Trig Stations of the 19thC Principal Triangulation
The Principal Triangulation of Britain was the first high-precision trigonometric survey of the whole of Great Britain (including Ireland), carried out between 1791 and 1853 under the auspices of the Board of Ordnance. The triangulation stations used were not the permanent markers of the 20th century Retriangulation which employed the well-known Hotine trig pillar along with a host of other permanent above or below ground markers that could be quickly re-located and re-used. It's not even clear what form the old stations took, but it is known that many of the sites were re-used for the Retriangulation, therefore, by studying old maps and the sites of the current pillars an educated guess can often be made as to what might have constituted an old station. This wiki page has been created to list marks on rocks that could possibly be old stations, some will be benchmarks in their own right and can be added to the Benchmark Database, others will not be benchmarks, typically an arrow engraved into a boulder with no datum line. This is by no means a definitive or exhaustive list and is largely speculative. It is hoped that keen triggers will add to the marks listed here. NB. Any re-formatting of the list to enhance presentation would be welcomed.
- Back Tor, South Yorkshire - SK 19759 90999 - large old arrow on flat rock approx 4.5m SW of the trig pillar.
- Crutchenber Fell, Lancashire - SD72216030 - old pivot benchmark, very worn. On flat rock close to edge and a few yards from pillar.
- Featherbed Moss, South Yorks - SK 19028 93863 - large old arrow on prominent boulder, no datum.
- Great Whernside, North Yorks - SE 00206 73911 - old pivot benchmark approx 4m east of trig pillar.
- Meldon Hill, Cumbria - NY 7722 2906 - old pivot benchmark approx 65m SE of the trig pillar.
- Newton Fell, Lancashire - SD71474748 - old pivot benchmark adjacent to pillar. Rock now on side. OS have as Destroyed 1/89.
- Parson's Pulpit, North Yorks - SD 91838 68751 - old pivot benchmark on a rock approx 3m west of trig surface block (converted pillar).
- Red Screes, Cumbria - NY39650875 - old pivot benchmark on loose rock at cairn shelter entrance.
- Roan Fell, Scottish Borders - NY 44960 92070 - old pivot benchmark on flat rock 2-3m SW trig pillar.
- Simon's Seat, North Yorks - SE 07891 59810 - old pivot benchmark on summit rocks approx 2m SW of trig pillar.
- Strandlud Hill, East Ayrshire - NS 58250 06060 - old pivot mark on summit boulder.
- Wella Crag, Cumbria - NY27652129 - old pivot benchmark on flat rock close to edge.
- Fan Llia, Powys - SN93791855 - old pivot benchmark on flat rock.
- Silver How, Cumbria - NY 32479 06645 - old pivot benchmark cut into bedrock just north of the summit cairn.