Otley Chevin

Chevin Forest Park

The Story of a Landscape

You are standing on the Chevin looking out over Wharfedale. Skipton is below the lefthorizon and York is on the right – on a clear, sunny day you can see York Minster!

The origin and evolution of the Chevin and the scenery before you are part ofgeological history. Here with the help of the Leeds Geological Association and the

West Yorkshire Geology Trust we have picked out some of the main elements of thestory of the landscape and invite you to look for some evidence yourself.

Chevin Forest Park is a Local Nature Reserve and is managed by Leeds City Council for your enjoyment.

18,000 YEARS AGO: THE WHARFEDALE GLACIERThe last great advance of ice in the Ice Age took placearound 20,000 years ago. The ice may have coveredthe Chevin: here we show it as it retreated (it finallymelted 10,000 years ago). This region was buriedunder much thicker ice in earlier glaciations but verylittle evidence remains. An arm of the Wharfedaleglacier flowed through the ‘Guiseley Gap’ to Airedale,leaving debris in the form of moraine, and boulder claymoulded into oval-shaped mounds known as drumlins,south-west of Menston.

What preceded the glaciers? The Dales existedas river valleys before the Ice Age, though themoving ice must have widened and deepenedthem. The rivers probably flowed eastwards asnow, cutting down through kilometres-thick layersof Jurassic and Cretaceous rock like those in EastYorkshire before carving into the Dales rocks.These layers have been stripped away by upliftand erosion in the past 60 million years.

year-round packice

ice sheet

tundra

The North Atlantic inMay 18,000 years

ago: the warm GulfStream flowed east

to Lisbon, whileBritain lay in the

path of polarcurrents. The

average annualtemperature was

-6oC to -9oC.

Although woolly mammoth and woolly rhinoceros (the greatest of ice-agemammals) might have roamed the tundra above the glaciers, the only animalremains found in Wharfedale and Airedale are those of wild horse, red deer, giantox and wild pig which grazed pastures on post-glacial and river deposits. Theywere hunted by small bands of nomadic Palaeolithic hunter-gatherers armed withspears and bows and arrows.

Ice-age animals

The Lanshaw Delves moraine

This strip of hummocky ground with trees at Reva above Menstonconsists of debris deposited at the edge of the Wharfedale glacier,which must have surmounted Reva Hill. It contains limestone blocksfrom the Dales which farmers have dug out for lime.

Almscliff Crag

Almscliff Crag is a conspicuous upstanding mass of Millstone Grit, theresult of an underwater landslip when the grit was being deposited,providing double the normal thickness with a structure different from thatin the adjacent gritstone layers.

Otley

Chevin

BoltonAbbey

Addingham

Ilkley

Beamsley

Askwith

WashburnValley

Burley inWharfedale

Menston

Guiseley

Pool inWharfedale

Bramhope

315 MILLION YEARS AGO (100 MILLION YEARS BEFORE THE DINOSAURS)

Above: Over a period of 10 million years inmid-Carboniferous times, rivers flowing outof mountainous lands north of Britain (theAtlantic didn’t exist then) deposited layersof sand and mud over a wide delta region.

Right: The rivers which deposited thesand and mud layers preserved in theChevin may have looked very like this riverin tropical Queensland. Successivesheets of sediment are deposited, andthen eroded and re-deposited, building uplayers which when buried deeply willharden into rock. The traditional name forthe Chevin rocks is ‘Millstone Grit’ butgeologists today class them as ‘Namurian’in age.

The continent of Gondwana 315million years ago in the middle of theCarboniferous period. An ice cap atthe South Pole periodically melted;sea level rose and low-lying coastalswamps were inundated. Thin mudlayers with marine fossils are laiddown. Such fossils are found in theChevin.

300 million years ago

At this time, continental collisions severely crumpled andstacked up rock layers in southern England. Stresses reachednorthern England, compressing the contents of rift-likesedimentary basins such as our local Craven Basin.

Older, deeper rock layers were arched upwards (you can seethis is in the Skipton quarries). The overlying layers of MillstoneGrit slope away from them southwards beneath the YorkshireCoalfield, forming a long scarp from Harewood to AddinghamEdge, of which the Chevin is a portion made prominent by theGuiseley Gap.

Above: A distinctive layering called ‘cross-bedding’can be seen in rock faces in many places on theChevin. Layers of sediment build up downstreamuntil a ‘hundred-year flood’ washes away their topsand the process starts afresh.

FORMATION OF CROSS BEDDING

1

2

3

SOURCELANDS

MILLSTONE GRITDELTA

LEEDSDeep Water

Shallow Water

Britain

This outcrop at CaleyCrags shows multiplecross-bedding formed ina turbulent riverenvironment. In quieterconditions, somearthropods or molluscshave left these traces asthey burrowed in thesediment (right).

ZONE OF STRONG FOLDING300 million years ago

Com

pres

sion

North of Englandsedimentary basins

BEDROCK OF THE CHEVIN TODAY

The Chevin in section looking towards Ilkley Moor. Grit and mudstone formations of theCarboniferous Millstone Grit Group dip down beneath Guiseley. Bands of mudstone with marinefossils give place upwards to sandy delta deposits with plant remains, reflecting the periodic rise andfall of sea level. Note the post-glacial landslips still active today.

Sections across Wharfedale

Slices through Wharfedale: the Millstone Grit layers are draped over a more compressed core ofolder rocks below Wharfedale which comes to the surface around Skipton. The compression datesfrom 300 million years ago.

Ilkley Moor

RiverWharfe

CHEVIN

OTLEY

Burley in WharfedaleMenston

DSS

GEC

AE MudstoneLandslip

G=Guiseley Grit, EC=East Carlton Grit, DSS=Doubler Stones Sandstone, AE=Addingham Edge Grit

Beamsley BeaconAddingham Edge

River Wharfe

Denton Moor

River Wharfe

Farnley Moor

River Wharfe

Ilkley Moor

Chevin

Otley

AE

AEAE

AE

AE AE

AE=Addingham Edge Grit

ALMSCLIFF CRAG

HARROGATE

ARTHINGTONVIADUCT

YORK

WHITE HORSEFARNLEY HALLOTLEY

SIMON’S SEATASKWITH

BEAMSLEYBEACON

SKIPTON

BURLEY INWHARFEDALE

ILKLEY

COW & CALF

Walk the Geology Trail

This leaflet is available from TheWhite House Café (see noticeboard for opening times) and OtleyLibrary.The walk starts at East ChevinQuarry car park and is about 3 kmlong.