J1486 : Bench Mark, Antrim

near to Antrim, Ireland

Bench Mark, Antrim
Bench Mark, Antrim
One of three bench marks in the porch of All Saints Parish Church in Antrim - seen in J1486 : Riverside, Antrim (1).
This mark is the oldest, dating from the 1st geodetic levelling of Ireland which took place in 1839-43. It consists of a cut mark with a copper bolt driven into the wall of the church; the letters "B" and "M" are also either side of the mark to signify what it is. The mark was in a line from Belfast to Antrim which began at Commercial Buildings in Belfast - see J3474 : Bench Mark, Belfast; this is the 37th mark in that line.
The original remarks for the mark describe it as
"Copper bolt driven into base of Antrim Church Tower; 0.1 ft below sill of door". It was initially levelled to 80.439 feet above sea level.
There are two other bench marks in the porch of the church - see J1486 : Flush Bracket, Antrim and J1486 : Bench Mark, Antrim. See also LinkExternal link for many other examples I have found.
Bench Mark
Bench marks were historically used to record the height above sea level of a location as surveyed against the Mean Sea Level data (taken at Clarendon Dock, Belfast, for Northern Ireland data, Newlyn in Cornwall for data in Great Britain and Portmoor Pier, Malin Head, for data relating to the Republic of Ireland). They were used as part of a greater surveying network by the UK Ordnance Survey, Ordnance Survey Northern Ireland (OSNI) and the Ordnance Survey Ireland (OSI). If the exact height of one bench mark is known then the exact height of the next can be found by measuring the difference in heights, through a process of spirit levelling. In this way hundreds of thousands of bench marks were sited all around the UK & Ireland from the mid 19th to late 20th centuries. There are several distinct types of bench mark:

- Fundamental bench marks have been constructed at selected sites where foundations can be set on stable strata such as bedrock . Each FBM consists of a buried chamber with a brass bolt set in the top of a granite pillar. See NG8825 : Dornie fundamental bench mark for an example. FBMs were used in Ireland as well as GB but those in Ireland do not have any surface markers, nor are they marked on standard maps.
- Flush brackets consist of metal plates about 90 mm wide and 175 mm long. Each bracket has a unique serial number. They are most commonly found on most Triangulation Pillars, some churches or on other important civic buildings. See J3270 : Flush Bracket, Belfast for an example.
- Cut bench marks are the commonest form of mark. They consist of a horizontal bar cut into a wall or brickwork and are found just about anywhere. A broad arrow is cut immediately below the centre of the horizontal bar. See J3372 : Bench Mark, Belfast for an example. The horizontal mark may be replaced by or contain a bolt - see J1486 : Bench Mark, Antrim.
Other marks include:
- Projecting bench marks such as SD8072 : Projecting Bracket Benchmark on St Oswald's Tower
- Bolt bench marks such as SJ1888 : OSBM bolt on Hilbre Island
- Rivet bench marks such as J3978 : Bench Mark, Holywood
- Pivot bench marks such as SJ2661 : Pivot bench mark on Leeswood Bridge

Bench marks are commonly found on older buildings or other semi-permanent features such as stone bridges or walls. Due to updated mapping techniques and technological advances such as GPS, bench marks are no longer maintained. Many are still in existence and the markers will probably remain until they are eventually destroyed by redevelopment or erosion.
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year taken
2011
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J1486, 126 images   (more nearby)
Photographer
  (find more nearby)
Image classification?
Supplemental image
Date Taken
Thursday, 19 May, 2011   (more nearby)
Submitted
Friday, 20 May, 2011
Geographical Context
City, Town centre  Religious sites  Historic sites and artefacts 
Place (from Tags)
Antrim 
Subject Location
Irish: geotagged! J 14914 86561 [1m precision]
WGS84: 54:42.8367N 6:13.0610W
Photographer Location
Irish: geotagged! J 14914 86561
View Direction
SOUTH (about 180 degrees)
Clickable map
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