Trig Stations of the 19thC Principal Triangulation

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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, or with a large hole at the apex of the arrow that might have taken a sighting staff. 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.

The Stations

Back Tor, South Yorkshire SK 1976 9100 Large old arrow on flat rock approx 4.5m SW of the trig pillar
Castle Dow, Perth and Kinross NN 9296 5135 Old pivot benchmark on embedded boulder at the highest point next to a small pile of stones
Crutchenber Fell, Lancashire SD 7221 6030 Old pivot benchmark, very worn. On flat rock close to edge and a few yards from pillar
Deerstone Moor, Lancashire SD 9093 3676 Hole in boulder with cut arrow
Fan Llia, Powys SN 9379 1855 Old pivot benchmark on flat rock
Featherbed Moss, South Yorks SK 1903 9386 Large old arrow on prominent boulder, no datum
Floddaymore, Western Isles NF 9142 5693 Cassini marker - circular hole drilled into embedded boulder
Great Whernside, North Yorks SE 0021 7391 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 SD 7147 4748 Old pivot benchmark adjacent to pillar, listed as an Old Trig in the OSGB36 database. Rock now on side. OS list it as Destroyed 1/89
Parson's Pulpit, North Yorks SD 9184 6875 Old pivot benchmark on a rock approx 3m west of trig surface block (converted pillar)
Red Screes, Cumbria NY 3965 0875 Old pivot benchmark on loose rock at cairn shelter entrance
Roan Fell, Scottish Borders NY 4496 9207 Old pivot benchmark on flat rock 2-3m SW trig pillar
Silver How, Cumbria NY 3248 0664 Old pivot benchmark cut into bedrock just north of the summit cairn
Simon's Seat, North Yorks SE 0789 5981 Old pivot benchmark on summit rocks approx 2m SW of trig pillar
Strandlud Hill, East Ayrshire NS 5825 0606 Old pivot mark on summit boulder
Thornthwaite Crag NY 4313 1001 Large arrow Pivot BM on rock next to large cairn
Ullioch Hill, Dumfries and Galloway NX 6869 6773 Old pivot benchmark cut into slab west of base of summit cairn
Walla Crag, Cumbria NY 2765 2129 Old pivot benchmark on flat rock close to edge.