). The Mam Tor Landslide, Geology & Mining Legacy around Castleton, Peak District National Park, Derbyshire, UK, in Culshaw, M.G., Reeves, H., Jefferson, I. & Spink, T. (eds) Engineering Geology for Tomorrow's Cities, Proceedings of the 10th Congress of The International Association for Engineering Geology and The Environment, Nottingham, UK, 6-10 September 2006. Geological SocietyLondon(CD-ROM).
Doornkamp, J.C., (1990) Landslides in Derbyshire. East Midlands Geographer, v. 13 pp.33-62.
National Trust: About Mam Tor, The Shivering Mountain (2009)
Rutter, E. H., Arkwright, J. C., Holloway, R. F. and Waghorn, D. (2003) Strains and displacements in the Mam Tor landslip, Derbyshire, England, Journal of the Geological Society of London v.160 (5) pp. 735-744.
Skempton, A. W., Leadbeaater, A. D. and Chandler, R. J. (1989) The Mam Tor landslide, north Derbyshire, Philosophical Transactions of the Royal Society of London, v. 329, No 1607, pp 503-547.
Walstra, J., Dixon, N. and Chandler, J. H. (2007) Historical aerial photographs for landslide assessment: two case histories. Quarterly Journal of Engineering Geology and Hydrogeology. V.40, Part 4, November, p315-332.
Waltham, T. and Dixon, N. (2000) Movement of the Mam Tor landslide, Derbyshire, UK, Quarterly Journal of Engineering Geology & Hydrogeology v.33 (2)pp.105-123.

Stratification and lichen

The cross stratification on this sandstone block on Froggatt Edge forms a sheltered micro-climate for lichen.

Friday 28 December 2012

Visean and Dinantian

According to an earlier blog on the Carboniferous the Dinantian is a series and the Visean a stage. According to the BGS book The Pennines and adjacent areas (p16) the Dinantian is a subsystem and the Visean a series which is divided into stages:

I am more inclined to believe the BGS over Wikipedia!

Whichever is true the geology of the Peak District is often described as Dinantian, Namurian and Westphalian which is a mixture of subsystem and series (on the BGS criteria) with the occasional mention of the Visean. Geologists always seem out to confuse.

 

Thursday 27 December 2012

System v Period

There seems to be a confusing mixing of chronologies with Carboniferous being both a Period and System. According to Wikipedia the TIME (geochronology) divisions are as follows:

Eon, era, period, epoch, age

The ROCK (chronostratigraphy) divisions which correspond to them are:

Eonthem, erathem, system, series, stage

Confusing....

Monday 24 December 2012

Counties

Here is a list of the five (or six if you split Yorkshire into South and West!) in which the Peak District lies, so beloved of local pub quizzes.

Cheshire
Derbyshire
Greater Manchester
Staffordshire
Yorkshire

Sunday 23 December 2012

When is a millstone not a millstone?


This is a good site on millstones and when a circular stone (like the ones above under Stanage Edge which ARE millstones!) is not a millstone.

Millstones - used in pairs to shear grains fed into a narrow gap between their faces; used in grist mills

Quern-stone - manual version of millstones

Grindstones - used to sharpen metal cutting tools etc. pushed against their edges

Pulp stones - a special type of grindstone that was quarried in large numbers in the late 19th and early 20th centuries: exported to Canada and Scandinavia to be mounted in machines used to pulp timber for paper making

Edge runners - cylindrical stones mounted on an axle and used to crush a variety of materials and even foodstuffs as they rolled around a pivot



Monday 17 December 2012

Geological excursions in the Sheffield region

Various (1967) University of Sheffield

1. The Wye Valley

2. Earl Sterndale Area

3. The Castleton Reef Belt and adjoining areas

4. The Carboniferous Limestone of the Stony Middleton Area

5. The Visean Rocks of the Matlock—Wirksworth—Monyash Area

6. The Ashover Area

7. The Crich Inlier

8. Volcanic Rocks in the Peak District

9. Some Mineral deposits of the Carboniferous Limestone of Derbyshire

10. Fossiliferous localities in the Namurian Rocks of Edale

11. Namurian Sedimentation in the High Peak

12. The Bradfield—Ewden Area

13. The Ashover and Chatsworth Grits in North-East Derbyshire

14. The Namurian and Basal Westphalian Rocks of the Beeley—Holymoorside Area

15. The Namurian and lowermost Westphalian Rocks in the southern part of the Goyt Syncline

16. Westphalian A Palaeontology and Stratigraphy of the Langsett—Penistone Area

17. The City of Sheffield

18. The litho-facies of a Lower Coal Measure Sandstone Unit between Sheffield and Brighouse

19. The Middle and Upper Coal Measures (Westphalian B and C) north-east of Sheffield

20. Conisborough

21. The Permo-Triassic Rocks of the Worksop Area

22. Scunthorpe

23. Kirton, Lincolnshire

24. Nettleton, Lincolnshire



The Living Landscape

Patrick Whitefield (2009) Permanent Publications

Reading the landscape is at the heart of this blog, not just in the Peak District but everywhere. This book is the book I have been looking for for ages, it brings together all I have learned and more into one volume. As a reminder for myself I made notes as I read it.

The landscape and how to read it

Four landscape forming factors: rocks, soil, climate and living things.

Or two: the natural and the human.

The four factors are constantly interacting. Rocks affect landforms. Landforms affect climate. Rocks and climate affect the soil. Soil and climate affect vegetation. Vegetation affects soil and climate.

Three important themes. Everything changes. Everything’s connected. Everything has multiple causes.

Different timescales: annual, succession, rotational (human controlled).

Rocks: the bones of the landscape

Most fundamental difference is basic v acidic. Basic - alkaline soils rich in plant nutrients, acidic - acid, nutrient poor soils.

Igneous rock: granite, acidic; basalt, basic.

Sedimentary rocks. Sandstone - acidic, nutrient poor soils. Sandy heaths were often common land as they are nutrient poor and often remain as common land now eg Hampstead Heath. Clay - alkaline, nutrient rich soils. Often used as agricultural land. Limestone (including chalk) almost always makes hills as it is so permeable that no erosive surface water remains. Limestone soils are very alkaline but not necessarily rich in other nutrients so not necessarily fertile. Coal measures are the major determinant in urban v rural landscapes.

Hills and valleys

Upfolds don't always form hills (although they can!). Downfolded rocks are compressed and hardened; upfolds are stretched and weakened. These erode away more quickly than the strengthened rocks of the downfold.

Young rivers form V-shaped valleys which twist and turn. Cultivation is on the hills above the valleys. Glaciers form U-shaped straight valleys where the cultivation is in the valley as the hills above are too exposed for cultivation.

The soil and what plants can tell us about it

Fundamental difference is between the well drained, nutrient poor sandy soils and the alkaline, plastic (and as a consequence not well drained) clay. Clay loams are nutrient rich but plastic (heavy) and was often used for wheat and beans. Easily worked sandy loams were used for vegetables (rabbits and bracken clues to sandy soil).

Soil types. Podsol - acid. Excessive drainage washes nutrients from surface to hard pan below. Often forms on granite and sandstone. Characteristic of heaths and moors. Too acid for worms! Brown earth - not too wet, not too dry. Very good for agriculture. Also found in forests and grasslands. Gley - heavy clay soil with high water table which forms a blue/grey layer. Too wet to cultivate so used for meadow or pasture. Too wet for worms! Peat - extreme waterlogging prevents decomposition leading to peat. Peat can often form when heather forms a hard pan on a podsol leading to poor drainage. Rendzina - thin, alkaline soil on limestone.

Plant indicator species. Strong indicators eg reeds always indicate wet soil v communities. Indicators can tell us about water content, acidity, levels of plant nutrients and light/heaviness. Water content: buttercups - moist not wet; rushes - wet most of year; reeds standing water at least part of year; compacted soil has poor drainage and is often wet - plantain can grow on compacted but not wet soil. Acidity: easy at extremes (heather, acid, old man’s beard, alkaline) but look out for exceptions.

Climate and microclimate

Aspect has an effect but not as much as in other countries or as much as the changes in rock/soil type. Altitude has a much greater effect. It is colder (1C per 100m), windier, wetter and cloudier. Frost pockets form in valleys where the cold air flows down from higher ground. Snow can be used to pick out the wind patterns by studying the drifts. Melting snow picks out the warmer and cooler parts of the landscape. Wind flagged trees show prevailing wind (south west) or effects of local landforms.

Heaths and moors

Heaths are usually sandy lowland areas with poor nutrients. Since the advent of fertilisation many of them were turned into agricultural land and they are now uncommon. Moors form on higher ground, usually acidic in nature. Many are semi natural, formed from woodland by grazing. They often follow the pattern of bracken on the slopes and heather or grass moor on the tops (if the slope is too steep heather will take over as the soil is too thin for bracken). Bracken is a very competitive plant but needs more in the way of bases, drainage and deeper soil than other moorland plants. It hates shallow soil, it hates wet feet: where there is shallow soil heather can grow, where it is wet grass and rushes grow. Alternatively gorse may grow on the slope and bracken a the bottom:

There's gold under bracken,

Silver under gorse,

And famine under heather

Moors are usually managed by burning for either grouse or sheep. Trees are more demanding than most heathland plants and often grow by streams where active erosion releases bases allowing them to grow quicker. Blanket bogs form peat where the rainfall is very high and drainage poor resulting in saturated soil. They are natural as they overwhelm the trees whic can't grow in these wet conditions. In the Pennines they often form on the western side at higher altitude, while heather moors form on the eastern side and lower down.

VEGETATION SUMMARY

The Heather Family

Heather or ling. Poor, acid soil, moist to dry, usually a podsol; tolerates thin soil.

Bell heather. Mixed with heather on drier soils, dominant on very dry ones.

Cross-leaved heath. Mixed with heather on wetter soils, dominant where it's too wet for heather.

Bilberry. Often on drier soil or boulders; shade tolerant and often grows in woods.

Plants of More Fertile Soils

Bracken. Deep, well-drained soil, richer and less acid than typical heather soil, usually a brown earth, usually on a slope; can out-compete other plants on a

favourable soil but is sensitive to trampling; altitude limited by cold.

Sweet grasses (bents and fescues). A mix of fine-leaved grasses, usually grazed down short because the animals like them; they grow on similar soils to bracken.

Gorse, common. Slightly poorer soils than bracken but sometimes more alkaline; not cold-tolerant.

Gorse, dwarf and western. Much smaller plants than common gone with similar soil preferences to heather.

Plants of Wet Soils

Matgrass. Similar soil to heather but often a bit wetter; both it and purple moorgrass may take over where heather is overgrazed.

Purple moorgrass. Similar soil to matgrass but usually a bit wetter still; often grows in big tussocks, especially when in a pure stand - very hard going for

walkers.

Bog myrtle. Wet to very wet soil, often with purple moorgrass; like the alder tree, it's a nitrogen-fixer.

Deergrass. Deep peat and bogs, very wet and acid.

Cottongrass. Bogs, even wetter than deergrass and including open water.

Bog moss. The ultimate peat-forming bog plant, only found in extremely wet conditions.

Water in the landscape

Springs form at the junction of permeable and impermeable rock such as limestone and clay. This is often at the boundary of hill and dale. Villages often built near a spring on this boundary with access to grazing and arable land.

Bogs can also form in valleys.

TYPES OF BOG

Blanket. Forms in regions of extremely high rainfall; covers all flat and gently sloping land in a layer of peat. Always acidic.

Valley. Forms in a low place where drainage is impeded, fed by drainage water. Can be acid (bog or moss) or alkaline (fen).

Raised. Forms on top of a valley bog, fed by rainfall. Always acidic.

The rest of the chapters in the book are less relevant to the Peak District or to my particular interests so I have only outlined them here.

The history of the landscape. Very interesting chapter about the farmed history of the landscape including the enclosures.

The three chapters wild animals and how to recognise their signs, niches or how plants and animals make their livings and succession how landscapes change through time are more about ecology than geology.

Woods play a large role in the landscape and there are three chapters are all about them - trees as individuals, the different kinds of woodland and how woods work. Lowland grassland, hedges & other field boundaries, and roads & paths complete the book contents.

Sunday 16 December 2012

Rocks and Fossils: The Peak District



I.M. Simpson (1982) Unwin Paperbacks

1 Edale and Kinder Scout

2 Castleton Area: Treak Cliff and Mam Tor

3 Castleton Area: Cave Dale and Dirtlow Rake

4 Eyam, High Rake and Coombs Dale

5 Tideswell Dale and Miller's Dale

6 Ashford and Monsal Dale

7 Lathkilldale

8 Youlgreave and Alport

9 Black Rock and Steeple Grange

10 Thorpe Cloud and Lower Dovedale

11 Hartington, Wolfscote Dale and the Tissington Trail

12 Ecton and the Manifold Valley

13 Hen Cloud, The Roaches and The Ramshaw Rocks

14 Parsley Hay, the High Peak and Tissington Trails

15 Goyt's Moss



Great Double Dyke – English Heritage Scheduled Monument 31229

Two parallel ditches have marked the boundary between Ashford and Hope land since local families bought it from the Danes in AD926 (SK218736).



Deep rake

At the end of the opencast workings on the OS map in grid square SK2273 (above Calver) the mine at the end of Deep Rake is visible.

 
 

 

Saturday 15 December 2012

Wednesday 12 December 2012

Rocky Rambles in the Peak District

Fred Broadhurst (2001) Sigma Leisure

A short introduction to Peak geology is followed by the walks. Nice overview section of the geology.

The walks:

Walk 1: Castleton - Cave Dale - Pin Dale

Limestones, Lava and Lead

Walk 2: Castleton - Lose Hill - Mam Tor

Ridge, Landslip and a Resurrected Sea Floor

Walk 3: Edale - Kinder Scout

Sandstone Scenery, Wind Sculptures

Walk 4: Monsal Dale

Landslips and Fossils

Walk 5: Millstone Edge - Stanage Edge

Millstones and Concretions

Walk 6: Wirksworth

National Stone Centre and Dolomite

Walk 7: Dovedale

Limestone Scenery

Walk 8: The Roaches, Lud's Church

Geology and Scenery

Walk 9: Earl Sterndale - Parkhouse Hill - Chrome Hill

Limestone 'Reefs'

Walk 10: Lyme Park - Cage Hill - Bowstones

Sandstones, Glacial features

Walk 11: Lyme Park - West Parkgate

Glacial Spillway, Fossil Soils and Fossil Ripple marks

Walk 12: Lathkill Dale

Limestones, Fossils and Lead Mines

Walk 13: Goyt's Moss - Shining Tor

Sandstone Scenery and Coal

Walk 14: Ashford-in-the-Water - Magpie Mine

'Black Marble' and Lead

Walk 15: Tegg's Nose

Sandstone and Sandstone Quarries

Walk 16: Tideswell Dale - Miller's Dale

Limestones and Lavas

Walk 17: Rowarth - Cown Edge

Faults, Folds and Landslips

Walk 18: Rowarth - Lantern Pike

Rocks and Topography



Monday 3 December 2012

Geology Explained in the Peak District



F. Wolverson Cope (1998). Scarthin Books

This was the first Peak geology book I bought and I found it hard going when I first got into geology (before I started on my OU degree!), so we shall see if it makes more sense now!

Oh dear. After a somewhat superfluous set of introductory chapters this book ploughs on with descriptions of specific areas. It is written for someone with a degree in geology and lacks the idea of a specific itinary which is present in the other 3+ geology walk books available. It is also very old fashioned. Give it a miss.

1 Geology In The Field Field equipment - the Countryside Code - the Peak DistrictNational Park

2 Identifying Rocks, Minerals and Fossils Rocks - minerals - fossils

3 The Geological Time-scale

4 Geological Structure of the Peak District

5 The Valley of the River Wye: Buxton to Little Longstone The Carboniferous basement - the sequence east of Woo Dale - the massif fades

6 The Valley of the River Goyt Millstone Grit and Namurian - pre-Namurian denudation - the Goyt Syncline - Namurian cyclic sedimentation - contorted beds

7 Castleton, Edale and Mam Tor Reef limestones - caves of the Castleton district - the Speedwell Vent - fossils of the reef limestones - the use of goniatites - the Namurian of the Edale valley

8 Bradwell Dale and Eyam Bradwell Dale - Eyam - the Eyam and Woo Dale boreholes

9 Monsal Dale and Ashford-in-the-Water The Hobs House Coral Band - igneous rocks in Monsal Dale - the Ashford marble

10 Matlock, the Via Gellia, and Brassington The Grangemill vents - lead mining in the Peak District - dolomitisation of limestones - Tertiary pocket deposits

11 Ashover Dinantian rocks of Ashover - Namurian rocks of Ashover

12 The Valley of the River Dove Reef limestones of Thorpe Cloud and Bunster

13 Chrome Hill and Parkhouse Hill

14 The Valley of the River Manifold

15 The Roaches and Goldsitch Moss The Rough Rock of Quarnford and Goldsitch - Namurian successions in the Peak District

16 Kinder Scout The Mam Tor Beds - the Shale Grit - the Kinder Scout Grit

17 Economic Geology of the Peak District General and water supply - mining - quarrying



Sunday 2 December 2012

Millstones and bedding

When there is good weather at this time of year it really is fantastic. Here are some iPhone shots taken under Stanage Edge.





Friday 30 November 2012

NE-SW Facing Dales


[Repost from gneisslife.blogspot.com 15 August 2011]

While walking in Wolfscote dale on Sunday I noticed that the right hand side (walking towards Hartington) was scree covered while the opposite side was not. Checking with the map later Wolfscote dale shows the same NE-SW facing orientation as Watlows dry valley (SXR216).
Cool!

Wednesday 14 November 2012

Rock Trails Peak District

A hillwalker's guide to the geology and scenery
Paul Gannon (2010) Pesda Press Ltd

This is one of several books which contain geology walks. I hope to do some of these next year, maybe combining walks from several books. In this blog entry I will be going through the first 8 chapters which are about the Peak District geology.

Chapter 1 - basement blocks

We start off with a description of the position of the PD at this time, south of the equator and slowly moving north. To the north is a mountain range, and an arc of higher ground to the south (the Wales-Brabant high) from which the Peaks High pokes out. To the north of the Peaks High is the Edale Basin and the the west the Widermerepool Gulf. The area is under extension causing the basins to sink.

Chapter 2 - layers of limestone

Limestone was formed in the shallow seas of the continually sinking basins and on the Peaks High when it went below sea level. Occasionally the sedimentation stopped as the plateau was above sea level (plant roots and soil found between some bedding. This forms the shelf limestone which was a lagoonal environment. At the edge of the shelf are apron reefs which are made from an algal reef and often have fore-reef and back-reef structures. The form a rim around the shelf limestone except in the south west where there is a ramp down to the Widermerepool Gulf. Knoll reefs formed within the main platform and are also known as mud mounds.

Chapter 3 - grains of grit

Sandstone formed by erosion of mountains in north forming deltas into freshwater (and occasionally seawater) in the sinking basin. It is the presence of layers of shale which forms the distinctive step and shelf topography.

Chapter 4 - lingering lignin

Coal was formed in a swampy tropical forest closer inland from the delta lobes. These forests were formed by plants which had a much higher proportion of bark and therefore lignin than modern trees.

Chapter 5 - faulted and folded

At the end of the Carboniferous and into the Permian plates crashed together to the south (finishing the assembly of Pangea). This halted the subsidence and instead the subsided land popped up on existing faults. The harder base of the white peak prevented serious folding resulting in the gentle dome of limestone. Especially to the west much folding took place resulting in many synclines and anticlines. Faults caused by the movement were mineralised by this tectonic activity.

Chapter 6 - drainage delights

Spring lines and landslips.

Chapter 7 - solution and superimposition

Sink holes, caves, dry valleys, stalactites and superimposed drainage.

Chapter 8 - peak and people

Exactly what it says.

The walks:

Walk #1 Kinder Scout

Walk #2 Bretton Clough

Walk #3 Mam Tor & Back Tor

Walk #4 Upper Dove & Manifold Valleys

Walk #5 Chrome Hill

Walk #6 High Wheeldon

Walk #7 Dove Valley - Wolfscote Dale

Walk #8 Lower Dovedale

Walk #9 Stanage Edge

Walk #10 Curbar Edge

Walk #11 The Roaches & Gradbach Hill

Walk #12 Lathkill Dale

Walk #13 Cave Dale & Winnats

Walk #14 NSC, Middleton Moor & Black Rock

Walk #15 Wye Valley

Sunday 11 November 2012

OUGS -The Roaches

[Repost from gneisslife.blogspot.com 22/05/2010]
East Midland's branch trip led by Gerry. Very hot (27 degrees!), so hot we didn't get all the way round.

Highlights:
1. The goyt syncline - a syncline plunging to the north


Ramshaw rocks (far side) taken from Roaches (foreground)

2. Cross bedding


3. Lud's church which was formed by a landslip (the photos of that were rubbish so here is an artistic one of Doxy pool instead)

Saturday 27 October 2012

Lepidodendron

There has been a fossilised tree root in Sheffield Botanical Gardens for as long as I can remember. It was not until they put up new signs earlier this year that it's significance became clear.


Clubmosses - fossilised plants that became coal

This is the fossil root of a giant clubmoss called a Lepidodendron that lived about 300 million years ago. It was found in the rocks between the coal seams that were dug out when Sheffield's railway station was being built in the late 1860s. Clubmosses were some of the earliest vascular plants. Today clubmosses still exist but they are small plants that usually grow in boggy areas. Fossils are usually formed when an organism dies and the contents of its cells are replaced with rock forming minerals. This fossil root was surrounded by hardened sediments before the tissues rotted away leaving a hollow mould which was filled with fine sand forming a perfect replica of the original root. During the Carboniferous period Sheffield was covered with vast forests of clubmosses that grew up to 30 meters tall. When they died they piled up and were turned to coal as they were buried and compressed. This coal was mined in the Sheffield area for fuel.

Thursday 25 October 2012

Ecton copper mine


[Re-post from 23/08/2012 gneisslife.blogspot.com]
On Sunday the walk took us past a disused mine as Ecton. A friend asked if it was a lead mine. I looked it up on google and found out that in fact it was a disused copper mine, the only one in the Peak District.
Ecton copper mine - Ecton mine was the source of the 5th Duke of Devonshire’s fortune and was the deepest mine in the world at that time.
The period of time between 1760 and 1790 was the heyday of this famous Peak District mine. The 5th Duke of Devonshire was the lucky owner when a vast deposit of high grade copper ore was discovered. The ore yielded as much as 60% copper, very high grade indeed, many copper ores that are mined today yield only 2 - 3%. This lasted for 30 years and was the source of money used to build Buxton’s Crescent and Stable Block (the latter was later to become the Devonshire Royal Hospital). Below is an image of a sample of chalcopyrite, photographed near the Ecton Copper mine.
In some places this rich ore body was 50m wide. Deeper in the mine, the copper was increasingly replaced by zinc. The shape of the ore body was described by a Dr. Joseph Watson as being a saddle deposit, this being the name that miners gave to locations where ore bodies had been folded by anticline/syncline formations. Samples of the ores from Ecton mine are held both at Chatsworth house in the Peak District and at the British museum in London. The grotto at Chatsworth is lined with chalcopyrites and calcite from the mine.
Ecton is unusual in the Peak District as it is the only source of copper mineralisation. Some lead and zinc ore has been extracted from this mine also. The mine is the deepest in the Peak District and may have been the deepest in the world at the time (at least 1800 feet deep in 1788). A reason for this record is the nature of the deposits - vertical ‘pipes’. Contemporary writers visiting the mine were obviously impressed by the beauty of the ores - yellow, gold, topaz, violet and azure all being mentioned. The ores responsible for this multifarious appearance were (mainly) chalcopyrites with oxides and carbonates. The gangue was mainly yellow calcite with fluorite and iron minerals.
The mine was worked in the 17th century, possibly earlier but never properly exploited. In 1723 a group of speculators re-opened Ecton mine but unfortunately ran out of money before the rich ore body was discovered. In 1763 and 1764 the output was over 1000 tons per year, although this was reduced by the end of the decade.

Sunday 21 October 2012

The beast of Black Rock

This prehistoric looking beast is an eroded outcrop of Ashover grit at the top of Black Rocks above Cromford (SK293558). The Black Rocks site was mined for lead, the spoil on the scree slope leading up to Black Rocks supports many interesting lead tolerant plants (leadworts). The scree slope is an ideal place to search for a variety of rocks and minerals. Other interesting habitats can be explored from Black Rocks, since it is near the boundary between limestone and gritstone. Cromford Moor has heather moorland and various types of woodland.

From Black Rocks we can see the huge outline of Dene Quarry. It produces crushed limestone for use on roads and in concrete.



Sunday 14 October 2012

Parkhouse Hill

The following is a re-post of a blog from gneisslife.blogspot.com from 27th June this year. It shows the reef topography of Parkhouse Hill and the geological setting.

A fantastic example of an apron reef at the edge of the Derbyshire Dome limestone plateaux.





Friday 12 October 2012

Rocks and Scenery of the Peak District


Trevor D. Ford (Landmark Collector's Library)

The first geology of the Peak District book I am going to read is this excellent little book published in 2006. The name of Trevor Ford will come up again and again in this blog as he has published widely on this subject. This book is aimed at the non specialist and is full of fantastic pictures to inspire an interest in geology. I will go through each chapter with a short synopsis a pattern I will repeat for all the books. In this way we can slowly build up our knowledge in bite sized pieces.

The limestones of the white peak

Limestones form the centre of the peak. They formed in warm tropical waters when Britain was near the equator in the Carboniferous. The area was an atoll like structure surrounded by reefs, although these did not form a continuous ring in time or space. The reefs were not formed of coral but algae and indeed some are better described as mud mounds than reefs. There was a lagoonal plateau in the middle.

Toadstones or volcanic lavas and ash falls

Bubbling under this atoll basalt lava seeped out onto the floor. There is also evidence of ash fall, hexagonal jointing and sills. Wow. Toadstone is a local name for this rock type but the origin is unclear.

The Millstone Grit

Surrounding the limestone to the west, north and east are the shale and sandstone sequences of the dark peak. These were formed by deltas resulting from the erosion of large mountains in the north. About 300 million years ago the lagoon subsided and the mountains raised resulting in the cessation of limestone and the deposition of sandstone which eventually covered the limestone.

Structures, folds and faults

There is a large scale anticline covering the whole of the South Pennines with the Derbyshire massif in the middle.

Minerals and mines

There is a long history of mining in the Peak District and we will return to it again and again. Galena, fluorspar, barite and calcite were all mined in the White Peak from deposits laid down at the end of the Carboniferous. Rakes and scrins are vertical fissure deposits with flats and pipes along the bedding or in caves. There is also Blue John but we will leave that for another day.

Before the ice age: the pocket deposits

Around Brassington are pockets of sand formed by the erosion of Triassic sandstones into a limestone basin 7 million years ago. Originally a sheet the pockets formed as the limestone eroded. They form an unusual landscape as the heathland vegetation of the silica pockets contrasts with the limestone vegetation.

The great ice age

The last ice advance, the Devensian (80-10 kya), did not reach the Peak District stopping only as far south as York and South Staffordshire. The earlier Anglian (470-420 kya) did reach the Peak but the flow was too slow to carve the U-shaped vallys.

The remaining 10 chapters are all short reports about more geomorphological features such as rivers, caves, dry valleys, landslips etc all of which I am sure we will have lots more to say about in the coming months.

This book is now out of print but it features many colour photos and geological sketch maps and is well worth getting hold of.