Ordnance Survey surveyor marks

Lots of discussion on social media this weekend about Ordnance Survey marks on the gritstone of the Dark Peak in the Peak District. A topic that fascinates me with every walk including a foray into the wilderness to try to find some elusive mark made more than a century and a half ago.

Top left is a benchmark used to establish height at a point on the footpath to Stanage End from Moscar.

Below that is a benchmark used to mark a survey position on Higger Tor.

Top right is a really interesting one. An arrow below a square box with a dot in the middle. This denotes a survey height taken from the ground and not estimated. On modern maps today these are denoted as a black dot with a height number as opposed to an orange dot which denotes a measurement taken from the air.

Bottom left is a lovely levelling bolt, indicating a survey position near Laddow Rocks.

Bottom right two survey marks, one for levelling and one for triangulation found on Back Tor on Derwent Edge. On the left hand mark is a benchmark made by Lieut Barlow RE when he carried out the triangulation in 185. The right hand mark denotes a spot height taken in 1854 by Capt Kerr RE to establish the contour lines.

All heights back then used the Liverpool datum and approximate average of the sea height there. Nowadays the OS maps use the Newlyn datum taken from the tidal measuring station in Newlyn Harbour, Cornwall.

 

Ordnance Survey Ephemera

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OS Map from 1852 showing position of survey benchmark.
Reproduced with the permission of the National Library of Scotland http://maps.nls.uk/index.html

There are quite a few bits of survey ephemera along Cut Gate in the Dark Peak. Benchmarks are much in evidence if you know where to look.

Just above the words “Lost Lad” on the 1852 Ordnance Survey map of Cut Gate, high above Langsett, there are two benchmarks denoted, the B.M followed by the elevation above Mean Sea Level in feet. Mean Sea Level in them days was taken from the measurements obtained at the Liverpool Datum, whereas today it is Newlyn. The first Benchmark happens just before the ford which is the turn off point for the spot height on Lost Lad itself. It is simple arrow beneath a line, but unusually is on a flat surface and not a vertical one, making it a little difficult to be accurate in the measurement. It is also accompanied by the initials RW, Rimmington Wilson the then landowner, chiselled at a later date and certainly with not as much skill.

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The Benchmark on a gritstone boulder on Cut Gate

Heading down the Cut Gate path towards Langsett a further benchmark can be found on the gate post of the boundary wall at Hingcliff Common.

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Benchmark shown on 1891 OS map on Cut Gate below Hingcliff Common
Reproduced with the permission of the National Library of Scotland http://maps.nls.uk/index.html

Grouse had been introduced onto the moors for several decades when the benchmark was carved so it would have looked pretty much the same as today with one exception. The Cut Gate track went through the gate posts where as today the line of the path goes someway to the south-east.

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Benchmark on the gate post along the line of the 1891 Cut Gate, Langsett

A surveying team would consist of a surveyor and his assistant. The surveyor took the reading and the assistant held the staff and lugged the equipment around. It was the surveyor who chiselled in the benchmark. I often try to imagine the team out in all weathers mapping the area. Around these two benchmarks are many more plus triangulation points on Hingcliff Hill and Pike Lowe to the east. The maps they produced are remarkably accurate and can still be followed today on the ground. The really interesting thing about old maps are the items marked that are no longer on modern-day maps.

History on Higger Tor

Yesterday I spent a few hours on Hathersage Moor and Higger Tor seeing if any benchmarks shown on old maps would still be evident today.

The image from the old map above is taken from a survey of the Moor carried out in 1852. Would the benchmarks shown still be there, did they actually exist or were they just markings on the map showing where a measurement had been taken from? What did they actually look like?

The one on Higger Tor, (Higher Tor), seemed to be the easiest to find. It’s the small arrow between the ‘r’ and ‘T’ of ‘Higger Tor’. The marking is not to scale obviously, nearby there is a triangle denting a triangulation point. It also has lots of features to aim from and sure enough that’s how it turned out. It took a while of rummaging around and at first I was looking for a benchmark on a vertical surface and chiselled in the style that is normally seen on buildings and gate posts. Then I found it, on a large flat stone, in the middle of the edge path. The marking was on a horizontal surface and pointed west, not north as in the map. It was a simple arrow with no levelling line at the tip of the arrow. The mark was still very clear, although if you weren’t looking for it you probably wouldn’t notice it. Did they take the measurement and then make the mark or vice versa? A Benchmark denoted a levelling point, hence the number, in feet, nearby, and the triangle marked the spot for triangulation. Are they one and the same place or was the triangulation in a different spot. Close by there was a spot that would have been perfect for a tripod and theodolite.

Dropping down from the Tor onto the Moor I set out to find the other two marks that are shown on the map as you head south-west towards the walled enclosure. Success was not to be mine. I needed to do a great deal more work on the position of the marks. The bracken hid many boulders and time had allowed moss and lichen to grow over a large number. I didn’t want to disturb too much so looked but could not find the two.

I did find other items of interest though. A possible burial cairn, complete with chamber. A partially finished grindstone, some way from the traditional grindstone fields and more markings that were different to the Ordnance Survey marks.

A few hours spent walking in the foot steps of surveyors and masons and perhaps Bronze Age man.

Triangulation Points

I like collecting things. Triangulation points are a favourite along with benchmarks that can be found along a walk or near to one.

There is something very satisfying about reaching a trig pillar, partly I guess because they invariably involve a walk up hill and a reward of sweeping views, weather permitting. There are 84 pillars within the Peak District National Park boundary and many more triangulation points and thousands more benchmarks.

Some are not shown on maps with the traditional blue triangle, the one at Hey Edge for instance, built but never used for triangulation, but was used for levelling, so does it not qualify for the blue triangle.

Some triangulation points are not even pillars. One of my walks takes in the Hunting Tower on the Chatsworth Estate, the triangulation point being the flagstaff. Another is the centre of the spire of All Saints Church in Bakewell.

With the advent of GPS the triangulation pillar network became largely redundant, but a few still do have a purpose. The pillar at Harland South, levelling bracket number 2998 is part of the Global Positioning Network and as such is protected by Ordnance Survey. A plate informs the visitor that any damage should be reported to the phone number.

Triangulation points always come in a minimum of three so a favoured walk of mine takes in the Hunting Tower at Chatsworth, the pillar at Birchen Edge along with the Three Ships and the pillar at Harland South, passing Hobs House, one of the first ancient monuments to have legal protection in the UK, on the way. Two pillars, one part of the Global Positioning System and one flagstaff on a hunting tower. Not bad for a day out.

Ordnance Survey Benchmarks

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Benchmark at Moscar SK 2305 8759

This is a levelling benchmark placed and used by Ordnance Survey. Its location is SK 2305 8759 at Moscar on the footpath from the A57 towards Stanage. The mark was made in 1961, is of the third order of surveying and is 600mm above ground level. Its datum is Newlyn. Originally the mark and boulder were on the west of the footpath but time and boots have now placed it east of the path.

There are some 500,000 benchmarks on the UK mainland, most no longer in use. They identify the height at a given point. The base line is the tidal measuring station at Newlyn in Cornwall, that is the point where all height measurements are taken from, including the 190 Fundamental Benchmarks which were the first order and therefore the most accurate, set in chambers deep underground on bedrock , these benchmarks are still in use today by the Global Positioning System for calculating the accuracy of the height calculation.

SK 24532 94653 Broomhead Moor Fundemental Benchmark TP0526 Chamber
SK 24532 94653 Broomhead Moor Fundamental Benchmark TP0526 Chamber

 

Trigpoint Walks 11

SK 1770 9697 Outer Edge 541m
SK 1770 9697 Outer Edge 541m

The classic walks of the Dark Peak offer the walker enjoyment of the highest order whatever the weather, come rain, snow or sunshine. The degree of isolation especially in winter when on a featureless high moorland deep in snow that is invariably being driven hard into the face by an unremitting wind, is a character building experience best savoured in warm surroundings with a hot mug of tea. The walker having endured such a day will quite rightly have earned the soft green hills of the White Peak the following spring.

The walk along the three triangulation pillars that look out over the Upper Derwent Valley is one of the great edge walks of The Peak District. It is not a long walk so there is plenty of time to stand and stare, or, better still find a vantage point and sit and watch, there will be much to view and learn.

I started from The Kings Tree at the end of the public road that winds its way up the valleys western side. A track leads across the young Derwent river via the Slippery Stones bridge, transplanted from the sunken Derwent Village, and heads off up the valley following the river. Above can be seen the edges that fringe the valley and it is to one of these that a shooting track climbs up from the river towards Crow Stones Edge and then onto the first trig at Outer Edge.

The views from the triangulation pillar are magnificent. Bleaklow, Kinder, The Great Ridge, Bamford Edge, West and North Yorkshire, all are there to be seen and no doubt on a crystal clear day well beyond that as well.

SK 1891 9569 Margery 546
SK 1891 9569 Margery 546m

The next triangulation pillar, Margery is in line with the valley and in a dry season is a pleasant walk, in wet and continuous rain it is a completely different matter. This is peat grough country, dark, thick, oozing, leg sucking. There is no avoiding it, so you might as well be prepared. Gaiters are a must as are tight laces to save lost boots. You can skirt some groughs but a strange and probably natural mathematical formula means that you can never ever escape the final ignominy of flailing about in a childish fashion whilst trying to look as though you are in control. It is also a natural law that having seen no one all day, as soon as you become stuck a ramblers group will appear out of nowhere, to ask if you need help, to which the answer is of course a firm NO.

From Margery I chose a little bit of a nav exercise, taking a bearing from Featherbed Moss to the shooting track of Dukes Road means a yomp across moorland, navigating between the wetter marsh areas to gain the track across Cartledge Bents. Near by is an old cross possibly used as a marker to the Grange at Abbey Clough nearby and well worth a visit.

SK 1976 9099 Back Tor 538
SK 1976 9099 Back Tor 538m

The slabbed track for Back Tor which can be seen on the skyline, threads through peat and bog, so at least the feet keep dry. I’m not sure about these paths, I agree they do reduce erosion and something had to be done, but they are sore on the feet, so I was glad on reaching Back Tor, to climb up to the trig, remove my boots and sit back and relax.

The vista really is superb, I was glad I had brought some binoculars so that I could watch the birds and hares and pick out favourite places on the horizon. After half an hours rest I set off down to Fairholmes visitor centre via moor, woodland and track, a great days walking whatever the weather.

 

Trigpoint Walks 9

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SK 2153 7789 Sir William Hill 429m

Spring for me, always heralds green pastures, rolling hills, white limestone, heavy showers and blue skies. It means for a period of walking in the White Peak where there is a release from peat bog, groughs and bleak desolate moorland.  The winter slog slips away to be replaced by a warming sun and longer days.

I chose the boundary between dark and white, strolling up from the plague village of Eyam towards the north and the dark.  Eyams an interesting place, one of Ranulph Feinnes heros for their selfless act of sealing themselves off from the outside world when the plague arrived, you can spend hours there tracing out the tragedy, just don’t go in tourist season.

My first trig objective was Sir William Hill, which gives wonderful panoramic views across the whole of the Peak District.  Its a gentle climb out of the village, through woodlands and across green pastures, at one point you pass an abandoned lead mine, redundant industrial buildings incongruous in the landscape. A large badger set protects the trig from the Eyam approach and the dogs spent long moments with the snouts down the entrances trying to figure what the scent was. The eye can see right up the Derwent Valley, across to Kinder and Bleaklow, down to Bakewell and across Froggatt and Curbar edges. I sat and took it all in until two people arrived and I left to let them have the trig and the views in peace.

SK 1084 7942 Abney Moor 416m
SK 1084 7942 Abney Moor 416m

I headed out to Abney Moor via Bretton Clough, a secluded valley sitting between the gritstone and limestone. The Abney Moor trig requires a degree of stealth, although I did not know this at the time. Crossing moorland to reach a stone wall that surrounds the glider airfield a decision has to be made. Do I hop over the wall and hope not to be noticed, or take the long walk round to ask permission. I know which is the right way and after choosing my course of action I strode through the gate that gives access to the trig from the airfield. There is a little plaque on the trig, placed there by  the glider club, which is ironic as they refuse access to  land based mortals. The views out to Castleton, Mam Tor and the Great Ridge are superb, below is industrial farm buildings blotting the landscape and filling every green patch with junk and rubbish. The sign on this side of the access gate stated no access to pedestrians, so I skirted the wall dropping down to reach a track that took me to Great Hucklow and the door of the pub slammed in my face just as I was about to enter, lovely people.

SK 1785 7397 Wardlow 370m
SK 1785 7397 Wardlow 370m

Head south along old walled trackways through rolling pasture, true limestone country this, the eye seeing for miles, and aim for Wardlow and another stealth trig, protected by drystone walls and gated farmland. No easy access and definitely walls and fences to climb over. This trig a high point in the land around, the vistas long and low, I sat in the fading light, my back to the pillar and just watched.  A bird of prey, I could not tell you which, soared up from Cressbrook Dale and quartered the land.

A long walk back to Eyam across pasture and through squeeze stiles, entering Eyam from the old Tideswell Lane and then along quieter streets to the end.