A Field Trip in Knaresborough - Part 3

 

Stepping Stones House

Of the 12 points of interest that had been identified for the Sheffield U3A Geology Group field trip in Knaresborough in July 2023, by the time that we stopped for our lunch at St. Robert's Cave, 8 of these had been visited and the afternoon turned into a much more lesiurely walk that mainly followed the bank of the River Nidd. 

 

The former Plompton corn mill

 

Crossing over Grimbalds Bridge and following the footpath, we passed the former Plompton corn mill, which is built in a reddened gritstone, but we didn't stop to look at it and proceeded to the river bank, where there is an exposure of the Lower Plompton Grit, which is pebbly and apparently shows trough cross-bedding, but we didn't spend any time looking for this.

 

A riverside exposure of the Lower Plompton Grit

 

From here, we had good views of the weir, where the Lower Plompton Grit also forms its foundations. On the adjoining river bank is Abbey Mill, another corn mill that the Mills Archive states once belonged to the monks of the nearby Cistercian abbey, which was actually the Trinitarian priory. It has apparently been rebuilt several times, with power being provided by water, steam and electricity, but it still retains its undershot waterwheel. 

 

A view of Abbey Mill and the weir

 

Following the footpath to the base of Grimbald Crag, everyone was too busy making their way around the tree roots to notice if this was the one referred to in Anthony Cooper’s Denys Smith Memorial Trip, which describes a path on the Carboniferous-Permian unconformity. 

 

The path beneath Grimbald Crag

 

There was no suitable point along this path for the group to stop and look at the yellow limestone of the Sprotbrough Member of the Cadeby Formation, which forms Grimbald Crag. I just took a few photographs, from which I can see that the limestone contains numerous vughs and solution hollows and has large scale cross-bedding. 

 

A view of Grimbald Crag

Just to the south of Grimbald Crag, the path crosses the Grimbald Crag Fault, with  a downthrow to the south that brings the mudstones of the Edlington Formation to the surface Although this formation was not exposed, as we followed the path through Birkham Wood, the poorly drained ground underfoot was muddy and care had to be taken where the path was very close to the river. 

 

The position of the Grimbald Crag Fault

 

On the Leeds Geologists Association (LGA) field trip guide that we were using, our next stopping point states that in the valley side above the path there are thinly bedded limestones of the Brotherton Formation but, although I could see what could be outcrops of these through the thick undergrowth, we didn't go and investigate them. 

 

A stream in Birkham Wood

 

The woodland that we were walking through and the riverbank opposite didn’t have any obvious landmarks to navigate by and nobody had a GPS device, so it wasn’t easy to pinpoint the next place on our agenda. Eventually, we came to a small stream that was traced back to an outcrop of thinly bedded limestone, where a spring forms at the junction with the underlying Edlington Formation, but water certainly wasn't gushing from it. 

 

The source of the spring noted in the LGA guide

 

The LGA guide states that the spring emerges along the line of the Grimbald Crag Fault, which brings the Cadeby Formation alongside the Brotherton Formation. We didn’t stop to look around the area, but I held back from the group to obtain a sample with my Estwing hammer, which is pale grey/brown in colour and is unlike the limestones from the Cadeby Formation seen on the walk.

 

A specimen of rock from the Brotherton Formation at the spring

 

When first very quick look at it with my hand lens when I collected it, I thought that it contained clear quartz grains but, closely examining it later, some surfaces have a finely botryoidal texture, some surfaces look porous and tufa like and, tested in several places, it scratches with a steel knife and reacts strongly with hydrochloric acid. 

 

The old quarry at Calcutts cricket ground

 

The last location was the old quarry at Calcutts cricket ground, to look at another exposure of the Sprotbrough Member of the Cadeby Formation, where I was more curious about the large cavities that have apparently been hollowed out of the abandoned quarry face, but nobody had any possible explanations for this. 

 

The quarry face at Calcutts cricket ground

The principal point of interest here is that the outcrop of the Cadeby Formation on the east side of the Nidd gorge is considerably thicker than in this quarry, which provides evidence that the ridge of limestone, upon which Knaresborough is set, is an original depositional feature and that the limestone thins away from it in all directions. 

 

An outcrop of limestone on Bland's Hill

Returning to Spitalcroft, where there are further exposures of yellow sandy limestone in some of the back gardens, we continued to Bland’s Hill and stopped at an exposure of limestone, which is not in the LGA guide or marked on old Ordnance Survey maps as a quarry. Its very pale, chalk like appearance is nothing like any exposure of the Cadeby Formation that I had seen before and I have wondered if it relates to the presence of petrifying springs, as occur a short distance to the west at Dropping Well. 

 

Lenses of green clay in the Bland's Hill limestone outcrop

 

The lower section is heavily weathered and broken down into a very fine powder and, in a few places, contains lenses of green clay that looks very similar in colour to that seen in the sandy variety of the Cadeby Formation found in Mansfield, Nottinghamshire, which is a feature of the White Mansfield stone and weathers to leave a texture that looks like old crinkled leather.

 

A sample of weathered limestone powder from Bland's Hill

 

I obtained a specimen of rock and placed some of the powder into a sample bag for later examination, along with the very fine grained orange material that I had collected from Abbey Road. Both samples feel soapy and not gritty when rubbed between the fingers and react strongly with hydrochloric acid, with a close examination using a hand lens of the rock specimen revealing an extremely fine granular texture and voids. 

 

A specimen of limestone from Bland's Hill

 

A Field Trip in Knaresborough - Part 2

 

A quarry exposure of the Carboniferous-Permian unconformity

Continuing the Sheffield U3A Geology Group field trip in Knaresborough on Abbey Road, having walked along Waterside to Low Bridge via Knaresborough Castle, our next stop was the old Bunker's Hill Quarry in the Sprotbrough Member of the Cadeby Formation, which is now occupied by the Low Bridge caravan park. 

 

Bunker's Hill Quarry

 

Looking from a distance, the form of the massive, cross-bedded oolites can be clearly seen in the south-west face of the quarry, which the 1934 edition of the 1:25,000 Ordnance Survey map - where it is named Low Bridge Quarry - shows as having lime kilns. 

 

The House in the Rock

 

Passing the House in the Rock, which can be seen at the top of the cliff, the Grade I Listed Chapel of Our Lady of the Crag is excavated into yellow sandy limestone in the lower part of the Sprotbrough Member, which is composed of large sub-aqueous, oolite sand waves.

 

The Chapel of Our Lady of the Crag

 

This chapel dates from the early C15, with late C17 and early C18 alterations and, although we could only see this at a distance from the roadside, with my zoom lens I could see the figure of a knight to the right of the door, which was probably made between 1695 and 1739. 

 

A cliff exposure on Abbey Road

 

A little further down Abbey Road, we gathered in the layby to have a closer look at the large scale cross-bedding and the very sandy lower part of the cliff, where I prised off a very small specimen of yellow limestone, which in places has distinegrated into an extremely fine grained orange silty material that I scooped into a sample bag.

 

Samples of yellow limestone and orange silt

 

Taking care on the narrow pathless road, we followed Abbey Crags and, as instructed by the version of the original walk by Anthony Cooper we were using - provided by Bill Fraser of the Leeds Geological Association - we looked for the Carboniferous-Permian unconformity behind No. 51a Abbey Road and, although the vegetation covered most of this, we did get a glimpse of the Upper Plompton Grit and the mainly obscured Cadeby Formation above. 

 

An exposure of the Upper Plompton Grit

 

Our next stop was the first of two old quarries on the east side of Abbey Road, opposite The Abbey, which was overgrown in places but there were some rock exposures where both the variegated yellow and red Upper Plompton Grit and the overlying Cadeby Formation could be seen - separated by the unconformity

Exposures of the Carboniferous-Permian unconformity

Retracing our steps back to Abbey Road, we continued for a short distance until our leader Dave, who had not found it easy to find some of the sites on his recce, took us to another quarry where there are more extensive quarry faces, which expose the unconformity between the Upper Plompton Grit and the Cadeby Formation. 

 

Upper Plompton Grit overlain by the Cadeby Formation

 

Just beyond this quarry, a roadside building is part of a group that is marked on old Ordnance Survey maps as a smithy, which is built out of red angular and poorly sorted Upper Plompton Grit that is presumably from one of these quarries. In one place, a block with pebbles displays graded bedding that shows that it has been placed upside down and not on its natural bed, as when removed from the quarry face. 

 

Upper Plompton Grit at the smithy

The next part of the walk passed modern houses and, except for an excellent view of the yellow limestone of the Cadeby Formation at Grimbald Crag across the River Nidd, there was nothing of interest to see until we reached Saint Robert's Cave, where we had lunch. 

 

A view of Grimbald Crag from Abbey Road

 

The Grade II* Listed cave and the foundations of an adjoining or outbuildings are associated with Saint Robert the Hermit (1160-1218), but there are no datable features. The guide that we were using suggests that the cross-bedded, oolitic dolomite exposed here probably represents the Wetherby Member of the Cadeby Formation and not the Sprotbrough Member, which we had seen elsewhere on our walk to date.

Saint Robert's Cave

A Field Trip in Knaresborough - Part 1

 

Knaresborough railway viaduct

As a very active member of the Sheffield U3A Geology Group, I am always on the lookout for potential field trips and, having seen the Denys Smith Memorial Trip: The Geology of Knaresborough Gorge by Another Cooper, who was the editor of the Doncaster Geodiversity Assessment, I immediately thought that a shortened walk based on this would be ideal for us.

 

The original field trip route by Anthony Cooper

 

Back in 2017, during a weekend visiting an old friend from Nottingham University, I had a good walk along the Nidd Gorge and was very impressed by the geology and the surrounding landscape and, although one or our members took it upon himself to undertake a recce while in the area with his wife, I undertook my own research so that I could provide geological input on the day. 

 

The British Geological Survey bedrock map of Knaresborough

 

Less than a week after my exploration of Blacka Moor Nature Reserve in Sheffield, the group met at the Conyngham Hall car park at the west side of High Bridge and, walking from here along Waterside to the Grade II* Listed railway viaduct (1851), I noted several examples of dolomitic limestone from the upper Sprotbrough Member of the Permian Cadeby Formation. 

 

An exposure of dolomitic limestone on Waterside

 

These oolitic limestones, which very often contain a high content of sand derived from the underlying Upper Carboniferous Addlethorpe Grit, show massive subaqueous dune bedding that was formed in a Bahamas Banks environment. The ridge on which Knaresborough is set appears to be a primary depositional feature, as the limestone thins away from it in all directions. 

 

Inspecting the gritstone at Knaresborough railway viaduct

 

We stopped to take a quick look at the buff/light brown pebbly gritstone used to build the viaduct, built by the Scottish engineer Thomas Grainger for the Leeds and Thirsk Railway. The Leeds Geological Association (LGA) guide, adapted from the original by Bill Fraser, which our leader Dave had chosen for the route, suggests that this may have been quarried from the Plompton Grit a few kilometres upstream at Scotton. 

 

The shelter on the cliff path to Knaresborough Castle

Making our way along the winding path up the cliff to Knaresborough Castle, we had our first opportunity to look at the limestone close up at a shelter half way up, where the cross-bedding dips to the north, before continuing up to the ruins of the castle. 

 

Views of Knaresborough Castle

 

With our leader just reading Bill Fraser’s notes, which I had already read and digested, I made my own observations of the various rocks that I was looking at and, when arriving at the castle grounds, I had a quick wander around to take a few photographs of the remains of the keep, the Courthouse Museum and Knaresborough war memorial, before rejoining the group and returning back to the gorge. 

 

Knaresborough war memorial

 

The next stop was to look at a vertical cliff section on Waterside, which exposes the unconformity at the base of the Cadeby Formation. Addlethorpe Grit forms the lowest part of the section, with the upper parts stained red by post Carboniferous weathering. Immediately above it are 6-7 m thick basal zone of reddish-buff coloured, sandy dolomite, containing blocks and fragments of eroded Addlethorpe Grit held together by a dolomite cement, with 17 m of dolomite above it. 

 

Views of the cliff face on Waterside

 

At Knaresborough, the uplift and erosion during the Permian period resulted in the removal of all the Coal Measures strata and the upper parts of the Millstone Grit Group. The landscape had undulating hills and ridges where the resistant sandstones and gritstones occurred with shallow valleys and hollows in the soft mudstones. 

 

The Carboniferous-Permian unconformity

 

The plane of the unconformity dips at an angle of approximately 15 degrees to the south and, just a little further along Waterside where the red sandy dolomite is not covered with rock netting, its very irregular nature is clearly visible. 

 

The remains of a fossilised tree

Below the unconformity, standing slightly proud from the surrounding Addlethorpe Grit, is the very weathered remains of a fossilised tree. Unlike others that our group had encountered in the Millstone Grit – at Whirlow, Otley Chevin and Ilkley Moor – its surface is very weathered and none of the patterns that are typical of Carboniferous tree fossils can be seen. 

 

Listed buildings on Waterside

 

Continuing along Waterside,  where I took a few photos of the listed buildings at Castle Mill and March House for the British Listed Buildings Photo Challenge - all of which are built in sandstone or brick and not Permian dolomitic limestone - and another quick snap of Low Bridge, which the Conservation Area Appraisal says was rebuilt with Magnesian Limestone in 1779.

 

Low Bridge

A Walk From Shorts Lane to Totley

 

An exposure of Greenmoor Rock at Akley Bank

On other walks that I have undertaken in Sheffield, following the courses of tributary streams to the principal rivers that eventually flow to the River Don – notably Totley Brook, Limb Brook, Charlton Brook and Hartley Brook Dike – I had found numerous small rock exposures in the stream banks and streambeds but, from Blacka Moor Nature Reserve to Shorts Lane I didn’t get to see much of the various streams that I passed on this occasion and certainly no outcrops. 

 

The path from Shorts Lane

 

Descending a small escarpment of the Middle Band Rock, which forms a substantial outcrop to the north of Shorts Lane, I continued along the public footpath and over Redcar Brook, which converges with Blacka Dyke to form Old Hay Brook. 

 

The gate at Avenue Farm

 

At Avenue Farm, the boundary walling is made of thinly bedded sandstone, which is very probably Greenmoor Rock that outcrops extensively to the south side of the railway line through Totley. The posts to the gate, which includes a kissing gate to prevent the passage of livestock, are made of gritstone from the Chatsworth Grit and are elaborately decorated. 

 

Greenmoor Rock walling at Avenue Farm

 

Continuing to Old Hay Lane and Hillfoot Lane, I crossed over a stile that is made out of large blocks of gritstone and is set next to the garden wall of Grove House, which is constructed with more thinly bedded Greenmoor Rock with gritstone quoins. 

 

A stile on Hillfoot Lane

 

I carried along the public footpath until I reached another stream, Needham’s Dyke, which joins Old Hay Brook just to the west of a bridge that I stopped to photograph before continuing along the path on the south side of the brook. 

 

A bridge over Old Hay Brook

 

A little further along the brook there is a weir, which usually indicates that this formed the site of a mill, but although a small pond is marked on the 1883 Ordnance Survey (OS) map, the only works marked in the vicinity is the Totley Forge further upstream, where scythes were made. 

 

A weir on Old Hay Brook

 

Within a few metres of finding this weir, the rural setting suddenly becomes very suburban on Totley Brook Road, which the 1883 and 1898 editions of the OS map show before and after the Totley Tunnel was completed in 1893 - as part of the Midland Railway line that linked Sheffield to Manchester, via the Hope Valley. 

 

The 1883 and 1898 Ordnance Survey maps of Totley

Walking along the north side of Totley Brook Road, I took note of the various large detached and semi-detached late Victorian and Edwardian villas, which look like they are also built out of Greenmoor Rock, but I was completely unaware of the U-shaped brick aqueduct that carries Old Hay Brook over the railway cutting.

 

Victorian and Edwardian villas on Totley Brook Road

 

I was particularly interested to see the Edwardian Arts and Crafts style detached house at No. 120, which has walling made of uncoursed angular blocks of sandstone, a sweeping red plain tile roof and two large round windows with red brick dressings.

 

No. 120 Totley Brook Road

 

Crossing over the deep railway cutting by the pedestrian bridge, the Totley Tunnel East signal box (1893) is a rare survivor of the Victorian railway age, which is surprisingly not a listed building and its continued existence must be thrown into doubt after it closed earlier this year. 

 

Totley Tunnel East signal box

 

Following Grove Walk, which is well above the level of the railway track, I walked along the north side of Old Hay Brook and stopped to have a good look at the large exposure of Greenmoor Rock along Akley Bank which, looking at various old OS maps, does not appear to be a quarry. 

 

The Greenmoor Rock at Akley Bank

 

Grove Walk continues along Akley Bank and, although I had my Estwing hammer with me, the thinly bedded Greenmoor Rock had disintegrated to the extent that a scree slope has formed beneath the exposure, which it made it difficult to gain access to the rock face. 

 

The Greenmoor Rock at Akley Bank

 

I was able to obtain a specimen of Greenmoor Rock from one of the loose pieces and, as with several other pieces of rock that I have collected from this formation in several parts of Sheffield, it is thinly bedded and extremely fine grained, with no quartz grains discernable under a hand lens, but it has occasional very small flakes of white muscovite mica. 

 

A specimen of Greenmoor Rock

 

At the top of Grove Walk I came to Quarry Road - a cul-de-sac with C20 houses - but the 1924 OS map (revised 1920) shows that a small quarry, which opened in the latter part of the C19, still operated here; however, by the time the 1939 edition (revised 1935-1936) was published, the area had been increasingly developed with housing and is no longer marked.

 

The 1924 Ordnance survey map of Akley Bank

 

Having explored a part of Sheffield that was very new to me, I finished my walk by making my way through the interwar housing estate to Baslow Road and carried on down this until I reached the Baslow Road/Grove Road bus stop, having covered a distance of 6.5 km and dropped from an elevation of 381 to 138 metres above sea level. 

 

The topography on my walk