Ordnance Survey map of Tickhill, whose 1902 edition was
reproduced in 2004, shows exactly where the benchmarks were with
their associated height above sea level. Curiously, the height
above sea level was given in feet and tenths of feet, not
inches. For example, the height at the benchmark on St Maryís
Church was given as 60.6 feet. Height above sea level was
measured initially from a reference point in Liverpool, using,
in particular from 1844, the mean sea level at Victoria Dock.
The Ordnance Survey replaced this measurement with the height of
mean sea level at Newlyn after taking measurements of sea levels
every 15 minutes, day and night, between 1915 and 1921.
Parts of Tickhill were among the first surveyed in England, in
the mid 19th Century, to establish height above sea
level. What was known as the first primary levelling took place
between 1840 and 1860. One route through Tickhill was included
in the Thorne to Stalybridge levelling between 1845 and 1846.
(In contrast, the measurement of the London to Doncaster route
was not undertaken until 1848-1851.) The precise places where
measurements were made through Tickhill were listed in an 1861
publication Ordnance Survey abstracts of the lines of spirit
by Colonel Sir Henry James. Here are the locations of benchmarks
from the Toll House in Sunderland Street to Worksop Road:
on South East angle of Tickhill Toll House: 1.33 feet above
centre of the road.
jamb-stone of door of John Graysonís house Tickhill: 1.28 feet
above centre of the road
centre of floor of Tickhill Market Cross: 2.29 feet above base
West face of St Maryís church tower Tickhill: 3.16 feet above
stone near bottom of wall adjoining small cottage at junction of
roads: 1.71 feet above centre of the road
Mark on the
9th milestone from Worksop 8th from
Doncaster East side of road: 2.94 feet above centre of the road
Some of these benchmarks have survived especially the benchmark
just to the right of St Maryís west door, the only one in
Tickhill to include a bolt made from gunmetal in the middle of
the horizontal bar above the arrow head shape. Another is close
by at the bottom of the wall near the junction of Church Lane
and Westgate. Other benchmarks have been obscured or removed.
For example, the pebbledashing of the Toll House has covered its
benchmark, while the benchmark on the centre of the floor of the
Buttercross has been removed and an unmarked paving stone placed
Another series of benchmarks follows the Northgate
route. One can be seen at the lower edge of the front wall of 30
Northgate. It is partly obscured by a drainpipe.
Measurements on maps from different periods are not necessarily
consistent. In part this is due to remeasuring: the second
levelling in England took place between 1912 and 1921 while a
third set of measurements were taken between 1950 and 1968.
However, another reason showed the unreliability of using
benchmarks on a variety of structures from walls to church
towers to gate posts to mile stones: subsidence. In mining areas
variations in height above sea level could change over time by
as much as 8 to 10 feet. The Ordnance Survey finally abandoned
the benchmark network in 1989 when it started to use satellite
technology known as the Global Positioning System.
following websites have further information: